1f7f3a55ecaa7bc0cb617c3a74ddfa9fffe94e02
[openssl.git] / doc / man7 / EVP_KDF-SSHKDF.pod
1 =pod
2
3 =head1 NAME
4
5 EVP_KDF-SSHKDF - The SSHKDF EVP_KDF implementation
6
7 =head1 DESCRIPTION
8
9 Support for computing the B<SSHKDF> KDF through the B<EVP_KDF> API.
10
11 The EVP_KDF-SSHKDF algorithm implements the SSHKDF key derivation function.
12 It is defined in RFC 4253, section 7.2 and is used by SSH to derive IVs,
13 encryption keys and integrity keys.
14 Five inputs are required to perform key derivation: The hashing function
15 (for example SHA256), the Initial Key, the Exchange Hash, the Session ID,
16 and the derivation key type.
17
18 =head2 Identity
19
20 "SSHKDF" is the name for this implementation; it
21 can be used with the EVP_KDF_fetch() function.
22
23 =head2 Supported parameters
24
25 The supported parameters are:
26
27 =over 4
28
29 =item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
30
31 =item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string>
32
33 =item "key" (B<OSSL_KDF_PARAM_KEY>) <octet string>
34
35 These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
36
37 =item "xcghash" (B<OSSL_KDF_PARAM_SSHKDF_XCGHASH>) <octet string>
38
39 =item "session_id" (B<OSSL_KDF_PARAM_SSHKDF_SESSION_ID>) <octet string>
40
41 These parameters set the respective values for the KDF.
42 If a value is already set, the contents are replaced.
43
44 =item "type" (B<OSSL_KDF_PARAM_SSHKDF_TYPE>) <integer>
45
46 This parameter sets the type for the SSHHKDF operation.
47 There are six supported types:
48
49 =over 4
50
51 =item EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV
52
53 The Initial IV from client to server.
54 A single char of value 65 (ASCII char 'A').
55
56 =item EVP_KDF_SSHKDF_TYPE_INITIAL_IV_SRV_TO_CLI
57
58 The Initial IV from server to client
59 A single char of value 66 (ASCII char 'B').
60
61 =item EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_CLI_TO_SRV
62
63 The Encryption Key from client to server
64 A single char of value 67 (ASCII char 'C').
65
66 =item EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_SRV_TO_CLI
67
68 The Encryption Key from server to client
69 A single char of value 68 (ASCII char 'D').
70
71 =item EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_CLI_TO_SRV
72
73 The Integrity Key from client to server
74 A single char of value 69 (ASCII char 'E').
75
76 =item EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_SRV_TO_CLI
77
78 The Integrity Key from client to server
79 A single char of value 70 (ASCII char 'F').
80
81 =back
82
83 =back
84
85 =head1 NOTES
86
87 A context for SSHKDF can be obtained by calling:
88
89  EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSHKDF", NULL);
90  EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
91
92 The output length of the SSHKDF derivation is specified via the I<keylen>
93 parameter to the L<EVP_KDF_derive(3)> function.
94 Since the SSHKDF output length is variable, calling L<EVP_KDF_size(3)>
95 to obtain the requisite length is not meaningful. The caller must
96 allocate a buffer of the desired length, and pass that buffer to the
97 L<EVP_KDF_derive(3)> function along with the desired length.
98
99 =head1 EXAMPLES
100
101 This example derives an 8 byte IV using SHA-256 with a 1K "key" and appropriate
102 "xcghash" and "session_id" values:
103
104  EVP_KDF *kdf;
105  EVP_KDF_CTX *kctx;
106  unsigned char key[1024] = "01234...";
107  unsigned char xcghash[32] = "012345...";
108  unsigned char session_id[32] = "012345...";
109  unsigned char out[8];
110  size_t outlen = sizeof(out);
111  OSSL_PARAM params[6], *p = params;
112
113  kdf = EVP_KDF_fetch(NULL, "SSHKDF", NULL);
114  kctx = EVP_KDF_CTX_new(kdf);
115  EVP_KDF_free(kdf);
116
117  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
118                                          SN_sha256, strlen(SN_sha256));
119  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
120                                           key, (size_t)1024);
121  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SSHKDF_XCGHASH,
122                                           xcghash, (size_t)32);
123  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
124                                           session_id, (size_t)32);
125  *p++ = OSSL_PARAM_construct_int(OSSL_KDF_PARAM_SSHKDF_TYPE,
126                                  EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV);
127  *p = OSSL_PARAM_construct_end();
128  if (EVP_KDF_CTX_set_params(kctx, params) <= 0)
129      /* Error */
130
131  if (EVP_KDF_derive(kctx, out, &outlen) <= 0)
132      /* Error */
133
134
135 =head1 CONFORMING TO
136
137 RFC 4253
138
139 =head1 SEE ALSO
140
141 L<EVP_KDF(3)>,
142 L<EVP_KDF_CTX_new(3)>,
143 L<EVP_KDF_CTX_free(3)>,
144 L<EVP_KDF_CTX_set_params(3)>,
145 L<EVP_KDF_size(3)>,
146 L<EVP_KDF_derive(3)>,
147 L<EVP_KDF(3)/PARAMETERS>
148
149 =head1 COPYRIGHT
150
151 Copyright 2016-2019 The OpenSSL Project Authors. All Rights Reserved.
152
153 Licensed under the OpenSSL license (the "License").  You may not use
154 this file except in compliance with the License.  You can obtain a copy
155 in the file LICENSE in the source distribution or at
156 L<https://www.openssl.org/source/license.html>.
157
158 =cut
159