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Title "EVP_KDF-X963 7" For nroff, turn off justification. Always turn off hyphenation; it makes
way too many mistakes in technical documents.
EVP_KDF-X963 - The X9.63-2001 EVP_KDF implementation Header "DESCRIPTION" The \s-1EVP_KDF-X963\s0 algorithm implements the key derivation function (X963KDF). X963KDF is used by Cryptographic Message Syntax (\s-1CMS\s0) for \s-1EC\s0 KeyAgreement, to derive a key using input such as a shared secret key and shared info. Subsection "Identity" \*(L"X963KDF\*(R" 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 "digest (OSSL_KDF_PARAM_DIGEST) <UTF8 string>"

These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1EVP_KDF\s0\|(3). Item "key (OSSL_KDF_PARAM_KEY) <octet string>" The shared secret used for key derivation. This parameter sets the secret. Item "info (OSSL_KDF_PARAM_INFO) <octet string>" This parameter specifies an optional value for shared info.

Header "NOTES" X963KDF is very similar to the \s-1SSKDF\s0 that uses a digest as the auxiliary function, X963KDF appends the counter to the secret, whereas \s-1SSKDF\s0 prepends the counter.

A context for X963KDF can be obtained by calling:

.Vb 2 EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL); EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf); .Ve

The output length of an X963KDF is specified via the keylen parameter to the EVP_KDF_derive\|(3) function.

Header "EXAMPLES" This example derives 10 bytes, with the secret key \*(L"secret\*(R" and sharedinfo value \*(L"label\*(R":

.Vb 4 EVP_KDF *kdf; EVP_KDF_CTX *kctx; unsigned char out[10]; OSSL_PARAM params[4], *p = params; \& kdf = EVP_KDF_fetch(NULL, "X963KDF", 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_INFO, "label", (size_t)5); *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" \*(L"\s-1SEC 1:\s0 Elliptic Curve Cryptography\*(R" Header "SEE ALSO" \s-1EVP_KDF\s0\|(3), \fBEVP_KDF_CTX_new\|(3), \fBEVP_KDF_CTX_free\|(3), \fBEVP_KDF_CTX_set_params\|(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.

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>.