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Editing: HMAC_Init.3
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.\" Automatically generated by Pod::Man 4.11 (Pod::Simple 3.35) .\" .\" Standard preamble: .\" ======================================================================== .de Sp \" Vertical space (when we can't use .PP) .if t .sp .5v .if n .sp .. .de Vb \" Begin verbatim text .ft CW .nf .ne \\$1 .. .de Ve \" End verbatim text .ft R .fi .. .\" Set up some character translations and predefined strings. \*(-- will .\" give an unbreakable dash, \*(PI will give pi, \*(L" will give a left .\" double quote, and \*(R" will give a right double quote. \*(C+ will .\" give a nicer C++. Capital omega is used to do unbreakable dashes and .\" therefore won't be available. \*(C` and \*(C' expand to `' in nroff, .\" nothing in troff, for use with C<>. .tr \(*W- .ds C+ C\v'-.1v'\h'-1p'\s-2+\h'-1p'+\s0\v'.1v'\h'-1p' .ie n \{\ . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} .el\{\ . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' . ds C` . ds C' 'br\} .\" .\" Escape single quotes in literal strings from groff's Unicode transform. .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" .\" If the F register is >0, we'll generate index entries on stderr for .\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index .\" entries marked with X<> in POD. Of course, you'll have to process the .\" output yourself in some meaningful fashion. .\" .\" Avoid warning from groff about undefined register 'F'. .de IX .. .nr rF 0 .if \n(.g .if rF .nr rF 1 .if (\n(rF:(\n(.g==0)) \{\ . if \nF \{\ . de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . if !\nF==2 \{\ . nr % 0 . nr F 2 . \} . \} .\} .rr rF .\" .\" Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2). .\" Fear. Run. Save yourself. No user-serviceable parts. . \" fudge factors for nroff and troff .if n \{\ . ds #H 0 . ds #V .8m . ds #F .3m . ds #[ \f1 . ds #] \fP .\} .if t \{\ . ds #H ((1u-(\\\\n(.fu%2u))*.13m) . ds #V .6m . ds #F 0 . ds #[ \& . ds #] \& .\} . \" simple accents for nroff and troff .if n \{\ . ds ' \& . ds ` \& . ds ^ \& . ds , \& . ds ~ ~ . ds / .\} .if t \{\ . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u" . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u' . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u' . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u' . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u' . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u' .\} . \" troff and (daisy-wheel) nroff accents .ds : \\k:\h'-(\\n(.wu*8/10-\*(#H+.1m+\*(#F)'\v'-\*(#V'\z.\h'.2m+\*(#F'.\h'|\\n:u'\v'\*(#V' .ds 8 \h'\*(#H'\(*b\h'-\*(#H' .ds o \\k:\h'-(\\n(.wu+\w'\(de'u-\*(#H)/2u'\v'-.3n'\*(#[\z\(de\v'.3n'\h'|\\n:u'\*(#] .ds d- \h'\*(#H'\(pd\h'-\w'~'u'\v'-.25m'\f2\(hy\fP\v'.25m'\h'-\*(#H' .ds D- D\\k:\h'-\w'D'u'\v'-.11m'\z\(hy\v'.11m'\h'|\\n:u' .ds th \*(#[\v'.3m'\s+1I\s-1\v'-.3m'\h'-(\w'I'u*2/3)'\s-1o\s+1\*(#] .ds Th \*(#[\s+2I\s-2\h'-\w'I'u*3/5'\v'-.3m'o\v'.3m'\*(#] .ds ae a\h'-(\w'a'u*4/10)'e .ds Ae A\h'-(\w'A'u*4/10)'E . \" corrections for vroff .if v .ds ~ \\k:\h'-(\\n(.wu*9/10-\*(#H)'\s-2\u~\d\s+2\h'|\\n:u' .if v .ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'\v'-.4m'^\v'.4m'\h'|\\n:u' . \" for low resolution devices (crt and lpr) .if \n(.H>23 .if \n(.V>19 \ \{\ . ds : e . ds 8 ss . ds o a . ds d- d\h'-1'\(ga . ds D- D\h'-1'\(hy . ds th \o'bp' . ds Th \o'LP' . ds ae ae . ds Ae AE .\} .rm #[ #] #H #V #F C .\" ======================================================================== .\" .IX Title "hmac 3" .TH hmac 3 "2019-12-20" "1.0.2u" "OpenSSL" .\" For nroff, turn off justification. Always turn off hyphenation; it makes .\" way too many mistakes in technical documents. .if n .ad l .nh .SH "NAME" HMAC, HMAC_CTX_init, HMAC_Init, HMAC_Init_ex, HMAC_Update, HMAC_Final, HMAC_CTX_cleanup, HMAC_cleanup \- HMAC message authentication code .SH "SYNOPSIS" .IX Header "SYNOPSIS" .Vb 1 \& #include <openssl/hmac.h> \& \& unsigned char *HMAC(const EVP_MD *evp_md, const void *key, \& int key_len, const unsigned char *d, int n, \& unsigned char *md, unsigned int *md_len); \& \& void HMAC_CTX_init(HMAC_CTX *ctx); \& \& int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len, \& const EVP_MD *md); \& int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len, \& const EVP_MD *md, ENGINE *impl); \& int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len); \& int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len); \& \& void HMAC_CTX_cleanup(HMAC_CTX *ctx); \& void HMAC_cleanup(HMAC_CTX *ctx); .Ve .SH "DESCRIPTION" .IX Header "DESCRIPTION" \&\s-1HMAC\s0 is a \s-1MAC\s0 (message authentication code), i.e. a keyed hash function used for message authentication, which is based on a hash function. .PP \&\s-1\fBHMAC\s0()\fR computes the message authentication code of the \fBn\fR bytes at \&\fBd\fR using the hash function \fBevp_md\fR and the key \fBkey\fR which is \&\fBkey_len\fR bytes long. .PP It places the result in \fBmd\fR (which must have space for the output of the hash function, which is no more than \fB\s-1EVP_MAX_MD_SIZE\s0\fR bytes). If \fBmd\fR is \s-1NULL,\s0 the digest is placed in a static array. The size of the output is placed in \fBmd_len\fR, unless it is \fB\s-1NULL\s0\fR. Note: passing a \s-1NULL\s0 value for \fBmd\fR to use the static array is not thread safe. .PP \&\fBevp_md\fR can be \fBEVP_sha1()\fR, \fBEVP_ripemd160()\fR etc. .PP \&\fBHMAC_CTX_init()\fR initialises a \fB\s-1HMAC_CTX\s0\fR before first use. It must be called. .PP \&\fBHMAC_CTX_cleanup()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR and releases any associated resources. It must be called when an \&\fB\s-1HMAC_CTX\s0\fR is no longer required. .PP \&\fBHMAC_cleanup()\fR is an alias for \fBHMAC_CTX_cleanup()\fR included for back compatibility with 0.9.6b, it is deprecated. .PP The following functions may be used if the message is not completely stored in memory: .PP \&\fBHMAC_Init()\fR initializes a \fB\s-1HMAC_CTX\s0\fR structure to use the hash function \fBevp_md\fR and the key \fBkey\fR which is \fBkey_len\fR bytes long. It is deprecated and only included for backward compatibility with OpenSSL 0.9.6b. .PP \&\fBHMAC_Init_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use the hash function \fBevp_md\fR and key \fBkey\fR. If both are \s-1NULL\s0 (or \fBevp_md\fR is the same as the previous digest used by \fBctx\fR and \fBkey\fR is \s-1NULL\s0) the existing key is reused. \fBctx\fR must have been created with \fBHMAC_CTX_new()\fR before the first use of an \fB\s-1HMAC_CTX\s0\fR in this function. \fBN.B. \fBHMAC_Init()\fB had this undocumented behaviour in previous versions of OpenSSL \- failure to switch to \fBHMAC_Init_ex()\fB in programs that expect it will cause them to stop working\fR. .PP \&\fB\s-1NB:\s0 if \fBHMAC_Init_ex()\fB is called with \fBkey\fB \s-1NULL\s0 and \fBevp_md\fB is not the same as the previous digest used by \fBctx\fB then an error is returned because reuse of an existing key with a different digest is not supported.\fR .PP \&\fBHMAC_Update()\fR can be called repeatedly with chunks of the message to be authenticated (\fBlen\fR bytes at \fBdata\fR). .PP \&\fBHMAC_Final()\fR places the message authentication code in \fBmd\fR, which must have space for the hash function output. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\s-1\fBHMAC\s0()\fR returns a pointer to the message authentication code or \s-1NULL\s0 if an error occurred. .PP \&\fBHMAC_Init_ex()\fR, \fBHMAC_Update()\fR and \fBHMAC_Final()\fR return 1 for success or 0 if an error occurred. .PP \&\fBHMAC_CTX_init()\fR and \fBHMAC_CTX_cleanup()\fR do not return values. .SH "CONFORMING TO" .IX Header "CONFORMING TO" \&\s-1RFC 2104\s0 .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBsha\fR\|(3), \fBevp\fR\|(3) .SH "HISTORY" .IX Header "HISTORY" \&\s-1\fBHMAC\s0()\fR, \fBHMAC_Init()\fR, \fBHMAC_Update()\fR, \fBHMAC_Final()\fR and \fBHMAC_cleanup()\fR are available since SSLeay 0.9.0. .PP \&\fBHMAC_CTX_init()\fR, \fBHMAC_Init_ex()\fR and \fBHMAC_CTX_cleanup()\fR are available since OpenSSL 0.9.7. .PP \&\fBHMAC_Init_ex()\fR, \fBHMAC_Update()\fR and \fBHMAC_Final()\fR did not return values in versions of OpenSSL before 1.0.0.
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