#include <openssl/evp.h> int EVP_VerifyInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl); int EVP_VerifyUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt); int EVP_VerifyFinal(EVP_MD_CTX *ctx,unsigned char *sigbuf, unsigned int siglen,EVP_PKEY *pkey); int EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);
EVP_VerifyInit_ex() sets up verification context ctx to use digest type from ENGINE impl. ctx must be initialized by calling EVP_MD_CTX_init() before calling this function.
EVP_VerifyUpdate() hashes cnt bytes of data at d into the verification context ctx. This function can be called several times on the same ctx to include additional data.
EVP_VerifyFinal() verifies the data in ctx using the public key pkey and against the siglen bytes at sigbuf.
EVP_VerifyFinal() returns 1 for a correct signature, 0 for failure and -1 if some other error occurred.
The error codes can be obtained by ERR_get_error(3).
Due to the link between message digests and public key algorithms the correct digest algorithm must be used with the correct public key type. A list of algorithms and associated public key algorithms appears in EVP_DigestInit(3).
The call to EVP_VerifyFinal() 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 the public key is passed in the call to EVP_SignFinal() any error relating to the private key (for example an unsuitable key and digest combination) will not be indicated until after potentially large amounts of data have been passed through EVP_SignUpdate().
It is not possible to change the signing parameters using these function.
EVP_VerifyInit_ex() was added in OpenSSL 0.9.7