The EVP signature verification routines are a high level interface to digital signatures.
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_VerifyInit() initializes verification context ctx to use the default implementation of digest type.