README.md

AutoIt to PHP Secure Communication (3DES)

This project provides a lightweight solution to securely transmit data from an AutoIt client to a PHP server using Triple DES (3DES) encryption in CBC mode.

🚀 Quick Start & Usage Examples

1. Client-Side (AutoIt)

The client automatically appends an "END" control suffix to your text, encrypts it, and converts it into a clean Hexadecimal string ready for HTTP transmission.

Example:

Global $SECRET_KEY = "MySecretKey"

; 1. Plaintext data to send
Local $sensitiveData = "User:Admin123"

; 2. Encrypt the data
Local $encryptedHex = _CryptSec($sensitiveData, True)
ConsoleWrite("Send this Hex string to your server: " & $encryptedHex & @CRLF)
; Expected Output: A long Hex string (e.g., 4E5A...)

; --- INTERNAL FUNCTION ---
Func _CryptSec($sText, $bEncrypt = True)
   Local $result = ""
   If $bEncrypt Then
      ; Appends "END" to verify integrity after decryption
      Local $plaintext = $sText & "END"
      Local $ciphertext = _Crypt_EncryptData($plaintext, $SECRET_KEY, $CALG_3DES)
      ; Convert binary to readable Hex
      $result = Hex($ciphertext)
   Else
      Local $raw = Binary("0x" & $sText)
      Local $decryptedBinary = _Crypt_DecryptData($raw, $SECRET_KEY, $CALG_3DES)
      ; Convert back to string and remove the "END" marker
      $result = StringTrimRight(BinaryToString($decryptedBinary), 3)
   EndIf
   Return $result
EndFunc

2. Server-Side (PHP)

The server receives the Hex string, validates it, decrypts it, and automatically verifies and strips the control suffix.

Example:

$secretKey = "MySecretKey";

// Assume this is received from AutoIt via HTTP POST
$receivedHex = $_POST['data'] ?? '4E5A...'; 

$decryptedData = decrypt_data($receivedHex, $secretKey);

if ($decryptedData !== false) {
    echo "Success! Decrypted data: " . $decryptedData; 
    // Output: User:Admin123
} else {
    echo "Error: Data was corrupted or the secret key is invalid.";
}

// --- INTERNAL FUNCTION ---
function decrypt_data($hexText, $secretKey) {
    // 1. Clean up '0x' prefix if present
    if (isset($hexText[1]) && $hexText[0] === '0' && ($hexText[1] === 'x' || $hexText[1] === 'X')) {
        $hexText = substr($hexText, 2);
    }

    // 2. Validate Hex format (must be even length and contain only 0-9, A-F)
    $len = strlen($hexText);
    if ($len < 16 || ($len & 1) || !ctype_xdigit($hexText)) {
        return false;
    }

    $rawBinary = hex2bin($hexText);
    if ($rawBinary === false) {
        return false;
    }

    // 3. Derive the 24-byte 3DES key (cached for maximum performance)
    static $keyCache = [], $lastKey = null, $lastDerivedKey = null;
    
    if ($secretKey !== $lastKey) {
        if (!isset($keyCache[$secretKey])) {
            $baseHash = md5($secretKey, true);
            static $IPAD16, $OPAD16, $IPAD48, $OPAD48;
            if ($IPAD16 === null) {
                $IPAD16 = str_repeat("\x36", 16);
                $OPAD16 = str_repeat("\x5C", 16);
                $IPAD48 = str_repeat("\x36", 48);
                $OPAD48 = str_repeat("\x5C", 48);
            }
            $keyCache[$secretKey] = substr(
                md5(($baseHash ^ $IPAD16) . $IPAD48, true) .
                md5(($baseHash ^ $OPAD16) . $OPAD48, true),
                0,
                24
            );
        }
        $lastKey = $secretKey;
        $lastDerivedKey = $keyCache[$secretKey];
    }

    // 4. Decrypt using OpenSSL (Zero IV)
    $decrypted = openssl_decrypt(
        $rawBinary,
        'des-ede3-cbc',
        $lastDerivedKey,
        OPENSSL_RAW_DATA,
        "\0\0\0\0\0\0\0\0"
    );

    // 5. Final check: Must end with "END"
    if ($decrypted === false || strlen($decrypted) < 3 || $decrypted[-1] !== 'D' || $decrypted[-2] !== 'N' || $decrypted[-3] !== 'E') {
        return false;
    }

    // Strip "END" and return the original message
    return substr($decrypted, 0, -3);
}

📌 Key Implementation Details

• Why the "END" suffix? Block ciphers like 3DES pad data with trailing null bytes (\0) to match block sizes. The "END" marker acts as a custom delimiter so the server knows exactly where the real data ends, while simultaneously serving as an integrity check to verify the correct password was used.
• Best Practices: Always transmit the encrypted Hex string via HTTP POST over an HTTPS connection. Avoid GET requests, as they leak encrypted payloads into server access logs and browser histories.