1EVP_KDF_SSHKDF(7)                   OpenSSL                  EVP_KDF_SSHKDF(7)
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NAME

6       EVP_KDF_SSHKDF - The SSHKDF EVP_KDF implementation
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DESCRIPTION

9       Support for computing the SSHKDF KDF through the EVP_KDF API.
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11       The EVP_KDF_SSHKDF algorithm implements the SSHKDF key derivation
12       function.  It is defined in RFC 4253, section 7.2 and is used by SSH to
13       derive IVs, encryption keys and integrity keys.  Five inputs are
14       required to perform key derivation: The hashing function (for example
15       SHA256), the Initial Key, the Exchange Hash, the Session ID, and the
16       derivation key type.
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18   Numeric identity
19       EVP_KDF_SSHKDF is the numeric identity for this implementation; it can
20       be used with the EVP_KDF_CTX_new_id() function.
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22   Supported controls
23       The supported controls are:
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25       EVP_KDF_CTRL_SET_MD
26       EVP_KDF_CTRL_SET_KEY
27           These controls work as described in "CONTROLS" in EVP_KDF_CTX(3).
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29       EVP_KDF_CTRL_SET_SSHKDF_XCGHASH
30       EVP_KDF_CTRL_SET_SSHKDF_SESSION_ID
31           These controls expect two arguments: "unsigned char *buffer",
32           "size_t length"
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34           They set the respective values to the first length bytes of the
35           buffer buffer. If a value is already set, the contents are
36           replaced.
37
38           EVP_KDF_ctrl_str() takes two type strings for these controls:
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40           "xcghash"
41           "session_id"
42               The value string is used as is.
43
44           "hexxcghash"
45           "hexsession_id"
46               The value string is expected to be a hexadecimal number, which
47               will be decoded before being passed on as the control value.
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49       EVP_KDF_CTRL_SET_SSHKDF_TYPE
50           This control expects one argument: "int mode"
51
52           Sets the type for the SSHHKDF operation. There are six supported
53           types:
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55           EVP_KDF_SSHKDF_TYPE_ININITAL_IV_CLI_TO_SRV
56               The Initial IV from client to server.  A single char of value
57               65 (ASCII char 'A').
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59           EVP_KDF_SSHKDF_TYPE_ININITAL_IV_SRV_TO_CLI
60               The Initial IV from server to client A single char of value 66
61               (ASCII char 'B').
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63           EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_CLI_TO_SRV
64               The Encryption Key from client to server A single char of value
65               67 (ASCII char 'C').
66
67           EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_SRV_TO_CLI
68               The Encryption Key from server to client A single char of value
69               68 (ASCII char 'D').
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71           EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_CLI_TO_SRV
72               The Integrity Key from client to server A single char of value
73               69 (ASCII char 'E').
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75           EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_SRV_TO_CLI
76               The Integrity Key from client to server A single char of value
77               70 (ASCII char 'F').
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79           EVP_KDF_ctrl_str() type string: "type"
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81           The value is a string of length one character. The only valid
82           values are the numerical values of the ASCII caracters: "A" (65) to
83           "F" (70).
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NOTES

86       A context for SSHKDF can be obtained by calling:
87
88        EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SSHKDF);
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90       The output length of the SSHKDF derivation is specified via the
91       "keylen" parameter to the EVP_KDF_derive(3) function.  Since the SSHKDF
92       output length is variable, calling EVP_KDF_size() to obtain the
93       requisite length is not meaningful. The caller must allocate a buffer
94       of the desired length, and pass that buffer to the EVP_KDF_derive(3)
95       function along with the desired length.
96

EXAMPLE

98       This example derives an 8 byte IV using SHA-256 with a 1K "key" and
99       appropriate "xcghash" and "session_id" values:
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101        EVP_KDF_CTX *kctx;
102        unsigned char key[1024] = "01234...";
103        unsigned char xcghash[32] = "012345...";
104        unsigned char session_id[32] = "012345...";
105        unsigned char out[8];
106        size_t outlen = sizeof(out);
107        kctx = EVP_KDF_CTX_new_id(EVP_KDF_SSHKDF);
108
109        if (EVP_KDF_CTX_set_md(kctx, EVP_sha256()) <= 0)
110            /* Error */
111        if (EVP_KDF_CTX_set1_key(kctx, key, 1024) <= 0)
112            /* Error */
113        if (EVP_KDF_CTX_set1_sshkdf_xcghash(kctx, xcghash, 32) <= 0)
114            /* Error */
115        if (EVP_KDF_CTX_set1_sshkdf_session_id(kctx, session_id, 32) <= 0)
116            /* Error */
117        if (EVP_KDF_CTX_set_sshkdf_type(kctx,
118                           EVP_KDF_SSHKDF_TYPE_ININITAL_IV_CLI_TO_SRV) <= 0)
119            /* Error */
120        if (EVP_KDF_derive(kctx, out, &outlen) <= 0)
121            /* Error */
122

CONFORMING TO

124       RFC 4253
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SEE ALSO

127       EVP_KDF_CTX, EVP_KDF_CTX_new_id(3), EVP_KDF_CTX_free(3),
128       EVP_KDF_ctrl(3), EVP_KDF_size(3), EVP_KDF_derive(3), "CONTROLS" in
129       EVP_KDF_CTX(3)
130

132       Copyright 2016-2018 The OpenSSL Project Authors. All Rights Reserved.
133
134       Licensed under the OpenSSL license (the "License").  You may not use
135       this file except in compliance with the License.  You can obtain a copy
136       in the file LICENSE in the source distribution or at
137       <https://www.openssl.org/source/license.html>.
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1411.1.1k                            2021-03-26                 EVP_KDF_SSHKDF(7)
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