EVP_KDF-TLS1_PRF - The TLS1 PRF EVP_KDF implementation
Support for computing the TLS1 PRF through the EVP_KDF API.
The EVP_KDF-TLS1_PRF algorithm implements the PRF used by TLS versions up to and including TLS 1.2.
"TLS1-PRF" is the name for this implementation; it can be used with the EVP_KDF_fetch() function.
The supported parameters are:
These parameters work as described in "PARAMETERS" in EVP_KDF(3).
The OSSL_KDF_PARAM_DIGEST parameter is used to set the message digest associated with the TLS PRF. EVP_md5_sha1() is treated as a special case which uses the PRF algorithm using both MD5 and SHA1 as used in TLS 1.0 and 1.1.
This parameter sets the secret value of the TLS PRF. Any existing secret value is replaced.
This parameter sets the context seed. The length of the context seed cannot exceed 1024 bytes; this should be more than enough for any normal use of the TLS PRF.
A context for the TLS PRF can be obtained by calling:
EVP_KDF *kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);The digest, secret value and seed must be set before a key is derived otherwise an error will occur.
The output length of the PRF is specified by the keylen parameter to the EVP_KDF_derive() function.
This example derives 10 bytes using SHA-256 with the secret key "secret" and seed value "seed":
EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[4], *p = params;
kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", 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_SECRET,
"secret", (size_t)6);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
"seed", (size_t)4);
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
error("EVP_KDF_derive");
}
EVP_KDF_CTX_free(kctx);RFC 2246, RFC 5246 and NIST SP 800-135 r1
EVP_KDF(3), EVP_KDF_CTX_new(3), EVP_KDF_CTX_free(3), EVP_KDF_CTX_set_params(3), EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)
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