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

 =pod

 =head1 NAME

 CMS_verify, CMS_get0_signers - verify a CMS SignedData structure

 =head1 SYNOPSIS

  #include <openssl/cms.h>

  int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store,
                 BIO *indata, BIO *out, unsigned int flags);

  STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);

 =head1 DESCRIPTION

 CMS_verify() verifies a CMS SignedData structure. B<cms> is the CMS_ContentInfo
 structure to verify. B<certs> is a set of certificates in which to search for
 the signing certificate(s). B<store> is a trusted certificate store used for
 chain verification. B<indata> is the detached content if the content is not
 present in B<cms>. The content is written to B<out> if it is not NULL.

 B<flags> is an optional set of flags, which can be used to modify the verify
 operation.

 CMS_get0_signers() retrieves the signing certificate(s) from B<cms>, it may only
 be called after a successful CMS_verify() operation.

 =head1 VERIFY PROCESS

 Normally the verify process proceeds as follows.

 Initially some sanity checks are performed on B<cms>. The type of B<cms> must
 be SignedData. There must be at least one signature on the data and if
 the content is detached B<indata> cannot be B<NULL>.

 An attempt is made to locate all the signing certificate(s), first looking in
 the B<certs> parameter (if it is not NULL) and then looking in any
 certificates contained in the B<cms> structure itself. If any signing
 certificate cannot be located the operation fails.

 Each signing certificate is chain verified using the B<smimesign> purpose and
 the supplied trusted certificate store. Any internal certificates in the message
 are used as untrusted CAs. If CRL checking is enabled in B<store> any internal
 CRLs are used in addition to attempting to look them up in B<store>. If any
 chain verify fails an error code is returned.

 Finally the signed content is read (and written to B<out> if it is not NULL)
 and the signature's checked.

 If all signature's verify correctly then the function is successful.

 Any of the following flags (ored together) can be passed in the B<flags>
 parameter to change the default verify behaviour.

 If B<CMS_NOINTERN> is set the certificates in the message itself are not
 searched when locating the signing certificate(s). This means that all the
 signing certificates must be in the B<certs> parameter.

 If B<CMS_NOCRL> is set and CRL checking is enabled in B<store> then any
 CRLs in the message itself are ignored.

 If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted
 from the content. If the content is not of type B<text/plain> then an error is
 returned.

 If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not
 verified, unless CMS_CADES flag is also set.

 If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not
 verified, unless CMS_CADES flag is also set.

 If B<CMS_CADES> is set, each signer certificate is checked against the
 ESS signingCertificate or ESS signingCertificateV2 extension
 that is required in the signed attributes of the signature.

 If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked.

 =head1 NOTES

 One application of B<CMS_NOINTERN> is to only accept messages signed by
 a small number of certificates. The acceptable certificates would be passed
 in the B<certs> parameter. In this case if the signer is not one of the
 certificates supplied in B<certs> then the verify will fail because the
 signer cannot be found.

 In some cases the standard techniques for looking up and validating
 certificates are not appropriate: for example an application may wish to
 lookup certificates in a database or perform customised verification. This
 can be achieved by setting and verifying the signers certificates manually
 using the signed data utility functions.

 Care should be taken when modifying the default verify behaviour, for example
 setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification
 and any modified content will be considered valid. This combination is however
 useful if one merely wishes to write the content to B<out> and its validity
 is not considered important.

 Chain verification should arguably be performed using the signing time rather
 than the current time. However, since the signing time is supplied by the
 signer it cannot be trusted without additional evidence (such as a trusted
 timestamp).

 =head1 RETURN VALUES

 CMS_verify() returns 1 for a successful verification and zero if an error
 occurred.

 CMS_get0_signers() returns all signers or NULL if an error occurred.

 The error can be obtained from L<ERR_get_error(3)>

 =head1 BUGS

 The trusted certificate store is not searched for the signing certificate,
 this is primarily due to the inadequacies of the current B<X509_STORE>
 functionality.

 The lack of single pass processing means that the signed content must all
 be held in memory if it is not detached.

 =head1 SEE ALSO

 L<OSSL_ESS_check_signing_certs(3)>,
 L<ERR_get_error(3)>, L<CMS_sign(3)>

 =head1 COPYRIGHT

 Copyright 2008-2021 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

	CMS_verify, CMS_get0_signers - verify a CMS SignedData structure

	=head1 SYNOPSIS

	#include <openssl/cms.h>

	int CMS_verify(CMS_ContentInfo cms, STACK_OF(X509) certs, X509_STORE *store,
	BIO indata, BIO out, unsigned int flags);

	STACK_OF(X509) CMS_get0_signers(CMS_ContentInfo cms);

	=head1 DESCRIPTION

	CMS_verify() verifies a CMS SignedData structure. B<cms> is the CMS_ContentInfo
	structure to verify. B<certs> is a set of certificates in which to search for
	the signing certificate(s). B<store> is a trusted certificate store used for
	chain verification. B<indata> is the detached content if the content is not
	present in B<cms>. The content is written to B<out> if it is not NULL.

	B<flags> is an optional set of flags, which can be used to modify the verify
	operation.

	CMS_get0_signers() retrieves the signing certificate(s) from B<cms>, it may only
	be called after a successful CMS_verify() operation.

	=head1 VERIFY PROCESS

	Normally the verify process proceeds as follows.

	Initially some sanity checks are performed on B<cms>. The type of B<cms> must
	be SignedData. There must be at least one signature on the data and if
	the content is detached B<indata> cannot be B<NULL>.

	An attempt is made to locate all the signing certificate(s), first looking in
	the B<certs> parameter (if it is not NULL) and then looking in any
	certificates contained in the B<cms> structure itself. If any signing
	certificate cannot be located the operation fails.

	Each signing certificate is chain verified using the B<smimesign> purpose and
	the supplied trusted certificate store. Any internal certificates in the message
	are used as untrusted CAs. If CRL checking is enabled in B<store> any internal
	CRLs are used in addition to attempting to look them up in B<store>. If any
	chain verify fails an error code is returned.

	Finally the signed content is read (and written to B<out> if it is not NULL)
	and the signature's checked.

	If all signature's verify correctly then the function is successful.

	Any of the following flags (ored together) can be passed in the B<flags>
	parameter to change the default verify behaviour.

	If B<CMS_NOINTERN> is set the certificates in the message itself are not
	searched when locating the signing certificate(s). This means that all the
	signing certificates must be in the B<certs> parameter.

	If B<CMS_NOCRL> is set and CRL checking is enabled in B<store> then any
	CRLs in the message itself are ignored.

	If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted
	from the content. If the content is not of type B<text/plain> then an error is
	returned.

	If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not
	verified, unless CMS_CADES flag is also set.

	If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not
	verified, unless CMS_CADES flag is also set.

	If B<CMS_CADES> is set, each signer certificate is checked against the
	ESS signingCertificate or ESS signingCertificateV2 extension
	that is required in the signed attributes of the signature.

	If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked.

	=head1 NOTES

	One application of B<CMS_NOINTERN> is to only accept messages signed by
	a small number of certificates. The acceptable certificates would be passed
	in the B<certs> parameter. In this case if the signer is not one of the
	certificates supplied in B<certs> then the verify will fail because the
	signer cannot be found.

	In some cases the standard techniques for looking up and validating
	certificates are not appropriate: for example an application may wish to
	lookup certificates in a database or perform customised verification. This
	can be achieved by setting and verifying the signers certificates manually
	using the signed data utility functions.

	Care should be taken when modifying the default verify behaviour, for example
	setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification
	and any modified content will be considered valid. This combination is however
	useful if one merely wishes to write the content to B<out> and its validity
	is not considered important.

	Chain verification should arguably be performed using the signing time rather
	than the current time. However, since the signing time is supplied by the
	signer it cannot be trusted without additional evidence (such as a trusted
	timestamp).

	=head1 RETURN VALUES

	CMS_verify() returns 1 for a successful verification and zero if an error
	occurred.

	CMS_get0_signers() returns all signers or NULL if an error occurred.

	The error can be obtained from L<ERR_get_error(3)>

	=head1 BUGS

	The trusted certificate store is not searched for the signing certificate,
	this is primarily due to the inadequacies of the current B<X509_STORE>
	functionality.

	The lack of single pass processing means that the signed content must all
	be held in memory if it is not detached.

	=head1 SEE ALSO

	L<OSSL_ESS_check_signing_certs(3)>,
	L<ERR_get_error(3)>, L<CMS_sign(3)>

	=head1 COPYRIGHT

	Copyright 2008-2021 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