aboutsummaryrefslogtreecommitdiffstats
path: root/lib/crypto/doc/src/crypto.xml
blob: cc72bde9cbb9c4580b47bf649005ac87a6283b7d (plain) (blame)
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
<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1999</year><year>2017</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    </legalnotice>

    <title>crypto</title>
  </header>
  <module>crypto</module>
  <modulesummary>Crypto Functions</modulesummary>
  <description>
    <p>This module provides a set of cryptographic functions.
      </p>
    <list type="bulleted">
      <item>
	<p>Hash functions -
	<url href="http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf"> Secure Hash Standard</url>,
	<url href="http://www.ietf.org/rfc/rfc1321.txt"> The MD5 Message Digest Algorithm (RFC 1321)</url> and
	<url href="http://www.ietf.org/rfc/rfc1320.txt">The MD4 Message Digest Algorithm (RFC 1320)</url>
	</p>
      </item>
      <item>
        <p>Hmac functions - <url href="http://www.ietf.org/rfc/rfc2104.txt"> Keyed-Hashing for Message Authentication (RFC 2104) </url></p>
      </item>
      <item>
        <p>Cmac functions - <url href="http://www.ietf.org/rfc/rfc4493.txt">The AES-CMAC Algorithm (RFC 4493)</url></p>
      </item>
      <item>
        <p>Block ciphers - <url href="http://csrc.nist.gov/groups/ST/toolkit/block_ciphers.html"> </url> DES and AES in
        Block Cipher Modes - <url href="http://csrc.nist.gov/groups/ST/toolkit/BCM/index.html"> ECB, CBC, CFB, OFB, CTR and GCM </url></p>
      </item>
      <item>
        <p><url href="http://www.ietf.org/rfc/rfc1321.txt"> RSA encryption RFC 1321 </url> </p>
      </item>
      <item>
        <p>Digital signatures <url href="http://csrc.nist.gov/publications/drafts/fips186-3/fips_186-3.pdf">Digital Signature Standard (DSS)</url> and<url href="http://csrc.nist.gov/groups/STM/cavp/documents/dss2/ecdsa2vs.pdf"> Elliptic Curve Digital
	Signature Algorithm (ECDSA) </url> </p>
      </item>
      <item>
        <p><url href="http://www.ietf.org/rfc/rfc2945.txt"> Secure Remote Password Protocol (SRP - RFC 2945) </url></p>
      </item>
      <item>
        <p>gcm: Dworkin, M., "Recommendation for Block Cipher Modes of
        Operation: Galois/Counter Mode (GCM) and GMAC",
        National Institute of Standards and Technology SP 800-
        38D, November 2007.</p>
      </item>
    </list>
  </description>

 <section>
    <title>DATA TYPES </title>

    <code>key_value() = integer() | binary() </code>
    <p>Always <c>binary()</c> when used as return value</p>

    <code>rsa_public() = [key_value()] = [E, N]  </code>
    <p> Where E is the public exponent and N is public modulus. </p>

    <code>rsa_private() = [key_value()] = [E, N, D] | [E, N, D, P1, P2, E1, E2, C] </code>
    <p>Where E is the public exponent, N is public modulus and D is
    the private exponent. The longer key format contains redundant
    information that will make the calculation faster. P1,P2 are first
    and second prime factors. E1,E2 are first and second exponents. C
    is the CRT coefficient. Terminology is taken from <url href="http://www.ietf.org/rfc/rfc3477.txt"> RFC 3447</url>.</p>

    <code>dss_public() = [key_value()] = [P, Q, G, Y] </code>
    <p>Where P, Q and G are the dss parameters and Y is the public key.</p>

    <code>dss_private() = [key_value()] = [P, Q, G, X] </code>
    <p>Where P, Q and G are the dss parameters and X is the private key.</p>

    <code>srp_public() = key_value() </code>
    <p>Where is <c>A</c> or <c>B</c> from <url href="http://srp.stanford.edu/design.html">SRP design</url></p>

    <code>srp_private() = key_value() </code>
    <p>Where is  <c>a</c> or <c>b</c> from <url href="http://srp.stanford.edu/design.html">SRP design</url></p>

    <p>Where Verifier is <c>v</c>, Generator is <c>g</c> and Prime is<c> N</c>, DerivedKey is <c>X</c>, and Scrambler is
    <c>u</c> (optional will be generated if not provided) from <url href="http://srp.stanford.edu/design.html">SRP design</url>
    Version = '3' |  '6' |  '6a'
    </p>

    <code>dh_public() = key_value() </code>

    <code>dh_private() = key_value() </code>

    <code>dh_params() = [key_value()] = [P, G] | [P, G, PrivateKeyBitLength]</code>

    <code>ecdh_public() = key_value() </code>

    <code>ecdh_private() = key_value() </code>

    <code>ecdh_params() = ec_named_curve() | ec_explicit_curve()</code>

    <code>ec_explicit_curve() =
    {ec_field(), Prime :: key_value(), Point :: key_value(), Order :: integer(),
     CoFactor :: none | integer()} </code>

    <code>ec_field() = {prime_field, Prime :: integer()} |
    {characteristic_two_field, M :: integer(), Basis :: ec_basis()}</code>

    <code>ec_basis() = {tpbasis, K :: non_neg_integer()} |
    {ppbasis, K1 :: non_neg_integer(), K2 :: non_neg_integer(), K3 :: non_neg_integer()} |
    onbasis</code>

    <code>ec_named_curve() ->
      sect571r1| sect571k1| sect409r1| sect409k1| secp521r1| secp384r1| secp224r1| secp224k1|
      secp192k1| secp160r2| secp128r2| secp128r1| sect233r1| sect233k1| sect193r2| sect193r1|
      sect131r2| sect131r1| sect283r1| sect283k1| sect163r2| secp256k1| secp160k1| secp160r1|
      secp112r2| secp112r1| sect113r2| sect113r1| sect239k1| sect163r1| sect163k1| secp256r1|
      secp192r1|
      brainpoolP160r1| brainpoolP160t1| brainpoolP192r1| brainpoolP192t1| brainpoolP224r1|
      brainpoolP224t1| brainpoolP256r1| brainpoolP256t1| brainpoolP320r1| brainpoolP320t1|
      brainpoolP384r1| brainpoolP384t1| brainpoolP512r1| brainpoolP512t1
    </code>
    <p>Note that the <em>sect</em> curves are GF2m (characteristic two) curves and are only supported if the
    underlying OpenSSL has support for them.
    See also <seealso marker="#supports-0">crypto:supports/0</seealso>
    </p>

    <code>engine_key_ref() = #{engine   := engine_ref(),
                               key_id   := key_id(),
                               password => password()}</code>

    <code>engine_key_ref() = term()</code>
    <p>The result of a call to <seealso marker="#engine_load-3">engine_load/3</seealso>.
    </p>

    <code>key_id() = string() | binary()</code>
    <p>Identifies the key to be used. The format depends on the loaded engine. It is passed to
    the <c>ENGINE_load_(private|public)_key</c> functions in libcrypto.
    </p>

    <code>password() = string() | binary()</code>
    <p>The key's password
    </p>

     <code>stream_cipher() = rc4 | aes_ctr </code>

     <code>block_cipher() = aes_cbc | aes_cfb8 | aes_cfb128 | aes_ige256 | blowfish_cbc |
     blowfish_cfb64 | des_cbc | des_cfb | des3_cbc | des3_cfb | des_ede3 | rc2_cbc </code>

     <code>aead_cipher() = aes_gcm | chacha20_poly1305 </code>

     <code>stream_key() = aes_key() | rc4_key() </code>

     <code>block_key() = aes_key() |  blowfish_key() | des_key()| des3_key() </code>

     <code>aes_key() = iodata() </code> <p>Key length is 128, 192 or 256 bits</p>

     <code>rc4_key() = iodata() </code> <p>Variable key length from 8 bits up to 2048 bits (usually between 40 and 256)</p>

     <code>blowfish_key() = iodata() </code> <p>Variable key length from 32 bits up to 448 bits</p>

     <code>des_key() = iodata() </code> <p>Key length is 64 bits (in CBC mode only 8 bits are used)</p>

     <code>des3_key() = [binary(), binary(), binary()] </code> <p>Each key part is 64 bits (in CBC mode only 8 bits are used)</p>

     <code>digest_type() =  md5 | sha | sha224 | sha256 | sha384 | sha512</code>

     <code>rsa_digest_type() = md5 | ripemd160 | sha | sha224 | sha256 | sha384 | sha512</code>

     <code>dss_digest_type() = sha | sha224 | sha256 | sha384 | sha512</code> <p>Note that the actual supported
     dss_digest_type depends on the underlying crypto library. In OpenSSL version >= 1.0.1 the listed digest are supported, while in 1.0.0 only sha, sha224 and sha256 are supported. In version 0.9.8 only sha is supported.</p>

     <code>ecdsa_digest_type() = sha | sha224 | sha256 | sha384 | sha512</code>

     <code>sign_options() = [{rsa_pad, rsa_sign_padding()} | {rsa_pss_saltlen, integer()}]</code>

     <code>rsa_sign_padding() = rsa_pkcs1_padding | rsa_pkcs1_pss_padding</code>

     <code> hash_algorithms() =  md5 | ripemd160 | sha | sha224 | sha256 | sha384 | sha512 </code> <p>md4 is also supported for hash_init/1 and hash/2.
     Note that both md4 and md5 are recommended only for compatibility with existing applications.
     </p>
     <code> cipher_algorithms() = aes_cbc | aes_cfb8 | aes_cfb128 | aes_ctr | aes_gcm |
     aes_ige256 | blowfish_cbc | blowfish_cfb64 | chacha20_poly1305 | des_cbc |
     des_cfb | des3_cbc | des3_cfb | des_ede3 | rc2_cbc | rc4 </code>
     <code> mac_algorithms() = hmac | cmac</code>
     <code> public_key_algorithms() = rsa |dss | ecdsa | dh | ecdh | ec_gf2m</code>
     <p>Note that ec_gf2m is not strictly a public key algorithm, but a restriction on what curves are supported
     with ecdsa and ecdh.
     </p>
     <code>engine_method_type() = engine_method_rsa | engine_method_dsa | engine_method_dh |
     engine_method_rand | engine_method_ecdh | engine_method_ecdsa |
     engine_method_ciphers | engine_method_digests | engine_method_store |
     engine_method_pkey_meths | engine_method_pkey_asn1_meths</code>

 </section>

  <funcs>
    <func>
      <name>block_encrypt(Type, Key, PlainText) -> CipherText</name>
      <fsummary>Encrypt <c>PlainText</c> according to <c>Type</c> block cipher</fsummary>
      <type>
  <v>Type = des_ecb | blowfish_ecb | aes_ecb </v>
  <v>Key = block_key() </v>
        <v>PlainText = iodata() </v>
      </type>
      <desc>
        <p>Encrypt <c>PlainText</c> according to <c>Type</c> block cipher.</p>
  <p>May throw exception <c>notsup</c> in case the chosen <c>Type</c>
  is not supported by the underlying OpenSSL implementation.</p>
      </desc>
    </func>

    <func>
      <name>block_decrypt(Type, Key, CipherText) -> PlainText</name>
      <fsummary>Decrypt <c>CipherText</c> according to <c>Type</c> block cipher</fsummary>
      <type>
  <v>Type = des_ecb | blowfish_ecb | aes_ecb </v>
  <v>Key = block_key() </v>
        <v>PlainText = iodata() </v>
      </type>
      <desc>
        <p>Decrypt <c>CipherText</c> according to <c>Type</c> block cipher.</p>
  <p>May throw exception <c>notsup</c> in case the chosen <c>Type</c>
  is not supported by the underlying OpenSSL implementation.</p>
      </desc>
    </func>

    <func>
      <name>block_encrypt(Type, Key, Ivec, PlainText) -> CipherText</name>
      <name>block_encrypt(AeadType, Key, Ivec, {AAD, PlainText}) -> {CipherText, CipherTag}</name>
      <name>block_encrypt(aes_gcm, Key, Ivec, {AAD, PlainText, TagLength}) -> {CipherText, CipherTag}</name>
      <fsummary>Encrypt <c>PlainText</c> according to <c>Type</c> block cipher</fsummary>
      <type>
	<v>Type = block_cipher() </v>
	<v>AeadType = aead_cipher() </v>
	<v>Key = block_key() </v>
        <v>PlainText = iodata() </v>
        <v>AAD = IVec = CipherText = CipherTag = binary()</v>
        <v>TagLength = 1..16</v>
      </type>
      <desc>
        <p>Encrypt <c>PlainText</c> according to <c>Type</c> block cipher.
	<c>IVec</c> is an arbitrary initializing vector.</p>
	<p>In AEAD (Authenticated Encryption with Associated Data) mode, encrypt
	<c>PlainText</c>according to <c>Type</c> block cipher and calculate
	<c>CipherTag</c> that also authenticates the <c>AAD</c> (Associated Authenticated Data).</p>
	<p>May throw exception <c>notsup</c> in case the chosen <c>Type</c>
	is not supported by the underlying OpenSSL implementation.</p>
      </desc>
    </func>

    <func>
      <name>block_decrypt(Type, Key, Ivec, CipherText) -> PlainText</name>
      <name>block_decrypt(AeadType, Key, Ivec, {AAD, CipherText, CipherTag}) -> PlainText | error</name>
      <fsummary>Decrypt <c>CipherText</c> according to <c>Type</c> block cipher</fsummary>
      <type>
	<v>Type = block_cipher() </v>
	<v>AeadType = aead_cipher() </v>
	<v>Key = block_key() </v>
        <v>PlainText = iodata() </v>
        <v>AAD = IVec = CipherText = CipherTag = binary()</v>
      </type>
      <desc>
        <p>Decrypt <c>CipherText</c> according to <c>Type</c> block cipher.
	<c>IVec</c> is an arbitrary initializing vector.</p>
        <p>In AEAD (Authenticated Encryption with Associated Data) mode, decrypt
	<c>CipherText</c>according to <c>Type</c> block cipher and check the authenticity
	the <c>PlainText</c> and <c>AAD</c> (Associated Authenticated Data) using the
	<c>CipherTag</c>. May return <c>error</c> if the decryption or validation fail's</p>
	<p>May throw exception <c>notsup</c> in case the chosen <c>Type</c>
	is not supported by the underlying OpenSSL implementation.</p>
      </desc>
    </func>

     <func>
      <name>bytes_to_integer(Bin) -> Integer </name>
      <fsummary>Convert binary representation, of an integer, to an Erlang integer.</fsummary>
      <type>
	<v>Bin = binary() - as returned by crypto functions</v>

        <v>Integer = integer() </v>
      </type>
      <desc>
        <p>Convert binary representation, of an integer, to an Erlang integer.
         </p>
      </desc>
    </func>

    <func>
      <name>compute_key(Type, OthersPublicKey, MyKey, Params) -> SharedSecret</name>
      <fsummary>Computes the shared secret</fsummary>
      <type>
	<v> Type = dh | ecdh | srp </v>
	<v>OthersPublicKey =  dh_public() | ecdh_public() | srp_public() </v>
	<v>MyKey = dh_private() | ecdh_private() | {srp_public(),srp_private()}</v>
	<v>Params = dh_params() | ecdh_params() | SrpUserParams | SrpHostParams</v>
	<v>SrpUserParams = {user, [DerivedKey::binary(), Prime::binary(), Generator::binary(), Version::atom() | [Scrambler:binary()]]} </v>
	<v>SrpHostParams = {host, [Verifier::binary(), Prime::binary(), Version::atom() | [Scrambler::binary]]} </v>
	<v>SharedSecret = binary()</v>
      </type>
      <desc>
	<p>Computes the shared secret from the private key and the other party's public key.
	 See also <seealso marker="public_key:public_key#compute_key-2">public_key:compute_key/2</seealso>
	</p>
      </desc>
    </func>

    <func>
      <name>exor(Data1, Data2) -> Result</name>
      <fsummary>XOR data</fsummary>
      <type>
	<v>Data1, Data2 = iodata()</v>
	<v>Result = binary()</v>
      </type>
      <desc>
	<p>Performs bit-wise XOR (exclusive or) on the data supplied.</p>
      </desc>
    </func>

   <func>
      <name>generate_key(Type, Params) -> {PublicKey, PrivKeyOut} </name>
      <name>generate_key(Type, Params, PrivKeyIn) -> {PublicKey, PrivKeyOut} </name>
      <fsummary>Generates a public key of type <c>Type</c></fsummary>
      <type>
	<v> Type = dh | ecdh | rsa | srp </v>
	<v>Params = dh_params() | ecdh_params() | RsaParams | SrpUserParams | SrpHostParams </v>
	<v>RsaParams = {ModulusSizeInBits::integer(), PublicExponent::key_value()}</v>
	<v>SrpUserParams = {user, [Generator::binary(), Prime::binary(), Version::atom()]}</v>
	<v>SrpHostParams = {host, [Verifier::binary(), Generator::binary(), Prime::binary(), Version::atom()]}</v>
	<v>PublicKey =  dh_public() | ecdh_public() | rsa_public() | srp_public() </v>
	<v>PrivKeyIn = undefined | dh_private() | ecdh_private() | srp_private() </v>
	<v>PrivKeyOut =  dh_private() | ecdh_private() | rsa_private() | srp_private() </v>
      </type>
      <desc>
	<p>Generates a public key of type <c>Type</c>.
	See also <seealso marker="public_key:public_key#generate_key-1">public_key:generate_key/1</seealso>.
	May throw exception an exception of class <c>error</c>:
        </p>
        <list type="bulleted">
          <item><c>badarg</c>: an argument is of wrong type or has an illegal value,</item>
	  <item><c>low_entropy</c>: the random generator failed due to lack of secure "randomness",</item>
          <item><c>computation_failed</c>: the computation fails of another reason than <c>low_entropy</c>.</item>
        </list>
	<note>
	  <p>RSA key generation is only available if the runtime was
	  built with dirty scheduler support. Otherwise, attempting to
	  generate an RSA key will throw exception <c>error:notsup</c>.</p>
	</note>
      </desc>
    </func>

     <func>
      <name>hash(Type, Data) -> Digest</name>
      <fsummary></fsummary>
      <type>
	<v>Type = md4 | hash_algorithms()</v>
	<v>Data = iodata()</v>
	<v>Digest = binary()</v>
      </type>
      <desc>
        <p>Computes a message digest of type <c>Type</c> from <c>Data</c>.</p>
	<p>May throw exception <c>notsup</c> in case the chosen <c>Type</c>
	is not supported by the underlying OpenSSL implementation.</p>
      </desc>
    </func>

    <func>
      <name>hash_init(Type) -> Context</name>
      <fsummary></fsummary>
      <type>
	<v>Type = md4 | hash_algorithms()</v>
      </type>
      <desc>
        <p>Initializes the context for streaming hash operations. <c>Type</c> determines
        which digest to use. The returned context should be used as argument
	to <seealso marker="#hash_update-2">hash_update</seealso>.</p>
	<p>May throw exception <c>notsup</c> in case the chosen <c>Type</c>
	is not supported by the underlying OpenSSL implementation.</p>
      </desc>
    </func>

    <func>
      <name>hash_update(Context, Data) -> NewContext</name>
      <fsummary></fsummary>
      <type>
	<v>Data = iodata()</v>
      </type>
      <desc>
        <p>Updates the digest represented by <c>Context</c> using the given <c>Data</c>. <c>Context</c>
        must have been generated using <seealso marker="#hash_init-1">hash_init</seealso>
	or a previous call to this function. <c>Data</c> can be any length. <c>NewContext</c>
        must be passed into the next call to <c>hash_update</c>
	or <seealso marker="#hash_final-1">hash_final</seealso>.</p>
      </desc>
    </func>
    <func>
      <name>hash_final(Context) -> Digest</name>
      <fsummary></fsummary>
      <type>
	<v>Digest = binary()</v>
      </type>
      <desc>
        <p>Finalizes the hash operation referenced by <c>Context</c> returned
	from a previous call to <seealso marker="#hash_update-2">hash_update</seealso>.
	The size of <c>Digest</c> is determined by the type of hash
	function used to generate it.</p>
      </desc>
    </func>

    <func>
      <name>hmac(Type, Key, Data) -> Mac</name>
      <name>hmac(Type, Key, Data, MacLength) -> Mac</name>
      <fsummary></fsummary>
      <type>
	<v>Type = hash_algorithms() - except ripemd160</v>
        <v>Key = iodata()</v>
	<v>Data = iodata()</v>
        <v>MacLength = integer()</v>
	<v>Mac = binary()</v>
      </type>
      <desc>
        <p>Computes a HMAC of type <c>Type</c> from <c>Data</c> using
        <c>Key</c> as the authentication key.</p> <p><c>MacLength</c>
        will limit the size of the resultant <c>Mac</c>.</p>
      </desc>
    </func>

    <func>
      <name>hmac_init(Type, Key) -> Context</name>
      <fsummary></fsummary>
      <type>
	<v>Type = hash_algorithms() - except ripemd160</v>
        <v>Key = iodata()</v>
        <v>Context = binary()</v>
      </type>
      <desc>
        <p>Initializes the context for streaming HMAC operations. <c>Type</c> determines
        which hash function to use in the HMAC operation. <c>Key</c> is the authentication
        key. The key can be any length.</p>
      </desc>
    </func>

    <func>
      <name>hmac_update(Context, Data) -> NewContext</name>
      <fsummary></fsummary>
      <type>
        <v>Context = NewContext = binary()</v>
        <v>Data = iodata()</v>
      </type>
      <desc>
        <p>Updates the HMAC represented by <c>Context</c> using the given <c>Data</c>. <c>Context</c>
        must have been generated using an HMAC init function (such as
        <seealso marker="#hmac_init-2">hmac_init</seealso>). <c>Data</c> can be any length. <c>NewContext</c>
        must be passed into the next call to <c>hmac_update</c>
	or to one of the functions <seealso marker="#hmac_final-1">hmac_final</seealso> and
	<seealso marker="#hmac_final_n-2">hmac_final_n</seealso>
	</p>
	<warning><p>Do not use a <c>Context</c> as argument in more than one
	call to	hmac_update or hmac_final. The semantics of reusing old contexts
	in any way is undefined and could even crash the VM in earlier releases.
	The reason for this limitation is a lack of support in the underlying
	OpenSSL	API.</p></warning>
      </desc>
    </func>

    <func>
      <name>hmac_final(Context) -> Mac</name>
      <fsummary></fsummary>
      <type>
        <v>Context = Mac = binary()</v>
      </type>
      <desc>
        <p>Finalizes the HMAC operation referenced by <c>Context</c>. The size of the resultant MAC is
        determined by the type of hash function used to generate it.</p>
      </desc>
    </func>

    <func>
      <name>hmac_final_n(Context, HashLen) -> Mac</name>
      <fsummary></fsummary>
      <type>
        <v>Context = Mac = binary()</v>
        <v>HashLen = non_neg_integer()</v>
      </type>
      <desc>
        <p>Finalizes the HMAC operation referenced by <c>Context</c>. <c>HashLen</c> must be greater than
        zero. <c>Mac</c> will be a binary with at most <c>HashLen</c> bytes. Note that if HashLen is greater than the actual number of bytes returned from the underlying hash, the returned hash will have fewer than <c>HashLen</c> bytes.</p>
      </desc>
    </func>

    <func>
      <name>cmac(Type, Key, Data) -> Mac</name>
      <name>cmac(Type, Key, Data, MacLength) -> Mac</name>
      <fsummary>Calculates the Cipher-based Message Authentication Code.</fsummary>
      <type>
        <v>Type = block_cipher()</v>
        <v>Key = iodata()</v>
        <v>Data = iodata()</v>
        <v>MacLength = integer()</v>
        <v>Mac = binary()</v>
      </type>
      <desc>
        <p>Computes a CMAC of type <c>Type</c> from <c>Data</c> using
        <c>Key</c> as the authentication key.</p> <p><c>MacLength</c>
        will limit the size of the resultant <c>Mac</c>.</p>
      </desc>
    </func>

    <func>
      <name>info_fips() -> Status</name>
      <fsummary>Provides information about the FIPS operating status.</fsummary>
      <type>
        <v>Status = enabled | not_enabled | not_supported</v>
      </type>
      <desc>
        <p>Provides information about the FIPS operating status of
        crypto and the underlying OpenSSL library. If crypto was built
        with FIPS support this can be either <c>enabled</c> (when
        running in FIPS mode) or <c>not_enabled</c>. For other builds
        this value is always <c>not_supported</c>.</p>
        <warning>
          <p>In FIPS mode all non-FIPS compliant algorithms are
          disabled and throw exception <c>not_supported</c>. Check
          <seealso marker="#supports-0">supports</seealso> that in
          FIPS mode returns the restricted list of available
          algorithms.</p>
        </warning>
      </desc>
    </func>

    <func>
      <name>info_lib() -> [{Name,VerNum,VerStr}]</name>
      <fsummary>Provides information about the libraries used by crypto.</fsummary>
      <type>
        <v>Name = binary()</v>
        <v>VerNum = integer()</v>
        <v>VerStr = binary()</v>
      </type>
      <desc>
        <p>Provides the name and version of the libraries used by crypto.</p>
        <p><c>Name</c> is the name of the library. <c>VerNum</c> is
        the numeric version according to the library's own versioning
        scheme. <c>VerStr</c> contains a text variant of the version.</p>
        <pre>
> <input>info_lib().</input>
[{&lt;&lt;"OpenSSL"&gt;&gt;,269484095,&lt;&lt;"OpenSSL 1.1.0c  10 Nov 2016""&gt;&gt;}]
        </pre>
	<note><p>
	  From OTP R16 the <em>numeric version</em> represents the version of the OpenSSL
	  <em>header files</em> (<c>openssl/opensslv.h</c>) used when crypto was compiled.
	  The text variant represents the OpenSSL library used at runtime.
	  In earlier OTP versions both numeric and text was taken from the library.
	</p></note>
      </desc>
    </func>

    <func>
      <name>mod_pow(N, P, M) -> Result</name>
      <fsummary>Computes the function: N^P mod M</fsummary>
      <type>
	<v>N, P, M = binary() | integer()</v>
	<v>Result = binary() | error</v>
      </type>
      <desc>
	<p>Computes the function <c>N^P mod M</c>.</p>
      </desc>
    </func>

    <func>
   <name>next_iv(Type, Data) -> NextIVec</name>
   <name>next_iv(Type, Data, IVec) -> NextIVec</name>
   <fsummary></fsummary>
   <type>
     <v>Type = des_cbc | des3_cbc | aes_cbc | des_cfb</v>
     <v>Data = iodata()</v>
     <v>IVec = NextIVec = binary()</v>
   </type>
   <desc>
     <p>Returns the initialization vector to be used in the next
     iteration of encrypt/decrypt of type <c>Type</c>. <c>Data</c> is the
     encrypted data from the previous iteration step. The <c>IVec</c>
     argument is only needed for <c>des_cfb</c> as the vector used
     in the previous iteration step.</p>
   </desc>
    </func>

    <func>
      <name>private_decrypt(Type, CipherText, PrivateKey, Padding) -> PlainText</name>
      <fsummary>Decrypts CipherText using the private Key.</fsummary>
      <type>
	<v>Type = rsa</v>
	<v>CipherText = binary()</v>
	<v>PrivateKey = rsa_private() | engine_key_ref()</v>
	<v>Padding = rsa_pkcs1_padding | rsa_pkcs1_oaep_padding | rsa_no_padding</v>
        <v>PlainText = binary()</v>
      </type>
      <desc>
	<p>Decrypts the <c>CipherText</c>, encrypted with
	<seealso marker="#public_encrypt-4">public_encrypt/4</seealso> (or equivalent function)
	  using the <c>PrivateKey</c>, and returns the
	  plaintext (message digest). This is a low level signature  verification operation
	used for instance by older versions of the SSL protocol.
	  See also <seealso marker="public_key:public_key#decrypt_private-2">public_key:decrypt_private/[2,3]</seealso>
	</p>
      </desc>
    </func>

    <func>
      <name>privkey_to_pubkey(Type, EnginePrivateKeyRef) -> PublicKey</name>
      <fsummary>Fetches a public key from an Engine stored private key.</fsummary>
      <type>
	<v>Type = rsa | dss</v>
	<v>EnginePrivateKeyRef = engine_key_ref()</v>
	<v>PublicKey =  rsa_public() | dss_public()</v>
      </type>
      <desc>
	<p>Fetches the corresponding public key from a private key stored in an Engine.
	The key must be of the type indicated by the Type parameter.
	</p>	
	<p>	  
	  May throw exception notsup in case there is 
	  no engine support in the underlying OpenSSL implementation.
	</p>
      </desc>
    </func>

    <func>
      <name>private_encrypt(Type, PlainText, PrivateKey, Padding) -> CipherText</name>
      <fsummary>Encrypts PlainText using the private Key.</fsummary>
      <type>
	<v>Type = rsa</v>
	<v>PlainText = binary()</v>
	<d> The size of the <c>PlainText</c> must be less
	than <c>byte_size(N)-11</c> if <c>rsa_pkcs1_padding</c> is
	used, and <c>byte_size(N)</c> if <c>rsa_no_padding</c> is
	used, where N is public modulus of the RSA key.</d>
	<v>PrivateKey = rsa_private() | engine_key_ref()</v>
	<v>Padding = rsa_pkcs1_padding | rsa_no_padding</v>
        <v>CipherText = binary()</v>
      </type>
      <desc>
	<p>Encrypts the <c>PlainText</c> using the <c>PrivateKey</c>
	and returns the ciphertext. This is a low level signature operation
	used for instance by older versions of the SSL protocol. See
	also <seealso
	marker="public_key:public_key#encrypt_private-2">public_key:encrypt_private/[2,3]</seealso>
	</p>
      </desc>
    </func>
    <func>
      <name>public_decrypt(Type, CipherText, PublicKey, Padding) -> PlainText</name>
      <fsummary>Decrypts CipherText using the public Key.</fsummary>
      <type>
	<v>Type = rsa</v>
	<v>CipherText = binary()</v>
	<v>PublicKey =  rsa_public() | engine_key_ref()</v>
	<v>Padding = rsa_pkcs1_padding | rsa_no_padding</v>
        <v>PlainText = binary()</v>
      </type>
      <desc>
	<p>Decrypts the <c>CipherText</c>, encrypted with
	<seealso marker="#private_encrypt-4">private_encrypt/4</seealso>(or equivalent function)
	  using the <c>PrivateKey</c>, and returns the
	  plaintext (message digest). This is a low level signature verification operation
	  used for instance by older versions of the SSL protocol.
	  See also <seealso marker="public_key:public_key#decrypt_public-2">public_key:decrypt_public/[2,3]</seealso>
	</p>
      </desc>
    </func>

    <func>
      <name>public_encrypt(Type, PlainText, PublicKey, Padding) -> CipherText</name>
      <fsummary>Encrypts PlainText using the public Key.</fsummary>
      <type>
	<v>Type = rsa</v>
	<v>PlainText = binary()</v>
	<d> The size of the <c>PlainText</c> must be less
	than <c>byte_size(N)-11</c> if <c>rsa_pkcs1_padding</c> is
	used, and <c>byte_size(N)</c> if <c>rsa_no_padding</c> is
	used, where N is public modulus of the RSA key.</d>
	<v>PublicKey = rsa_public() | engine_key_ref()</v>
	<v>Padding = rsa_pkcs1_padding | rsa_pkcs1_oaep_padding | rsa_no_padding</v>
        <v>CipherText = binary()</v>
      </type>
      <desc>
	<p>Encrypts the <c>PlainText</c> (message digest) using the <c>PublicKey</c>
	and returns the <c>CipherText</c>. This is a low level signature operation
	used for instance by older versions of the SSL protocol. See also <seealso
	marker="public_key:public_key#encrypt_public-2">public_key:encrypt_public/[2,3]</seealso>
	</p>
      </desc>
    </func>

    <func>
      <name>rand_seed(Seed) -> ok</name>
      <fsummary>Set the seed for random bytes generation</fsummary>
      <type>
        <v>Seed = binary()</v>
      </type>
      <desc>
        <p>Set the seed for PRNG to the given binary. This calls the
        RAND_seed function from openssl. Only use this if the system
        you are running on does not have enough "randomness" built in.
        Normally this is when
        <seealso marker="#strong_rand_bytes/1">strong_rand_bytes/1</seealso>
        throws <c>low_entropy</c></p>
      </desc>
    </func>

     <func>
      <name>rand_uniform(Lo, Hi) -> N</name>
      <fsummary>Generate a random number</fsummary>
      <type>
        <v>Lo, Hi, N = integer()</v>
      </type>
      <desc>
        <p>Generate a random number <c><![CDATA[N, Lo =< N < Hi.]]></c> Uses the
	<c>crypto</c> library pseudo-random number generator.
	<c>Hi</c> must be larger than <c>Lo</c>.</p>
      </desc>
    </func>

    <func>
      <name>sign(Algorithm, DigestType, Msg, Key) -> binary()</name>
      <name>sign(Algorithm, DigestType, Msg, Key, Options) -> binary()</name>
      <fsummary> Create digital signature.</fsummary>
      <type>
	<v>Algorithm = rsa | dss | ecdsa </v>
	<v>Msg = binary() | {digest,binary()}</v>
	<d>The msg is either the binary "cleartext" data to be
	signed or it is the hashed value of "cleartext" i.e. the
	digest (plaintext).</d>
	<v>DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()</v>
	<v>Key = rsa_private() | dss_private() | [ecdh_private(),ecdh_params()] | engine_key_ref()</v>
	<v>Options = sign_options()</v>
      </type>
      <desc>
	<p>Creates a digital signature.</p>
	<p>Algorithm <c>dss</c> can only be used together with digest type
	<c>sha</c>.</p>
	<p>See also <seealso marker="public_key:public_key#sign-3">public_key:sign/3</seealso>.</p>
      </desc>
    </func>

    <func>
      <name>start() -> ok</name>
      <fsummary> Equivalent to application:start(crypto). </fsummary>
      <desc>
        <p> Equivalent to application:start(crypto).</p>
      </desc>
    </func>
    <func>
      <name>stop() -> ok</name>
      <fsummary> Equivalent to application:stop(crypto).</fsummary>
      <desc>
        <p> Equivalent to application:stop(crypto).</p>
      </desc>
    </func>

    <func>
      <name>strong_rand_bytes(N) -> binary()</name>
      <fsummary>Generate a binary of random bytes</fsummary>
      <type>
        <v>N = integer()</v>
      </type>
      <desc>
        <p>Generates N bytes randomly uniform 0..255, and returns the
        result in a binary. Uses a cryptographically secure prng seeded and
        periodically mixed with operating system provided entropy. By default
        this is the <c>RAND_bytes</c> method from OpenSSL.</p>
	<p>May throw exception <c>low_entropy</c> in case the random generator
	failed due to lack of secure "randomness".</p>
      </desc>
    </func>

    <func>
      <name>rand_seed() -> rand:state()</name>
      <fsummary>Strong random number generation plugin state</fsummary>
      <desc>
	<p>
          Creates state object for
	  <seealso marker="stdlib:rand">random number generation</seealso>,
          in order to generate cryptographically strong random numbers
          (based on OpenSSL's <c>BN_rand_range</c>),
          and saves it in the process dictionary before returning it as well.
          See also
	  <seealso marker="stdlib:rand#seed-1">rand:seed/1</seealso> and
	  <seealso marker="#rand_seed_s-0">rand_seed_s/0</seealso>.
	</p>
	<p>
	  When using the state object from this function the 
	  <seealso marker="stdlib:rand">rand</seealso> functions using it
	  may throw exception <c>low_entropy</c> in case the random generator
	  failed due to lack of secure "randomness".
	</p>
        <p><em>Example</em></p>
        <pre>
_ = crypto:rand_seed(),
_IntegerValue = rand:uniform(42), % [1; 42]
_FloatValue = rand:uniform().     % [0.0; 1.0[</pre>
      </desc>
    </func>

    <func>
      <name>rand_seed_s() -> rand:state()</name>
      <fsummary>Strong random number generation plugin state</fsummary>
      <desc>
	<p>
          Creates state object for
	  <seealso marker="stdlib:rand">random number generation</seealso>,
          in order to generate cryptographically strongly random numbers
          (based on OpenSSL's <c>BN_rand_range</c>).
          See also
	  <seealso marker="stdlib:rand#seed_s-1">rand:seed_s/1</seealso>.
	</p>
	<p>
	  When using the state object from this function the 
	  <seealso marker="stdlib:rand">rand</seealso> functions using it
	  may throw exception <c>low_entropy</c> in case the random generator
	  failed due to lack of secure "randomness".
	</p>
	<note>
	  <p>
	    The state returned from this function can not be used
	    to get a reproducable random sequence as from
	    the other 
	    <seealso marker="stdlib:rand">rand</seealso>
	    functions,
	    since reproducability does not match cryptographically safe.
	  </p>
	  <p>
	    The only supported usage is to generate one distinct
	    random sequence from this start state.
	  </p>
	</note>
      </desc>
    </func>

    <func>
      <name>rand_seed_alg(Alg) -> rand:state()</name>
      <fsummary>Strong random number generation plugin state</fsummary>
      <type>
        <v>Alg = crypto | crypto_cache</v>
      </type>
      <desc>
	<marker id="rand_seed_alg-1" />
	<p>
          Creates state object for
	  <seealso marker="stdlib:rand">random number generation</seealso>,
          in order to generate cryptographically strong random numbers.
          See also
	  <seealso marker="stdlib:rand#seed-1">rand:seed/1</seealso> and
	  <seealso marker="#rand_seed_alg_s-1">rand_seed_alg_s/1</seealso>.
	</p>
	<p>
	  When using the state object from this function the 
	  <seealso marker="stdlib:rand">rand</seealso> functions using it
	  may throw exception <c>low_entropy</c> in case the random generator
	  failed due to lack of secure "randomness".
	</p>
	<p>
	  The cache size can be changed from its default value using the
	  <seealso marker="crypto_app">
	    crypto app's
	  </seealso> configuration parameter <c>rand_cache_size</c>.
	</p>
        <p><em>Example</em></p>
        <pre>
_ = crypto:rand_seed_alg(crypto_cache),
_IntegerValue = rand:uniform(42), % [1; 42]
_FloatValue = rand:uniform().     % [0.0; 1.0[</pre>
      </desc>
    </func>

    <func>
      <name>rand_seed_alg_s(Alg) -> rand:state()</name>
      <fsummary>Strong random number generation plugin state</fsummary>
      <type>
        <v>Alg = crypto | crypto_cache</v>
      </type>
      <desc>
	<marker id="rand_seed_alg_s-1" />
	<p>
          Creates state object for
	  <seealso marker="stdlib:rand">random number generation</seealso>,
          in order to generate cryptographically strongly random numbers.
          See also
	  <seealso marker="stdlib:rand#seed_s-1">rand:seed_s/1</seealso>.
	</p>
	<p>
	  If <c>Alg</c> is <c>crypto</c> this function behaves exactly like
	  <seealso marker="#rand_seed_s-0">rand_seed_s/0</seealso>.
	</p>
	<p>
	  If <c>Alg</c> is <c>crypto_cache</c> this function
	  fetches random data with OpenSSL's <c>RAND_bytes</c>
	  and caches it for speed using an internal word size
	  of 56 bits that makes calculations fast on 64 bit machines.
	</p>
	<p>
	  When using the state object from this function the 
	  <seealso marker="stdlib:rand">rand</seealso> functions using it
	  may throw exception <c>low_entropy</c> in case the random generator
	  failed due to lack of secure "randomness".
	</p>
	<p>
	  The cache size can be changed from its default value using the
	  <seealso marker="crypto_app">
	    crypto app's
	  </seealso> configuration parameter <c>rand_cache_size</c>.
	</p>
	<note>
	  <p>
	    The state returned from this function can not be used
	    to get a reproducable random sequence as from
	    the other 
	    <seealso marker="stdlib:rand">rand</seealso>
	    functions,
	    since reproducability does not match cryptographically safe.
	  </p>
	  <p>
	    In fact since random data is cached some numbers may
	    get reproduced if you try, but this is unpredictable.
	  </p>
	  <p>
	    The only supported usage is to generate one distinct
	    random sequence from this start state.
	  </p>
	</note>
      </desc>
    </func>

    <func>
      <name>stream_init(Type, Key) -> State</name>
      <fsummary></fsummary>
      <type>
	<v>Type = rc4 </v>
        <v>State = opaque() </v>
        <v>Key = iodata()</v>
      </type>
      <desc>
        <p>Initializes the state for use in RC4 stream encryption
        <seealso marker="#stream_encrypt-2">stream_encrypt</seealso> and
        <seealso marker="#stream_decrypt-2">stream_decrypt</seealso></p>
      </desc>
    </func>

   <func>
      <name>stream_init(Type, Key, IVec) -> State</name>
      <fsummary></fsummary>
      <type>
	<v>Type = aes_ctr </v>
        <v>State = opaque() </v>
        <v>Key = iodata()</v>
        <v>IVec = binary()</v>
      </type>
      <desc>
        <p>Initializes the state for use in streaming AES encryption using Counter mode (CTR).
        <c>Key</c> is the AES key and must be either 128, 192, or 256 bits long. <c>IVec</c> is
        an arbitrary initializing vector of 128 bits (16 bytes). This state is for use with
        <seealso marker="#stream_encrypt-2">stream_encrypt</seealso> and
        <seealso marker="#stream_decrypt-2">stream_decrypt</seealso>.</p>
      </desc>
    </func>

    <func>
      <name>stream_encrypt(State, PlainText) -> { NewState, CipherText}</name>
      <fsummary></fsummary>
      <type>
        <v>Text = iodata()</v>
        <v>CipherText = binary()</v>
      </type>
      <desc>
	<p>Encrypts <c>PlainText</c> according to the stream cipher <c>Type</c> specified in stream_init/3.
	<c>Text</c> can be any number of bytes. The initial <c>State</c> is created using
        <seealso marker="#stream_init-2">stream_init</seealso>.
	<c>NewState</c> must be passed into the next call to <c>stream_encrypt</c>.</p>
      </desc>
    </func>

    <func>
      <name>stream_decrypt(State, CipherText) -> { NewState, PlainText }</name>
      <fsummary></fsummary>
      <type>
        <v>CipherText = iodata()</v>
        <v>PlainText = binary()</v>
      </type>
      <desc>
	<p>Decrypts <c>CipherText</c> according to the stream cipher <c>Type</c> specified in stream_init/3.
	<c>PlainText</c> can be any number of bytes. The initial <c>State</c> is created using
        <seealso marker="#stream_init-2">stream_init</seealso>.
	<c>NewState</c> must be passed into the next call to <c>stream_decrypt</c>.</p>
      </desc>
    </func>

   <func>
      <name>supports() -> AlgorithmList </name>
      <fsummary>Provide a list of available crypto algorithms.</fsummary>
      <type>
      <v> AlgorithmList =  [{hashs, [hash_algorithms()]},
                            {ciphers, [cipher_algorithms()]},
			    {public_keys, [public_key_algorithms()]},
			    {macs, [mac_algorithms()]}]
      </v>
      </type>
      <desc>
        <p> Can be used to determine which crypto algorithms that are supported
	by the underlying OpenSSL library</p>
      </desc>
    </func>

    <func>
      <name>ec_curves() -> EllipticCurveList </name>
      <fsummary>Provide a list of available named elliptic curves.</fsummary>
      <type>
      <v>EllipticCurveList = [ec_named_curve()]</v>
      </type>
      <desc>
        <p>Can be used to determine which named elliptic curves are supported.</p>
      </desc>
    </func>

    <func>
      <name>ec_curve(NamedCurve) -> EllipticCurve </name>
      <fsummary>Get the defining parameters of a elliptic curve.</fsummary>
      <type>
      <v>NamedCurve = ec_named_curve()</v>
      <v>EllipticCurve = ec_explicit_curve()</v>
      </type>
      <desc>
        <p>Return the defining parameters of a elliptic curve.</p>
      </desc>
    </func>

  <func>
      <name>verify(Algorithm, DigestType, Msg, Signature, Key) -> boolean()</name>
      <name>verify(Algorithm, DigestType, Msg, Signature, Key, Options) -> boolean()</name>
      <fsummary>Verifies a digital signature.</fsummary>
      <type>
	<v> Algorithm = rsa | dss | ecdsa </v>
	<v>Msg = binary() | {digest,binary()}</v>
	<d>The msg is either the binary "cleartext" data
        or it is the hashed value of "cleartext" i.e. the digest (plaintext).</d>
	<v>DigestType = rsa_digest_type() | dss_digest_type() | ecdsa_digest_type()</v>
	<v>Signature = binary()</v>
	<v>Key = rsa_public() | dss_public() | [ecdh_public(),ecdh_params()] | engine_key_ref()</v>
	<v>Options = sign_options()</v>
      </type>
      <desc>
	<p>Verifies a digital signature</p>
	<p>Algorithm <c>dss</c> can only be used together with digest type
	<c>sha</c>.</p>

	<p>See also <seealso marker="public_key:public_key#verify-4">public_key:verify/4</seealso>.</p>
      </desc>
    </func>

    <!-- Engine functions -->
    <func>
      <name>engine_get_all_methods() -> Result</name>
      <fsummary>Return list of all possible engine methods</fsummary>
      <type>
	<v>Result = [EngineMethod::atom()]</v>
      </type>
      <desc>
	<p>
	  Returns a list of all possible engine methods.
	</p>
	<p>	  
	  May throw exception notsup in case there is 
	  no engine support in the underlying OpenSSL implementation.
	</p>
	<p>
	  See also the chapter <seealso marker="crypto:engine_load#engine_load">Engine Load</seealso>
	  in the User's Guide.
	</p>
      </desc>
    </func>

    <func>
      <name>engine_load(EngineId, PreCmds, PostCmds) -> Result</name>
      <fsummary>Dynamical load an encryption engine</fsummary>
      <type>
	<v>EngineId = unicode:chardata()</v>
	<v>PreCmds, PostCmds = [{unicode:chardata(), unicode:chardata()}]</v>
	<v>Result = {ok, Engine::term()} | {error, Reason::term()}</v>
      </type>
      <desc>
	<p>
	  Loads the OpenSSL engine given by <c>EngineId</c> if it is available and then returns ok and
	  an engine handle. This function is the same as calling <c>engine_load/4</c> with 
	  <c>EngineMethods</c> set to a list of all the possible methods.  An error tuple is 
	  returned if the engine can't be loaded.
	</p>
	<p>
	  The function throws a badarg if the parameters are in wrong format.
	  It may also throw the exception notsup in case there is 
	  no engine support in the underlying OpenSSL implementation.
	</p>
	<p>
	  See also the chapter <seealso marker="crypto:engine_load#engine_load">Engine Load</seealso>
	  in the User's Guide.
	</p>
      </desc>
    </func>

    <func>
      <name>engine_load(EngineId, PreCmds, PostCmds, EngineMethods) -> Result</name>
      <fsummary>Dynamical load an encryption engine</fsummary>
      <type>
	<v>EngineId = unicode:chardata()</v>
	<v>PreCmds, PostCmds = [{unicode:chardata(), unicode:chardata()}]</v>
	<v>EngineMethods = [engine_method_type()]</v>
	<v>Result = {ok, Engine::term()} | {error, Reason::term()}</v>
      </type>
      <desc>
	<p>
	  Loads the OpenSSL engine given by <c>EngineId</c> if it is available and then returns ok and
	  an engine handle. An error tuple is returned if the engine can't be loaded.
	</p>
	<p>
	  The function throws a badarg if the parameters are in wrong format.
	  It may also throw the exception notsup in case there is 
	  no engine support in the underlying OpenSSL implementation.
	</p>
	<p>
	  See also the chapter <seealso marker="crypto:engine_load#engine_load">Engine Load</seealso>
	  in the User's Guide.
	</p>
      </desc>
    </func>

    <func>
      <name>engine_unload(Engine) -> Result</name>
      <fsummary>Dynamical load an encryption engine</fsummary>
      <type>
	<v>Engine = term()</v>
	<v>Result = ok | {error, Reason::term()}</v>
      </type>
      <desc>
	<p>
	  Unloads the OpenSSL engine given by <c>EngineId</c>.
	  An error tuple is returned if the engine can't be unloaded.
	</p>
	<p>
	  The function throws a badarg if the parameter is in wrong format.
	  It may also throw the exception notsup in case there is 
	  no engine support in the underlying OpenSSL implementation.
	</p>
	<p>
	  See also the chapter <seealso marker="crypto:engine_load#engine_load">Engine Load</seealso>
	  in the User's Guide.
	</p>
      </desc>
    </func>

    <func>
      <name>engine_list() -> Result</name>
      <fsummary>List the known engine ids</fsummary>
      <type>
	<v>Result = [EngineId::unicode:chardata()]</v>
      </type>
      <desc>
	<p>List the id's of all engines in OpenSSL's internal list.</p>
	<p>
	  It may also throw the exception notsup in case there is 
	  no engine support in the underlying OpenSSL implementation.
	</p>
	<p>
	  See also the chapter <seealso marker="crypto:engine_load#engine_load">Engine Load</seealso> 
	  in the User's Guide.
	</p>
      </desc>
    </func>

 </funcs>

  <!-- Maybe put this in the users guide -->
  <!-- <section> -->
  <!--   <title>DES in CBC mode</title> -->
  <!--   <p>The Data Encryption Standard (DES) defines an algorithm for -->
  <!--     encrypting and decrypting an 8 byte quantity using an 8 byte key -->
  <!--     (actually only 56 bits of the key is used). -->
  <!--     </p> -->
  <!--   <p>When it comes to encrypting and decrypting blocks that are -->
  <!--     multiples of 8 bytes various modes are defined (NIST SP -->
  <!--     800-38A). One of those modes is the Cipher Block Chaining (CBC) -->
  <!--     mode, where the encryption of an 8 byte segment depend not only -->
  <!--     of the contents of the segment itself, but also on the result of -->
  <!--     encrypting the previous segment: the encryption of the previous -->
  <!--     segment becomes the initializing vector of the encryption of the -->
  <!--     current segment. -->
  <!--     </p> -->
  <!--   <p>Thus the encryption of every segment depends on the encryption -->
  <!--     key (which is secret) and the encryption of the previous -->
  <!--     segment, except the first segment which has to be provided with -->
  <!--     an initial initializing vector. That vector could be chosen at -->
  <!--     random, or be a counter of some kind. It does not have to be -->
  <!--     secret. -->
  <!--     </p> -->
  <!--   <p>The following example is drawn from the old FIPS 81 standard -->
  <!--     (replaced by NIST SP 800-38A), where both the plain text and the -->
  <!--     resulting cipher text is settled. The following code fragment -->
  <!--     returns `true'. -->
  <!--     </p> -->
  <!--   <pre><![CDATA[ -->

  <!--     Key = <<16#01,16#23,16#45,16#67,16#89,16#ab,16#cd,16#ef>>, -->
  <!--     IVec = <<16#12,16#34,16#56,16#78,16#90,16#ab,16#cd,16#ef>>, -->
  <!--     P = "Now is the time for all ", -->
  <!--     C = crypto:des_cbc_encrypt(Key, IVec, P), -->
  <!--        % Which is the same as  -->
  <!--     P1 = "Now is t", P2 = "he time ", P3 = "for all ", -->
  <!--     C1 = crypto:des_cbc_encrypt(Key, IVec, P1), -->
  <!--     C2 = crypto:des_cbc_encrypt(Key, C1, P2), -->
  <!--     C3 = crypto:des_cbc_encrypt(Key, C2, P3), -->

  <!--     C = <<C1/binary, C2/binary, C3/binary>>, -->
  <!--     C = <<16#e5,16#c7,16#cd,16#de,16#87,16#2b,16#f2,16#7c, -->
  <!--            16#43,16#e9,16#34,16#00,16#8c,16#38,16#9c,16#0f, -->
  <!--            16#68,16#37,16#88,16#49,16#9a,16#7c,16#05,16#f6>>, -->
  <!--     <<"Now is the time for all ">> ==  -->
  <!--                       crypto:des_cbc_decrypt(Key, IVec, C). -->
  <!--   ]]></pre> -->
  <!--   <p>The following is true for the DES CBC mode. For all -->
  <!--     decompositions <c>P1 ++ P2 = P</c> of a plain text message -->
  <!--     <c>P</c> (where the length of all quantities are multiples of 8 -->
  <!--     bytes), the encryption <c>C</c> of <c>P</c> is equal to <c>C1 ++ -->
  <!--     C2</c>, where <c>C1</c> is obtained by encrypting <c>P1</c> with -->
  <!--     <c>Key</c> and the initializing vector <c>IVec</c>, and where -->
  <!--     <c>C2</c> is obtained by encrypting <c>P2</c> with <c>Key</c> -->
  <!--     and the initializing vector <c>last8(C1)</c>, -->
  <!--     where <c>last(Binary)</c> denotes the last 8 bytes of the -->
  <!--     binary <c>Binary</c>. -->
  <!--     </p> -->
  <!--   <p>Similarly, for all decompositions <c>C1 ++ C2 = C</c> of a -->
  <!--     cipher text message <c>C</c> (where the length of all quantities -->
  <!--     are multiples of 8 bytes), the decryption <c>P</c> of <c>C</c> -->
  <!--     is equal to <c>P1 ++ P2</c>, where <c>P1</c> is obtained by -->
  <!--     decrypting <c>C1</c> with <c>Key</c> and the initializing vector -->
  <!--     <c>IVec</c>, and where <c>P2</c> is obtained by decrypting -->
  <!--     <c>C2</c> with <c>Key</c> and the initializing vector -->
  <!--     <c>last8(C1)</c>, where <c>last8(Binary)</c> is as above. -->
  <!--     </p> -->
  <!--   <p>For DES3 (which uses three 64 bit keys) the situation is the -->
  <!--     same. -->
  <!--   </p> -->
  <!-- </section> -->
</erlref>