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EVP_DIGESTVERIFYINIT(3)		    OpenSSL	       EVP_DIGESTVERIFYINIT(3)

NAME
       EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal,
       EVP_DigestVerify	- 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);
	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_DigestSignInit() (which
       means the EVP_PKEY_CTX is created inside	EVP_DigestSignInit() and it
       will be freed automatically when	the EVP_MD_CTX is freed).

       No EVP_PKEY_CTX will be created by EVP_DigsetSignInit() if the passed
       ctx has already been assigned one via EVP_MD_CTX_set_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 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_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)

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

COPYRIGHT
       Copyright 2006-2018 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>.

1.1.1a				  2018-11-20	       EVP_DIGESTVERIFYINIT(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | NOTES | SEE ALSO | HISTORY | COPYRIGHT

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