82 lines
3.2 KiB
Text
82 lines
3.2 KiB
Text
=pod
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=head1 NAME
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EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal - EVP signature verification functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
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int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t siglen);
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=head1 DESCRIPTION
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The EVP signature routines are a high level interface to digital signatures.
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EVP_DigestVerifyInit() sets up verification context B<ctx> to use digest
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B<type> from ENGINE B<impl> and public key B<pkey>. B<ctx> must be initialized
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with EVP_MD_CTX_init() before calling this function. If B<pctx> is not NULL the
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EVP_PKEY_CTX of the verification operation will be written to B<*pctx>: this
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can be used to set alternative verification options.
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EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the
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verification context B<ctx>. This function can be called several times on the
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same B<ctx> to include additional data. This function is currently implemented
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using a macro.
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EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in
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B<sig> of length B<siglen>.
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=head1 RETURN VALUES
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EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0
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or a negative value for failure. In particular a return value of -2 indicates
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the operation is not supported by the public key algorithm.
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Unlike other functions the return value 0 from EVP_DigestVerifyFinal() only
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indicates that the signature did not not verify successfully (that is tbs did
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not match the original data or the signature was of invalid form) it is not an
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indication of a more serious error.
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The error codes can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>.
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=head1 NOTES
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The B<EVP> interface to digital signatures should almost always be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the algorithm used and much more flexible.
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In previous versions of OpenSSL there was a link between message digest types
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and public key algorithms. This meant that "clone" digests such as EVP_dss1()
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needed to be used to sign using SHA1 and DSA. This is no longer necessary and
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the use of clone digest is now discouraged.
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For some key types and parameters the random number generator must be seeded
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or the operation will fail.
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The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest
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context. This means that calls to EVP_VerifyUpdate() and EVP_VerifyFinal() can
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be called later to digest and verify additional data.
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Since only a copy of the digest context is ever finalized the context must
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be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak
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will occur.
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=head1 SEE ALSO
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L<EVP_DigestSignInit(3)|EVP_DigestSignInit(3)>,
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L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>,
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L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
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L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>,
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L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)>
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=head1 HISTORY
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EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal()
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were first added to OpenSSL 1.0.0.
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=cut
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