Description
mixed 
openssl_pkcs7_verify ( string filename, int flags [, string outfilename [, array cainfo [, string extracerts]]] )
    openssl_pkcs7_verify() reads the S/MIME message
    contained in the filename specified by filename and
    examines the digital signature.  It returns TRUE if the signature is
    verified, FALSE if it is not correct (the message has been tampered with,
    or the signing certificate is invalid), or -1 on error.
   
    flags can be used to affect how the signature is
    verified - see PKCS7 constants
    for more information.
   
    If the outfilename is specified, it should be a
    string holding the name of a file into which the certificates of the
    persons that signed the messages will be stored in PEM format.
   
    If the cainfo is specified, it should hold
    information about the trusted CA certificates to use in the verification
    process - see certificate
    verification for more information about this parameter.
   
    If the extracerts is specified, it is the filename
    of a file containing a bunch of certificates to use as untrusted CAs.