Manage to make it work at last.$dn = array( "countryName" => "XX", "stateOrProvinceName" => "Location", "localityName" => "Local", "organizationName" => "Sample Organization", "organizationalUnitName" => "Organizational Unit", "commonName" => "Sample", "emailAddress" => "contactus@email.com");// Generate a new private (and public) key pair$privkey = openssl_pkey_new(array( "private_key_bits" => 4096, "private_key_type" => OPENSSL_KEYTYPE_RSA,));// Generate a certificate signing request$csr = openssl_csr_new($dn, $privkey, array('digest_alg' => 'sha512'));// Generate a self-signed cert, valid for 365 days$x509 = openssl_csr_sign($csr, null, $privkey, $days=365, array('digest_alg' => 'sha512'));// Save your private key, CSR and self-signed cert for later useopenssl_csr_export($csr, $csrout) and var_dump($csrout); // .csropenssl_x509_export($x509, $certout) and var_dump($certout); // .crt.pemopenssl_pkey_export($privkey, $pkeyout, "user_defined_password") and var_dump($pkeyout); // .key.pemif(openssl_cms_sign ( "file_to_sign", "Sample.p7m" , $x509 , $privkey, null , 0 , 0 , null )){ echo "SIGNED SUCCESSFULLY! Sample.p7m created... \r\n";}else{ echo "SIGNED FAILED!\r\n";}