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Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" EVP_KDF\-SSHKDF \- The SSHKDF EVP_KDF implementation .SH "DESCRIPTION" .IX Header "DESCRIPTION" Support for computing the \fB\s-1SSHKDF\s0\fR \s-1KDF\s0 through the \fB\s-1EVP_KDF\s0\fR \s-1API.\s0 .PP The \s-1EVP_KDF\-SSHKDF\s0 algorithm implements the \s-1SSHKDF\s0 key derivation function. It is defined in \s-1RFC 4253,\s0 section 7.2 and is used by \s-1SSH\s0 to derive IVs, encryption keys and integrity keys. Five inputs are required to perform key derivation: The hashing function (for example \s-1SHA256\s0), the Initial Key, the Exchange Hash, the Session \s-1ID,\s0 and the derivation key type. .SS "Identity" .IX Subsection "Identity" \&\*(L"\s-1SSHKDF\*(R"\s0 is the name for this implementation; it can be used with the \fBEVP_KDF_fetch()\fR function. .SS "Supported parameters" .IX Subsection "Supported parameters" The supported parameters are: .ie n .IP """properties"" (\fB\s-1OSSL_KDF_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4 .el .IP "``properties'' (\fB\s-1OSSL_KDF_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4 .IX Item "properties (OSSL_KDF_PARAM_PROPERTIES) " .PD 0 .ie n .IP """digest"" (\fB\s-1OSSL_KDF_PARAM_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4 .el .IP "``digest'' (\fB\s-1OSSL_KDF_PARAM_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4 .IX Item "digest (OSSL_KDF_PARAM_DIGEST) " .ie n .IP """key"" (\fB\s-1OSSL_KDF_PARAM_KEY\s0\fR) " 4 .el .IP "``key'' (\fB\s-1OSSL_KDF_PARAM_KEY\s0\fR) " 4 .IX Item "key (OSSL_KDF_PARAM_KEY) " .PD These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_KDF\s0\fR\|(3). .ie n .IP """xcghash"" (\fB\s-1OSSL_KDF_PARAM_SSHKDF_XCGHASH\s0\fR) " 4 .el .IP "``xcghash'' (\fB\s-1OSSL_KDF_PARAM_SSHKDF_XCGHASH\s0\fR) " 4 .IX Item "xcghash (OSSL_KDF_PARAM_SSHKDF_XCGHASH) " .PD 0 .ie n .IP """session_id"" (\fB\s-1OSSL_KDF_PARAM_SSHKDF_SESSION_ID\s0\fR) " 4 .el .IP "``session_id'' (\fB\s-1OSSL_KDF_PARAM_SSHKDF_SESSION_ID\s0\fR) " 4 .IX Item "session_id (OSSL_KDF_PARAM_SSHKDF_SESSION_ID) " .PD These parameters set the respective values for the \s-1KDF.\s0 If a value is already set, the contents are replaced. .ie n .IP """type"" (\fB\s-1OSSL_KDF_PARAM_SSHKDF_TYPE\s0\fR) <\s-1UTF8\s0 string>" 4 .el .IP "``type'' (\fB\s-1OSSL_KDF_PARAM_SSHKDF_TYPE\s0\fR) <\s-1UTF8\s0 string>" 4 .IX Item "type (OSSL_KDF_PARAM_SSHKDF_TYPE) " This parameter sets the type for the \s-1SSHKDF\s0 operation. There are six supported types: .RS 4 .IP "\s-1EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV\s0" 4 .IX Item "EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV" The Initial \s-1IV\s0 from client to server. A single char of value 65 (\s-1ASCII\s0 char 'A'). .IP "\s-1EVP_KDF_SSHKDF_TYPE_INITIAL_IV_SRV_TO_CLI\s0" 4 .IX Item "EVP_KDF_SSHKDF_TYPE_INITIAL_IV_SRV_TO_CLI" The Initial \s-1IV\s0 from server to client A single char of value 66 (\s-1ASCII\s0 char 'B'). .IP "\s-1EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_CLI_TO_SRV\s0" 4 .IX Item "EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_CLI_TO_SRV" The Encryption Key from client to server A single char of value 67 (\s-1ASCII\s0 char 'C'). .IP "\s-1EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_SRV_TO_CLI\s0" 4 .IX Item "EVP_KDF_SSHKDF_TYPE_ENCRYPTION_KEY_SRV_TO_CLI" The Encryption Key from server to client A single char of value 68 (\s-1ASCII\s0 char 'D'). .IP "\s-1EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_CLI_TO_SRV\s0" 4 .IX Item "EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_CLI_TO_SRV" The Integrity Key from client to server A single char of value 69 (\s-1ASCII\s0 char 'E'). .IP "\s-1EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_SRV_TO_CLI\s0" 4 .IX Item "EVP_KDF_SSHKDF_TYPE_INTEGRITY_KEY_SRV_TO_CLI" The Integrity Key from client to server A single char of value 70 (\s-1ASCII\s0 char 'F'). .RE .RS 4 .RE .SH "NOTES" .IX Header "NOTES" A context for \s-1SSHKDF\s0 can be obtained by calling: .PP .Vb 2 \& EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSHKDF", NULL); \& EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf); .Ve .PP The output length of the \s-1SSHKDF\s0 derivation is specified via the \fIkeylen\fR parameter to the \fBEVP_KDF_derive\fR\|(3) function. Since the \s-1SSHKDF\s0 output length is variable, calling \fBEVP_KDF_CTX_get_kdf_size\fR\|(3) to obtain the requisite length is not meaningful. The caller must allocate a buffer of the desired length, and pass that buffer to the \&\fBEVP_KDF_derive\fR\|(3) function along with the desired length. .SH "EXAMPLES" .IX Header "EXAMPLES" This example derives an 8 byte \s-1IV\s0 using \s-1SHA\-256\s0 with a 1K \*(L"key\*(R" and appropriate \&\*(L"xcghash\*(R" and \*(L"session_id\*(R" values: .PP .Vb 9 \& EVP_KDF *kdf; \& EVP_KDF_CTX *kctx; \& char type = EVP_KDF_SSHKDF_TYPE_INITIAL_IV_CLI_TO_SRV; \& 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); \& OSSL_PARAM params[6], *p = params; \& \& kdf = EVP_KDF_fetch(NULL, "SSHKDF", NULL); \& kctx = EVP_KDF_CTX_new(kdf); \& EVP_KDF_free(kdf); \& \& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST, \& SN_sha256, strlen(SN_sha256)); \& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY, \& key, (size_t)1024); \& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SSHKDF_XCGHASH, \& xcghash, (size_t)32); \& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SSHKDF_SESSION_ID, \& session_id, (size_t)32); \& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_SSHKDF_TYPE, \& &type, sizeof(type)); \& *p = OSSL_PARAM_construct_end(); \& if (EVP_KDF_derive(kctx, out, outlen, params) <= 0) \& /* Error */ .Ve .SH "CONFORMING TO" .IX Header "CONFORMING TO" \&\s-1RFC 4253\s0 .SH "SEE ALSO" .IX Header "SEE ALSO" \&\s-1\fBEVP_KDF\s0\fR\|(3), \&\fBEVP_KDF_CTX_new\fR\|(3), \&\fBEVP_KDF_CTX_free\fR\|(3), \&\fBEVP_KDF_CTX_set_params\fR\|(3), \&\fBEVP_KDF_CTX_get_kdf_size\fR\|(3), \&\fBEVP_KDF_derive\fR\|(3), \&\*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_KDF\s0\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" This functionality was added in OpenSSL 3.0. .SH "COPYRIGHT" .IX Header "COPYRIGHT" Copyright 2016\-2022 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use this file except in compliance with the License. You can obtain a copy in the file \s-1LICENSE\s0 in the source distribution or at .