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EVP_VerifyInit(3)                   OpenSSL                  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().
       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.
       The previous two bugs are fixed in the newer EVP_VerifyDigest*()
       function.
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

1.0.2k                            2017-01-26                 EVP_VerifyInit(3)