| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | HMAC,
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| 6 | HMAC_CTX_new,
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| 7 | HMAC_CTX_reset,
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| 8 | HMAC_CTX_free,
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| 9 | HMAC_Init,
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| 10 | HMAC_Init_ex,
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| 11 | HMAC_Update,
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| 12 | HMAC_Final,
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| 13 | HMAC_CTX_copy,
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| 14 | HMAC_CTX_set_flags,
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| 15 | HMAC_CTX_get_md,
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| 16 | HMAC_size
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| 17 | - HMAC message authentication code
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| 18 |
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| 19 | =head1 SYNOPSIS
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| 20 |
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| 21 | #include <openssl/hmac.h>
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| 22 |
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| 23 | unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
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| 24 | int key_len, const unsigned char *d, size_t n,
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| 25 | unsigned char *md, unsigned int *md_len);
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| 26 |
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| 27 | HMAC_CTX *HMAC_CTX_new(void);
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| 28 | int HMAC_CTX_reset(HMAC_CTX *ctx);
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| 29 |
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| 30 | int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
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| 31 | const EVP_MD *md, ENGINE *impl);
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| 32 | int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, size_t len);
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| 33 | int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
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| 34 |
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| 35 | void HMAC_CTX_free(HMAC_CTX *ctx);
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| 36 |
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| 37 | int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
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| 38 | void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
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| 39 | const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
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| 40 |
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| 41 | size_t HMAC_size(const HMAC_CTX *e);
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| 42 |
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| 43 | Deprecated:
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| 44 |
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| 45 | #if OPENSSL_API_COMPAT < 0x10100000L
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| 46 | int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
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| 47 | const EVP_MD *md);
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| 48 | #endif
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| 49 |
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| 50 | =head1 DESCRIPTION
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| 51 |
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| 52 | HMAC is a MAC (message authentication code), i.e. a keyed hash
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| 53 | function used for message authentication, which is based on a hash
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| 54 | function.
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| 55 |
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| 56 | HMAC() computes the message authentication code of the B<n> bytes at
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| 57 | B<d> using the hash function B<evp_md> and the key B<key> which is
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| 58 | B<key_len> bytes long.
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| 59 |
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| 60 | It places the result in B<md> (which must have space for the output of
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| 61 | the hash function, which is no more than B<EVP_MAX_MD_SIZE> bytes).
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| 62 | If B<md> is NULL, the digest is placed in a static array. The size of
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| 63 | the output is placed in B<md_len>, unless it is B<NULL>. Note: passing a NULL
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| 64 | value for B<md> to use the static array is not thread safe.
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| 65 |
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| 66 | B<evp_md> is a message digest such as EVP_sha1(), EVP_ripemd160() etc. HMAC does
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| 67 | not support variable output length digests such as EVP_shake128() and
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| 68 | EVP_shake256().
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| 69 |
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| 70 | HMAC_CTX_new() creates a new HMAC_CTX in heap memory.
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| 71 |
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| 72 | HMAC_CTX_reset() zeros an existing B<HMAC_CTX> and associated
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| 73 | resources, making it suitable for new computations as if it was newly
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| 74 | created with HMAC_CTX_new().
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| 75 |
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| 76 | HMAC_CTX_free() erases the key and other data from the B<HMAC_CTX>,
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| 77 | releases any associated resources and finally frees the B<HMAC_CTX>
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| 78 | itself.
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| 79 |
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| 80 | The following functions may be used if the message is not completely
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| 81 | stored in memory:
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| 82 |
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| 83 | HMAC_Init_ex() initializes or reuses a B<HMAC_CTX> structure to use the hash
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| 84 | function B<evp_md> and key B<key>. If both are NULL, or if B<key> is NULL
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| 85 | and B<evp_md> is the same as the previous call, then the
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| 86 | existing key is
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| 87 | reused. B<ctx> must have been created with HMAC_CTX_new() before the first use
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| 88 | of an B<HMAC_CTX> in this function.
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| 89 |
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| 90 | If HMAC_Init_ex() is called with B<key> NULL and B<evp_md> is not the
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| 91 | same as the previous digest used by B<ctx> then an error is returned
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| 92 | because reuse of an existing key with a different digest is not supported.
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| 93 |
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| 94 | HMAC_Init() initializes a B<HMAC_CTX> structure to use the hash
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| 95 | function B<evp_md> and the key B<key> which is B<key_len> bytes
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| 96 | long.
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| 97 |
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| 98 | HMAC_Update() can be called repeatedly with chunks of the message to
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| 99 | be authenticated (B<len> bytes at B<data>).
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| 100 |
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| 101 | HMAC_Final() places the message authentication code in B<md>, which
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| 102 | must have space for the hash function output.
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| 103 |
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| 104 | HMAC_CTX_copy() copies all of the internal state from B<sctx> into B<dctx>.
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| 105 |
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| 106 | HMAC_CTX_set_flags() applies the specified flags to the internal EVP_MD_CTXs.
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| 107 | These flags have the same meaning as for L<EVP_MD_CTX_set_flags(3)>.
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| 108 |
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| 109 | HMAC_CTX_get_md() returns the EVP_MD that has previously been set for the
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| 110 | supplied HMAC_CTX.
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| 111 |
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| 112 | HMAC_size() returns the length in bytes of the underlying hash function output.
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| 113 |
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| 114 | =head1 RETURN VALUES
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| 115 |
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| 116 | HMAC() returns a pointer to the message authentication code or NULL if
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| 117 | an error occurred.
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| 118 |
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| 119 | HMAC_CTX_new() returns a pointer to a new B<HMAC_CTX> on success or
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| 120 | B<NULL> if an error occurred.
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| 121 |
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| 122 | HMAC_CTX_reset(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and
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| 123 | HMAC_CTX_copy() return 1 for success or 0 if an error occurred.
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| 124 |
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| 125 | HMAC_CTX_get_md() return the EVP_MD previously set for the supplied HMAC_CTX or
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| 126 | NULL if no EVP_MD has been set.
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| 127 |
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| 128 | HMAC_size() returns the length in bytes of the underlying hash function output
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| 129 | or zero on error.
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| 130 |
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| 131 | =head1 CONFORMING TO
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| 132 |
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| 133 | RFC 2104
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| 134 |
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| 135 | =head1 SEE ALSO
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| 136 |
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| 137 | L<SHA1(3)>, L<evp(7)>
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| 138 |
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| 139 | =head1 HISTORY
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| 140 |
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| 141 | HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL 1.1.0.
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| 142 |
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| 143 | HMAC_CTX_cleanup() existed in OpenSSL before version 1.1.0.
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| 144 |
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| 145 | HMAC_CTX_new(), HMAC_CTX_free() and HMAC_CTX_get_md() are new in OpenSSL 1.1.0.
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| 146 |
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| 147 | HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in
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| 148 | OpenSSL before version 1.0.0.
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| 149 |
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| 150 | =head1 COPYRIGHT
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| 151 |
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| 152 | Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
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| 153 |
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| 154 | Licensed under the OpenSSL license (the "License"). You may not use
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| 155 | this file except in compliance with the License. You can obtain a copy
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| 156 | in the file LICENSE in the source distribution or at
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| 157 | L<https://www.openssl.org/source/license.html>.
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| 158 |
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| 159 | =cut
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