Merge from vendor branch OPENSSL:
[dragonfly.git] / secure / lib / libcrypto / man / hmac.3
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124.\" ========================================================================
125.\"
126.IX Title "hmac 3"
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127.TH hmac 3 "2007-10-24" "0.9.8g" "OpenSSL"
128.\" For nroff, turn off justification. Always turn off hyphenation; it makes
129.\" way too many mistakes in technical documents.
130.if n .ad l
131.nh
984263bc 132.SH "NAME"
74dab6c2 133HMAC, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- HMAC message
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134authentication code
135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 1
138\& #include <openssl/hmac.h>
2eaa1526 139\&
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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);
2eaa1526 143\&
984263bc 144\& void HMAC_CTX_init(HMAC_CTX *ctx);
2eaa1526 145\&
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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,
c6e28a8e 149\& const EVP_MD *md, ENGINE *impl);
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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);
2eaa1526 152\&
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153\& void HMAC_CTX_cleanup(HMAC_CTX *ctx);
154\& void HMAC_cleanup(HMAC_CTX *ctx);
155.Ve
156.SH "DESCRIPTION"
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157.IX Header "DESCRIPTION"
158\&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash
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159function used for message authentication, which is based on a hash
160function.
161.PP
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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.
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165.PP
166It places the result in \fBmd\fR (which must have space for the output of
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167the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
168If \fBmd\fR is \s-1NULL\s0, the digest is placed in a static array. The size of
169the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR.
984263bc 170.PP
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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
173been set in a previous call to \fIHMAC_Init()\fR for that \fB\s-1HMAC_CTX\s0\fR.
984263bc 174.PP
8b0cefbb 175\&\fIHMAC_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be
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176called.
177.PP
8b0cefbb 178\&\fIHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR
984263bc 179and releases any associated resources. It must be called when an
8b0cefbb 180\&\fB\s-1HMAC_CTX\s0\fR is no longer required.
984263bc 181.PP
8b0cefbb 182\&\fIHMAC_cleanup()\fR is an alias for \fIHMAC_CTX_cleanup()\fR included for back
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183compatibility with 0.9.6b, it is deprecated.
184.PP
185The following functions may be used if the message is not completely
186stored in memory:
187.PP
8b0cefbb 188\&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
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189function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes
190long. It is deprecated and only included for backward compatibility
191with OpenSSL 0.9.6b.
192.PP
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193\&\fIHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use
194the function \fBevp_md\fR and key \fBkey\fR. Either can be \s-1NULL\s0, in which
984263bc 195case the existing one will be reused. \fIHMAC_CTX_init()\fR must have been
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196called before the first use of an \fB\s-1HMAC_CTX\s0\fR in this
197function. \fBN.B. \f(BIHMAC_Init()\fB had this undocumented behaviour in
198previous versions of OpenSSL \- failure to switch to \f(BIHMAC_Init_ex()\fB in
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199programs that expect it will cause them to stop working\fR.
200.PP
8b0cefbb 201\&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
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202be authenticated (\fBlen\fR bytes at \fBdata\fR).
203.PP
8b0cefbb 204\&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
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205must have space for the hash function output.
206.SH "RETURN VALUES"
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207.IX Header "RETURN VALUES"
208\&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code.
984263bc 209.PP
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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.
984263bc 212.SH "CONFORMING TO"
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213.IX Header "CONFORMING TO"
214\&\s-1RFC\s0 2104
984263bc 215.SH "SEE ALSO"
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216.IX Header "SEE ALSO"
217\&\fIsha\fR\|(3), \fIevp\fR\|(3)
984263bc 218.SH "HISTORY"
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219.IX Header "HISTORY"
220\&\s-1\fIHMAC\s0()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
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221are available since SSLeay 0.9.0.
222.PP
8b0cefbb 223\&\fIHMAC_CTX_init()\fR, \fIHMAC_Init_ex()\fR and \fIHMAC_CTX_cleanup()\fR are available
984263bc 224since OpenSSL 0.9.7.