112 lines
3.8 KiB
Plaintext
112 lines
3.8 KiB
Plaintext
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=pod
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=head1 NAME
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HMAC, HMAC_CTX_init, HMAC_Init, HMAC_Init_ex, HMAC_Update, HMAC_Final, HMAC_CTX_cleanup,
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HMAC_cleanup - 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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void HMAC_CTX_init(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_cleanup(HMAC_CTX *ctx);
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void HMAC_cleanup(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>. Note: passing a NULL
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value for B<md> to use the static array is not thread safe.
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B<evp_md> can be EVP_sha1(), EVP_ripemd160() etc.
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HMAC_CTX_init() initialises a B<HMAC_CTX> before first use. It must be
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called.
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HMAC_CTX_cleanup() erases the key and other data from the B<HMAC_CTX>
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and releases any associated resources. It must be called when an
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B<HMAC_CTX> is no longer required.
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HMAC_cleanup() is an alias for HMAC_CTX_cleanup() included for back
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compatibility with 0.9.6b, it is deprecated.
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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 the hash
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function B<evp_md> and key B<key>. If both are NULL (or B<evp_md> is the same
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as the previous digest used by B<ctx> and B<key> is NULL) the existing key is
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reused. B<ctx> must have been created with HMAC_CTX_new() before the first use
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of an B<HMAC_CTX> in this function. B<N.B. HMAC_Init() had this undocumented
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behaviour in previous versions of OpenSSL - failure to switch to HMAC_Init_ex()
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in programs that expect it will cause them to stop working>.
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B<NB: if HMAC_Init_ex() is called with B<key> NULL and B<evp_md> is not the
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same as the previous digest used by B<ctx> 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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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_Init_ex(), HMAC_Update() and HMAC_Final() return 1 for success or 0 if
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an error occurred.
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HMAC_CTX_init() and HMAC_CTX_cleanup() 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)|sha(3)>, L<evp(3)|evp(3)>
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=head1 HISTORY
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HMAC(), HMAC_Init(), HMAC_Update(), HMAC_Final() and HMAC_cleanup()
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are available since SSLeay 0.9.0.
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HMAC_CTX_init(), HMAC_Init_ex() and HMAC_CTX_cleanup() are available
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since OpenSSL 0.9.7.
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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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