.\" -*- mode: troff; coding: utf-8 -*- .\" Automatically generated by Pod::Man 5.0102 (Pod::Simple 3.45) .\" .\" 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 .. .\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>. .ie n \{\ . ds C` "" . ds C' "" 'br\} .el\{\ . 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 .\" ======================================================================== .\" .IX Title "HMAC 3ssl" .TH HMAC 3ssl 2024-10-23 3.4.0 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_new, HMAC_CTX_reset, HMAC_CTX_free, HMAC_Init, HMAC_Init_ex, HMAC_Update, HMAC_Final, HMAC_CTX_copy, HMAC_CTX_set_flags, HMAC_CTX_get_md, HMAC_size \&\- HMAC message authentication code .SH SYNOPSIS .IX Header "SYNOPSIS" .Vb 1 \& #include \& \& unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len, \& const unsigned char *data, size_t data_len, \& unsigned char *md, unsigned int *md_len); .Ve .PP The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining \fBOPENSSL_API_COMPAT\fR with a suitable version value, see \fBopenssl_user_macros\fR\|(7): .PP .Vb 2 \& HMAC_CTX *HMAC_CTX_new(void); \& int HMAC_CTX_reset(HMAC_CTX *ctx); \& \& 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, size_t len); \& int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len); \& \& void HMAC_CTX_free(HMAC_CTX *ctx); \& \& int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx); \& void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags); \& const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx); \& \& size_t HMAC_size(const HMAC_CTX *e); .Ve .PP The following function has been deprecated since OpenSSL 1.1.0, and can be hidden entirely by defining \fBOPENSSL_API_COMPAT\fR with a suitable version value, see \fBopenssl_user_macros\fR\|(7): .PP .Vb 2 \& int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len, \& const EVP_MD *md); .Ve .SH DESCRIPTION .IX Header "DESCRIPTION" HMAC is a MAC (message authentication code), i.e. a keyed hash function used for message authentication, which is based on a hash function. .PP \&\fBHMAC()\fR computes the message authentication code of the \fIdata_len\fR bytes at \&\fIdata\fR using the hash function \fIevp_md\fR and the key \fIkey\fR which is \&\fIkey_len\fR bytes long. The \fIkey\fR may also be NULL with \fIkey_len\fR being 0. .PP It places the result in \fImd\fR (which must have space for the output of the hash function, which is no more than \fBEVP_MAX_MD_SIZE\fR bytes). If \fImd\fR is NULL, the digest is placed in a static array. The size of the output is placed in \fImd_len\fR, unless it is NULL. Note: passing a NULL value for \fImd\fR to use the static array is not thread safe. .PP \&\fIevp_md\fR is a message digest such as \fBEVP_sha1()\fR, \fBEVP_ripemd160()\fR etc. HMAC does not support variable output length digests such as \fBEVP_shake128()\fR and \&\fBEVP_shake256()\fR. .PP \&\fBHMAC()\fR uses the default \fBOSSL_LIB_CTX\fR. Use \fBEVP_Q_mac\fR\|(3) instead if a library context is required. .PP All of the functions described below are deprecated. Applications should instead use \fBEVP_MAC_CTX_new\fR\|(3), \fBEVP_MAC_CTX_free\fR\|(3), \&\fBEVP_MAC_init\fR\|(3), \fBEVP_MAC_update\fR\|(3) and \fBEVP_MAC_final\fR\|(3) or the 'quick' single-shot MAC function \fBEVP_Q_mac\fR\|(3). .PP \&\fBHMAC_CTX_new()\fR creates a new HMAC_CTX in heap memory. .PP \&\fBHMAC_CTX_reset()\fR clears an existing \fBHMAC_CTX\fR and associated resources, making it suitable for new computations as if it was newly created with \fBHMAC_CTX_new()\fR. .PP \&\fBHMAC_CTX_free()\fR erases the key and other data from the \fBHMAC_CTX\fR, releases any associated resources and finally frees the \fBHMAC_CTX\fR itself. If the argument is NULL, nothing is done. .PP The following functions may be used if the message is not completely stored in memory: .PP \&\fBHMAC_Init_ex()\fR initializes or reuses a \fBHMAC_CTX\fR structure to use the hash function \fIevp_md\fR and key \fIkey\fR. If both are NULL, or if \fIkey\fR is NULL and \fIevp_md\fR is the same as the previous call, then the existing key is reused. \fIctx\fR must have been created with \fBHMAC_CTX_new()\fR before the first use of an \fBHMAC_CTX\fR in this function. .PP If \fBHMAC_Init_ex()\fR is called with \fIkey\fR NULL and \fIevp_md\fR is not the same as the previous digest used by \fIctx\fR then an error is returned because reuse of an existing key with a different digest is not supported. .PP \&\fBHMAC_Init()\fR initializes a \fBHMAC_CTX\fR structure to use the hash function \fIevp_md\fR and the key \fIkey\fR which is \fIkey_len\fR bytes long. .PP \&\fBHMAC_Update()\fR can be called repeatedly with chunks of the message to be authenticated (\fIlen\fR bytes at \fIdata\fR). .PP \&\fBHMAC_Final()\fR places the message authentication code in \fImd\fR, which must have space for the hash function output. .PP \&\fBHMAC_CTX_copy()\fR copies all of the internal state from \fIsctx\fR into \fIdctx\fR. .PP \&\fBHMAC_CTX_set_flags()\fR applies the specified flags to the internal EVP_MD_CTXs. These flags have the same meaning as for \fBEVP_MD_CTX_set_flags\fR\|(3). .PP \&\fBHMAC_CTX_get_md()\fR returns the EVP_MD that has previously been set for the supplied HMAC_CTX. .PP \&\fBHMAC_size()\fR returns the length in bytes of the underlying hash function output. .SH "RETURN VALUES" .IX Header "RETURN VALUES" \&\fBHMAC()\fR returns a pointer to the message authentication code or NULL if an error occurred. .PP \&\fBHMAC_CTX_new()\fR returns a pointer to a new \fBHMAC_CTX\fR on success or NULL if an error occurred. .PP \&\fBHMAC_CTX_reset()\fR, \fBHMAC_Init_ex()\fR, \fBHMAC_Update()\fR, \fBHMAC_Final()\fR and \&\fBHMAC_CTX_copy()\fR return 1 for success or 0 if an error occurred. .PP \&\fBHMAC_CTX_get_md()\fR return the EVP_MD previously set for the supplied HMAC_CTX or NULL if no EVP_MD has been set. .PP \&\fBHMAC_size()\fR returns the length in bytes of the underlying hash function output or zero on error. .SH "CONFORMING TO" .IX Header "CONFORMING TO" RFC 2104 .SH "SEE ALSO" .IX Header "SEE ALSO" \&\fBSHA1\fR\|(3), \fBEVP_Q_mac\fR\|(3), \fBevp\fR\|(7) .SH HISTORY .IX Header "HISTORY" All functions except for \fBHMAC()\fR were deprecated in OpenSSL 3.0. .PP \&\fBHMAC_CTX_init()\fR was replaced with \fBHMAC_CTX_reset()\fR in OpenSSL 1.1.0. .PP \&\fBHMAC_CTX_cleanup()\fR existed in OpenSSL before version 1.1.0. .PP \&\fBHMAC_CTX_new()\fR, \fBHMAC_CTX_free()\fR and \fBHMAC_CTX_get_md()\fR are new in OpenSSL 1.1.0. .PP \&\fBHMAC_Init_ex()\fR, \fBHMAC_Update()\fR and \fBHMAC_Final()\fR did not return values in OpenSSL before version 1.0.0. .SH COPYRIGHT .IX Header "COPYRIGHT" Copyright 2000\-2024 The OpenSSL Project Authors. All Rights Reserved. .PP Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at .