PKCS7_verify, PKCS7_get0_signers - verify a PKCS#7 signedData structure
int PKCS7_verify(PKCS7 *p7, STACK_OF(X509) *certs, X509_STORE *store, BIO *indata, BIO *out, int flags);
STACK_OF(X509) *PKCS7_get0_signers(PKCS7 *p7, STACK_OF(X509) *certs, int flags);
verifies a PKCS#7 signedData structure. p7
PKCS7 structure to verify. certs
is a set of certificates in which to
search for the signer's certificate. store
is a trusted certificate
store (used for chain verification). indata
is the signed data if the
content is not present in p7
(that is it is detached). The content is
written to out
if it is not NULL.
is an optional set of flags, which can be used to modify the verify
retrieves the signer's certificates from p7
it does not
check their validity or whether any signatures are valid.
parameters have the same meanings as in
Normally the verify process proceeds as follows.
Initially some sanity checks are performed on p7
. The type of p7
must be signedData. There must be at least one signature on the data and if
the content is detached indata
cannot be NULL
. If the content is
not detached and indata
is not NULL
, then the structure has both
embedded and external content. To treat this as an error, use the flag
. The default behavior allows this, for
compatibility with older versions of OpenSSL.
An attempt is made to locate all the signer's certificates, first looking in the
parameter (if it is not NULL
) and then looking in any
certificates contained in the p7
structure itself. If any signer's
certificates cannot be located the operation fails.
Each signer's certificate is chain verified using the smimesign
and the supplied trusted certificate store. Any internal certificates in the
message are used as untrusted CAs. If any chain verify fails an error code is
Finally the signed content is read (and written to out
is 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 flags
parameter to change the default verify behaviour. Only the flag
is meaningful to PKCS7_get0_signers()
is set the certificates in the message itself are not
searched when locating the signer's certificate. This means that all the
signers certificates must be in the certs
If the PKCS7_TEXT
flag is set MIME headers for type text/plain
deleted from the content. If the content is not of type text/plain
an error is returned.
is set the signer's certificates are not chain
is set then the certificates contained in the message
are not used as untrusted CAs. This means that the whole verify chain (apart
from the signer's certificate) must be contained in the trusted store.
is set then the signatures on the data are not checked.
One application of PKCS7_NOINTERN
is to only accept messages signed by a
small number of certificates. The acceptable certificates would be passed in
parameter. In this case if the signer is not one of the
certificates supplied in certs
then the verify will fail because the
signer cannot be found.
Care should be taken when modifying the default verify behaviour, for example
will totally disable all
verification and any signed message will be considered valid. This combination
is however useful if one merely wishes to write the content to out
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
returns one for a successful verification and zero if an
returns all signers or NULL
if an error
The error can be obtained from ERR_get_error(3)
The trusted certificate store is not searched for the signers certificate, this
is primarily due to the inadequacies of the current X509_STORE
The lack of single pass processing and need to hold all data in memory as
mentioned in PKCS7_sign()
also applies to PKCS7_verify()
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