Merge branch 'vendor/OPENSSL'
[dragonfly.git] / secure / lib / libcrypto / man / hmac.3
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129.\" ========================================================================
130.\"
131.IX Title "hmac 3"
18ed9402 132.TH hmac 3 "2008-09-27" "0.9.8i" "OpenSSL"
984263bc 133.SH "NAME"
74dab6c2 134HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- HMAC message
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135authentication code
136.SH "SYNOPSIS"
8b0cefbb 137.IX Header "SYNOPSIS"
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138.Vb 1
139\& #include <openssl/hmac.h>
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140.Ve
141.PP
142.Vb 3
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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);
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146.Ve
147.PP
148.Vb 1
984263bc 149\& void HMAC_CTX_init(HMAC_CTX *ctx);
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150.Ve
151.PP
152.Vb 6
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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,
c6e28a8e 156\& const EVP_MD *md, ENGINE *impl);
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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);
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159.Ve
160.PP
161.Vb 2
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162\& void HMAC_CTX_cleanup(HMAC_CTX *ctx);
163\& void HMAC_cleanup(HMAC_CTX *ctx);
164.Ve
165.SH "DESCRIPTION"
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166.IX Header "DESCRIPTION"
167\&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash
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168function used for message authentication, which is based on a hash
169function.
170.PP
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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.
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174.PP
175It places the result in \fBmd\fR (which must have space for the output of
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176the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
177If \fBmd\fR is \s-1NULL\s0, the digest is placed in a static array. The size of
178the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR.
984263bc 179.PP
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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
182been set in a previous call to \fIHMAC_Init()\fR for that \fB\s-1HMAC_CTX\s0\fR.
984263bc 183.PP
8b0cefbb 184\&\fIHMAC_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be
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185called.
186.PP
8b0cefbb 187\&\fIHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR
984263bc 188and releases any associated resources. It must be called when an
8b0cefbb 189\&\fB\s-1HMAC_CTX\s0\fR is no longer required.
984263bc 190.PP
8b0cefbb 191\&\fIHMAC_cleanup()\fR is an alias for \fIHMAC_CTX_cleanup()\fR included for back
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192compatibility with 0.9.6b, it is deprecated.
193.PP
194The following functions may be used if the message is not completely
195stored in memory:
196.PP
8b0cefbb 197\&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
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198function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
199long. It is deprecated and only included for backward compatibility
200with OpenSSL 0.9.6b.
201.PP
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202\&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use
203the function \fBevp_md\fR and key \fBkey\fR. Either can be \s-1NULL\s0, in which
984263bc 204case the existing one will be reused. \fIHMAC_CTX_init()\fR must have been
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205called before the first use of an \fB\s-1HMAC_CTX\s0\fR in this
206function. \fBN.B. \f(BIHMAC_Init()\fB had this undocumented behaviour in
207previous versions of OpenSSL \- failure to switch to \f(BIHMAC_Init_ex()\fB in
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208programs that expect it will cause them to stop working\fR.
209.PP
8b0cefbb 210\&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
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211be authenticated (\fBlen\fR bytes at \fBdata\fR).
212.PP
8b0cefbb 213\&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
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214must have space for the hash function output.
215.SH "RETURN VALUES"
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216.IX Header "RETURN VALUES"
217\&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code.
984263bc 218.PP
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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.
984263bc 221.SH "CONFORMING TO"
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222.IX Header "CONFORMING TO"
223\&\s-1RFC\s0 2104
984263bc 224.SH "SEE ALSO"
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225.IX Header "SEE ALSO"
226\&\fIsha\fR\|(3), \fIevp\fR\|(3)
984263bc 227.SH "HISTORY"
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228.IX Header "HISTORY"
229\&\s-1\fIHMAC\s0()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
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230are available since SSLeay 0.9.0.
231.PP
8b0cefbb 232\&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR and \fIHMAC_CTX_cleanup()\fR are available
984263bc 233since OpenSSL 0.9.7.