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EVP_DIGESTVERIFYINIT(3ossl)	    OpenSSL	   EVP_DIGESTVERIFYINIT(3ossl)

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

SYNOPSIS
	#include <openssl/evp.h>

	int EVP_DigestVerifyInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
				    const char *mdname,	OSSL_LIB_CTX *libctx,
				    const char *props, EVP_PKEY	*pkey);
	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.  Input data is digested first before	the signature
       verification takes place.

       EVP_DigestVerifyInit_ex() sets up verification context ctx to use a
       digest with the name mdname and public key pkey.	The name of the	digest
       to be used is passed to the provider of the signature algorithm in use.
       How that	provider interprets the	digest name is provider	specific. The
       provider	may implement that digest directly itself or it	may
       (optionally) choose to fetch it (which could result in a	digest from a
       different provider being	selected). If the provider supports fetching
       the digest then it may use the props argument for the properties	to be
       used during the fetch.

       The pkey	algorithm is used to fetch a EVP_SIGNATURE method implicitly,
       to be used for the actual signing. See "Implicit	fetch" in provider(7)
       for more	information about implicit fetches.

       The OpenSSL default and legacy providers	support	fetching digests and
       can fetch those digests from any	available provider. The	OpenSSL	fips
       provider	also supports fetching digests but will	only fetch digests
       that are	themselves implemented inside the fips provider.

       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_ex() (which	means the EVP_PKEY_CTX
       is created inside EVP_DigestVerifyInit_ex() and it will be freed
       automatically when the EVP_MD_CTX is freed). If the EVP_PKEY_CTX	to be
       used is created by EVP_DigestVerifyInit_ex then it will use the
       OSSL_LIB_CTX specified in libctx	and the	property query string
       specified in props.

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

       Not all digests can be used for all key types. The following
       combinations apply.

       DSA Supports SHA1, SHA224, SHA256, SHA384 and SHA512

       ECDSA
	   Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3

       RSA with	no padding
	   Supports no digests (the digest type	must be	NULL)

       RSA with	X931 padding
	   Supports SHA1, SHA256, SHA384 and SHA512

       All other RSA padding types
	   Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1,	MD2,
	   MD4,	MDC2, SHA3-224,	SHA3-256, SHA3-384, SHA3-512

       Ed25519 and Ed448
	   Support no digests (the digest type must be NULL)

       HMAC
	   Supports any	digest

       CMAC, Poly1305 and Siphash
	   Will	ignore any digest provided.

       If RSA-PSS is used and restrictions apply then the digest must match.

       EVP_DigestVerifyInit() works in the same	way as
       EVP_DigestVerifyInit_ex() except	that the mdname	parameter will be
       inferred	from the supplied digest type, and props will be NULL. Where
       supplied	the ENGINE e will be used for the signature verification and
       digest algorithm	implementations. e may be NULL.

       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.

       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), openssl-dgst(1),	RAND(7)

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

       EVP_DigestVerifyInit_ex() was added in OpenSSL 3.0.

       EVP_DigestVerifyUpdate()	was converted from a macro to a	function in
       OpenSSL 3.0.

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

       Licensed	under the Apache License 2.0 (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>.

3.0.0-beta1+quic		  2021-06-19	   EVP_DIGESTVERIFYINIT(3ossl)

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

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