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132 .TH hmac 3 "2005-12-03" "0.9.8a" "OpenSSL"
134 HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- HMAC message
137 .IX Header "SYNOPSIS"
139 \& #include <openssl/hmac.h>
143 \& unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
144 \& int key_len, const unsigned char *d, int n,
145 \& unsigned char *md, unsigned int *md_len);
149 \& void HMAC_CTX_init(HMAC_CTX *ctx);
153 \& void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
154 \& const EVP_MD *md);
155 \& void HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
156 \& const EVP_MD *md);
157 \& void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
158 \& void 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.
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_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be
187 \&\fIHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR
188 and releases any associated resources. It must be called when an
189 \&\fB\s-1HMAC_CTX\s0\fR is no longer required.
191 \&\fIHMAC_cleanup()\fR is an alias for \fIHMAC_CTX_cleanup()\fR included for back
192 compatibility with 0.9.6b, it is deprecated.
194 The following functions may be used if the message is not completely
197 \&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
198 function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
199 long. It is deprecated and only included for backward compatibility
202 \&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use
203 the function \fBevp_md\fR and key \fBkey\fR. Either can be \s-1NULL\s0, in which
204 case the existing one will be reused. \fIHMAC_CTX_init()\fR must have been
205 called before the first use of an \fB\s-1HMAC_CTX\s0\fR in this
206 function. \fBN.B. \f(BIHMAC_Init()\fB had this undocumented behaviour in
207 previous versions of OpenSSL \- failure to switch to \f(BIHMAC_Init_ex()\fB in
208 programs that expect it will cause them to stop working\fR.
210 \&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
211 be authenticated (\fBlen\fR bytes at \fBdata\fR).
213 \&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
214 must have space for the hash function output.
216 .IX Header "RETURN VALUES"
217 \&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code.
219 \&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and
220 \&\fIHMAC_CTX_cleanup()\fR do not return values.
222 .IX Header "CONFORMING TO"
225 .IX Header "SEE ALSO"
226 \&\fIsha\fR\|(3), \fIevp\fR\|(3)
229 \&\s-1\fIHMAC\s0()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
230 are available since SSLeay 0.9.0.
232 \&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR and \fIHMAC_CTX_cleanup()\fR are available