a528d4f0a9
If something was "present in all versions" of SSLeay, or if it was added to a version of SSLeay (and therefore predates OpenSSL), remove mention of it. Documentation history now starts with OpenSSL. Remove mention of all history before OpenSSL 0.9.8, inclusive. Remove all AUTHOR sections. Reviewed-by: Tim Hudson <tjh@openssl.org>
122 lines
4.6 KiB
Text
122 lines
4.6 KiB
Text
=pod
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=head1 NAME
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CMS_verify, CMS_get0_signers - verify a CMS SignedData structure
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=head1 SYNOPSIS
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#include <openssl/cms.h>
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int CMS_verify(CMS_ContentInfo *cms, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, unsigned int flags);
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STACK_OF(X509) *CMS_get0_signers(CMS_ContentInfo *cms);
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=head1 DESCRIPTION
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CMS_verify() verifies a CMS SignedData structure. B<cms> is the CMS_ContentInfo
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structure to verify. B<certs> is a set of certificates in which to search for
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the signing certificate(s). B<store> is a trusted certificate store used for
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chain verification. B<indata> is the detached content if the content is not
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present in B<cms>. The content is written to B<out> if it is not NULL.
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B<flags> is an optional set of flags, which can be used to modify the verify
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operation.
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CMS_get0_signers() retrieves the signing certificate(s) from B<cms>, it must
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be called after a successful CMS_verify() operation.
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=head1 VERIFY PROCESS
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Normally the verify process proceeds as follows.
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Initially some sanity checks are performed on B<cms>. The type of B<cms> must
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be SignedData. There must be at least one signature on the data and if
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the content is detached B<indata> cannot be B<NULL>.
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An attempt is made to locate all the signing certificate(s), first looking in
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the B<certs> parameter (if it is not NULL) and then looking in any
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certificates contained in the B<cms> structure itself. If any signing
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certificate cannot be located the operation fails.
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Each signing certificate is chain verified using the B<smimesign> purpose and
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the supplied trusted certificate store. Any internal certificates in the message
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are used as untrusted CAs. If CRL checking is enabled in B<store> any internal
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CRLs are used in addition to attempting to look them up in B<store>. If any
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chain verify fails an error code is returned.
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Finally the signed content is read (and written to B<out> is it is not NULL)
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and the signature's checked.
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If all signature's verify correctly then the function is successful.
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Any of the following flags (ored together) can be passed in the B<flags>
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parameter to change the default verify behaviour.
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If B<CMS_NOINTERN> is set the certificates in the message itself are not
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searched when locating the signing certificate(s). This means that all the
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signing certificates must be in the B<certs> parameter.
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If B<CMS_NOCRL> is set and CRL checking is enabled in B<store> then any
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CRLs in the message itself are ignored.
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If the B<CMS_TEXT> flag is set MIME headers for type B<text/plain> are deleted
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from the content. If the content is not of type B<text/plain> then an error is
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returned.
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If B<CMS_NO_SIGNER_CERT_VERIFY> is set the signing certificates are not
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verified.
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If B<CMS_NO_ATTR_VERIFY> is set the signed attributes signature is not
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verified.
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If B<CMS_NO_CONTENT_VERIFY> is set then the content digest is not checked.
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=head1 NOTES
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One application of B<CMS_NOINTERN> is to only accept messages signed by
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a small number of certificates. The acceptable certificates would be passed
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in the B<certs> parameter. In this case if the signer is not one of the
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certificates supplied in B<certs> then the verify will fail because the
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signer cannot be found.
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In some cases the standard techniques for looking up and validating
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certificates are not appropriate: for example an application may wish to
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lookup certificates in a database or perform customised verification. This
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can be achieved by setting and verifying the signers certificates manually
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using the signed data utility functions.
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Care should be taken when modifying the default verify behaviour, for example
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setting B<CMS_NO_CONTENT_VERIFY> will totally disable all content verification
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and any modified content will be considered valid. This combination is however
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useful if one merely wishes to write the content to B<out> and its validity
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is not considered important.
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Chain verification should arguably be performed using the signing time rather
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than the current time. However since the signing time is supplied by the
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signer it cannot be trusted without additional evidence (such as a trusted
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timestamp).
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=head1 RETURN VALUES
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CMS_verify() returns 1 for a successful verification and zero if an error
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occurred.
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CMS_get0_signers() returns all signers or NULL if an error occurred.
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The error can be obtained from L<ERR_get_error(3)>
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=head1 BUGS
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The trusted certificate store is not searched for the signing certificate,
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this is primarily due to the inadequacies of the current B<X509_STORE>
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functionality.
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The lack of single pass processing means that the signed content must all
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be held in memory if it is not detached.
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=head1 SEE ALSO
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L<ERR_get_error(3)>, L<CMS_sign(3)>
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=cut
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