1=pod 2 3=head1 NAME 4 5EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal - EVP signature verification functions 6 7=head1 SYNOPSIS 8 9 #include <openssl/evp.h> 10 11 int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx, 12 const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey); 13 int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); 14 int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t siglen); 15 16=head1 DESCRIPTION 17 18The EVP signature routines are a high level interface to digital signatures. 19 20EVP_DigestVerifyInit() sets up verification context B<ctx> to use digest 21B<type> from ENGINE B<impl> and public key B<pkey>. B<ctx> must be initialized 22with EVP_MD_CTX_init() before calling this function. If B<pctx> is not NULL the 23EVP_PKEY_CTX of the verification operation will be written to B<*pctx>: this 24can be used to set alternative verification options. 25 26EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the 27verification context B<ctx>. This function can be called several times on the 28same B<ctx> to include additional data. This function is currently implemented 29using a macro. 30 31EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in 32B<sig> of length B<siglen>. 33 34=head1 RETURN VALUES 35 36EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for success and 0 37or a negative value for failure. In particular a return value of -2 indicates 38the operation is not supported by the public key algorithm. 39 40Unlike other functions the return value 0 from EVP_DigestVerifyFinal() only 41indicates that the signature did not verify successfully (that is tbs did 42not match the original data or the signature was of invalid form) it is not an 43indication of a more serious error. 44 45The error codes can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>. 46 47=head1 NOTES 48 49The B<EVP> interface to digital signatures should almost always be used in 50preference to the low level interfaces. This is because the code then becomes 51transparent to the algorithm used and much more flexible. 52 53In previous versions of OpenSSL there was a link between message digest types 54and public key algorithms. This meant that "clone" digests such as EVP_dss1() 55needed to be used to sign using SHA1 and DSA. This is no longer necessary and 56the use of clone digest is now discouraged. 57 58For some key types and parameters the random number generator must be seeded 59or the operation will fail. 60 61The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest 62context. This means that EVP_VerifyUpdate() and EVP_VerifyFinal() can 63be called later to digest and verify additional data. 64 65Since only a copy of the digest context is ever finalized the context must 66be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak 67will occur. 68 69=head1 SEE ALSO 70 71L<EVP_DigestSignInit(3)|EVP_DigestSignInit(3)>, 72L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>, 73L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>, 74L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>, 75L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)> 76 77=head1 HISTORY 78 79EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() 80were first added to OpenSSL 1.0.0. 81 82=cut 83