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Diffstat (limited to 'doc/crypto/EVP_DigestVerifyInit.pod')
| -rw-r--r-- | doc/crypto/EVP_DigestVerifyInit.pod | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/doc/crypto/EVP_DigestVerifyInit.pod b/doc/crypto/EVP_DigestVerifyInit.pod new file mode 100644 index 0000000000..f224488978 --- /dev/null +++ b/doc/crypto/EVP_DigestVerifyInit.pod @@ -0,0 +1,82 @@ +=pod + +=head1 NAME + +EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal - EVP signature verification functions + +=head1 SYNOPSIS + + #include <openssl/evp.h> + + int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, + const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); + int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); + int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t siglen); + +=head1 DESCRIPTION + +The EVP signature routines are a high level interface to digital signatures. + +EVP_DigestVerifyInit() sets up verification context B<ctx> to use digest +B<type> from ENGINE B<impl> and public key B<pkey>. B<ctx> must be initialized +with EVP_MD_CTX_init() before calling this function. If B<pctx> is not NULL the +EVP_PKEY_CTX of the verification operation will be written to B<*pctx>: this +can be used to set alternative verification options. + +EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the +verification context B<ctx>. This function can be called several times on the +same B<ctx> to include additional data. This function is currently implemented +using a macro. + +EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in +B<sig> of length B<siglen>. + +=head1 RETURN VALUES + +EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0 +or a negative value for failure. In particular a return value of -2 indicates +the operation is not supported by the public key algorithm. + +Unlike other functions the return value 0 from EVP_DigestVerifyFinal() only +indicates that the signature did not not verify successfully (that is tbs did +not match the original data or the signature was of invalid form) it is not an +indication of a more serious error. + +The error codes can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>. + +=head1 NOTES + +The B<EVP> interface to digital signatures should almost always be used in +preference to the low level interfaces. This is because the code then becomes +transparent to the algorithm used and much more flexible. + +In previous versions of OpenSSL there was a link between message digest types +and public key algorithms. This meant that "clone" digests such as EVP_dss1() +needed to be used to sign using SHA1 and DSA. This is no longer necessary and +the use of clone digest is now discouraged. + +For some key types and parameters the random number generator must be seeded +or the operation will fail. + +The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest +context. This means that calls to EVP_VerifyUpdate() and EVP_VerifyFinal() can +be called later to digest and verify additional data. + +Since only a copy of the digest context is ever finalized the context must +be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak +will occur. + +=head1 SEE ALSO + +L<EVP_DigestSignInit(3)|EVP_DigestSignInit(3)>, +L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>, +L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>, +L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>, +L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)> + +=head1 HISTORY + +EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() +were first added to OpenSSL 1.0.0. + +=cut |