217 lines
6.5 KiB
Groff
217 lines
6.5 KiB
Groff
.\" $NetBSD: openssl_hmac.3,v 1.1 2001/04/12 10:45:48 itojun Exp $
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.\" Thu Apr 12 19:27:12 2001
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.\" ======================================================================
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.\"
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.IX Title "hmac 3"
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.TH hmac 3 "0.9.6a" "2001-04-12" "OpenSSL"
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.UC
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.SH "NAME"
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\&\s-1HMAC\s0, HMAC_Init, HMAC_Update, HMAC_Final, HMAC_cleanup \- \s-1HMAC\s0 message
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authentication code
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.SH "LIBRARY"
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libcrypto, -lcrypto
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.SH "SYNOPSIS"
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.IX Header "SYNOPSIS"
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.Vb 1
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\& #include <openssl/hmac.h>
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.Ve
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.Vb 3
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\& unsigned char *HMAC(const EVP_MD *evp_md, const void *key,
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\& int key_len, const unsigned char *d, int n,
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\& unsigned char *md, unsigned int *md_len);
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.Ve
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.Vb 4
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\& void HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
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\& const EVP_MD *md);
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\& void HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
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\& void HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
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.Ve
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.Vb 1
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\& void HMAC_cleanup(HMAC_CTX *ctx);
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.Ve
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.SH "DESCRIPTION"
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.IX Header "DESCRIPTION"
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\&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash
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function used for message authentication, which is based on a hash
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function.
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.PP
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\&\fIHMAC()\fR computes the message authentication code of the \fBn\fR bytes at
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\&\fBd\fR using the hash function \fBevp_md\fR and the key \fBkey\fR which is
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\&\fBkey_len\fR bytes long.
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.PP
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It places the result in \fBmd\fR (which must have space for the output of
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the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes).
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If \fBmd\fR is \s-1NULL\s0, the digest is placed in a static array. The size of
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the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR.
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.PP
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\&\fBevp_md\fR can be \fIEVP_sha1()\fR, \fIEVP_ripemd160()\fR etc.
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\&\fBkey\fR and \fBevp_md\fR may be \fB\s-1NULL\s0\fR if a key and hash function have
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been set in a previous call to \fIHMAC_Init()\fR for that \fB\s-1HMAC_CTX\s0\fR.
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.PP
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\&\fIHMAC_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR.
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.PP
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The following functions may be used if the message is not completely
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stored in memory:
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.PP
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\&\fIHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
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function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes long.
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.PP
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\&\fIHMAC_Update()\fR can be called repeatedly with chunks of the message to
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be authenticated (\fBlen\fR bytes at \fBdata\fR).
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.PP
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\&\fIHMAC_Final()\fR places the message authentication code in \fBmd\fR, which
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must have space for the hash function output.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\fIHMAC()\fR returns a pointer to the message authentication code.
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.PP
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\&\fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR do not
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return values.
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.SH "CONFORMING TO"
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.IX Header "CONFORMING TO"
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\&\s-1RFC\s0 2104
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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openssl_sha(3), openssl_evp(3)
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.SH "HISTORY"
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.IX Header "HISTORY"
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\&\fIHMAC()\fR, \fIHMAC_Init()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and \fIHMAC_cleanup()\fR
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are available since SSLeay 0.9.0.
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