108 lines
3.5 KiB
Text
108 lines
3.5 KiB
Text
=pod
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=head1 NAME
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HMAC, HMAC_CTX_new, HMAC_CTX_reset, HMAC_CTX_free, HMAC_Init, HMAC_Init_ex, HMAC_Update, HMAC_Final - HMAC message authentication code
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=head1 SYNOPSIS
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#include <openssl/hmac.h>
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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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HMAC_CTX *HMAC_CTX_new(void);
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int HMAC_CTX_reset(HMAC_CTX *ctx);
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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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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, int len);
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int HMAC_Final(HMAC_CTX *ctx, unsigned char *md, unsigned int *len);
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void HMAC_CTX_free(HMAC_CTX *ctx);
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=head1 DESCRIPTION
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HMAC is a MAC (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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HMAC() computes the message authentication code of the B<n> bytes at
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B<d> using the hash function B<evp_md> and the key B<key> which is
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B<key_len> bytes long.
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It places the result in B<md> (which must have space for the output of
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the hash function, which is no more than B<EVP_MAX_MD_SIZE> bytes).
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If B<md> is NULL, the digest is placed in a static array. The size of
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the output is placed in B<md_len>, unless it is B<NULL>.
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B<evp_md> can be EVP_sha1(), EVP_ripemd160() etc.
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HMAC_CTX_new() creates a new HMAC_CTX in heap memory.
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HMAC_CTX_reset() zeroes an existing B<HMAC_CTX> and associated
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resources, making it suitable for new computations as if it was newly
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created with HMAC_CTX_new().
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HMAC_CTX_free() erases the key and other data from the B<HMAC_CTX>,
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releases any associated resources and finally frees the B<HMAC_CTX>
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itself.
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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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HMAC_Init() initializes a B<HMAC_CTX> structure to use the hash
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function B<evp_md> and the key B<key> which is B<key_len> bytes
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long. It is deprecated and only included for backward compatibility
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with OpenSSL 0.9.6b.
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HMAC_Init_ex() initializes or reuses a B<HMAC_CTX> structure to use
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the function B<evp_md> and key B<key>. Either can be NULL, in which
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case the existing one will be reused. B<ctx> must have been created
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with HMAC_CTX_new() before the first use of an B<HMAC_CTX> in this
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function. B<N.B. HMAC_Init() had this undocumented behaviour in
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previous versions of OpenSSL - failure to switch to HMAC_Init_ex() in
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programs that expect it will cause them to stop working>.
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HMAC_Update() can be called repeatedly with chunks of the message to
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be authenticated (B<len> bytes at B<data>).
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HMAC_Final() places the message authentication code in B<md>, which
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must have space for the hash function output.
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=head1 RETURN VALUES
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HMAC() returns a pointer to the message authentication code or NULL if
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an error occurred.
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HMAC_CTX_new() returns a pointer to a new B<HMAC_CTX> on success or
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B<NULL> if an error occurred.
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HMAC_CTX_reset(), HMAC_Init_ex(), HMAC_Update() and HMAC_Final() return 1
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for success or 0 if an error occurred.
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HMAC_CTX_free() do not return values.
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=head1 CONFORMING TO
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RFC 2104
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=head1 SEE ALSO
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L<sha(3)>, L<evp(3)>
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=head1 HISTORY
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HMAC_CTX_init() was replaced with HMAC_CTX_reset() in OpenSSL versions 1.1.
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HMAC_CTX_cleanup() existed in OpenSSL versions before 1.1.
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HMAC_CTX_new() and HMAC_CTX_free() are new in OpenSSL version 1.1.
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HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in
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versions of OpenSSL before 1.0.0.
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=cut
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