doc/man3/EVP_DigestVerifyInit.pod - third_party/openssl - Git at Google

 =pod

 =head1 NAME

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

 =head1 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,
                              const OSSL_PARAM params[]);
  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);

 =head1 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 B<ctx> to use a
 digest with the name B<mdname> and public key B<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 B<props> argument
 for the properties to be used during the fetch. Finally, the passed parameters
 I<params>, if not NULL, are set on the context before returning.

 The I<pkey> algorithm is used to fetch a B<EVP_SIGNATURE> method implicitly, to
 be used for the actual signing. See L<provider(7)/Implicit fetch> 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.

 B<ctx> must be created with EVP_MD_CTX_new() before calling this function. If
 B<pctx> is not NULL, the EVP_PKEY_CTX of the verification operation will be
 written to B<*pctx>: this can be used to set alternative verification options.
 Note that any existing value in B<*pctx> is overwritten. The EVP_PKEY_CTX value
 returned must not be freed directly by the application if B<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 B<OSSL_LIB_CTX> specified
 in I<libctx> and the property query string specified in I<props>.

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

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

 =over 4

 =item DSA

 Supports SHA1, SHA224, SHA256, SHA384 and SHA512

 =item ECDSA

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

 =item RSA with no padding

 Supports no digests (the digest B<type> must be NULL)

 =item RSA with X931 padding

 Supports SHA1, SHA256, SHA384 and SHA512

 =item 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

 =item Ed25519 and Ed448

 Support no digests (the digest B<type> must be NULL)

 =item HMAC

 Supports any digest

 =item CMAC, Poly1305 and Siphash

 Will ignore any digest provided.

 =back

 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 B<mdname> parameter will be
 inferred from the supplied digest B<type>, and B<props> will be NULL. Where
 supplied the ENGINE B<e> will be used for the signature verification and digest
 algorithm implementations. B<e> may be NULL.

 EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the
 verification context B<ctx>. This function can be called several times on the
 same B<ctx> to include additional data.

 EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in
 B<sig> of length B<siglen>.

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

 =head1 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, B<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 L<ERR_get_error(3)>.

 =head1 NOTES

 The B<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 L<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.

 EVP_DigestVerifyInit() and EVP_DigestVerifyInit_ex() functions can be called
 multiple times on a context and the parameters set by previous calls should be
 preserved if the I<pkey> parameter is NULL. The call then just resets the state
 of the I<ctx>.

 =head1 SEE ALSO

 L<EVP_DigestSignInit(3)>,
 L<EVP_DigestInit(3)>,
 L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
 L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
 L<SHA1(3)>, L<openssl-dgst(1)>,
 L<RAND(7)>

 =head1 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.

 =head1 COPYRIGHT

 Copyright 2006-2021 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
 L<https://www.openssl.org/source/license.html>.

 =cut
	=pod

	=head1 NAME

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

	=head1 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,
	const OSSL_PARAM params[]);
	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);

	=head1 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 B<ctx> to use a
	digest with the name B<mdname> and public key B<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 B<props> argument
	for the properties to be used during the fetch. Finally, the passed parameters
	I<params>, if not NULL, are set on the context before returning.

	The I<pkey> algorithm is used to fetch a B<EVP_SIGNATURE> method implicitly, to
	be used for the actual signing. See L<provider(7)/Implicit fetch> 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.

	B<ctx> must be created with EVP_MD_CTX_new() before calling this function. If
	B<pctx> is not NULL, the EVP_PKEY_CTX of the verification operation will be
	written to B<*pctx>: this can be used to set alternative verification options.
	Note that any existing value in B<*pctx> is overwritten. The EVP_PKEY_CTX value
	returned must not be freed directly by the application if B<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 B<OSSL_LIB_CTX> specified
	in I<libctx> and the property query string specified in I<props>.

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

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

	=over 4

	=item DSA

	Supports SHA1, SHA224, SHA256, SHA384 and SHA512

	=item ECDSA

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

	=item RSA with no padding

	Supports no digests (the digest B<type> must be NULL)

	=item RSA with X931 padding

	Supports SHA1, SHA256, SHA384 and SHA512

	=item 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

	=item Ed25519 and Ed448

	Support no digests (the digest B<type> must be NULL)

	=item HMAC

	Supports any digest

	=item CMAC, Poly1305 and Siphash

	Will ignore any digest provided.

	=back

	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 B<mdname> parameter will be
	inferred from the supplied digest B<type>, and B<props> will be NULL. Where
	supplied the ENGINE B<e> will be used for the signature verification and digest
	algorithm implementations. B<e> may be NULL.

	EVP_DigestVerifyUpdate() hashes B<cnt> bytes of data at B<d> into the
	verification context B<ctx>. This function can be called several times on the
	same B<ctx> to include additional data.

	EVP_DigestVerifyFinal() verifies the data in B<ctx> against the signature in
	B<sig> of length B<siglen>.

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

	=head1 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, B<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 L<ERR_get_error(3)>.

	=head1 NOTES

	The B<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 L<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.

	EVP_DigestVerifyInit() and EVP_DigestVerifyInit_ex() functions can be called
	multiple times on a context and the parameters set by previous calls should be
	preserved if the I<pkey> parameter is NULL. The call then just resets the state
	of the I<ctx>.

	=head1 SEE ALSO

	L<EVP_DigestSignInit(3)>,
	L<EVP_DigestInit(3)>,
	L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
	L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
	L<SHA1(3)>, L<openssl-dgst(1)>,
	L<RAND(7)>

	=head1 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.

	=head1 COPYRIGHT

	Copyright 2006-2021 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
	L<https://www.openssl.org/source/license.html>.

	=cut