Allow passing $tag for non-authenticated encryption

openssl_encrypt() currently throws a warning if the $tag out
parameter is passed for a non-authenticated cipher. This violates
the principle that a function should behave the same if a parameter
is not passed, and if the default value is passed for the parameter.

I believe this warning should simply be dropped and the $tag be
populated with null, as is already the case. Otherwise, it is not
possible to use openssl_encrypt() in generic wrapper APIs, that are
compatible with both authenticated and non-authenticated encryption.

Closes GH-6333.

Author: nikic

ext/openssl/openssl.c

@@ -6744,8 +6744,6 @@ PHP_OPENSSL_API zend_string* php_openssl_encrypt(char *data, size_t data_len, ch
 			}
 		} else if (tag) {
 			ZEND_TRY_ASSIGN_REF_NULL(tag);
-			php_error_docref(NULL, E_WARNING,
-					"The authenticated tag cannot be provided for cipher that doesn not support AEAD");
 		} else if (mode.is_aead) {
 			php_error_docref(NULL, E_WARNING, "A tag should be provided when using AEAD mode");
 			zend_string_release_ex(outbuf, 0);

ext/openssl/tests/openssl_decrypt_basic.phpt

@@ -28,9 +28,16 @@ var_dump(rtrim($output));
 $encrypted = openssl_encrypt($data, "bf-ecb", $password, OPENSSL_DONT_ZERO_PAD_KEY);
 $output = openssl_decrypt($encrypted, "bf-ecb", $password, OPENSSL_DONT_ZERO_PAD_KEY);
 var_dump($output);
+
+// It's okay to pass $tag for a non-authenticated cipher.
+// It will be populated with null in that case.
+openssl_encrypt($data, $method, $password, 0, $iv, $tag);
+var_dump($tag);
+
 ?>
 --EXPECT--
 string(45) "openssl_encrypt() and openssl_decrypt() tests"
 string(45) "openssl_encrypt() and openssl_decrypt() tests"
 string(45) "openssl_encrypt() and openssl_decrypt() tests"
 string(45) "openssl_encrypt() and openssl_decrypt() tests"
+NULL

ext/openssl/tests/openssl_decrypt_error.phpt

@@ -23,8 +23,6 @@ var_dump(openssl_decrypt(array(), $method, $password));
 var_dump(openssl_decrypt($encrypted, array(), $password));
 var_dump(openssl_decrypt($encrypted, $method, array()));
 
-// invalid using of an authentication tag
-var_dump(openssl_encrypt($data, $method, $password, 0, $iv, $wrong));
 ?>
 --EXPECTF--
 Warning: openssl_encrypt(): Using an empty Initialization Vector (iv) is potentially insecure and not recommended in %s on line %d
@@ -53,6 +51,3 @@ NULL
 
 Warning: openssl_decrypt() expects parameter 3 to be string, array given in %s on line %d
 NULL
-
-Warning: openssl_encrypt(): The authenticated tag cannot be provided for cipher that doesn not support AEAD in %s on line %d
-string(44) "yof6cPPH4mLee6TOc0YQSrh4dvywMqxGUyjp0lV6+aM="

ext/openssl/tests/openssl_encrypt_error.phpt

@@ -21,9 +21,6 @@ var_dump(openssl_encrypt($arr, $method, $object));
 var_dump(openssl_encrypt($data, $arr, $object));
 var_dump(openssl_encrypt($data, $method, $arr));
 
-// invalid using of an authentication tag
-var_dump(openssl_encrypt($data, $method, $password, 0, $iv, $wrong));
-
 // padding of the key is disabled
 var_dump(openssl_encrypt($data, $method, $password, OPENSSL_DONT_ZERO_PAD_KEY, $iv));
 ?>
@@ -49,8 +46,5 @@ NULL
 Warning: openssl_encrypt() expects parameter 3 to be string, array given in %s on line %d
 NULL
 
-Warning: openssl_encrypt(): The authenticated tag cannot be provided for cipher that doesn not support AEAD in %s on line %d
-string(44) "iPR4HulskuaP5Z6me5uImk6BqVyJG73+63tkPauVZYk="
-
 Warning: openssl_encrypt(): Key length cannot be set for the cipher method in %s on line %d
 bool(false)