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136 .TH hmac 3 "2015-03-19" "1.0.1m" "OpenSSL"
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142 HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- HMAC message
145 .IX Header "SYNOPSIS"
147 \& #include <openssl/hmac.h>
149 \& unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
150 \& int key_len, const unsigned char *d, int n,
151 \& unsigned char *md, unsigned int *md_len);
153 \& void HMAC_CTX_init(HMAC_CTX *ctx);
155 \& int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
156 \& const EVP_MD *md);
157 \& int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
158 \& const EVP_MD *md, ENGINE *impl);
159 \& int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
160 \& int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
162 \& void HMAC_CTX_cleanup(HMAC_CTX *ctx);
163 \& void HMAC_cleanup(HMAC_CTX *ctx);
166 .IX Header "DESCRIPTION"
167 \&\s-1HMAC\s0 is a \s-1MAC \s0(message authentication code), i.e. a keyed hash
168 function used for message authentication, which is based on a hash
171 \&\s-1\fIHMAC\s0()\fR computes the message authentication code of the \fBn\fR bytes at
172 \&\fBd\fR using the hash function \fBevp_md\fR and the key \fBkey\fR which is
173 \&\fBkey_len\fR bytes long.
175 It places the result in \fBmd\fR (which must have space for the output of
176 the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
177 If \fBmd\fR is \s-1NULL,\s0 the digest is placed in a static array. The size of
178 the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR.
180 \&\fBevp_md\fR can be \fIEVP_sha1()\fR, \fIEVP_ripemd160()\fR etc.
182 \&\fIHMAC_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be
185 \&\fIHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR
186 and releases any associated resources. It must be called when an
187 \&\fB\s-1HMAC_CTX\s0\fR is no longer required.
189 \&\fIHMAC_cleanup()\fR is an alias for \fIHMAC_CTX_cleanup()\fR included for back
190 compatibility with 0.9.6b, it is deprecated.
192 The following functions may be used if the message is not completely
195 \&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
196 function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
197 long. It is deprecated and only included for backward compatibility
200 \&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use
201 the function \fBevp_md\fR and key \fBkey\fR. Either can be \s-1NULL,\s0 in which
202 case the existing one will be reused. \fIHMAC_CTX_init()\fR must have been
203 called before the first use of an \fB\s-1HMAC_CTX\s0\fR in this
204 function. \fBN.B. \f(BIHMAC_Init()\fB had this undocumented behaviour in
205 previous versions of OpenSSL \- failure to switch to \f(BIHMAC_Init_ex()\fB in
206 programs that expect it will cause them to stop working\fR.
208 \&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
209 be authenticated (\fBlen\fR bytes at \fBdata\fR).
211 \&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
212 must have space for the hash function output.
214 .IX Header "RETURN VALUES"
215 \&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code or \s-1NULL\s0 if
218 \&\fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR and \fIHMAC_Final()\fR return 1 for success or 0 if
221 \&\fIHMAC_CTX_init()\fR and \fIHMAC_CTX_cleanup()\fR do not return values.
223 .IX Header "CONFORMING TO"
226 .IX Header "SEE ALSO"
227 \&\fIsha\fR\|(3), \fIevp\fR\|(3)
230 \&\s-1\fIHMAC\s0()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
231 are available since SSLeay 0.9.0.
233 \&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR and \fIHMAC_CTX_cleanup()\fR are available
236 \&\fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR and \fIHMAC_Final()\fR did not return values in
237 versions of OpenSSL before 1.0.0.