decrypting the encrypted salt for HAFAS MAC params

0-about.md

• discussion
• CyberChef recipe
• interactive Node.js version

run Node.js code:

const decryptMACSalt = require('./decrypt-mac-salt')

const decrypted = decryptMACSalt('rGhXPq+xAlvJd8T8cMnojdD0IoaOY53X7DPAbcXYe5g=')
console.log(decrypted.toString('hex'))

run Java code:

javac MACSaltDecrypter.java
java MACSaltDecrypter rGhXPq+xAlvJd8T8cMnojdD0IoaOY53X7DPAbcXYe5g=

1-decrypt-mac-salt.js

'use strict'

const crypto = require('crypto')

// todo: is this the same for all HAFAS endpoints?
const key = Buffer.from('61483646387a527569426e6d33336655', 'hex')
const iv = Buffer.alloc(16, 0)

const decryptMACSalt = (encryptedSalt) => {
	const decipher = crypto.createDecipheriv('aes-128-cbc', key, iv)

	return Buffer.concat([
		decipher.update(Buffer.from(encryptedSalt, 'base64')),
		decipher.final()
	])
}

module.exports = decryptMACSalt

2-MACSaltDecrypter.java

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import javax.crypto.spec.IvParameterSpec;
import java.util.Base64;
import java.nio.charset.StandardCharsets;

class MACSaltDecrypter {
	public static byte[] decrypt(byte[] hci) {
		try {
			byte[] key = new byte[]{ 97, 72, 54, 70, 56, 122, 82, 117, 105, 66, 110, 109, 51, 51, 102, 85 };

			SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
			Cipher instance = Cipher.getInstance("AES/CBC/PKCS5Padding");
			instance.init(Cipher.DECRYPT_MODE, secretKeySpec, new IvParameterSpec(new byte[16]));

			return instance.doFinal(Base64.getDecoder().decode(hci));
		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	public static void main (String[] args) {
		byte[] encrypted = args[0].getBytes(StandardCharsets.UTF_8);
		byte[] decrypted = MACSaltDecrypter.decrypt(encrypted);

		StringBuilder asHex = new StringBuilder(decrypted.length * 2);
		for (byte b: decrypted) asHex.append(String.format("%02x", b));
		System.out.println(asHex.toString());
	}
}