308 lines
11 KiB
Plaintext
308 lines
11 KiB
Plaintext
.\" Automatically generated by Pod::Man 2.27 (Pod::Simple 3.28)
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.\" ========================================================================
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.\"
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.IX Title "HMAC 3ossl"
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.TH HMAC 3ossl "2024-01-30" "3.2.1" "OpenSSL"
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes
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.\" way too many mistakes in technical documents.
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.if n .ad l
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.nh
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.SH "NAME"
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HMAC,
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HMAC_CTX_new,
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HMAC_CTX_reset,
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HMAC_CTX_free,
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HMAC_Init,
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HMAC_Init_ex,
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HMAC_Update,
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HMAC_Final,
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HMAC_CTX_copy,
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HMAC_CTX_set_flags,
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HMAC_CTX_get_md,
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HMAC_size
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\&\- HMAC message authentication code
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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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\&
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\& unsigned char *HMAC(const EVP_MD *evp_md, const void *key, int key_len,
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\& const unsigned char *data, size_t data_len,
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\& unsigned char *md, unsigned int *md_len);
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.Ve
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.PP
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The following functions have been deprecated since OpenSSL 3.0, and can be
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hidden entirely by defining \fB\s-1OPENSSL_API_COMPAT\s0\fR with a suitable version value,
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see \fIopenssl_user_macros\fR\|(7):
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.PP
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.Vb 2
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\& HMAC_CTX *HMAC_CTX_new(void);
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\& int HMAC_CTX_reset(HMAC_CTX *ctx);
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\&
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\& int HMAC_Init_ex(HMAC_CTX *ctx, const void *key, int key_len,
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\& const EVP_MD *md, ENGINE *impl);
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\& int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, size_t len);
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\& int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
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\&
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\& void HMAC_CTX_free(HMAC_CTX *ctx);
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\&
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\& int HMAC_CTX_copy(HMAC_CTX *dctx, HMAC_CTX *sctx);
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\& void HMAC_CTX_set_flags(HMAC_CTX *ctx, unsigned long flags);
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\& const EVP_MD *HMAC_CTX_get_md(const HMAC_CTX *ctx);
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\&
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\& size_t HMAC_size(const HMAC_CTX *e);
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.Ve
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.PP
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The following function has been deprecated since OpenSSL 1.1.0, and can be
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hidden entirely by defining \fB\s-1OPENSSL_API_COMPAT\s0\fR with a suitable version value,
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see \fIopenssl_user_macros\fR\|(7):
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.PP
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.Vb 2
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\& int HMAC_Init(HMAC_CTX *ctx, const void *key, int key_len,
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\& const EVP_MD *md);
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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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\&\s-1\fIHMAC\s0()\fR computes the message authentication code of the \fIdata_len\fR bytes at
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\&\fIdata\fR using the hash function \fIevp_md\fR and the key \fIkey\fR which is
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\&\fIkey_len\fR bytes long. The \fIkey\fR may also be \s-1NULL\s0 with \fIkey_len\fR being 0.
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.PP
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It places the result in \fImd\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 \fImd\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 \fImd_len\fR, unless it is \s-1NULL.\s0 Note: passing a \s-1NULL\s0
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value for \fImd\fR to use the static array is not thread safe.
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.PP
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\&\fIevp_md\fR is a message digest such as \fIEVP_sha1()\fR, \fIEVP_ripemd160()\fR etc.
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\&\s-1HMAC\s0 does not support variable output length digests such as \fIEVP_shake128()\fR and
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\&\fIEVP_shake256()\fR.
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.PP
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\&\s-1\fIHMAC\s0()\fR uses the default \fB\s-1OSSL_LIB_CTX\s0\fR.
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Use \fIEVP_Q_mac\fR\|(3) instead if a library context is required.
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.PP
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All of the functions described below are deprecated.
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Applications should instead use \fIEVP_MAC_CTX_new\fR\|(3), \fIEVP_MAC_CTX_free\fR\|(3),
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\&\fIEVP_MAC_init\fR\|(3), \fIEVP_MAC_update\fR\|(3) and \fIEVP_MAC_final\fR\|(3)
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or the 'quick' single-shot \s-1MAC\s0 function \fIEVP_Q_mac\fR\|(3).
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.PP
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\&\fIHMAC_CTX_new()\fR creates a new \s-1HMAC_CTX\s0 in heap memory.
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.PP
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\&\fIHMAC_CTX_reset()\fR clears an existing \fB\s-1HMAC_CTX\s0\fR and associated
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resources, making it suitable for new computations as if it was newly
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created with \fIHMAC_CTX_new()\fR.
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.PP
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\&\fIHMAC_CTX_free()\fR erases the key and other data from the \fB\s-1HMAC_CTX\s0\fR,
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releases any associated resources and finally frees the \fB\s-1HMAC_CTX\s0\fR
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itself.
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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_ex()\fR initializes or reuses a \fB\s-1HMAC_CTX\s0\fR structure to use the hash
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function \fIevp_md\fR and key \fIkey\fR. If both are \s-1NULL,\s0 or if \fIkey\fR is \s-1NULL\s0
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and \fIevp_md\fR is the same as the previous call, then the
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existing key is
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reused. \fIctx\fR must have been created with \fIHMAC_CTX_new()\fR before the first use
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of an \fB\s-1HMAC_CTX\s0\fR in this function.
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.PP
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If \fIHMAC_Init_ex()\fR is called with \fIkey\fR \s-1NULL\s0 and \fIevp_md\fR is not the
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same as the previous digest used by \fIctx\fR then an error is returned
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because reuse of an existing key with a different digest is not supported.
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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 \fIevp_md\fR and the key \fIkey\fR which is \fIkey_len\fR bytes
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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 (\fIlen\fR bytes at \fIdata\fR).
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.PP
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\&\fIHMAC_Final()\fR places the message authentication code in \fImd\fR, which
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must have space for the hash function output.
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.PP
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\&\fIHMAC_CTX_copy()\fR copies all of the internal state from \fIsctx\fR into \fIdctx\fR.
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.PP
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\&\fIHMAC_CTX_set_flags()\fR applies the specified flags to the internal EVP_MD_CTXs.
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These flags have the same meaning as for \fIEVP_MD_CTX_set_flags\fR\|(3).
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.PP
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\&\fIHMAC_CTX_get_md()\fR returns the \s-1EVP_MD\s0 that has previously been set for the
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supplied \s-1HMAC_CTX.\s0
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.PP
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\&\fIHMAC_size()\fR returns the length in bytes of the underlying hash function output.
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.SH "RETURN VALUES"
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.IX Header "RETURN VALUES"
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\&\s-1\fIHMAC\s0()\fR returns a pointer to the message authentication code or \s-1NULL\s0 if
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an error occurred.
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.PP
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\&\fIHMAC_CTX_new()\fR returns a pointer to a new \fB\s-1HMAC_CTX\s0\fR on success or
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\&\s-1NULL\s0 if an error occurred.
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.PP
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\&\fIHMAC_CTX_reset()\fR, \fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR, \fIHMAC_Final()\fR and
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\&\fIHMAC_CTX_copy()\fR return 1 for success or 0 if an error occurred.
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.PP
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\&\fIHMAC_CTX_get_md()\fR return the \s-1EVP_MD\s0 previously set for the supplied \s-1HMAC_CTX\s0 or
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\&\s-1NULL\s0 if no \s-1EVP_MD\s0 has been set.
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.PP
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\&\fIHMAC_size()\fR returns the length in bytes of the underlying hash function output
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or zero on error.
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.SH "CONFORMING TO"
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.IX Header "CONFORMING TO"
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\&\s-1RFC 2104\s0
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.SH "SEE ALSO"
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.IX Header "SEE ALSO"
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\&\s-1\fISHA1\s0\fR\|(3), \fIEVP_Q_mac\fR\|(3), \fIevp\fR\|(7)
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.SH "HISTORY"
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.IX Header "HISTORY"
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All functions except for \s-1\fIHMAC\s0()\fR were deprecated in OpenSSL 3.0.
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.PP
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\&\fIHMAC_CTX_init()\fR was replaced with \fIHMAC_CTX_reset()\fR in OpenSSL 1.1.0.
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.PP
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\&\fIHMAC_CTX_cleanup()\fR existed in OpenSSL before version 1.1.0.
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.PP
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\&\fIHMAC_CTX_new()\fR, \fIHMAC_CTX_free()\fR and \fIHMAC_CTX_get_md()\fR are new in OpenSSL 1.1.0.
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.PP
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\&\fIHMAC_Init_ex()\fR, \fIHMAC_Update()\fR and \fIHMAC_Final()\fR did not return values in
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OpenSSL before version 1.0.0.
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.SH "COPYRIGHT"
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.IX Header "COPYRIGHT"
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Copyright 2000\-2021 The OpenSSL Project Authors. All Rights Reserved.
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.PP
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Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file \s-1LICENSE\s0 in the source distribution or at
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<https://www.openssl.org/source/license.html>.
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