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, const 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 40EVP_DigestVerifyFinal() returns 1 for success; any other value indicates 41failure. A return value of zero indicates that the signature did not verify 42successfully (that is, tbs did not match the original data or the signature had 43an invalid form), while other values indicate a more serious error (and 44sometimes also indicate an invalid signature form). 45 46The error codes can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>. 47 48=head1 NOTES 49 50The B<EVP> interface to digital signatures should almost always be used in 51preference to the low level interfaces. This is because the code then becomes 52transparent to the algorithm used and much more flexible. 53 54In previous versions of OpenSSL there was a link between message digest types 55and public key algorithms. This meant that "clone" digests such as EVP_dss1() 56needed to be used to sign using SHA1 and DSA. This is no longer necessary and 57the use of clone digest is now discouraged. 58 59For some key types and parameters the random number generator must be seeded 60or the operation will fail. 61 62The call to EVP_DigestVerifyFinal() internally finalizes a copy of the digest 63context. This means that EVP_VerifyUpdate() and EVP_VerifyFinal() can 64be called later to digest and verify additional data. 65 66Since only a copy of the digest context is ever finalized the context must 67be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak 68will occur. 69 70=head1 SEE ALSO 71 72L<EVP_DigestSignInit(3)|EVP_DigestSignInit(3)>, 73L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>, 74L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>, 75L<md5(3)|md5(3)>, L<mdc2(3)|mdc2(3)>, L<ripemd(3)|ripemd(3)>, 76L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)> 77 78=head1 HISTORY 79 80EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and EVP_DigestVerifyFinal() 81were first added to OpenSSL 1.0.0. 82 83=cut 84