Merge branch 'vendor/OPENSSL'
[dragonfly.git] / secure / lib / libcrypto / man / hmac.3
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132.\" ========================================================================
133.\"
134.IX Title "hmac 3"
fc468453 135.TH hmac 3 "2010-02-27" "0.9.8m" "OpenSSL"
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136.\" For nroff, turn off justification. Always turn off hyphenation; it makes
137.\" way too many mistakes in technical documents.
138.if n .ad l
139.nh
984263bc 140.SH "NAME"
74dab6c2 141HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- HMAC message
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142authentication code
143.SH "SYNOPSIS"
8b0cefbb 144.IX Header "SYNOPSIS"
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145.Vb 1
146\& #include <openssl/hmac.h>
e257b235 147\&
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148\& unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
149\& int key_len, const unsigned char *d, int n,
150\& unsigned char *md, unsigned int *md_len);
e257b235 151\&
984263bc 152\& void HMAC_CTX_init(HMAC_CTX *ctx);
e257b235 153\&
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154\& void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
155\& const EVP_MD *md);
156\& void HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
c6e28a8e 157\& const EVP_MD *md, ENGINE *impl);
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158\& void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
159\& void HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
e257b235 160\&
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161\& void HMAC_CTX_cleanup(HMAC_CTX *ctx);
162\& void HMAC_cleanup(HMAC_CTX *ctx);
163.Ve
164.SH "DESCRIPTION"
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165.IX Header "DESCRIPTION"
166\&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash
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167function used for message authentication, which is based on a hash
168function.
169.PP
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170\&\s-1\fIHMAC\s0()\fR computes the message authentication code of the \fBn\fR bytes at
171\&\fBd\fR using the hash function \fBevp_md\fR and the key \fBkey\fR which is
172\&\fBkey_len\fR bytes long.
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173.PP
174It places the result in \fBmd\fR (which must have space for the output of
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175the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
176If \fBmd\fR is \s-1NULL\s0, the digest is placed in a static array. The size of
177the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR.
984263bc 178.PP
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179\&\fBevp_md\fR can be \fIEVP_sha1()\fR, \fIEVP_ripemd160()\fR etc.
180\&\fBkey\fR and \fBevp_md\fR may be \fB\s-1NULL\s0\fR if a key and hash function have
181been set in a previous call to \fIHMAC_Init()\fR for that \fB\s-1HMAC_CTX\s0\fR.
984263bc 182.PP
8b0cefbb 183\&\fIHMAC_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be
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184called.
185.PP
8b0cefbb 186\&\fIHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR
984263bc 187and releases any associated resources. It must be called when an
8b0cefbb 188\&\fB\s-1HMAC_CTX\s0\fR is no longer required.
984263bc 189.PP
8b0cefbb 190\&\fIHMAC_cleanup()\fR is an alias for \fIHMAC_CTX_cleanup()\fR included for back
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191compatibility with 0.9.6b, it is deprecated.
192.PP
193The following functions may be used if the message is not completely
194stored in memory:
195.PP
8b0cefbb 196\&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
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197function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
198long. It is deprecated and only included for backward compatibility
199with OpenSSL 0.9.6b.
200.PP
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201\&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use
202the function \fBevp_md\fR and key \fBkey\fR. Either can be \s-1NULL\s0, in which
984263bc 203case the existing one will be reused. \fIHMAC_CTX_init()\fR must have been
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204called before the first use of an \fB\s-1HMAC_CTX\s0\fR in this
205function. \fBN.B. \f(BIHMAC_Init()\fB had this undocumented behaviour in
206previous versions of OpenSSL \- failure to switch to \f(BIHMAC_Init_ex()\fB in
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207programs that expect it will cause them to stop working\fR.
208.PP
8b0cefbb 209\&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
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210be authenticated (\fBlen\fR bytes at \fBdata\fR).
211.PP
8b0cefbb 212\&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
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213must have space for the hash function output.
214.SH "RETURN VALUES"
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215.IX Header "RETURN VALUES"
216\&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code.
984263bc 217.PP
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218\&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and
219\&\fIHMAC_CTX_cleanup()\fR do not return values.
984263bc 220.SH "CONFORMING TO"
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221.IX Header "CONFORMING TO"
222\&\s-1RFC\s0 2104
984263bc 223.SH "SEE ALSO"
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224.IX Header "SEE ALSO"
225\&\fIsha\fR\|(3), \fIevp\fR\|(3)
984263bc 226.SH "HISTORY"
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227.IX Header "HISTORY"
228\&\s-1\fIHMAC\s0()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
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229are available since SSLeay 0.9.0.
230.PP
8b0cefbb 231\&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR and \fIHMAC_CTX_cleanup()\fR are available
984263bc 232since OpenSSL 0.9.7.