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EVP_KDF_SSHKDF(7)                   OpenSSL                  EVP_KDF_SSHKDF(7)
NAME
       EVP_KDF_SSHKDF - The SSHKDF EVP_KDF implementation
DESCRIPTION
       Support for computing the SSHKDF KDF through the EVP_KDF API.
       The EVP_KDF_SSHKDF algorithm implements the SSHKDF key derivation
       function.  It is defined in RFC 4253, section 7.2 and is used by SSH to
       derive IVs, encryption keys and integrity keys.  Five inputs are
       required to perform key derivation: The hashing function (for example
       SHA256), the Initial Key, the Exchange Hash, the Session ID, and the
       derivation key type.
   Numeric identity
       EVP_KDF_SSHKDF is the numeric identity for this implementation; it can
       be used with the EVP_KDF_CTX_new_id() function.
   Supported controls
       The supported controls are:
       EVP_KDF_CTRL_SET_MD
       EVP_KDF_CTRL_SET_KEY
           These controls work as described in "CONTROLS" in EVP_KDF_CTX(3).
       EVP_KDF_CTRL_SET_SSHKDF_XCGHASH
       EVP_KDF_CTRL_SET_SSHKDF_SESSION_ID
           These controls expect two arguments: "unsigned char *buffer",
           "size_t length"
           They set the respective values to the first length bytes of the
           buffer buffer. If a value is already set, the contents are
           replaced.
           EVP_KDF_ctrl_str() takes two type strings for these controls:
           "xcghash"
           "session_id"
               The value string is used as is.
           "hexxcghash"
           "hexsession_id"
               The value string is expected to be a hexadecimal number, which
               will be decoded before being passed on as the control value.
       EVP_KDF_CTRL_SET_SSHKDF_TYPE
           This control expects one argument: "int mode"
           Sets the type for the SSHHKDF operation. There are six supported
           types:
           EVP_KDF_SSHKDF_TYPE_ININITAL_IV_CLI_TO_SRV
               The Initial IV from client to server.  A single char of value
               65 (ASCII char 'A').
           EVP_KDF_SSHKDF_TYPE_ININITAL_IV_SRV_TO_CLI
               The Initial IV from server to client A single char of value 66
               (ASCII char 'B').
           EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_CLI_TO_SRV
               The Encryption Key from client to server A single char of value
               67 (ASCII char 'C').
           EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_SRV_TO_CLI
               The Encryption Key from server to client A single char of value
               68 (ASCII char 'D').
           EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_CLI_TO_SRV
               The Integrity Key from client to server A single char of value
               69 (ASCII char 'E').
           EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_SRV_TO_CLI
               The Integrity Key from client to server A single char of value
               70 (ASCII char 'F').
           EVP_KDF_ctrl_str() type string: "type"
           The value is a string of length one character. The only valid
           values are the numerical values of the ASCII caracters: "A" (65) to
           "F" (70).
NOTES
       A context for SSHKDF can be obtained by calling:
        EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SSHKDF);
       The output length of the SSHKDF derivation is specified via the
       "keylen" parameter to the EVP_KDF_derive(3) function.  Since the SSHKDF
       output length is variable, calling EVP_KDF_size() to obtain the
       requisite length is not meaningful. The caller must allocate a buffer
       of the desired length, and pass that buffer to the EVP_KDF_derive(3)
       function along with the desired length.
EXAMPLE
       This example derives an 8 byte IV using SHA-256 with a 1K "key" and
       appropriate "xcghash" and "session_id" values:
        EVP_KDF_CTX *kctx;
        unsigned char key[1024] = "01234...";
        unsigned char xcghash[32] = "012345...";
        unsigned char session_id[32] = "012345...";
        unsigned char out[8];
        size_t outlen = sizeof(out);
        kctx = EVP_KDF_CTX_new_id(EVP_KDF_SSHKDF);
        if (EVP_KDF_CTX_set_md(kctx, EVP_sha256()) <= 0)
            /* Error */
        if (EVP_KDF_CTX_set1_key(kctx, key, 1024) <= 0)
            /* Error */
        if (EVP_KDF_CTX_set1_sshkdf_xcghash(kctx, xcghash, 32) <= 0)
            /* Error */
        if (EVP_KDF_CTX_set1_sshkdf_session_id(kctx, session_id, 32) <= 0)
            /* Error */
        if (EVP_KDF_CTX_set_sshkdf_type(kctx,
                           EVP_KDF_SSHKDF_TYPE_ININITAL_IV_CLI_TO_SRV) <= 0)
            /* Error */
        if (EVP_KDF_derive(kctx, out, &outlen) <= 0)
            /* Error */
CONFORMING TO
       RFC 4253
SEE ALSO
       EVP_KDF_CTX, EVP_KDF_CTX_new_id(3), EVP_KDF_CTX_free(3),
       EVP_KDF_ctrl(3), EVP_KDF_size(3), EVP_KDF_derive(3), "CONTROLS" in
       EVP_KDF_CTX(3)
COPYRIGHT
       Copyright 2016-2018 The OpenSSL Project Authors. All Rights Reserved.
       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>;.
1.1.1k                            2024-10-09                 EVP_KDF_SSHKDF(7)