EVP_VerifyInit(3)

     NAME
          EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal - EVP
          signature verification functions

     SYNOPSIS
           #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);


     DESCRIPTION
          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.

     RETURN VALUES
          EVP_VerifyInit_ex() and EVP_VerifyUpdate() return 1 for
          success and 0 for failure.

          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).

     NOTES
          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).
          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 only a copy of the digest context is ever finalized
          the context must be cleaned up after use by calling
          EVP_MD_CTX_cleanup() or a memory leak will occur.

     BUGS
          Older versions of this documentation wrongly stated that
          calls to EVP_VerifyUpdate() could not be made after calling
          EVP_VerifyFinal().

     SEE ALSO
          evp(3), EVP_SignInit(3), EVP_DigestInit(3), err(3), evp(3),
          hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)

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

          EVP_VerifyInit_ex() was added in OpenSSL 0.9.7