John Davidson

Message:

Could anyone help me to figure out a decryption algorithm for data that is encrypted in PHP using AES-256-CBC. I have tried lots of different ways, but I think I am messing up when trying to replicate the method of recreating they Key/IV in Dart and keep getting exceptions such as:

RangeError (end): Invalid value: Not in inclusive range 0..16:

The PHP code that does the encryption (which cannot be changed as the encrypted strings are provided by a third party) is as follows:

function encrypt( $string, $encrypt=true) {

    $secret_key = 'SuperSecretKey';

    $secret_iv = 'SuperSecretBLOCK';

    $output = false;

    $encrypt_method = "AES-256-CBC";

    $key = hash( 'sha256', $secret_key );

    $iv = substr( hash( 'sha256', $secret_iv ), 0, 16 );

    if($encrypt) {

        $output = base64_encode( openssl_encrypt( $string, $encrypt_method, $key, 0, $iv ) );

    } else {

        $output = openssl_decrypt( base64_decode( $string ), $encrypt_method, $key, 0, $iv );

    }

    return $output;

}

For example, if the encryption routine in PHP were called to encrypt the string "This is a Test!", the result would be:

ZHArWURDY2FkelBtSGY5c1AzdTNBZz09

It is this result that I am attempting to decrypt in Dart and not having any luck!

Here is what I have so far that is resulting in the exception referenced above:

import 'package:encrypt/encrypt.dart';

import 'package:crypto/crypto.dart';

import 'dart:convert' show utf8;



String extractPayload(String payload) {

      String strPwd = 'SuperSecretKey';

      String strIv = 'SuperSecretBLOCK';

      var iv = sha256.convert(utf8.encode(strIv));

      var key = sha256.convert(utf8.encode(strPwd));

      IV ivObj = IV.fromUtf8(iv.toString());

      Key keyObj = Key.fromUtf8(key.toString());

      final encrypter = Encrypter(AES(keyObj));

      final decrypted = encrypter.decrypt(Encrypted.from64(payload), iv: ivObj);

      print(decrypted);

      return decrypted;

}

Any suggestions welcome,
Thanks

---

My Answer:
AES-256-CBC';

$key = hash('sha256', $secret_key);
$iv = substr(hash('sha256', $secret_iv), 0, 16);

if ($encrypt) {
$output = openssl_encrypt($string, $encrypt_method, $key, 0, $iv);
$output = base64_encode($output);
} else {
$output = openssl_decrypt(base64_decode($string), $encrypt_method, $key, 0, $iv);
}

return $output;
}

In Dart, you can use the `encrypt` package to decrypt the data encrypted in PHP using AES-256-CBC. Here is an example of how you can decrypt the data in Dart:

dart
import 'package:encrypt/encrypt.dart';
import 'package:pointycastle/export.dart';
import 'dart:convert';

void main() {
final key = Key.fromUtf8('SuperSecretKey');
final iv = IV.fromUtf8('SuperSecretBLOCK');

final encrypter = Encrypter(AES(key, mode: AESMode.cbc));

final encrypted = 'encrypted_string_here';
final decrypted = encrypter.decrypt64(encrypted, iv: iv);

print(decrypted);
}


Make sure to replace `'encrypted_string_here'` with the actual encrypted string you received from the PHP encryption function. Also, ensure that you have added the `encrypt` package to your Dart project by adding it to your `pubspec.yaml` file:

yaml
dependencies:
encrypt: ^5.0.0


This should help you decrypt the data encrypted in PHP using AES-256-CBC in Dart. Let me know if you have any further questions or issues.