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Title "EVP_KDF-KB 7" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
EVP_KDF-KB - The Key-Based EVP_KDF implementation Header "DESCRIPTION" The \s-1EVP_KDF-KB\s0 algorithm implements the Key-Based key derivation function (\s-1KBKDF\s0). \s-1KBKDF\s0 derives a key from repeated application of a keyed \s-1MAC\s0 to an input secret (and other optional values). Subsection "Identity" \*(L"\s-1KBKDF\*(R"\s0 is the name for this implementation; it can be used with the \fBEVP_KDF_fetch() function. Subsection "Supported parameters" The supported parameters are: Item "mode (OSSL_KDF_PARAM_MODE) <UTF8 string>" The mode parameter determines which flavor of \s-1KBKDF\s0 to use - currently the choices are \*(L"counter\*(R" and \*(L"feedback\*(R". \*(L"counter\*(R" is the default, and will be used if unspecified. Item "mac (OSSL_KDF_PARAM_MAC) <UTF8 string>" The value is either \s-1CMAC\s0 or \s-1HMAC.\s0 Item "digest (OSSL_KDF_PARAM_DIGEST) <UTF8 string>"

0 Item "cipher (OSSL_KDF_PARAM_CIPHER) <UTF8 string>" Item "properties (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>" Item "key (OSSL_KDF_PARAM_KEY) <octet string>" Item "salt (OSSL_KDF_PARAM_SALT) <octet string>"

Item """info (OSSL_KDF_PARAM_INFO) <octet string>" Item "seed (OSSL_KDF_PARAM_SEED) <octet string>"

The seed parameter is unused in counter mode. Item "use-l (OSSL_KDF_PARAM_KBKDF_USE_L) <integer>" Set to 0 to disable use of the optional Fixed Input data 'L' (see \s-1SP800-108\s0). The default value of 1 will be used if unspecified. Item "use-separator (OSSL_KDF_PARAM_KBKDF_USE_SEPARATOR) <integer>" Set to 0 to disable use of the optional Fixed Input data 'zero separator' (see \s-1SP800-108\s0) that is placed between the Label and Context. The default value of 1 will be used if unspecified.

Depending on whether mac is \s-1CMAC\s0 or \s-1HMAC,\s0 either digest or cipher is required (respectively) and the other is unused.

The parameters key, salt, info, and seed correspond to \s-1KI,\s0 Label, Context, and \s-1IV\s0 (respectively) in \s-1SP800-108.\s0 As in that document, salt, info, and seed are optional and may be omitted.

\*(L"mac\*(R", \*(L"digest\*(R", cipher\*(L" and \*(R"properties" are described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1EVP_KDF\s0\|(3).

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

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

The output length of an \s-1KBKDF\s0 is specified via the \*(C`keylen\*(C' parameter to the EVP_KDF_derive\|(3) function.

Note that currently OpenSSL only implements counter and feedback modes. Other variants may be supported in the future.

Header "EXAMPLES" This example derives 10 bytes using \s-1COUNTER-HMAC-SHA256,\s0 with \s-1KI\s0 \*(L"secret\*(R", Label \*(L"label\*(R", and Context \*(L"context\*(R".

.Vb 4 EVP_KDF *kdf; EVP_KDF_CTX *kctx; unsigned char out[10]; OSSL_PARAM params[6], *p = params; \& kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL); kctx = EVP_KDF_CTX_new(kdf); EVP_KDF_free(kdf); \& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST, "SHA2-256", 0); *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC, "HMAC", 0); *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY, "secret", strlen("secret")); *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT, "label", strlen("label")); *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO, "context", strlen("context")); *p = OSSL_PARAM_construct_end(); if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) error("EVP_KDF_derive"); \& EVP_KDF_CTX_free(kctx); .Ve

This example derives 10 bytes using \s-1FEEDBACK-CMAC-AES256,\s0 with \s-1KI\s0 \*(L"secret\*(R", Label \*(L"label\*(R", and \s-1IV\s0 \*(L"sixteen bytes iv\*(R".

.Vb 5 EVP_KDF *kdf; EVP_KDF_CTX *kctx; unsigned char out[10]; OSSL_PARAM params[8], *p = params; unsigned char *iv = "sixteen bytes iv"; \& kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL); kctx = EVP_KDF_CTX_new(kdf); EVP_KDF_free(kdf); \& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER, "AES256", 0); *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC, "CMAC", 0); *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MODE, "FEEDBACK", 0); *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY, "secret", strlen("secret")); *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT, "label", strlen("label")); *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO, "context", strlen("context")); *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED, iv, strlen(iv)); *p = OSSL_PARAM_construct_end(); if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) error("EVP_KDF_derive"); \& EVP_KDF_CTX_free(kctx); .Ve

Header "CONFORMING TO" \s-1NIST SP800-108, IETF RFC 6803, IETF RFC 8009.\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 2019-2021 The OpenSSL Project Authors. All Rights Reserved. Copyright 2019 Red Hat, Inc.

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>.