/usr/man/cat.3/EVP_DigestVerifyUpdate.3.Z

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 signa-
       tures.

       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. Note
       that any existing value in *pctx is overwritten. The EVP_PKEY_CTX value
       returned must not be freed directly by the application (it will be
       freed automatically when the EVP_MD_CTX is freed).

       EVP_DigestVerifyUpdate() hashes cnt bytes of data at d into the verifi-
       cation context ctx. This function can be called several times on the
       same ctx to include additional data. This function is currently imple-
       mented 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 suc-
       cess 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 indi-
       cates 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_VerifyFi-
       nal() 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 mem-
       ory 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_DigestVerify-
       Final() were first added to OpenSSL 1.0.0.

1.0.2t                            2019-09-10           EVP_DigestVerifyInit(3)
See also EVP_DigestVerifyFinal(3)
See also EVP_DigestVerifyInit(3)