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132 .TH HMAC 3 "2018-09-11" "1.1.1" "OpenSSL"
133 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
134 .\" way too many mistakes in technical documents.
138 HMAC, HMAC_CTX_new, HMAC_CTX_reset, HMAC_CTX_free, HMAC_Init, HMAC_Init_ex, HMAC_Update, HMAC_Final, HMAC_CTX_copy, HMAC_CTX_set_flags, HMAC_CTX_get_md, HMAC_size \&\- HMAC message authentication code
140 .IX Header "SYNOPSIS"
142 \& #include <openssl/hmac.h>
144 \& unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
145 \& int key_len, const unsigned char *d, int n,
146 \& unsigned char *md, unsigned int *md_len);
148 \& HMAC_CTX *HMAC_CTX_new(void);
149 \& int HMAC_CTX_reset(HMAC_CTX *ctx);
151 \& int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
152 \& const EVP_MD *md, ENGINE *impl);
153 \& int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
154 \& int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
156 \& void HMAC_CTX_free(HMAC_CTX *ctx);
158 \& int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
159 \& void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
160 \& const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
162 \& size_t HMAC_size(const HMAC_CTX *e);
168 \& #if OPENSSL_API_COMPAT < 0x10100000L
169 \& int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
170 \& const EVP_MD *md);
174 .IX Header "DESCRIPTION"
175 \&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash
176 function used for message authentication, which is based on a hash
179 \&\s-1\fIHMAC\s0()\fR computes the message authentication code of the \fBn\fR bytes at
180 \&\fBd\fR using the hash function \fBevp_md\fR and the key \fBkey\fR which is
181 \&\fBkey_len\fR bytes long.
183 It places the result in \fBmd\fR (which must have space for the output of
184 the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
185 If \fBmd\fR is \s-1NULL,\s0 the digest is placed in a static array. The size of
186 the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR. Note: passing a \s-1NULL\s0
187 value for \fBmd\fR to use the static array is not thread safe.
189 \&\fBevp_md\fR can be \fIEVP_sha1()\fR, \fIEVP_ripemd160()\fR etc.
191 \&\fIHMAC_CTX_new()\fR creates a new \s-1HMAC_CTX\s0 in heap memory.
193 \&\fIHMAC_CTX_reset()\fR zeroes an existing \fB\s-1HMAC_CTX\s0\fR and associated
194 resources, making it suitable for new computations as if it was newly
195 created with \fIHMAC_CTX_new()\fR.
197 \&\fIHMAC_CTX_free()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR,
198 releases any associated resources and finally frees the \fB\s-1HMAC_CTX\s0\fR
201 The following functions may be used if the message is not completely
204 \&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
205 function \fBevp_md\fR and key \fBkey\fR. If both are \s-1NULL,\s0 or if \fBkey\fR is \s-1NULL\s0
206 and \fBevp_md\fR is the same as the previous call, then the
208 reused. \fBctx\fR must have been created with \fIHMAC_CTX_new()\fR before the first use
209 of an \fB\s-1HMAC_CTX\s0\fR in this function.
211 If \fIHMAC_Init_ex()\fR is called with \fBkey\fR \s-1NULL\s0 and \fBevp_md\fR is not the
212 same as the previous digest used by \fBctx\fR then an error is returned
213 because reuse of an existing key with a different digest is not supported.
215 \&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
216 function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
219 \&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
220 be authenticated (\fBlen\fR bytes at \fBdata\fR).
222 \&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
223 must have space for the hash function output.
225 \&\fIHMAC_CTX_copy()\fR copies all of the internal state from \fBsctx\fR into \fBdctx\fR.
227 \&\fIHMAC_CTX_set_flags()\fR applies the specified flags to the internal EVP_MD_CTXs.
228 These flags have the same meaning as for \fIEVP_MD_CTX_set_flags\fR\|(3).
230 \&\fIHMAC_CTX_get_md()\fR returns the \s-1EVP_MD\s0 that has previously been set for the
231 supplied \s-1HMAC_CTX.\s0
233 \&\fIHMAC_size()\fR returns the length in bytes of the underlying hash function output.
235 .IX Header "RETURN VALUES"
236 \&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code or \s-1NULL\s0 if
239 \&\fIHMAC_CTX_new()\fR returns a pointer to a new \fB\s-1HMAC_CTX\s0\fR on success or
240 \&\fB\s-1NULL\s0\fR if an error occurred.
242 \&\fIHMAC_CTX_reset()\fR, \fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and
243 \&\fIHMAC_CTX_copy()\fR return 1 for success or 0 if an error occurred.
245 \&\fIHMAC_CTX_get_md()\fR return the \s-1EVP_MD\s0 previously set for the supplied \s-1HMAC_CTX\s0 or
246 \&\s-1NULL\s0 if no \s-1EVP_MD\s0 has been set.
248 \&\fIHMAC_size()\fR returns the length in bytes of the underlying hash function output
251 .IX Header "CONFORMING TO"
254 .IX Header "SEE ALSO"
255 \&\s-1\fISHA1\s0\fR\|(3), \fIevp\fR\|(7)
258 \&\fIHMAC_CTX_init()\fR was replaced with \fIHMAC_CTX_reset()\fR in OpenSSL 1.1.0.
260 \&\fIHMAC_CTX_cleanup()\fR existed in OpenSSL before version 1.1.0.
262 \&\fIHMAC_CTX_new()\fR, \fIHMAC_CTX_free()\fR and \fIHMAC_CTX_get_md()\fR are new in OpenSSL 1.1.0.
264 \&\fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR and \fIHMAC_Final()\fR did not return values in
265 OpenSSL before version 1.0.0.
267 .IX Header "COPYRIGHT"
268 Copyright 2000\-2016 The OpenSSL Project Authors. All Rights Reserved.
270 Licensed under the OpenSSL license (the \*(L"License\*(R"). You may not use
271 this file except in compliance with the License. You can obtain a copy
272 in the file \s-1LICENSE\s0 in the source distribution or at
273 <https://www.openssl.org/source/license.html>.