mirror of https://github.com/openssl/openssl
174 lines
5.8 KiB
Plaintext
174 lines
5.8 KiB
Plaintext
=pod
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=head1 NAME
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HMAC,
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HMAC_CTX_new,
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HMAC_CTX_reset,
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HMAC_CTX_free,
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HMAC_Init,
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HMAC_Init_ex,
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HMAC_Update,
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HMAC_Final,
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HMAC_CTX_copy,
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HMAC_CTX_set_flags,
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HMAC_CTX_get_md,
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HMAC_size
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- HMAC message authentication code
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=head1 SYNOPSIS
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#include <openssl/hmac.h>
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unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len,
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const unsigned char *data, size_t data_len,
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unsigned char *md, unsigned int *md_len);
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The following functions have been deprecated since OpenSSL 3.0, and can be
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hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
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see L<openssl_user_macros(7)>:
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HMAC_CTX *HMAC_CTX_new(void);
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int HMAC_CTX_reset(HMAC_CTX *ctx);
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int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
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const EVP_MD *md, ENGINE *impl);
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int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, size_t len);
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int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
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void HMAC_CTX_free(HMAC_CTX *ctx);
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int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
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void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
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const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
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size_t HMAC_size(const HMAC_CTX *e);
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The following function has been deprecated since OpenSSL 1.1.0, and can be
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hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
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see L<openssl_user_macros(7)>:
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int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
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const EVP_MD *md);
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=head1 DESCRIPTION
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HMAC is a MAC (message authentication code), i.e. a keyed hash
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function used for message authentication, which is based on a hash
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function.
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HMAC() computes the message authentication code of the I<data_len> bytes at
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I<data> using the hash function I<evp_md> and the key I<key> which is
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I<key_len> bytes long. The I<key> may also be NULL with I<key_len> being 0.
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It places the result in I<md> (which must have space for the output of
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the hash function, which is no more than B<EVP_MAX_MD_SIZE> bytes).
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If I<md> is NULL, the digest is placed in a static array. The size of
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the output is placed in I<md_len>, unless it is NULL. Note: passing a NULL
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value for I<md> to use the static array is not thread safe.
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I<evp_md> is a message digest such as EVP_sha1(), EVP_ripemd160() etc.
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HMAC does not support variable output length digests such as EVP_shake128() and
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EVP_shake256().
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HMAC() uses the default B<OSSL_LIB_CTX>.
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Use L<EVP_Q_mac(3)> instead if a library context is required.
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All of the functions described below are deprecated.
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Applications should instead use L<EVP_MAC_CTX_new(3)>, L<EVP_MAC_CTX_free(3)>,
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L<EVP_MAC_init(3)>, L<EVP_MAC_update(3)> and L<EVP_MAC_final(3)>
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or the 'quick' single-shot MAC function L<EVP_Q_mac(3)>.
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HMAC_CTX_new() creates a new HMAC_CTX in heap memory.
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HMAC_CTX_reset() clears an existing B<HMAC_CTX> and associated
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resources, making it suitable for new computations as if it was newly
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created with HMAC_CTX_new().
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HMAC_CTX_free() erases the key and other data from the B<HMAC_CTX>,
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releases any associated resources and finally frees the B<HMAC_CTX>
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itself.
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The following functions may be used if the message is not completely
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stored in memory:
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HMAC_Init_ex() initializes or reuses a B<HMAC_CTX> structure to use the hash
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function I<evp_md> and key I<key>. If both are NULL, or if I<key> is NULL
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and I<evp_md> is the same as the previous call, then the
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existing key is
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reused. I<ctx> must have been created with HMAC_CTX_new() before the first use
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of an B<HMAC_CTX> in this function.
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If HMAC_Init_ex() is called with I<key> NULL and I<evp_md> is not the
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same as the previous digest used by I<ctx> then an error is returned
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because reuse of an existing key with a different digest is not supported.
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HMAC_Init() initializes a B<HMAC_CTX> structure to use the hash
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function I<evp_md> and the key I<key> which is I<key_len> bytes
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long.
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HMAC_Update() can be called repeatedly with chunks of the message to
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be authenticated (I<len> bytes at I<data>).
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HMAC_Final() places the message authentication code in I<md>, which
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must have space for the hash function output.
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HMAC_CTX_copy() copies all of the internal state from I<sctx> into I<dctx>.
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HMAC_CTX_set_flags() applies the specified flags to the internal EVP_MD_CTXs.
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These flags have the same meaning as for L<EVP_MD_CTX_set_flags(3)>.
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HMAC_CTX_get_md() returns the EVP_MD that has previously been set for the
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supplied HMAC_CTX.
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HMAC_size() returns the length in bytes of the underlying hash function output.
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=head1 RETURN VALUES
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HMAC() returns a pointer to the message authentication code or NULL if
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an error occurred.
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HMAC_CTX_new() returns a pointer to a new B<HMAC_CTX> on success or
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NULL if an error occurred.
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HMAC_CTX_reset(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and
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HMAC_CTX_copy() return 1 for success or 0 if an error occurred.
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HMAC_CTX_get_md() return the EVP_MD previously set for the supplied HMAC_CTX or
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NULL if no EVP_MD has been set.
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HMAC_size() returns the length in bytes of the underlying hash function output
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or zero on error.
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=head1 CONFORMING TO
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RFC 2104
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=head1 SEE ALSO
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L<SHA1(3)>, EVP_Q_mac(3), L<evp(7)>
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=head1 HISTORY
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All functions except for HMAC() were deprecated in OpenSSL 3.0.
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HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL 1.1.0.
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HMAC_CTX_cleanup() existed in OpenSSL before version 1.1.0.
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HMAC_CTX_new(), HMAC_CTX_free() and HMAC_CTX_get_md() are new in OpenSSL 1.1.0.
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HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in
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OpenSSL before version 1.0.0.
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=head1 COPYRIGHT
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Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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