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EVP_DigestVerifyInit(3)             OpenSSL            EVP_DigestVerifyInit(3)

NAME
       EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal -
       EVP signature verification functions
SYNOPSIS
        #include <openssl/evp.h>
        int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
                               const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
        int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
        int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig, size_t siglen);
DESCRIPTION
       The EVP signature routines are a high level interface to digital
       signatures.
       EVP_DigestVerifyInit() sets up verification context ctx to use digest
       type from ENGINE impl and public key pkey. ctx must be initialized with
       EVP_MD_CTX_init() before calling this function. If pctx is not NULL the
       EVP_PKEY_CTX of the verification operation will be written to *pctx:
       this can be used to set alternative verification options.
       EVP_DigestVerifyUpdate() 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. This function is currently
       implemented using a macro.
       EVP_DigestVerifyFinal() verifies the data in ctx against the signature
       in sig of length siglen.
RETURN VALUES
       EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for
       success and 0 or a negative value for failure. In particular a return
       value of -2 indicates the operation is not supported by the public key
       algorithm.
       EVP_DigestVerifyFinal() returns 1 for success; any other value
       indicates failure.  A return value of zero indicates that the signature
       did not verify successfully (that is, tbs did not match the original
       data or the signature had an invalid form), while other values indicate
       a more serious error (and sometimes also indicate an invalid signature
       form).
       The error codes can be obtained from 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.
       In previous versions of OpenSSL there was a link between message digest
       types and public key algorithms. This meant that "clone" digests such
       as EVP_dss1() needed to be used to sign using SHA1 and DSA. This is no
       longer necessary and the use of clone digest is now discouraged.
       For some key types and parameters the random number generator must be
       seeded or the operation will fail.
       The call to EVP_DigestVerifyFinal() internally finalizes a copy of the
       digest context. This means that 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.
SEE ALSO
       EVP_DigestSignInit(3), EVP_DigestInit(3), err(3), evp(3), hmac(3),
       md2(3), md5(3), mdc2(3), ripemd(3), sha(3), dgst(1)
HISTORY
       EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and
       EVP_DigestVerifyFinal() were first added to OpenSSL 1.0.0.

1.0.2k                            2017-01-26           EVP_DigestVerifyInit(3)