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Title "EVP_KDF-KRB5KDF 7ossl" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
EVP_KDF-KRB5KDF - The RFC3961 Krb5 KDF EVP_KDF implementation Header "DESCRIPTION" Support for computing the \s-1KRB5KDF\s0 \s-1KDF\s0 through the \s-1EVP_KDF\s0 \s-1API.\s0

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.

Subsection "Identity" \*(L"\s-1KRB5KDF\*(R"\s0 is the name for this implementation; it can be used with the EVP_KDF_fetch() function. Subsection "Supported parameters" The supported parameters are: Item "properties (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>"

0 Item "cipher (OSSL_KDF_PARAM_CIPHER) <UTF8 string>" Item "key (OSSL_KDF_PARAM_KEY) <octet string>"

These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1EVP_KDF\s0\|(3). Item "constant (OSSL_KDF_PARAM_CONSTANT) <octet string>" This parameter sets the constant value for the \s-1KDF.\s0 If a value is already set, the contents are replaced.

Header "NOTES" A context for \s-1KRB5KDF\s0 can be obtained by calling:

.Vb 2 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KRB5KDF", NULL); EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf); .Ve

The output length of the \s-1KRB5KDF\s0 derivation is specified via the keylen parameter to the EVP_KDF_derive\|(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\|(3) to obtain the requisite length returns the correct length only after the cipher is set. Prior to that \s-1EVP_MAX_KEY_LENGTH\s0 is returned. The caller must allocate a buffer of the correct length for the chosen cipher, and pass that buffer to the EVP_KDF_derive\|(3) function along with that length.

Header "EXAMPLES" This example derives a key using the \s-1AES-128-CBC\s0 cipher:

.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

Header "CONFORMING TO" \s-1RFC 3961\s0 Header "SEE ALSO" \s-1EVP_KDF\s0\|(3), \fBEVP_KDF_CTX_free\|(3), \fBEVP_KDF_CTX_get_kdf_size\|(3), \fBEVP_KDF_derive\|(3), \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1EVP_KDF\s0\|(3) Header "HISTORY" This functionality was added in OpenSSL 3.0. Header "COPYRIGHT" Copyright 2016-2021 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>.