Updated: 2021/Apr/14


EVP_DigestVerifyInit(3)             OpenSSL            EVP_DigestVerifyInit(3)



NAME
       EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal,
       EVP_DigestVerify - EVP signature verification functions

LIBRARY
       libcrypto, -lcrypto

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);
        int EVP_DigestVerify(EVP_MD_CTX *ctx, const unsigned char *sigret,
                             size_t siglen, const unsigned char *tbs, size_t tbslen);

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 e and public key pkey. ctx must be created with
       EVP_MD_CTX_new() 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 if ctx is not assigned an
       EVP_PKEY_CTX value before being passed to EVP_DigestVerifyInit() (which
       means the EVP_PKEY_CTX is created inside EVP_DigestVerifyInit() and it
       will be freed automatically when the EVP_MD_CTX is freed).

       No EVP_PKEY_CTX will be created by EVP_DigestSignInit() if the passed
       ctx has already been assigned one via EVP_MD_CTX_set_pkey_ctx(3). See
       also SM2(7).

       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.

       EVP_DigestVerify() verifies tbslen bytes at tbs against the signature
       in sig of length siglen.

RETURN VALUES
       EVP_DigestVerifyInit() and EVP_DigestVerifyUpdate() return 1 for
       success and 0 for failure.

       EVP_DigestVerifyFinal() and EVP_DigestVerify() return 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.

       EVP_DigestVerify() is a one shot operation which verifies a single
       block of data in one function. For algorithms that support streaming it
       is equivalent to calling EVP_DigestVerifyUpdate() and
       EVP_DigestVerifyFinal(). For algorithms which do not support streaming
       (e.g. PureEdDSA) it is the only way to verify data.

       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.  If the automatic seeding or reseeding of the OpenSSL CSPRNG
       fails due to external circumstances (see RAND(7)), 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_free() or a memory
       leak will occur.

SEE ALSO
       EVP_DigestSignInit(3), EVP_DigestInit(3), evp(7), HMAC(3), MD2(3),
       MD5(3), MDC2(3), RIPEMD160(3), SHA1(3), dgst(1), RAND(7)

HISTORY
       EVP_DigestVerifyInit(), EVP_DigestVerifyUpdate() and
       EVP_DigestVerifyFinal() were added in OpenSSL 1.0.0.

COPYRIGHT
       Copyright 2006-2020 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the OpenSSL license (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



1.1.1i                            2020-12-10           EVP_DigestVerifyInit(3)