1HMAC(3ossl) OpenSSL HMAC(3ossl)
2
6 HMAC, HMAC_CTX_new, HMAC_CTX_reset, HMAC_CTX_free, HMAC_Init,
7 HMAC_Init_ex, HMAC_Update, HMAC_Final, HMAC_CTX_copy,
8 HMAC_CTX_set_flags, HMAC_CTX_get_md, HMAC_size - HMAC message
9 authentication code
10
12 #include <openssl/hmac.h>
13 unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len,
15 const unsigned char *data, size_t data_len,
16 unsigned char *md, unsigned int *md_len);
17 The following functions have been deprecated since OpenSSL 3.0, and can
19 be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
20 version value, see openssl_user_macros(7):
21 HMAC_CTX *HMAC_CTX_new(void);
23 int HMAC_CTX_reset(HMAC_CTX *ctx);
24 int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
26 const EVP_MD *md, ENGINE *impl);
27 int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, size_t len);
28 int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
29 void HMAC_CTX_free(HMAC_CTX *ctx);
31 int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
33 void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
34 const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
35 size_t HMAC_size(const HMAC_CTX *e);
37 The following function has been deprecated since OpenSSL 1.1.0, and can
39 be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
40 version value, see openssl_user_macros(7):
41 int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
43 const EVP_MD *md);
44
46 HMAC is a MAC (message authentication code), i.e. a keyed hash function
47 used for message authentication, which is based on a hash function.
48 HMAC() computes the message authentication code of the data_len bytes
50 at data using the hash function evp_md and the key key which is key_len
51 bytes long. The key may also be NULL with key_len being 0.
52 It places the result in md (which must have space for the output of the
54 hash function, which is no more than EVP_MAX_MD_SIZE bytes). If md is
55 NULL, the digest is placed in a static array. The size of the output
56 is placed in md_len, unless it is NULL. Note: passing a NULL value for
57 md to use the static array is not thread safe.
58 evp_md is a message digest such as EVP_sha1(), EVP_ripemd160() etc.
60 HMAC does not support variable output length digests such as
61 EVP_shake128() and EVP_shake256().
62 HMAC() uses the default OSSL_LIB_CTX. Use EVP_Q_mac(3) instead if a
64 library context is required.
65 All of the functions described below are deprecated. Applications
67 should instead use EVP_MAC_CTX_new(3), EVP_MAC_CTX_free(3),
68 EVP_MAC_init(3), EVP_MAC_update(3) and EVP_MAC_final(3) or the 'quick'
69 single-shot MAC function EVP_Q_mac(3).
70 HMAC_CTX_new() creates a new HMAC_CTX in heap memory.
72 HMAC_CTX_reset() clears an existing HMAC_CTX and associated resources,
74 making it suitable for new computations as if it was newly created with
75 HMAC_CTX_new().
76 HMAC_CTX_free() erases the key and other data from the HMAC_CTX,
78 releases any associated resources and finally frees the HMAC_CTX
79 itself.
80 The following functions may be used if the message is not completely
82 stored in memory:
83 HMAC_Init_ex() initializes or reuses a HMAC_CTX structure to use the
85 hash function evp_md and key key. If both are NULL, or if key is NULL
86 and evp_md is the same as the previous call, then the existing key is
87 reused. ctx must have been created with HMAC_CTX_new() before the first
88 use of an HMAC_CTX in this function.
89 If HMAC_Init_ex() is called with key NULL and evp_md is not the same as
91 the previous digest used by ctx then an error is returned because reuse
92 of an existing key with a different digest is not supported.
93 HMAC_Init() initializes a HMAC_CTX structure to use the hash function
95 evp_md and the key key which is key_len bytes long.
96 HMAC_Update() can be called repeatedly with chunks of the message to be
98 authenticated (len bytes at data).
99 HMAC_Final() places the message authentication code in md, which must
101 have space for the hash function output.
102 HMAC_CTX_copy() copies all of the internal state from sctx into dctx.
104 HMAC_CTX_set_flags() applies the specified flags to the internal
106 EVP_MD_CTXs. These flags have the same meaning as for
107 EVP_MD_CTX_set_flags(3).
108 HMAC_CTX_get_md() returns the EVP_MD that has previously been set for
110 the supplied HMAC_CTX.
111 HMAC_size() returns the length in bytes of the underlying hash function
113 output.
114
116 HMAC() returns a pointer to the message authentication code or NULL if
117 an error occurred.
118 HMAC_CTX_new() returns a pointer to a new HMAC_CTX on success or NULL
120 if an error occurred.
121 HMAC_CTX_reset(), HMAC_Init_ex(), HMAC_Update(), HMAC_Final() and
123 HMAC_CTX_copy() return 1 for success or 0 if an error occurred.
124 HMAC_CTX_get_md() return the EVP_MD previously set for the supplied
126 HMAC_CTX or NULL if no EVP_MD has been set.
127 HMAC_size() returns the length in bytes of the underlying hash function
129 output or zero on error.
130
132 RFC 2104
133
135 SHA1(3), EVP_Q_mac(3), evp(7)
136
138 All functions except for HMAC() were deprecated in OpenSSL 3.0.
139 HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL 1.1.0.
141 HMAC_CTX_cleanup() existed in OpenSSL before version 1.1.0.
143 HMAC_CTX_new(), HMAC_CTX_free() and HMAC_CTX_get_md() are new in
145 OpenSSL 1.1.0.
146 HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in
148 OpenSSL before version 1.0.0.
149
151 Copyright 2000-2022 The OpenSSL Project Authors. All Rights Reserved.
152 Licensed under the Apache License 2.0 (the "License"). You may not use
154 this file except in compliance with the License. You can obtain a copy
155 in the file LICENSE in the source distribution or at
156 <https://www.openssl.org/source/license.html>.
1573.1.1 2023-08-31 HMAC(3ossl)