17 - HMAC message authentication code
21 #include <openssl/hmac.h>
23 unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len,
24 const unsigned char *data, size_t data_len,
25 unsigned char *md, unsigned int *md_len);
27 The following functions have been deprecated since OpenSSL 3.0, and can be
28 hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
29 see L<openssl_user_macros(7)>:
31 HMAC_CTX *HMAC_CTX_new(void);
32 int HMAC_CTX_reset(HMAC_CTX *ctx);
34 int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
35 const EVP_MD *md, ENGINE *impl);
36 int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, size_t len);
37 int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
39 void HMAC_CTX_free(HMAC_CTX *ctx);
41 int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
42 void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
43 const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
45 size_t HMAC_size(const HMAC_CTX *e);
47 The following function has been deprecated since OpenSSL 1.1.0, and can be
48 hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
49 see L<openssl_user_macros(7)>:
51 int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
56 HMAC is a MAC (message authentication code), i.e. a keyed hash
57 function used for message authentication, which is based on a hash
60 HMAC() computes the message authentication code of the I<data_len> bytes at
61 I<data> using the hash function I<evp_md> and the key I<key> which is
62 I<key_len> bytes long. The I<key> may also be NULL with I<key_len> being 0.
64 It places the result in I<md> (which must have space for the output of
65 the hash function, which is no more than B<EVP_MAX_MD_SIZE> bytes).
66 If I<md> is NULL, the digest is placed in a static array. The size of
67 the output is placed in I<md_len>, unless it is NULL. Note: passing a NULL
68 value for I<md> to use the static array is not thread safe.
70 I<evp_md> is a message digest such as EVP_sha1(), EVP_ripemd160() etc.
71 HMAC does not support variable output length digests such as EVP_shake128() and
74 All of the functions described below are deprecated.
75 Applications should instead use L<EVP_MAC_CTX_new(3)>, L<EVP_MAC_CTX_free(3)>,
76 L<EVP_MAC_init(3)>, L<EVP_MAC_update(3)> and L<EVP_MAC_final(3)>
77 or the 'quick' single-shot MAC function L<EVP_Q_mac(3)>.
79 HMAC_CTX_new() creates a new HMAC_CTX in heap memory.
81 HMAC_CTX_reset() clears an existing B<HMAC_CTX> and associated
82 resources, making it suitable for new computations as if it was newly
83 created with HMAC_CTX_new().
85 HMAC_CTX_free() erases the key and other data from the B<HMAC_CTX>,
86 releases any associated resources and finally frees the B<HMAC_CTX>
89 The following functions may be used if the message is not completely
92 HMAC_Init_ex() initializes or reuses a B<HMAC_CTX> structure to use the hash
93 function I<evp_md> and key I<key>. If both are NULL, or if I<key> is NULL
94 and I<evp_md> is the same as the previous call, then the
96 reused. I<ctx> must have been created with HMAC_CTX_new() before the first use
97 of an B<HMAC_CTX> in this function.
99 If HMAC_Init_ex() is called with I<key> NULL and I<evp_md> is not the
100 same as the previous digest used by I<ctx> then an error is returned
101 because reuse of an existing key with a different digest is not supported.
103 HMAC_Init() initializes a B<HMAC_CTX> structure to use the hash
104 function I<evp_md> and the key I<key> which is I<key_len> bytes
107 HMAC_Update() can be called repeatedly with chunks of the message to
108 be authenticated (I<len> bytes at I<data>).
110 HMAC_Final() places the message authentication code in I<md>, which
111 must have space for the hash function output.
113 HMAC_CTX_copy() copies all of the internal state from I<sctx> into I<dctx>.
115 HMAC_CTX_set_flags() applies the specified flags to the internal EVP_MD_CTXs.
116 These flags have the same meaning as for L<EVP_MD_CTX_set_flags(3)>.
118 HMAC_CTX_get_md() returns the EVP_MD that has previously been set for the
121 HMAC_size() returns the length in bytes of the underlying hash function output.
125 HMAC() returns a pointer to the message authentication code or NULL if
128 HMAC_CTX_new() returns a pointer to a new B<HMAC_CTX> on success or
129 NULL if an error occurred.
131 HMAC_CTX_reset(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and
132 HMAC_CTX_copy() return 1 for success or 0 if an error occurred.
134 HMAC_CTX_get_md() return the EVP_MD previously set for the supplied HMAC_CTX or
135 NULL if no EVP_MD has been set.
137 HMAC_size() returns the length in bytes of the underlying hash function output
146 L<SHA1(3)>, EVP_Q_mac(3), L<evp(7)>
150 All functions except for HMAC() were deprecated in OpenSSL 3.0.
152 HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL 1.1.0.
154 HMAC_CTX_cleanup() existed in OpenSSL before version 1.1.0.
156 HMAC_CTX_new(), HMAC_CTX_free() and HMAC_CTX_get_md() are new in OpenSSL 1.1.0.
158 HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in
159 OpenSSL before version 1.0.0.
163 Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
165 Licensed under the Apache License 2.0 (the "License"). You may not use
166 this file except in compliance with the License. You can obtain a copy
167 in the file LICENSE in the source distribution or at
168 L<https://www.openssl.org/source/license.html>.