PHP Manual . ... This function is EXPERIMENTAL . ... Be warned and use this function at your own risk. openssl_pkcs7_sign () takes the contents of the file named infilename and signs them using the certificate and it's matching private key specified by signcert and privkey parameters. headers is an array of headers that will be prepended to the data after it has been signed (see openssl_pkcs7_encrypt() for more information about the format of this parameter. flags can be used ...