EVP_VerifyInit

EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal ? EVP signature verification functions

 #include <openssl/evp.h>

 void EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);
 void 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);

The EVP signature verification routines are a high level interface to digital signatures.

EVP_VerifyInit() initialises a verification context ctx to using digest type: this will typically be supplied by a function such as EVP_sha1().

EVP_VerifyUpdate() hashes cnt bytes of data at d into the verification context ctx. This funtion 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. After calling EVP_VerifyFinal() no additional calls to EVP_VerifyUpdate() can be made, but EVP_VerifyInit() can be called to initialiase a new verification operation.

EVP_VerifyInit() and EVP_VerifyUpdate() do not return values.

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).

The 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.

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).

Several of the functions do not return values: maybe they should. Although the internal digest operations will never fail some future hardware based operations might.

EVP_SignInit(3), EVP_DigestInit(3), err(3), evp(3), hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3), digest(1)

EVP_VerifyInit(), EVP_VerifyUpdate() and EVP_VerifyFinal() are available in all versions of SSLeay and OpenSSL.