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141 .TH hmac 3 "0.9.6e" "2000-11-12" "OpenSSL"
144 \&\s-1HMAC\s0, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- \s-1HMAC\s0 message
147 .IX Header "SYNOPSIS"
149 \& #include <openssl/hmac.h>
152 \& unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
153 \& int key_len, const unsigned char *d, int n,
154 \& unsigned char *md, unsigned int *md_len);
157 \& void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
158 \& const EVP_MD *md);
159 \& void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
160 \& void HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
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 \&\fIHMAC()\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.
181 \&\fBkey\fR and \fBevp_md\fR may be \fB\s-1NULL\s0\fR if a key and hash function have
182 been set in a previous call to \fIHMAC_Init()\fR for that \fB\s-1HMAC_CTX\s0\fR.
184 \&\fIHMAC_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR.
186 The following functions may be used if the message is not completely
189 \&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
190 function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes long.
192 \&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
193 be authenticated (\fBlen\fR bytes at \fBdata\fR).
195 \&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
196 must have space for the hash function output.
198 .IX Header "RETURN VALUES"
199 \&\fIHMAC()\fR returns a pointer to the message authentication code.
201 \&\fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR do not
204 .IX Header "CONFORMING TO"
207 .IX Header "SEE ALSO"
211 \&\fIHMAC()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
212 are available since SSLeay 0.9.0.