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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\-KRB5KDF \- The RFC3961 Krb5 KDF EVP_KDF implementation .SH "DESCRIPTION" .IX Header "DESCRIPTION" Support for computing the \fB\s-1KRB5KDF\s0\fR \s-1KDF\s0 through the \fB\s-1EVP_KDF\s0\fR \s-1API.\s0 .PP The \s-1EVP_KDF\-KRB5KDF\s0 algorithm implements the key derivation function defined in \s-1RFC 3961,\s0 section 5.1 and is used by Krb5 to derive session keys. Three inputs are required to perform key derivation: a cipher, (for example \&\s-1AES\-128\-CBC\s0), the initial key, and a constant. .SS "Identity" .IX Subsection "Identity" \&\*(L"\s-1KRB5KDF\*(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 """cipher"" (\fB\s-1OSSL_KDF_PARAM_CIPHER\s0\fR) <\s-1UTF8\s0 string>" 4 .el .IP "``cipher'' (\fB\s-1OSSL_KDF_PARAM_CIPHER\s0\fR) <\s-1UTF8\s0 string>" 4 .IX Item "cipher (OSSL_KDF_PARAM_CIPHER) " .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 """constant"" (\fB\s-1OSSL_KDF_PARAM_CONSTANT\s0\fR) " 4 .el .IP "``constant'' (\fB\s-1OSSL_KDF_PARAM_CONSTANT\s0\fR) " 4 .IX Item "constant (OSSL_KDF_PARAM_CONSTANT) " This parameter sets the constant value for the \s-1KDF.\s0 If a value is already set, the contents are replaced. .SH "NOTES" .IX Header "NOTES" A context for \s-1KRB5KDF\s0 can be obtained by calling: .PP .Vb 2 \& EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL); \& EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf); .Ve .PP The output length of the \s-1KRB5KDF\s0 derivation is specified via the \fIkeylen\fR parameter to the \fBEVP_KDF_derive\fR\|(3) function, and \s-1MUST\s0 match the key length for the chosen cipher or an error is returned. Moreover, the constant's length must not exceed the block size of the cipher. Since the \s-1KRB5KDF\s0 output length depends on the chosen cipher, calling \&\fBEVP_KDF_CTX_get_kdf_size\fR\|(3) to obtain the requisite length returns the correct length only after the cipher is set. Prior to that \fB\s-1EVP_MAX_KEY_LENGTH\s0\fR is returned. The caller must allocate a buffer of the correct length for the chosen cipher, and pass that buffer to the \fBEVP_KDF_derive\fR\|(3) function along with that length. .SH "EXAMPLES" .IX Header "EXAMPLES" This example derives a key using the \s-1AES\-128\-CBC\s0 cipher: .PP .Vb 7 \& EVP_KDF *kdf; \& EVP_KDF_CTX *kctx; \& unsigned char key[16] = "01234..."; \& unsigned char constant[] = "I\*(Aqm a constant"; \& unsigned char out[16]; \& size_t outlen = sizeof(out); \& OSSL_PARAM params[4], *p = params; \& \& kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL); \& kctx = EVP_KDF_CTX_new(kdf); \& EVP_KDF_free(kdf); \& \& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER, \& SN_aes_128_cbc, \& strlen(SN_aes_128_cbc)); \& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY, \& key, (size_t)16); \& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_CONSTANT, \& constant, strlen(constant)); \& *p = OSSL_PARAM_construct_end(); \& if (EVP_KDF_derive(kctx, out, outlen, params) <= 0) \& /* Error */ \& \& EVP_KDF_CTX_free(kctx); .Ve .SH "CONFORMING TO" .IX Header "CONFORMING TO" \&\s-1RFC 3961\s0 .SH "SEE ALSO" .IX Header "SEE ALSO" \&\s-1\fBEVP_KDF\s0\fR\|(3), \&\fBEVP_KDF_CTX_free\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\-2021 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 .