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89 lines
2.9 KiB
Plaintext
89 lines
2.9 KiB
Plaintext
=pod
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=head1 NAME
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EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal - EVP signature verification functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_VerifyInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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int EVP_VerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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int EVP_VerifyFinal(EVP_MD_CTX *ctx,unsigned char *sigbuf, unsigned int siglen,EVP_PKEY *pkey);
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int EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);
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=head1 DESCRIPTION
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The EVP signature verification routines are a high level interface to digital
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signatures.
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EVP_VerifyInit_ex() sets up verification context B<ctx> to use digest
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B<type> from ENGINE B<impl>. B<ctx> must be created by calling
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EVP_MD_CTX_new() before calling this function.
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EVP_VerifyUpdate() 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.
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EVP_VerifyFinal() verifies the data in B<ctx> using the public key B<pkey>
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and against the B<siglen> bytes at B<sigbuf>.
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EVP_VerifyInit() initializes verification context B<ctx> to use the default
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implementation of digest B<type>.
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=head1 RETURN VALUES
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EVP_VerifyInit_ex() and EVP_VerifyUpdate() return 1 for success and 0 for
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failure.
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EVP_VerifyFinal() returns 1 for a correct signature, 0 for failure and -1 if some
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other error occurred.
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The error codes can be obtained by L<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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Due to the link between message digests and public key algorithms the correct
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digest algorithm must be used with the correct public key type. A list of
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algorithms and associated public key algorithms appears in
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L<EVP_DigestInit(3)>.
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The call to EVP_VerifyFinal() internally finalizes a copy of the digest context.
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This means that calls to EVP_VerifyUpdate() and EVP_VerifyFinal() can be called
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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 BUGS
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Older versions of this documentation wrongly stated that calls to
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EVP_VerifyUpdate() could not be made after calling EVP_VerifyFinal().
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Since the public key is passed in the call to EVP_SignFinal() any error
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relating to the private key (for example an unsuitable key and digest
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combination) will not be indicated until after potentially large amounts of
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data have been passed through EVP_SignUpdate().
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It is not possible to change the signing parameters using these function.
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The previous two bugs are fixed in the newer EVP_VerifyDigest*() function.
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=head1 SEE ALSO
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L<evp(3)>,
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L<EVP_SignInit(3)>,
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L<EVP_DigestInit(3)>, L<err(3)>,
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L<evp(3)>, L<hmac(3)>, L<md2(3)>,
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L<md5(3)>, L<mdc2(3)>, L<ripemd(3)>,
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L<sha(3)>, L<dgst(1)>
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=cut
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