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Title "EVP_PKEY_CTX_SET_TLS1_PRF_MD 3ossl" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
EVP_PKEY_CTX_set_tls1_prf_md, EVP_PKEY_CTX_set1_tls1_prf_secret, EVP_PKEY_CTX_add1_tls1_prf_seed - TLS PRF key derivation algorithm Header "SYNOPSIS" .Vb 1 #include <openssl/kdf.h> \& int EVP_PKEY_CTX_set_tls1_prf_md(EVP_PKEY_CTX *pctx, const EVP_MD *md); int EVP_PKEY_CTX_set1_tls1_prf_secret(EVP_PKEY_CTX *pctx, unsigned char *sec, int seclen); int EVP_PKEY_CTX_add1_tls1_prf_seed(EVP_PKEY_CTX *pctx, unsigned char *seed, int seedlen); .Ve Header "DESCRIPTION" The \s-1EVP_PKEY_TLS1_PRF\s0 algorithm implements the \s-1PRF\s0 key derivation function for \s-1TLS.\s0 It has no associated private key and only implements key derivation using EVP_PKEY_derive\|(3).

\fBEVP_PKEY_set_tls1_prf_md() sets the message digest associated with the \s-1TLS PRF.\s0 EVP_md5_sha1() is treated as a special case which uses the \s-1PRF\s0 algorithm using both \s-1MD5\s0 and \s-1SHA1\s0 as used in \s-1TLS 1.0\s0 and 1.1.

\fBEVP_PKEY_CTX_set_tls1_prf_secret() sets the secret value of the \s-1TLS PRF\s0 to seclen bytes of the buffer sec. Any existing secret value is replaced and any seed is reset.

\fBEVP_PKEY_CTX_add1_tls1_prf_seed() sets the seed to seedlen bytes of seed. If a seed is already set it is appended to the existing value.

Header "STRING CTRLS" The \s-1TLS PRF\s0 also supports string based control operations using \fBEVP_PKEY_CTX_ctrl_str\|(3). The type parameter \*(L"md\*(R" uses the supplied value as the name of the digest algorithm to use. The type parameters \*(L"secret\*(R" and \*(L"seed\*(R" use the supplied value parameter as a secret or seed value. The names \*(L"hexsecret\*(R" and \*(L"hexseed\*(R" are similar except they take a hex string which is converted to binary. Header "NOTES" A context for the \s-1TLS PRF\s0 can be obtained by calling:

.Vb 1 EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL); .Ve

The digest, secret value and seed must be set before a key is derived or an error occurs.

The total length of all seeds cannot exceed 1024 bytes in length: this should be more than enough for any normal use of the \s-1TLS PRF.\s0

The output length of the \s-1PRF\s0 is specified by the length parameter in the \fBEVP_PKEY_derive() function. Since the output length is variable, setting the buffer to \s-1NULL\s0 is not meaningful for the \s-1TLS PRF.\s0

Optimised versions of the \s-1TLS PRF\s0 can be implemented in an \s-1ENGINE.\s0

Header "RETURN VALUES" All these functions return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm. Header "EXAMPLES" This example derives 10 bytes using \s-1SHA-256\s0 with the secret key \*(L"secret\*(R" and seed value \*(L"seed\*(R":

.Vb 3 EVP_PKEY_CTX *pctx; unsigned char out[10]; size_t outlen = sizeof(out); \& pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL); if (EVP_PKEY_derive_init(pctx) <= 0) /* Error */ if (EVP_PKEY_CTX_set_tls1_prf_md(pctx, EVP_sha256()) <= 0) /* Error */ if (EVP_PKEY_CTX_set1_tls1_prf_secret(pctx, "secret", 6) <= 0) /* Error */ if (EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, "seed", 4) <= 0) /* Error */ if (EVP_PKEY_derive(pctx, out, &outlen) <= 0) /* Error */ .Ve

Header "SEE ALSO" \fBEVP_PKEY_CTX_new\|(3), \fBEVP_PKEY_CTX_ctrl_str\|(3), \fBEVP_PKEY_derive\|(3) Header "HISTORY" All of the functions described here were converted from macros to functions in OpenSSL 3.0. Header "COPYRIGHT" Copyright 2016-2020 The OpenSSL Project Authors. All Rights Reserved.

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 <https://www.openssl.org/source/license.html>.