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127 .TH hmac 3 "2007-10-24" "0.9.8g" "OpenSSL"
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133 HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- HMAC message
136 .IX Header "SYNOPSIS"
138 \& #include <openssl/hmac.h>
140 \& unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
141 \& int key_len, const unsigned char *d, int n,
142 \& unsigned char *md, unsigned int *md_len);
144 \& void HMAC_CTX_init(HMAC_CTX *ctx);
146 \& void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
147 \& const EVP_MD *md);
148 \& void HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
149 \& const EVP_MD *md, ENGINE *impl);
150 \& void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
151 \& void HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
153 \& void HMAC_CTX_cleanup(HMAC_CTX *ctx);
154 \& void HMAC_cleanup(HMAC_CTX *ctx);
157 .IX Header "DESCRIPTION"
158 \&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash
159 function used for message authentication, which is based on a hash
162 \&\s-1\fIHMAC\s0()\fR computes the message authentication code of the \fBn\fR bytes at
163 \&\fBd\fR using the hash function \fBevp_md\fR and the key \fBkey\fR which is
164 \&\fBkey_len\fR bytes long.
166 It places the result in \fBmd\fR (which must have space for the output of
167 the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
168 If \fBmd\fR is \s-1NULL\s0, the digest is placed in a static array. The size of
169 the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR.
171 \&\fBevp_md\fR can be \fIEVP_sha1()\fR, \fIEVP_ripemd160()\fR etc.
172 \&\fBkey\fR and \fBevp_md\fR may be \fB\s-1NULL\s0\fR if a key and hash function have
173 been set in a previous call to \fIHMAC_Init()\fR for that \fB\s-1HMAC_CTX\s0\fR.
175 \&\fIHMAC_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be
178 \&\fIHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR
179 and releases any associated resources. It must be called when an
180 \&\fB\s-1HMAC_CTX\s0\fR is no longer required.
182 \&\fIHMAC_cleanup()\fR is an alias for \fIHMAC_CTX_cleanup()\fR included for back
183 compatibility with 0.9.6b, it is deprecated.
185 The following functions may be used if the message is not completely
188 \&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
189 function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
190 long. It is deprecated and only included for backward compatibility
193 \&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use
194 the function \fBevp_md\fR and key \fBkey\fR. Either can be \s-1NULL\s0, in which
195 case the existing one will be reused. \fIHMAC_CTX_init()\fR must have been
196 called before the first use of an \fB\s-1HMAC_CTX\s0\fR in this
197 function. \fBN.B. \f(BIHMAC_Init()\fB had this undocumented behaviour in
198 previous versions of OpenSSL \- failure to switch to \f(BIHMAC_Init_ex()\fB in
199 programs that expect it will cause them to stop working\fR.
201 \&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
202 be authenticated (\fBlen\fR bytes at \fBdata\fR).
204 \&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
205 must have space for the hash function output.
207 .IX Header "RETURN VALUES"
208 \&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code.
210 \&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and
211 \&\fIHMAC_CTX_cleanup()\fR do not return values.
213 .IX Header "CONFORMING TO"
216 .IX Header "SEE ALSO"
217 \&\fIsha\fR\|(3), \fIevp\fR\|(3)
220 \&\s-1\fIHMAC\s0()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
221 are available since SSLeay 0.9.0.
223 \&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR and \fIHMAC_CTX_cleanup()\fR are available