118 lines
4.5 KiB
Text
118 lines
4.5 KiB
Text
=pod
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=head1 NAME
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PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure
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=head1 SYNOPSIS
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#include <openssl/pkcs7.h>
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int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, int flags);
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STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
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=head1 DESCRIPTION
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PKCS7_verify() verifies a PKCS#7 signedData structure. B<p7> is the PKCS7
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structure to verify. B<certs> is a set of certificates in which to search for
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the signer's certificate. B<store> is a trusted certficate store (used for
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chain verification). B<indata> is the signed data if the content is not
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present in B<p7> (that is it is detached). The content is written to B<out>
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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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PKCS7_get0_signers() retrieves the signer's certificates from B<p7>, it does
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B<not> check their validity or whether any signatures are valid. The B<certs>
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and B<flags> parameters have the same meanings as in PKCS7_verify().
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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<p7>. The type of B<p7> 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 signer's certificates, first looking in
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the B<certs> parameter (if it is not B<NULL>) and then looking in any certificates
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contained in the B<p7> structure itself. If any signer's certificates cannot be
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located the operation fails.
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Each signer's 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 any 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) and
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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> parameter
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to change the default verify behaviour. Only the flag B<PKCS7_NOINTERN> is
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meaningful to PKCS7_get0_signers().
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If B<PKCS7_NOINTERN> is set the certificates in the message itself are not
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searched when locating the signer's certificate. This means that all the signers
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certificates must be in the B<certs> parameter.
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If the B<PKCS7_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<PKCS7_NOVERIFY> is set the signer's certificates are not chain verified.
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If B<PKCS7_NOCHAIN> is set then the certificates contained in the message are
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not used as untrusted CAs. This means that the whole verify chain (apart from
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the signer's certificate) must be contained in the trusted store.
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If B<PKCS7_NOSIGS> is set then the signatures on the data are not checked.
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=head1 NOTES
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One application of B<PKCS7_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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Care should be taken when modifying the default verify behaviour, for example
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setting B<PKCS7_NOVERIFY|PKCS7_NOSIGS> will totally disable all verification
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and any signed message 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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PKCS7_verify() returns one for a successful verification and zero
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if an error occurs.
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PKCS7_get0_signers() returns all signers or B<NULL> if an error occurred.
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The error can be obtained from L<ERR_get_error(3)|ERR_get_error(3)>
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=head1 BUGS
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The trusted certificate store is not searched for the signers 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 and need to hold all data in memory as
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mentioned in PKCS7_sign() also applies to PKCS7_verify().
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=head1 SEE ALSO
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L<ERR_get_error(3)|ERR_get_error(3)>, L<PKCS7_sign(3)|PKCS7_sign(3)>
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=head1 HISTORY
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PKCS7_verify() was added to OpenSSL 0.9.5
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=cut
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