Linux 2.6 - man page for pkcs7_verify (linux section 3SSL)
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PKCS7_verify(3SSL) OpenSSL PKCS7_verify(3SSL)
PKCS7_verify - 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);
PKCS7_verify() verifies a PKCS#7 signedData structure. p7 is the PKCS7 structure to
verify. certs is a set of certificates in which to search for the signer's certificate.
store is a trusted certficate 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.
flags is an optional set of flags, which can be used to modify the verify operation.
PKCS7_get0_signers() retrieves the signer's certificates from p7, it does not check their
validity or whether any signatures are valid. The certs and flags parameters have the same
meanings as in PKCS7_verify().
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
An attempt is made to locate all the signer's certificates, first looking in the certs
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 purpose 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 returned.
Finally the signed content is read (and written to out is it is not NULL) and the
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 PKCS7_NOINTERN is meaningful to
If PKCS7_NOINTERN 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 parameter.
If the PKCS7_TEXT flag is set MIME headers for type text/plain are deleted from the
content. If the content is not of type text/plain then an error is returned.
If PKCS7_NOVERIFY is set the signer's certificates are not chain verified.
If PKCS7_NOCHAIN 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.
If PKCS7_NOSIGS 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 the certs 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 setting
PKCS7_NOVERIFY|PKCS7_NOSIGS 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 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).
PKCS7_verify() returns 1 for a successful verification and zero or a negative value if an
PKCS7_get0_signers() returns all signers or NULL if an error occurred.
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 functionality.
The lack of single pass processing and need to hold all data in memory as mentioned in
PKCS7_sign() also applies to PKCS7_verify().
PKCS7_verify() was added to OpenSSL 0.9.5
1.0.0e 2006-05-14 PKCS7_verify(3SSL)
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