summaryrefslogtreecommitdiffstats
path: root/Documentation/DocBook/crypto-API.tmpl
blob: 07df23ea06e4936d6de435ba4c862ffdb4b299d1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>

<book id="KernelCryptoAPI">
 <bookinfo>
  <title>Linux Kernel Crypto API</title>

  <authorgroup>
   <author>
    <firstname>Stephan</firstname>
    <surname>Mueller</surname>
    <affiliation>
     <address>
      <email>smueller@chronox.de</email>
     </address>
    </affiliation>
   </author>
   <author>
    <firstname>Marek</firstname>
    <surname>Vasut</surname>
    <affiliation>
     <address>
      <email>marek@denx.de</email>
     </address>
    </affiliation>
   </author>
  </authorgroup>

  <copyright>
   <year>2014</year>
   <holder>Stephan Mueller</holder>
  </copyright>


  <legalnotice>
   <para>
     This documentation is free software; you can redistribute
     it and/or modify it under the terms of the GNU General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later
     version.
   </para>

   <para>
     This program is distributed in the hope that it will be
     useful, but WITHOUT ANY WARRANTY; without even the implied
     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
     See the GNU General Public License for more details.
   </para>

   <para>
     You should have received a copy of the GNU General Public
     License along with this program; if not, write to the Free
     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
     MA 02111-1307 USA
   </para>

   <para>
     For more details see the file COPYING in the source
     distribution of Linux.
   </para>
  </legalnotice>
 </bookinfo>

 <toc></toc>

 <chapter id="Intro">
  <title>Kernel Crypto API Interface Specification</title>

   <sect1><title>Introduction</title>

    <para>
     The kernel crypto API offers a rich set of cryptographic ciphers as
     well as other data transformation mechanisms and methods to invoke
     these. This document contains a description of the API and provides
     example code.
    </para>

    <para>
     To understand and properly use the kernel crypto API a brief
     explanation of its structure is given. Based on the architecture,
     the API can be separated into different components. Following the
     architecture specification, hints to developers of ciphers are
     provided. Pointers to the API function call  documentation are
     given at the end.
    </para>

    <para>
     The kernel crypto API refers to all algorithms as "transformations".
     Therefore, a cipher handle variable usually has the name "tfm".
     Besides cryptographic operations, the kernel crypto API also knows
     compression transformations and handles them the same way as ciphers.
    </para>

    <para>
     The kernel crypto API serves the following entity types:

     <itemizedlist>
      <listitem>
       <para>consumers requesting cryptographic services</para>
      </listitem>
      <listitem>
      <para>data transformation implementations (typically ciphers)
       that can be called by consumers using the kernel crypto
       API</para>
      </listitem>
     </itemizedlist>
    </para>

    <para>
     This specification is intended for consumers of the kernel crypto
     API as well as for developers implementing ciphers. This API
     specification, however, does not discuss all API calls available
     to data transformation implementations (i.e. implementations of
     ciphers and other transformations (such as CRC or even compression
     algorithms) that can register with the kernel crypto API).
    </para>

    <para>
     Note: The terms "transformation" and cipher algorithm are used
     interchangeably.
    </para>
   </sect1>

   <sect1><title>Terminology</title>
    <para>
     The transformation implementation is an actual code or interface
     to hardware which implements a certain transformation with precisely
     defined behavior.
    </para>

    <para>
     The transformation object (TFM) is an instance of a transformation
     implementation. There can be multiple transformation objects
     associated with a single transformation implementation. Each of
     those transformation objects is held by a crypto API consumer or
     another transformation. Transformation object is allocated when a
     crypto API consumer requests a transformation implementation.
     The consumer is then provided with a structure, which contains
     a transformation object (TFM).
    </para>

    <para>
     The structure that contains transformation objects may also be
     referred to as a "cipher handle". Such a cipher handle is always
     subject to the following phases that are reflected in the API calls
     applicable to such a cipher handle:
    </para>

    <orderedlist>
     <listitem>
      <para>Initialization of a cipher handle.</para>
     </listitem>
     <listitem>
      <para>Execution of all intended cipher operations applicable
      for the handle where the cipher handle must be furnished to
      every API call.</para>
     </listitem>
     <listitem>
      <para>Destruction of a cipher handle.</para>
     </listitem>
    </orderedlist>

    <para>
     When using the initialization API calls, a cipher handle is
     created and returned to the consumer. Therefore, please refer
     to all initialization API calls that refer to the data
     structure type a consumer is expected to receive and subsequently
     to use. The initialization API calls have all the same naming
     conventions of crypto_alloc_*.
    </para>

    <para>
     The transformation context is private data associated with
     the transformation object.
    </para>
   </sect1>
  </chapter>

  <chapter id="Architecture"><title>Kernel Crypto API Architecture</title>
   <sect1><title>Cipher algorithm types</title>
    <para>
     The kernel crypto API provides different API calls for the
     following cipher types:

     <itemizedlist>
      <listitem><para>Symmetric ciphers</para></listitem>
      <listitem><para>AEAD ciphers</para></listitem>
      <listitem><para>Message digest, including keyed message digest</para></listitem>
      <listitem><para>Random number generation</para></listitem>
      <listitem><para>User space interface</para></listitem>
     </itemizedlist>
    </para>
   </sect1>

   <sect1><title>Ciphers And Templates</title>
    <para>
     The kernel crypto API provides implementations of single block
     ciphers and message digests. In addition, the kernel crypto API
     provides numerous "templates" that can be used in conjunction
     with the single block ciphers and message digests. Templates
     include all types of block chaining mode, the HMAC mechanism, etc.
    </para>

    <para>
     Single block ciphers and message digests can either be directly
     used by a caller or invoked together with a template to form
     multi-block ciphers or keyed message digests.
    </para>

    <para>
     A single block cipher may even be called with multiple templates.
     However, templates cannot be used without a single cipher.
    </para>

    <para>
     See /proc/crypto and search for "name". For example:

     <itemizedlist>
      <listitem><para>aes</para></listitem>
      <listitem><para>ecb(aes)</para></listitem>
      <listitem><para>cmac(aes)</para></listitem>
      <listitem><para>ccm(aes)</para></listitem>
      <listitem><para>rfc4106(gcm(aes))</para></listitem>
      <listitem><para>sha1</para></listitem>
      <listitem><para>hmac(sha1)</para></listitem>
      <listitem><para>authenc(hmac(sha1),cbc(aes))</para></listitem>
     </itemizedlist>
    </para>

    <para>
     In these examples, "aes" and "sha1" are the ciphers and all
     others are the templates.
    </para>
   </sect1>

   <sect1><title>Synchronous And Asynchronous Operation</title>
    <para>
     The kernel crypto API provides synchronous and asynchronous
     API operations.
    </para>

    <para>
     When using the synchronous API operation, the caller invokes
     a cipher operation which is performed synchronously by the
     kernel crypto API. That means, the caller waits until the
     cipher operation completes. Therefore, the kernel crypto API
     calls work like regular function calls. For synchronous
     operation, the set of API calls is small and conceptually
     similar to any other crypto library.
    </para>

    <para>
     Asynchronous operation is provided by the kernel crypto API
     which implies that the invocation of a cipher operation will
     complete almost instantly. That invocation triggers the
     cipher operation but it does not signal its completion. Before
     invoking a cipher operation, the caller must provide a callback
     function the kernel crypto API can invoke to signal the
     completion of the cipher operation. Furthermore, the caller
     must ensure it can handle such asynchronous events by applying
     appropriate locking around its data. The kernel crypto API
     does not perform any special serialization operation to protect
     the caller's data integrity.
    </para>
   </sect1>

   <sect1><title>Crypto API Cipher References And Priority</title>
    <para>
     A cipher is referenced by the caller with a string. That string
     has the following semantics:

     <programlisting>
	template(single block cipher)
     </programlisting>

     where "template" and "single block cipher" is the aforementioned
     template and single block cipher, respectively. If applicable,
     additional templates may enclose other templates, such as

      <programlisting>
	template1(template2(single block cipher)))
      </programlisting>
    </para>

    <para>
     The kernel crypto API may provide multiple implementations of a
     template or a single block cipher. For example, AES on newer
     Intel hardware has the following implementations: AES-NI,
     assembler implementation, or straight C. Now, when using the
     string "aes" with the kernel crypto API, which cipher
     implementation is used? The answer to that question is the
     priority number assigned to each cipher implementation by the
     kernel crypto API. When a caller uses the string to refer to a
     cipher during initialization of a cipher handle, the kernel
     crypto API looks up all implementations providing an
     implementation with that name and selects the implementation
     with the highest priority.
    </para>

    <para>
     Now, a caller may have the need to refer to a specific cipher
     implementation and thus does not want to rely on the
     priority-based selection. To accommodate this scenario, the
     kernel crypto API allows the cipher implementation to register
     a unique name in addition to common names. When using that
     unique name, a caller is therefore always sure to refer to
     the intended cipher implementation.
    </para>

    <para>
     The list of available ciphers is given in /proc/crypto. However,
     that list does not specify all possible permutations of
     templates and ciphers. Each block listed in /proc/crypto may
     contain the following information -- if one of the components
     listed as follows are not applicable to a cipher, it is not
     displayed:
    </para>

    <itemizedlist>
     <listitem>
      <para>name: the generic name of the cipher that is subject
       to the priority-based selection -- this name can be used by
       the cipher allocation API calls (all names listed above are
       examples for such generic names)</para>
     </listitem>
     <listitem>
      <para>driver: the unique name of the cipher -- this name can
       be used by the cipher allocation API calls</para>
     </listitem>
     <listitem>
      <para>module: the kernel module providing the cipher
       implementation (or "kernel" for statically linked ciphers)</para>
     </listitem>
     <listitem>
      <para>priority: the priority value of the cipher implementation</para>
     </listitem>
     <listitem>
      <para>refcnt: the reference count of the respective cipher
       (i.e. the number of current consumers of this cipher)</para>
     </listitem>
     <listitem>
      <para>selftest: specification whether the self test for the
       cipher passed</para>
     </listitem>
     <listitem>
      <para>type:
       <itemizedlist>
        <listitem>
         <para>blkcipher for synchronous block ciphers</para>
        </listitem>
        <listitem>
         <para>ablkcipher for asynchronous block ciphers</para>
        </listitem>
        <listitem>
         <para>cipher for single block ciphers that may be used with
          an additional template</para>
        </listitem>
        <listitem>
         <para>shash for synchronous message digest</para>
        </listitem>
        <listitem>
         <para>ahash for asynchronous message digest</para>
        </listitem>
        <listitem>
         <para>aead for AEAD cipher type</para>
        </listitem>
        <listitem>
         <para>compression for compression type transformations</para>
        </listitem>
        <listitem>
         <para>rng for random number generator</para>
        </listitem>
        <listitem>
         <para>givcipher for cipher with associated IV generator
          (see the geniv entry below for the specification of the
          IV generator type used by the cipher implementation)</para>
        </listitem>
       </itemizedlist>
      </para>
     </listitem>
     <listitem>
      <para>blocksize: blocksize of cipher in bytes</para>
     </listitem>
     <listitem>
      <para>keysize: key size in bytes</para>
     </listitem>
     <listitem>
      <para>ivsize: IV size in bytes</para>
     </listitem>
     <listitem>
      <para>seedsize: required size of seed data for random number
       generator</para>
     </listitem>
     <listitem>
      <para>digestsize: output size of the message digest</para>
     </listitem>
     <listitem>
      <para>geniv: IV generation type:
       <itemizedlist>
        <listitem>
         <para>eseqiv for encrypted sequence number based IV
          generation</para>
        </listitem>
        <listitem>
         <para>seqiv for sequence number based IV generation</para>
        </listitem>
        <listitem>
         <para>chainiv for chain iv generation</para>
        </listitem>
        <listitem>
         <para>&lt;builtin&gt; is a marker that the cipher implements
          IV generation and handling as it is specific to the given
          cipher</para>
        </listitem>
       </itemizedlist>
      </para>
     </listitem>
    </itemizedlist>
   </sect1>

   <sect1><title>Key Sizes</title>
    <para>
     When allocating a cipher handle, the caller only specifies the
     cipher type. Symmetric ciphers, however, typically support
     multiple key sizes (e.g. AES-128 vs. AES-192 vs. AES-256).
     These key sizes are determined with the length of the provided
     key. Thus, the kernel crypto API does not provide a separate
     way to select the particular symmetric cipher key size.
    </para>
   </sect1>

   <sect1><title>Cipher Allocation Type And Masks</title>
    <para>
     The different cipher handle allocation functions allow the
     specification of a type and mask flag. Both parameters have
     the following meaning (and are therefore not covered in the
     subsequent sections).
    </para>

    <para>
     The type flag specifies the type of the cipher algorithm.
     The caller usually provides a 0 when the caller wants the
     default handling. Otherwise, the caller may provide the
     following selections which match the the aforementioned
     cipher types:
    </para>

    <itemizedlist>
     <listitem>
      <para>CRYPTO_ALG_TYPE_CIPHER Single block cipher</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_COMPRESS Compression</para>
     </listitem>
     <listitem>
     <para>CRYPTO_ALG_TYPE_AEAD Authenticated Encryption with
      Associated Data (MAC)</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_BLKCIPHER Synchronous multi-block cipher</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_ABLKCIPHER Asynchronous multi-block cipher</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_GIVCIPHER Asynchronous multi-block
       cipher packed together with an IV generator (see geniv field
       in the /proc/crypto listing for the known IV generators)</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_DIGEST Raw message digest</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_HASH Alias for CRYPTO_ALG_TYPE_DIGEST</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_SHASH Synchronous multi-block hash</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_AHASH Asynchronous multi-block hash</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_RNG Random Number Generation</para>
     </listitem>
     <listitem>
      <para>CRYPTO_ALG_TYPE_PCOMPRESS Enhanced version of
       CRYPTO_ALG_TYPE_COMPRESS allowing for segmented compression /
       decompression instead of performing the operation on one
       segment only. CRYPTO_ALG_TYPE_PCOMPRESS is intended to replace
       CRYPTO_ALG_TYPE_COMPRESS once existing consumers are converted.</para>
     </listitem>
    </itemizedlist>

    <para>
     The mask flag restricts the type of cipher. The only allowed
     flag is CRYPTO_ALG_ASYNC to restrict the cipher lookup function
     to asynchronous ciphers. Usually, a caller provides a 0 for the
     mask flag.
    </para>

    <para>
     When the caller provides a mask and type specification, the
     caller limits the search the kernel crypto API can perform for
     a suitable cipher implementation for the given cipher name.
     That means, even when a caller uses a cipher name that exists
     during its initialization call, the kernel crypto API may not
     select it due to the used type and mask field.
    </para>
   </sect1>

   <sect1><title>Internal Structure of Kernel Crypto API</title>

    <para>
     The kernel crypto API has an internal structure where a cipher
     implementation may use many layers and indirections. This section
     shall help to clarify how the kernel crypto API uses
     various components to implement the complete cipher.
    </para>

    <para>
     The following subsections explain the internal structure based
     on existing cipher implementations. The first section addresses
     the most complex scenario where all other scenarios form a logical
     subset.
    </para>

    <sect2><title>Generic AEAD Cipher Structure</title>

     <para>
      The following ASCII art decomposes the kernel crypto API layers
      when using the AEAD cipher with the automated IV generation. The
      shown example is used by the IPSEC layer.
     </para>

     <para>
      For other use cases of AEAD ciphers, the ASCII art applies as
      well, but the caller may not use the AEAD cipher with a separate
      IV generator. In this case, the caller must generate the IV.
     </para>

     <para>
      The depicted example decomposes the AEAD cipher of GCM(AES) based
      on the generic C implementations (gcm.c, aes-generic.c, ctr.c,
      ghash-generic.c, seqiv.c). The generic implementation serves as an
      example showing the complete logic of the kernel crypto API.
     </para>

     <para>
      It is possible that some streamlined cipher implementations (like
      AES-NI) provide implementations merging aspects which in the view
      of the kernel crypto API cannot be decomposed into layers any more.
      In case of the AES-NI implementation, the CTR mode, the GHASH
      implementation and the AES cipher are all merged into one cipher
      implementation registered with the kernel crypto API. In this case,
      the concept described by the following ASCII art applies too. However,
      the decomposition of GCM into the individual sub-components
      by the kernel crypto API is not done any more.
     </para>

     <para>
      Each block in the following ASCII art is an independent cipher
      instance obtained from the kernel crypto API. Each block
      is accessed by the caller or by other blocks using the API functions
      defined by the kernel crypto API for the cipher implementation type.
     </para>

     <para>
      The blocks below indicate the cipher type as well as the specific
      logic implemented in the cipher.
     </para>

     <para>
      The ASCII art picture also indicates the call structure, i.e. who
      calls which component. The arrows point to the invoked block
      where the caller uses the API applicable to the cipher type
      specified for the block.
     </para>

     <programlisting>
<![CDATA[
kernel crypto API                                |   IPSEC Layer
                                                 |
+-----------+                                    |
|           |            (1)
|   aead    | <-----------------------------------  esp_output
|  (seqiv)  | ---+
+-----------+    |
                 | (2)
+-----------+    |
|           | <--+                (2)
|   aead    | <-----------------------------------  esp_input
|   (gcm)   | ------------+
+-----------+             |
      | (3)               | (5)
      v                   v
+-----------+       +-----------+
|           |       |           |
| ablkcipher|       |   ahash   |
|   (ctr)   | ---+  |  (ghash)  |
+-----------+    |  +-----------+
                 |
+-----------+    | (4)
|           | <--+
|   cipher  |
|   (aes)   |
+-----------+
]]>
     </programlisting>

     <para>
      The following call sequence is applicable when the IPSEC layer
      triggers an encryption operation with the esp_output function. During
      configuration, the administrator set up the use of rfc4106(gcm(aes)) as
      the cipher for ESP. The following call sequence is now depicted in the
      ASCII art above:
     </para>

     <orderedlist>
      <listitem>
       <para>
        esp_output() invokes crypto_aead_encrypt() to trigger an encryption
        operation of the AEAD cipher with IV generator.
       </para>

       <para>
        In case of GCM, the SEQIV implementation is registered as GIVCIPHER
        in crypto_rfc4106_alloc().
       </para>

       <para>
        The SEQIV performs its operation to generate an IV where the core
        function is seqiv_geniv().
       </para>
      </listitem>

      <listitem>
       <para>
        Now, SEQIV uses the AEAD API function calls to invoke the associated
        AEAD cipher. In our case, during the instantiation of SEQIV, the
        cipher handle for GCM is provided to SEQIV. This means that SEQIV
        invokes AEAD cipher operations with the GCM cipher handle.
       </para>

       <para>
        During instantiation of the GCM handle, the CTR(AES) and GHASH
        ciphers are instantiated. The cipher handles for CTR(AES) and GHASH
        are retained for later use.
       </para>

       <para>
        The GCM implementation is responsible to invoke the CTR mode AES and
        the GHASH cipher in the right manner to implement the GCM
        specification.
       </para>
      </listitem>

      <listitem>
       <para>
        The GCM AEAD cipher type implementation now invokes the ABLKCIPHER API
        with the instantiated CTR(AES) cipher handle.
       </para>

       <para>
	During instantiation of the CTR(AES) cipher, the CIPHER type
	implementation of AES is instantiated. The cipher handle for AES is
	retained.
       </para>

       <para>
        That means that the ABLKCIPHER implementation of CTR(AES) only
        implements the CTR block chaining mode. After performing the block
        chaining operation, the CIPHER implementation of AES is invoked.
       </para>
      </listitem>

      <listitem>
       <para>
        The ABLKCIPHER of CTR(AES) now invokes the CIPHER API with the AES
        cipher handle to encrypt one block.
       </para>
      </listitem>

      <listitem>
       <para>
        The GCM AEAD implementation also invokes the GHASH cipher
        implementation via the AHASH API.
       </para>
      </listitem>
     </orderedlist>

     <para>
      When the IPSEC layer triggers the esp_input() function, the same call
      sequence is followed with the only difference that the operation starts
      with step (2).
     </para>
    </sect2>

    <sect2><title>Generic Block Cipher Structure</title>
     <para>
      Generic block ciphers follow the same concept as depicted with the ASCII
      art picture above.
     </para>

     <para>
      For example, CBC(AES) is implemented with cbc.c, and aes-generic.c. The
      ASCII art picture above applies as well with the difference that only
      step (4) is used and the ABLKCIPHER block chaining mode is CBC.
     </para>
    </sect2>

    <sect2><title>Generic Keyed Message Digest Structure</title>
     <para>
      Keyed message digest implementations again follow the same concept as
      depicted in the ASCII art picture above.
     </para>

     <para>
      For example, HMAC(SHA256) is implemented with hmac.c and
      sha256_generic.c. The following ASCII art illustrates the
      implementation:
     </para>

     <programlisting>
<![CDATA[
kernel crypto API            |       Caller
                             |
+-----------+         (1)    |
|           | <------------------  some_function
|   ahash   |
|   (hmac)  | ---+
+-----------+    |
                 | (2)
+-----------+    |
|           | <--+
|   shash   |
|  (sha256) |
+-----------+
]]>
     </programlisting>

     <para>
      The following call sequence is applicable when a caller triggers
      an HMAC operation:
     </para>

     <orderedlist>
      <listitem>
       <para>
        The AHASH API functions are invoked by the caller. The HMAC
        implementation performs its operation as needed.
       </para>

       <para>
        During initialization of the HMAC cipher, the SHASH cipher type of
        SHA256 is instantiated. The cipher handle for the SHA256 instance is
        retained.
       </para>

       <para>
        At one time, the HMAC implementation requires a SHA256 operation
        where the SHA256 cipher handle is used.
       </para>
      </listitem>

      <listitem>
       <para>
        The HMAC instance now invokes the SHASH API with the SHA256
        cipher handle to calculate the message digest.
       </para>
      </listitem>
     </orderedlist>
    </sect2>
   </sect1>
  </chapter>

  <chapter id="Development"><title>Developing Cipher Algorithms</title>
   <sect1><title>Registering And Unregistering Transformation</title>
    <para>
     There are three distinct types of registration functions in
     the Crypto API. One is used to register a generic cryptographic
     transformation, while the other two are specific to HASH
     transformations and COMPRESSion. We will discuss the latter
     two in a separate chapter, here we will only look at the
     generic ones.
    </para>

    <para>
     Before discussing the register functions, the data structure
     to be filled with each, struct crypto_alg, must be considered
     -- see below for a description of this data structure.
    </para>

    <para>
     The generic registration functions can be found in
     include/linux/crypto.h and their definition can be seen below.
     The former function registers a single transformation, while
     the latter works on an array of transformation descriptions.
     The latter is useful when registering transformations in bulk.
    </para>

    <programlisting>
   int crypto_register_alg(struct crypto_alg *alg);
   int crypto_register_algs(struct crypto_alg *algs, int count);
    </programlisting>

    <para>
     The counterparts to those functions are listed below.
    </para>

    <programlisting>
   int crypto_unregister_alg(struct crypto_alg *alg);
   int crypto_unregister_algs(struct crypto_alg *algs, int count);
    </programlisting>

    <para>
     Notice that both registration and unregistration functions
     do return a value, so make sure to handle errors. A return
     code of zero implies success. Any return code &lt; 0 implies
     an error.
    </para>

    <para>
     The bulk registration / unregistration functions require
     that struct crypto_alg is an array of count size. These
     functions simply loop over that array and register /
     unregister each individual algorithm. If an error occurs,
     the loop is terminated at the offending algorithm definition.
     That means, the algorithms prior to the offending algorithm
     are successfully registered. Note, the caller has no way of
     knowing which cipher implementations have successfully
     registered. If this is important to know, the caller should
     loop through the different implementations using the single
     instance *_alg functions for each individual implementation.
    </para>
   </sect1>

   <sect1><title>Single-Block Symmetric Ciphers [CIPHER]</title>
    <para>
     Example of transformations: aes, arc4, ...
    </para>

    <para>
     This section describes the simplest of all transformation
     implementations, that being the CIPHER type used for symmetric
     ciphers. The CIPHER type is used for transformations which
     operate on exactly one block at a time and there are no
     dependencies between blocks at all.
    </para>

    <sect2><title>Registration specifics</title>
     <para>
      The registration of [CIPHER] algorithm is specific in that
      struct crypto_alg field .cra_type is empty. The .cra_u.cipher
      has to be filled in with proper callbacks to implement this
      transformation.
     </para>

     <para>
      See struct cipher_alg below.
     </para>
    </sect2>

    <sect2><title>Cipher Definition With struct cipher_alg</title>
     <para>
      Struct cipher_alg defines a single block cipher.
     </para>

     <para>
      Here are schematics of how these functions are called when
      operated from other part of the kernel. Note that the
      .cia_setkey() call might happen before or after any of these
      schematics happen, but must not happen during any of these
      are in-flight.
     </para>

     <para>
      <programlisting>
         KEY ---.    PLAINTEXT ---.
                v                 v
          .cia_setkey() -&gt; .cia_encrypt()
                                  |
                                  '-----&gt; CIPHERTEXT
      </programlisting>
     </para>

     <para>
      Please note that a pattern where .cia_setkey() is called
      multiple times is also valid:
     </para>

     <para>
      <programlisting>

  KEY1 --.    PLAINTEXT1 --.         KEY2 --.    PLAINTEXT2 --.
         v                 v                v                 v
   .cia_setkey() -&gt; .cia_encrypt() -&gt; .cia_setkey() -&gt; .cia_encrypt()
                           |                                  |
                           '---&gt; CIPHERTEXT1                  '---&gt; CIPHERTEXT2
      </programlisting>
     </para>

    </sect2>
   </sect1>

   <sect1><title>Multi-Block Ciphers [BLKCIPHER] [ABLKCIPHER]</title>
    <para>
     Example of transformations: cbc(aes), ecb(arc4), ...
    </para>

    <para>
     This section describes the multi-block cipher transformation
     implementations for both synchronous [BLKCIPHER] and
     asynchronous [ABLKCIPHER] case. The multi-block ciphers are
     used for transformations which operate on scatterlists of
     data supplied to the transformation functions. They output
     the result into a scatterlist of data as well.
    </para>

    <sect2><title>Registration Specifics</title>

     <para>
      The registration of [BLKCIPHER] or [ABLKCIPHER] algorithms
      is one of the most standard procedures throughout the crypto API.
     </para>

     <para>
      Note, if a cipher implementation requires a proper alignment
      of data, the caller should use the functions of
      crypto_blkcipher_alignmask() or crypto_ablkcipher_alignmask()
      respectively to identify a memory alignment mask. The kernel
      crypto API is able to process requests that are unaligned.
      This implies, however, additional overhead as the kernel
      crypto API needs to perform the realignment of the data which
      may imply moving of data.
     </para>
    </sect2>

    <sect2><title>Cipher Definition With struct blkcipher_alg and ablkcipher_alg</title>
     <para>
      Struct blkcipher_alg defines a synchronous block cipher whereas
      struct ablkcipher_alg defines an asynchronous block cipher.
     </para>

     <para>
      Please refer to the single block cipher description for schematics
      of the block cipher usage. The usage patterns are exactly the same
      for [ABLKCIPHER] and [BLKCIPHER] as they are for plain [CIPHER].
     </para>
    </sect2>

    <sect2><title>Specifics Of Asynchronous Multi-Block Cipher</title>
     <para>
      There are a couple of specifics to the [ABLKCIPHER] interface.
     </para>

     <para>
      First of all, some of the drivers will want to use the
      Generic ScatterWalk in case the hardware needs to be fed
      separate chunks of the scatterlist which contains the
      plaintext and will contain the ciphertext. Please refer
      to the ScatterWalk interface offered by the Linux kernel
      scatter / gather list implementation.
     </para>
    </sect2>
   </sect1>

   <sect1><title>Hashing [HASH]</title>

    <para>
     Example of transformations: crc32, md5, sha1, sha256,...
    </para>

    <sect2><title>Registering And Unregistering The Transformation</title>

     <para>
      There are multiple ways to register a HASH transformation,
      depending on whether the transformation is synchronous [SHASH]
      or asynchronous [AHASH] and the amount of HASH transformations
      we are registering. You can find the prototypes defined in
      include/crypto/internal/hash.h:
     </para>

     <programlisting>
   int crypto_register_ahash(struct ahash_alg *alg);

   int crypto_register_shash(struct shash_alg *alg);
   int crypto_register_shashes(struct shash_alg *algs, int count);
     </programlisting>

     <para>
      The respective counterparts for unregistering the HASH
      transformation are as follows:
     </para>

     <programlisting>
   int crypto_unregister_ahash(struct ahash_alg *alg);

   int crypto_unregister_shash(struct shash_alg *alg);
   int crypto_unregister_shashes(struct shash_alg *algs, int count);
     </programlisting>
    </sect2>

    <sect2><title>Cipher Definition With struct shash_alg and ahash_alg</title>
     <para>
      Here are schematics of how these functions are called when
      operated from other part of the kernel. Note that the .setkey()
      call might happen before or after any of these schematics happen,
      but must not happen during any of these are in-flight. Please note
      that calling .init() followed immediately by .finish() is also a
      perfectly valid transformation.
     </para>

     <programlisting>
   I)   DATA -----------.
                        v
         .init() -&gt; .update() -&gt; .final()      ! .update() might not be called
                     ^    |         |            at all in this scenario.
                     '----'         '---&gt; HASH

   II)  DATA -----------.-----------.
                        v           v
         .init() -&gt; .update() -&gt; .finup()      ! .update() may not be called
                     ^    |         |            at all in this scenario.
                     '----'         '---&gt; HASH

   III) DATA -----------.
                        v
                    .digest()                  ! The entire process is handled
                        |                        by the .digest() call.
                        '---------------&gt; HASH
     </programlisting>

     <para>
      Here is a schematic of how the .export()/.import() functions are
      called when used from another part of the kernel.
     </para>

     <programlisting>
   KEY--.                 DATA--.
        v                       v                  ! .update() may not be called
    .setkey() -&gt; .init() -&gt; .update() -&gt; .export()   at all in this scenario.
                             ^     |         |
                             '-----'         '--&gt; PARTIAL_HASH

   ----------- other transformations happen here -----------

   PARTIAL_HASH--.   DATA1--.
                 v          v
             .import -&gt; .update() -&gt; .final()     ! .update() may not be called
                         ^    |         |           at all in this scenario.
                         '----'         '--&gt; HASH1

   PARTIAL_HASH--.   DATA2-.
                 v         v
             .import -&gt; .finup()
                           |
                           '---------------&gt; HASH2
     </programlisting>
    </sect2>

    <sect2><title>Specifics Of Asynchronous HASH Transformation</title>
     <para>
      Some of the drivers will want to use the Generic ScatterWalk
      in case the implementation needs to be fed separate chunks of the
      scatterlist which contains the input data. The buffer containing
      the resulting hash will always be properly aligned to
      .cra_alignmask so there is no need to worry about this.
     </para>
    </sect2>
   </sect1>
  </chapter>

  <chapter id="User"><title>User Space Interface</title>
   <sect1><title>Introduction</title>
    <para>
     The concepts of the kernel crypto API visible to kernel space is fully
     applicable to the user space interface as well. Therefore, the kernel
     crypto API high level discussion for the in-kernel use cases applies
     here as well.
    </para>

    <para>
     The major difference, however, is that user space can only act as a
     consumer and never as a provider of a transformation or cipher algorithm.
    </para>

    <para>
     The following covers the user space interface exported by the kernel
     crypto API. A working example of this description is libkcapi that
     can be obtained from [1]. That library can be used by user space
     applications that require cryptographic services from the kernel.
    </para>

    <para>
     Some details of the in-kernel kernel crypto API aspects do not
     apply to user space, however. This includes the difference between
     synchronous and asynchronous invocations. The user space API call
     is fully synchronous.
    </para>

    <para>
     [1] <ulink url="http://www.chronox.de/libkcapi.html">http://www.chronox.de/libkcapi.html</ulink>
    </para>

   </sect1>

   <sect1><title>User Space API General Remarks</title>
    <para>
     The kernel crypto API is accessible from user space. Currently,
     the following ciphers are accessible:
    </para>

    <itemizedlist>
     <listitem>
      <para>Message digest including keyed message digest (HMAC, CMAC)</para>
     </listitem>

     <listitem>
      <para>Symmetric ciphers</para>
     </listitem>

     <listitem>
      <para>AEAD ciphers</para>
     </listitem>

     <listitem>
      <para>Random Number Generators</para>
     </listitem>
    </itemizedlist>

    <para>
     The interface is provided via socket type using the type AF_ALG.
     In addition, the setsockopt option type is SOL_ALG. In case the
     user space header files do not export these flags yet, use the
     following macros:
    </para>

    <programlisting>
#ifndef AF_ALG
#define AF_ALG 38
#endif
#ifndef SOL_ALG
#define SOL_ALG 279
#endif
    </programlisting>

    <para>
     A cipher is accessed with the same name as done for the in-kernel
     API calls. This includes the generic vs. unique naming schema for
     ciphers as well as the enforcement of priorities for generic names.
    </para>

    <para>
     To interact with the kernel crypto API, a socket must be
     created by the user space application. User space invokes the cipher
     operation with the send()/write() system call family. The result of the
     cipher operation is obtained with the read()/recv() system call family.
    </para>

    <para>
     The following API calls assume that the socket descriptor
     is already opened by the user space application and discusses only
     the kernel crypto API specific invocations.
    </para>

    <para>
     To initialize the socket interface, the following sequence has to
     be performed by the consumer:
    </para>

    <orderedlist>
     <listitem>
      <para>
       Create a socket of type AF_ALG with the struct sockaddr_alg
       parameter specified below for the different cipher types.
      </para>
     </listitem>

     <listitem>
      <para>
       Invoke bind with the socket descriptor
      </para>
     </listitem>

     <listitem>
      <para>
       Invoke accept with the socket descriptor. The accept system call
       returns a new file descriptor that is to be used to interact with
       the particular cipher instance. When invoking send/write or recv/read
       system calls to send data to the kernel or obtain data from the
       kernel, the file descriptor returned by accept must be used.
      </para>
     </listitem>
    </orderedlist>
   </sect1>

   <sect1><title>In-place Cipher operation</title>
    <para>
     Just like the in-kernel operation of the kernel crypto API, the user
     space interface allows the cipher operation in-place. That means that
     the input buffer used for the send/write system call and the output
     buffer used by the read/recv system call may be one and the same.
     This is of particular interest for symmetric cipher operations where a
     copying of the output data to its final destination can be avoided.
    </para>

    <para>
     If a consumer on the other hand wants to maintain the plaintext and
     the ciphertext in different memory locations, all a consumer needs
     to do is to provide different memory pointers for the encryption and
     decryption operation.
    </para>
   </sect1>

   <sect1><title>Message Digest API</title>
    <para>
     The message digest type to be used for the cipher operation is
     selected when invoking the bind syscall. bind requires the caller
     to provide a filled struct sockaddr data structure. This data
     structure must be filled as follows:
    </para>

    <programlisting>
struct sockaddr_alg sa = {
	.salg_family = AF_ALG,
	.salg_type = "hash", /* this selects the hash logic in the kernel */
	.salg_name = "sha1" /* this is the cipher name */
};
    </programlisting>

    <para>
     The salg_type value "hash" applies to message digests and keyed
     message digests. Though, a keyed message digest is referenced by
     the appropriate salg_name. Please see below for the setsockopt
     interface that explains how the key can be set for a keyed message
     digest.
    </para>

    <para>
     Using the send() system call, the application provides the data that
     should be processed with the message digest. The send system call
     allows the following flags to be specified:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       MSG_MORE: If this flag is set, the send system call acts like a
       message digest update function where the final hash is not
       yet calculated. If the flag is not set, the send system call
       calculates the final message digest immediately.
      </para>
     </listitem>
    </itemizedlist>

    <para>
     With the recv() system call, the application can read the message
     digest from the kernel crypto API. If the buffer is too small for the
     message digest, the flag MSG_TRUNC is set by the kernel.
    </para>

    <para>
     In order to set a message digest key, the calling application must use
     the setsockopt() option of ALG_SET_KEY. If the key is not set the HMAC
     operation is performed without the initial HMAC state change caused by
     the key.
    </para>
   </sect1>

   <sect1><title>Symmetric Cipher API</title>
    <para>
     The operation is very similar to the message digest discussion.
     During initialization, the struct sockaddr data structure must be
     filled as follows:
    </para>

    <programlisting>
struct sockaddr_alg sa = {
	.salg_family = AF_ALG,
	.salg_type = "skcipher", /* this selects the symmetric cipher */
	.salg_name = "cbc(aes)" /* this is the cipher name */
};
    </programlisting>

    <para>
     Before data can be sent to the kernel using the write/send system
     call family, the consumer must set the key. The key setting is
     described with the setsockopt invocation below.
    </para>

    <para>
     Using the sendmsg() system call, the application provides the data that should be processed for encryption or decryption. In addition, the IV is
     specified with the data structure provided by the sendmsg() system call.
    </para>

    <para>
     The sendmsg system call parameter of struct msghdr is embedded into the
     struct cmsghdr data structure. See recv(2) and cmsg(3) for more
     information on how the cmsghdr data structure is used together with the
     send/recv system call family. That cmsghdr data structure holds the
     following information specified with a separate header instances:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       specification of the cipher operation type with one of these flags:
      </para>
      <itemizedlist>
       <listitem>
        <para>ALG_OP_ENCRYPT - encryption of data</para>
       </listitem>
       <listitem>
        <para>ALG_OP_DECRYPT - decryption of data</para>
       </listitem>
      </itemizedlist>
     </listitem>

     <listitem>
      <para>
       specification of the IV information marked with the flag ALG_SET_IV
      </para>
     </listitem>
    </itemizedlist>

    <para>
     The send system call family allows the following flag to be specified:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       MSG_MORE: If this flag is set, the send system call acts like a
       cipher update function where more input data is expected
       with a subsequent invocation of the send system call.
      </para>
     </listitem>
    </itemizedlist>

    <para>
     Note: The kernel reports -EINVAL for any unexpected data. The caller
     must make sure that all data matches the constraints given in
     /proc/crypto for the selected cipher.
    </para>

    <para>
     With the recv() system call, the application can read the result of
     the cipher operation from the kernel crypto API. The output buffer
     must be at least as large as to hold all blocks of the encrypted or
     decrypted data. If the output data size is smaller, only as many
     blocks are returned that fit into that output buffer size.
    </para>
   </sect1>

   <sect1><title>AEAD Cipher API</title>
    <para>
     The operation is very similar to the symmetric cipher discussion.
     During initialization, the struct sockaddr data structure must be
     filled as follows:
    </para>

    <programlisting>
struct sockaddr_alg sa = {
	.salg_family = AF_ALG,
	.salg_type = "aead", /* this selects the symmetric cipher */
	.salg_name = "gcm(aes)" /* this is the cipher name */
};
    </programlisting>

    <para>
     Before data can be sent to the kernel using the write/send system
     call family, the consumer must set the key. The key setting is
     described with the setsockopt invocation below.
    </para>

    <para>
     In addition, before data can be sent to the kernel using the
     write/send system call family, the consumer must set the authentication
     tag size. To set the authentication tag size, the caller must use the
     setsockopt invocation described below.
    </para>

    <para>
     Using the sendmsg() system call, the application provides the data that should be processed for encryption or decryption. In addition, the IV is
     specified with the data structure provided by the sendmsg() system call.
    </para>

    <para>
     The sendmsg system call parameter of struct msghdr is embedded into the
     struct cmsghdr data structure. See recv(2) and cmsg(3) for more
     information on how the cmsghdr data structure is used together with the
     send/recv system call family. That cmsghdr data structure holds the
     following information specified with a separate header instances:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       specification of the cipher operation type with one of these flags:
      </para>
      <itemizedlist>
       <listitem>
        <para>ALG_OP_ENCRYPT - encryption of data</para>
       </listitem>
       <listitem>
        <para>ALG_OP_DECRYPT - decryption of data</para>
       </listitem>
      </itemizedlist>
     </listitem>

     <listitem>
      <para>
       specification of the IV information marked with the flag ALG_SET_IV
      </para>
     </listitem>

     <listitem>
      <para>
       specification of the associated authentication data (AAD) with the
       flag ALG_SET_AEAD_ASSOCLEN. The AAD is sent to the kernel together
       with the plaintext / ciphertext. See below for the memory structure.
      </para>
     </listitem>
    </itemizedlist>

    <para>
     The send system call family allows the following flag to be specified:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       MSG_MORE: If this flag is set, the send system call acts like a
       cipher update function where more input data is expected
       with a subsequent invocation of the send system call.
      </para>
     </listitem>
    </itemizedlist>

    <para>
     Note: The kernel reports -EINVAL for any unexpected data. The caller
     must make sure that all data matches the constraints given in
     /proc/crypto for the selected cipher.
    </para>

    <para>
     With the recv() system call, the application can read the result of
     the cipher operation from the kernel crypto API. The output buffer
     must be at least as large as defined with the memory structure below.
     If the output data size is smaller, the cipher operation is not performed.
    </para>

    <para>
     The authenticated decryption operation may indicate an integrity error.
     Such breach in integrity is marked with the -EBADMSG error code.
    </para>

    <sect2><title>AEAD Memory Structure</title>
     <para>
      The AEAD cipher operates with the following information that
      is communicated between user and kernel space as one data stream:
     </para>

     <itemizedlist>
      <listitem>
       <para>plaintext or ciphertext</para>
      </listitem>

      <listitem>
       <para>associated authentication data (AAD)</para>
      </listitem>

      <listitem>
       <para>authentication tag</para>
      </listitem>
     </itemizedlist>

     <para>
      The sizes of the AAD and the authentication tag are provided with
      the sendmsg and setsockopt calls (see there). As the kernel knows
      the size of the entire data stream, the kernel is now able to
      calculate the right offsets of the data components in the data
      stream.
     </para>

     <para>
      The user space caller must arrange the aforementioned information
      in the following order:
     </para>

     <itemizedlist>
      <listitem>
       <para>
        AEAD encryption input: AAD || plaintext
       </para>
      </listitem>

      <listitem>
       <para>
        AEAD decryption input: AAD || ciphertext || authentication tag
       </para>
      </listitem>
     </itemizedlist>

     <para>
      The output buffer the user space caller provides must be at least as
      large to hold the following data:
     </para>

     <itemizedlist>
      <listitem>
       <para>
        AEAD encryption output: ciphertext || authentication tag
       </para>
      </listitem>

      <listitem>
       <para>
        AEAD decryption output: plaintext
       </para>
      </listitem>
     </itemizedlist>
    </sect2>
   </sect1>

   <sect1><title>Random Number Generator API</title>
    <para>
     Again, the operation is very similar to the other APIs.
     During initialization, the struct sockaddr data structure must be
     filled as follows:
    </para>

    <programlisting>
struct sockaddr_alg sa = {
	.salg_family = AF_ALG,
	.salg_type = "rng", /* this selects the symmetric cipher */
	.salg_name = "drbg_nopr_sha256" /* this is the cipher name */
};
    </programlisting>

    <para>
     Depending on the RNG type, the RNG must be seeded. The seed is provided
     using the setsockopt interface to set the key. For example, the
     ansi_cprng requires a seed. The DRBGs do not require a seed, but
     may be seeded.
    </para>

    <para>
     Using the read()/recvmsg() system calls, random numbers can be obtained.
     The kernel generates at most 128 bytes in one call. If user space
     requires more data, multiple calls to read()/recvmsg() must be made.
    </para>

    <para>
     WARNING: The user space caller may invoke the initially mentioned
     accept system call multiple times. In this case, the returned file
     descriptors have the same state.
    </para>

   </sect1>

   <sect1><title>Zero-Copy Interface</title>
    <para>
     In addition to the send/write/read/recv system call family, the AF_ALG
     interface can be accessed with the zero-copy interface of splice/vmsplice.
     As the name indicates, the kernel tries to avoid a copy operation into
     kernel space.
    </para>

    <para>
     The zero-copy operation requires data to be aligned at the page boundary.
     Non-aligned data can be used as well, but may require more operations of
     the kernel which would defeat the speed gains obtained from the zero-copy
     interface.
    </para>

    <para>
     The system-interent limit for the size of one zero-copy operation is
     16 pages. If more data is to be sent to AF_ALG, user space must slice
     the input into segments with a maximum size of 16 pages.
    </para>

    <para>
     Zero-copy can be used with the following code example (a complete working
     example is provided with libkcapi):
    </para>

    <programlisting>
int pipes[2];

pipe(pipes);
/* input data in iov */
vmsplice(pipes[1], iov, iovlen, SPLICE_F_GIFT);
/* opfd is the file descriptor returned from accept() system call */
splice(pipes[0], NULL, opfd, NULL, ret, 0);
read(opfd, out, outlen);
    </programlisting>

   </sect1>

   <sect1><title>Setsockopt Interface</title>
    <para>
     In addition to the read/recv and send/write system call handling
     to send and retrieve data subject to the cipher operation, a consumer
     also needs to set the additional information for the cipher operation.
     This additional information is set using the setsockopt system call
     that must be invoked with the file descriptor of the open cipher
     (i.e. the file descriptor returned by the accept system call).
    </para>

    <para>
     Each setsockopt invocation must use the level SOL_ALG.
    </para>

    <para>
     The setsockopt interface allows setting the following data using
     the mentioned optname:
    </para>

    <itemizedlist>
     <listitem>
      <para>
       ALG_SET_KEY -- Setting the key. Key setting is applicable to:
      </para>
      <itemizedlist>
       <listitem>
        <para>the skcipher cipher type (symmetric ciphers)</para>
       </listitem>
       <listitem>
        <para>the hash cipher type (keyed message digests)</para>
       </listitem>
       <listitem>
        <para>the AEAD cipher type</para>
       </listitem>
       <listitem>
        <para>the RNG cipher type to provide the seed</para>
       </listitem>
      </itemizedlist>
     </listitem>

     <listitem>
      <para>
       ALG_SET_AEAD_AUTHSIZE -- Setting the authentication tag size
       for AEAD ciphers. For a encryption operation, the authentication
       tag of the given size will be generated. For a decryption operation,
       the provided ciphertext is assumed to contain an authentication tag
       of the given size (see section about AEAD memory layout below).
      </para>
     </listitem>
    </itemizedlist>

   </sect1>

   <sect1><title>User space API example</title>
    <para>
     Please see [1] for libkcapi which provides an easy-to-use wrapper
     around the aforementioned Netlink kernel interface. [1] also contains
     a test application that invokes all libkcapi API calls.
    </para>

    <para>
     [1] <ulink url="http://www.chronox.de/libkcapi.html">http://www.chronox.de/libkcapi.html</ulink>
    </para>

   </sect1>

  </chapter>

  <chapter id="API"><title>Programming Interface</title>
   <para>
    Please note that the kernel crypto API contains the AEAD givcrypt
    API (crypto_aead_giv* and aead_givcrypt_* function calls in
    include/crypto/aead.h). This API is obsolete and will be removed
    in the future. To obtain the functionality of an AEAD cipher with
    internal IV generation, use the IV generator as a regular cipher.
    For example, rfc4106(gcm(aes)) is the AEAD cipher with external
    IV generation and seqniv(rfc4106(gcm(aes))) implies that the kernel
    crypto API generates the IV. Different IV generators are available.
   </para>
   <sect1><title>Block Cipher Context Data Structures</title>
!Pinclude/linux/crypto.h Block Cipher Context Data Structures
!Finclude/crypto/aead.h aead_request
   </sect1>
   <sect1><title>Block Cipher Algorithm Definitions</title>
!Pinclude/linux/crypto.h Block Cipher Algorithm Definitions
!Finclude/linux/crypto.h crypto_alg
!Finclude/linux/crypto.h ablkcipher_alg
!Finclude/crypto/aead.h aead_alg
!Finclude/linux/crypto.h blkcipher_alg
!Finclude/linux/crypto.h cipher_alg
!Finclude/crypto/rng.h rng_alg
   </sect1>
   <sect1><title>Asynchronous Block Cipher API</title>
!Pinclude/linux/crypto.h Asynchronous Block Cipher API
!Finclude/linux/crypto.h crypto_alloc_ablkcipher
!Finclude/linux/crypto.h crypto_free_ablkcipher
!Finclude/linux/crypto.h crypto_has_ablkcipher
!Finclude/linux/crypto.h crypto_ablkcipher_ivsize
!Finclude/linux/crypto.h crypto_ablkcipher_blocksize
!Finclude/linux/crypto.h crypto_ablkcipher_setkey
!Finclude/linux/crypto.h crypto_ablkcipher_reqtfm
!Finclude/linux/crypto.h crypto_ablkcipher_encrypt
!Finclude/linux/crypto.h crypto_ablkcipher_decrypt
   </sect1>
   <sect1><title>Asynchronous Cipher Request Handle</title>
!Pinclude/linux/crypto.h Asynchronous Cipher Request Handle
!Finclude/linux/crypto.h crypto_ablkcipher_reqsize
!Finclude/linux/crypto.h ablkcipher_request_set_tfm
!Finclude/linux/crypto.h ablkcipher_request_alloc
!Finclude/linux/crypto.h ablkcipher_request_free
!Finclude/linux/crypto.h ablkcipher_request_set_callback
!Finclude/linux/crypto.h ablkcipher_request_set_crypt
   </sect1>
   <sect1><title>Authenticated Encryption With Associated Data (AEAD) Cipher API</title>
!Pinclude/crypto/aead.h Authenticated Encryption With Associated Data (AEAD) Cipher API
!Finclude/crypto/aead.h crypto_alloc_aead
!Finclude/crypto/aead.h crypto_free_aead
!Finclude/crypto/aead.h crypto_aead_ivsize
!Finclude/crypto/aead.h crypto_aead_authsize
!Finclude/crypto/aead.h crypto_aead_blocksize
!Finclude/crypto/aead.h crypto_aead_setkey
!Finclude/crypto/aead.h crypto_aead_setauthsize
!Finclude/crypto/aead.h crypto_aead_encrypt
!Finclude/crypto/aead.h crypto_aead_decrypt
   </sect1>
   <sect1><title>Asynchronous AEAD Request Handle</title>
!Pinclude/crypto/aead.h Asynchronous AEAD Request Handle
!Finclude/crypto/aead.h crypto_aead_reqsize
!Finclude/crypto/aead.h aead_request_set_tfm
!Finclude/crypto/aead.h aead_request_alloc
!Finclude/crypto/aead.h aead_request_free
!Finclude/crypto/aead.h aead_request_set_callback
!Finclude/crypto/aead.h aead_request_set_crypt
!Finclude/crypto/aead.h aead_request_set_assoc
!Finclude/crypto/aead.h aead_request_set_ad
   </sect1>
   <sect1><title>Synchronous Block Cipher API</title>
!Pinclude/linux/crypto.h Synchronous Block Cipher API
!Finclude/linux/crypto.h crypto_alloc_blkcipher
!Finclude/linux/crypto.h crypto_free_blkcipher
!Finclude/linux/crypto.h crypto_has_blkcipher
!Finclude/linux/crypto.h crypto_blkcipher_name
!Finclude/linux/crypto.h crypto_blkcipher_ivsize
!Finclude/linux/crypto.h crypto_blkcipher_blocksize
!Finclude/linux/crypto.h crypto_blkcipher_setkey
!Finclude/linux/crypto.h crypto_blkcipher_encrypt
!Finclude/linux/crypto.h crypto_blkcipher_encrypt_iv
!Finclude/linux/crypto.h crypto_blkcipher_decrypt
!Finclude/linux/crypto.h crypto_blkcipher_decrypt_iv
!Finclude/linux/crypto.h crypto_blkcipher_set_iv
!Finclude/linux/crypto.h crypto_blkcipher_get_iv
   </sect1>
   <sect1><title>Single Block Cipher API</title>
!Pinclude/linux/crypto.h Single Block Cipher API
!Finclude/linux/crypto.h crypto_alloc_cipher
!Finclude/linux/crypto.h crypto_free_cipher
!Finclude/linux/crypto.h crypto_has_cipher
!Finclude/linux/crypto.h crypto_cipher_blocksize
!Finclude/linux/crypto.h crypto_cipher_setkey
!Finclude/linux/crypto.h crypto_cipher_encrypt_one
!Finclude/linux/crypto.h crypto_cipher_decrypt_one
   </sect1>
   <sect1><title>Synchronous Message Digest API</title>
!Pinclude/linux/crypto.h Synchronous Message Digest API
!Finclude/linux/crypto.h crypto_alloc_hash
!Finclude/linux/crypto.h crypto_free_hash
!Finclude/linux/crypto.h crypto_has_hash
!Finclude/linux/crypto.h crypto_hash_blocksize
!Finclude/linux/crypto.h crypto_hash_digestsize
!Finclude/linux/crypto.h crypto_hash_init
!Finclude/linux/crypto.h crypto_hash_update
!Finclude/linux/crypto.h crypto_hash_final
!Finclude/linux/crypto.h crypto_hash_digest
!Finclude/linux/crypto.h crypto_hash_setkey
   </sect1>
   <sect1><title>Message Digest Algorithm Definitions</title>
!Pinclude/crypto/hash.h Message Digest Algorithm Definitions
!Finclude/crypto/hash.h hash_alg_common
!Finclude/crypto/hash.h ahash_alg
!Finclude/crypto/hash.h shash_alg
   </sect1>
   <sect1><title>Asynchronous Message Digest API</title>
!Pinclude/crypto/hash.h Asynchronous Message Digest API
!Finclude/crypto/hash.h crypto_alloc_ahash
!Finclude/crypto/hash.h crypto_free_ahash
!Finclude/crypto/hash.h crypto_ahash_init
!Finclude/crypto/hash.h crypto_ahash_digestsize
!Finclude/crypto/hash.h crypto_ahash_reqtfm
!Finclude/crypto/hash.h crypto_ahash_reqsize
!Finclude/crypto/hash.h crypto_ahash_setkey
!Finclude/crypto/hash.h crypto_ahash_finup
!Finclude/crypto/hash.h crypto_ahash_final
!Finclude/crypto/hash.h crypto_ahash_digest
!Finclude/crypto/hash.h crypto_ahash_export
!Finclude/crypto/hash.h crypto_ahash_import
   </sect1>
   <sect1><title>Asynchronous Hash Request Handle</title>
!Pinclude/crypto/hash.h Asynchronous Hash Request Handle
!Finclude/crypto/hash.h ahash_request_set_tfm
!Finclude/crypto/hash.h ahash_request_alloc
!Finclude/crypto/hash.h ahash_request_free
!Finclude/crypto/hash.h ahash_request_set_callback
!Finclude/crypto/hash.h ahash_request_set_crypt
   </sect1>
   <sect1><title>Synchronous Message Digest API</title>
!Pinclude/crypto/hash.h Synchronous Message Digest API
!Finclude/crypto/hash.h crypto_alloc_shash
!Finclude/crypto/hash.h crypto_free_shash
!Finclude/crypto/hash.h crypto_shash_blocksize
!Finclude/crypto/hash.h crypto_shash_digestsize
!Finclude/crypto/hash.h crypto_shash_descsize
!Finclude/crypto/hash.h crypto_shash_setkey
!Finclude/crypto/hash.h crypto_shash_digest
!Finclude/crypto/hash.h crypto_shash_export
!Finclude/crypto/hash.h crypto_shash_import
!Finclude/crypto/hash.h crypto_shash_init
!Finclude/crypto/hash.h crypto_shash_update
!Finclude/crypto/hash.h crypto_shash_final
!Finclude/crypto/hash.h crypto_shash_finup
   </sect1>
   <sect1><title>Crypto API Random Number API</title>
!Pinclude/crypto/rng.h Random number generator API
!Finclude/crypto/rng.h crypto_alloc_rng
!Finclude/crypto/rng.h crypto_rng_alg
!Finclude/crypto/rng.h crypto_free_rng
!Finclude/crypto/rng.h crypto_rng_get_bytes
!Finclude/crypto/rng.h crypto_rng_reset
!Finclude/crypto/rng.h crypto_rng_seedsize
!Cinclude/crypto/rng.h
   </sect1>
  </chapter>

  <chapter id="Code"><title>Code Examples</title>
   <sect1><title>Code Example For Asynchronous Block Cipher Operation</title>
    <programlisting>

struct tcrypt_result {
	struct completion completion;
	int err;
};

/* tie all data structures together */
struct ablkcipher_def {
	struct scatterlist sg;
	struct crypto_ablkcipher *tfm;
	struct ablkcipher_request *req;
	struct tcrypt_result result;
};

/* Callback function */
static void test_ablkcipher_cb(struct crypto_async_request *req, int error)
{
	struct tcrypt_result *result = req-&gt;data;

	if (error == -EINPROGRESS)
		return;
	result-&gt;err = error;
	complete(&amp;result-&gt;completion);
	pr_info("Encryption finished successfully\n");
}

/* Perform cipher operation */
static unsigned int test_ablkcipher_encdec(struct ablkcipher_def *ablk,
					   int enc)
{
	int rc = 0;

	if (enc)
		rc = crypto_ablkcipher_encrypt(ablk-&gt;req);
	else
		rc = crypto_ablkcipher_decrypt(ablk-&gt;req);

	switch (rc) {
	case 0:
		break;
	case -EINPROGRESS:
	case -EBUSY:
		rc = wait_for_completion_interruptible(
			&amp;ablk-&gt;result.completion);
		if (!rc &amp;&amp; !ablk-&gt;result.err) {
			reinit_completion(&amp;ablk-&gt;result.completion);
			break;
		}
	default:
		pr_info("ablkcipher encrypt returned with %d result %d\n",
		       rc, ablk-&gt;result.err);
		break;
	}
	init_completion(&amp;ablk-&gt;result.completion);

	return rc;
}

/* Initialize and trigger cipher operation */
static int test_ablkcipher(void)
{
	struct ablkcipher_def ablk;
	struct crypto_ablkcipher *ablkcipher = NULL;
	struct ablkcipher_request *req = NULL;
	char *scratchpad = NULL;
	char *ivdata = NULL;
	unsigned char key[32];
	int ret = -EFAULT;

	ablkcipher = crypto_alloc_ablkcipher("cbc-aes-aesni", 0, 0);
	if (IS_ERR(ablkcipher)) {
		pr_info("could not allocate ablkcipher handle\n");
		return PTR_ERR(ablkcipher);
	}

	req = ablkcipher_request_alloc(ablkcipher, GFP_KERNEL);
	if (IS_ERR(req)) {
		pr_info("could not allocate request queue\n");
		ret = PTR_ERR(req);
		goto out;
	}

	ablkcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
					test_ablkcipher_cb,
					&amp;ablk.result);

	/* AES 256 with random key */
	get_random_bytes(&amp;key, 32);
	if (crypto_ablkcipher_setkey(ablkcipher, key, 32)) {
		pr_info("key could not be set\n");
		ret = -EAGAIN;
		goto out;
	}

	/* IV will be random */
	ivdata = kmalloc(16, GFP_KERNEL);
	if (!ivdata) {
		pr_info("could not allocate ivdata\n");
		goto out;
	}
	get_random_bytes(ivdata, 16);

	/* Input data will be random */
	scratchpad = kmalloc(16, GFP_KERNEL);
	if (!scratchpad) {
		pr_info("could not allocate scratchpad\n");
		goto out;
	}
	get_random_bytes(scratchpad, 16);

	ablk.tfm = ablkcipher;
	ablk.req = req;

	/* We encrypt one block */
	sg_init_one(&amp;ablk.sg, scratchpad, 16);
	ablkcipher_request_set_crypt(req, &amp;ablk.sg, &amp;ablk.sg, 16, ivdata);
	init_completion(&amp;ablk.result.completion);

	/* encrypt data */
	ret = test_ablkcipher_encdec(&amp;ablk, 1);
	if (ret)
		goto out;

	pr_info("Encryption triggered successfully\n");

out:
	if (ablkcipher)
		crypto_free_ablkcipher(ablkcipher);
	if (req)
		ablkcipher_request_free(req);
	if (ivdata)
		kfree(ivdata);
	if (scratchpad)
		kfree(scratchpad);
	return ret;
}
    </programlisting>
   </sect1>

   <sect1><title>Code Example For Synchronous Block Cipher Operation</title>
    <programlisting>

static int test_blkcipher(void)
{
	struct crypto_blkcipher *blkcipher = NULL;
	char *cipher = "cbc(aes)";
	// AES 128
	charkey =
"\x12\x34\x56\x78\x90\xab\xcd\xef\x12\x34\x56\x78\x90\xab\xcd\xef";
	chariv =
"\x12\x34\x56\x78\x90\xab\xcd\xef\x12\x34\x56\x78\x90\xab\xcd\xef";
	unsigned int ivsize = 0;
	char *scratchpad = NULL; // holds plaintext and ciphertext
	struct scatterlist sg;
	struct blkcipher_desc desc;
	int ret = -EFAULT;

	blkcipher = crypto_alloc_blkcipher(cipher, 0, 0);
	if (IS_ERR(blkcipher)) {
		printk("could not allocate blkcipher handle for %s\n", cipher);
		return -PTR_ERR(blkcipher);
	}

	if (crypto_blkcipher_setkey(blkcipher, key, strlen(key))) {
		printk("key could not be set\n");
		ret = -EAGAIN;
		goto out;
	}

	ivsize = crypto_blkcipher_ivsize(blkcipher);
	if (ivsize) {
		if (ivsize != strlen(iv))
			printk("IV length differs from expected length\n");
		crypto_blkcipher_set_iv(blkcipher, iv, ivsize);
	}

	scratchpad = kmalloc(crypto_blkcipher_blocksize(blkcipher), GFP_KERNEL);
	if (!scratchpad) {
		printk("could not allocate scratchpad for %s\n", cipher);
		goto out;
	}
	/* get some random data that we want to encrypt */
	get_random_bytes(scratchpad, crypto_blkcipher_blocksize(blkcipher));

	desc.flags = 0;
	desc.tfm = blkcipher;
	sg_init_one(&amp;sg, scratchpad, crypto_blkcipher_blocksize(blkcipher));

	/* encrypt data in place */
	crypto_blkcipher_encrypt(&amp;desc, &amp;sg, &amp;sg,
				 crypto_blkcipher_blocksize(blkcipher));

	/* decrypt data in place
	 * crypto_blkcipher_decrypt(&amp;desc, &amp;sg, &amp;sg,
	 */			 crypto_blkcipher_blocksize(blkcipher));


	printk("Cipher operation completed\n");
	return 0;

out:
	if (blkcipher)
		crypto_free_blkcipher(blkcipher);
	if (scratchpad)
		kzfree(scratchpad);
	return ret;
}
    </programlisting>
   </sect1>

   <sect1><title>Code Example For Use of Operational State Memory With SHASH</title>
    <programlisting>

struct sdesc {
	struct shash_desc shash;
	char ctx[];
};

static struct sdescinit_sdesc(struct crypto_shash *alg)
{
	struct sdescsdesc;
	int size;

	size = sizeof(struct shash_desc) + crypto_shash_descsize(alg);
	sdesc = kmalloc(size, GFP_KERNEL);
	if (!sdesc)
		return ERR_PTR(-ENOMEM);
	sdesc-&gt;shash.tfm = alg;
	sdesc-&gt;shash.flags = 0x0;
	return sdesc;
}

static int calc_hash(struct crypto_shashalg,
		     const unsigned chardata, unsigned int datalen,
		     unsigned chardigest) {
	struct sdescsdesc;
	int ret;

	sdesc = init_sdesc(alg);
	if (IS_ERR(sdesc)) {
		pr_info("trusted_key: can't alloc %s\n", hash_alg);
		return PTR_ERR(sdesc);
	}

	ret = crypto_shash_digest(&amp;sdesc-&gt;shash, data, datalen, digest);
	kfree(sdesc);
	return ret;
}
    </programlisting>
   </sect1>

   <sect1><title>Code Example For Random Number Generator Usage</title>
    <programlisting>

static int get_random_numbers(u8 *buf, unsigned int len)
{
	struct crypto_rngrng = NULL;
	chardrbg = "drbg_nopr_sha256"; /* Hash DRBG with SHA-256, no PR */
	int ret;

	if (!buf || !len) {
		pr_debug("No output buffer provided\n");
		return -EINVAL;
	}

	rng = crypto_alloc_rng(drbg, 0, 0);
	if (IS_ERR(rng)) {
		pr_debug("could not allocate RNG handle for %s\n", drbg);
		return -PTR_ERR(rng);
	}

	ret = crypto_rng_get_bytes(rng, buf, len);
	if (ret &lt; 0)
		pr_debug("generation of random numbers failed\n");
	else if (ret == 0)
		pr_debug("RNG returned no data");
	else
		pr_debug("RNG returned %d bytes of data\n", ret);

out:
	crypto_free_rng(rng);
	return ret;
}
    </programlisting>
   </sect1>
  </chapter>
 </book>