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Insecure encryption algorithm - Insecure Elliptic Curve

Need​

Upgrade to a secure elliptic curve algorithm

Context​

  • Requirement of PHP 7.0 or later for running the application
  • Usage of phpseclib/phpseclib for secure communication and encryption in PHP

Description​

Non compliant code​

<?php

namespace App\\Http\\Controllers;

use Illuminate\\Http\\Request;
use phpseclib\\Crypt\\RSA;
use phpseclib\\Math\\BigInteger;

class EncryptionController extends Controller
{
    public function encryptData(Request $request)
    {
        $rsa = new RSA();
        $rsa->setPublicKeyFormat(RSA::PUBLIC_FORMAT_OPENSSH);
        $rsa->setPrivateKeyFormat(RSA::PRIVATE_FORMAT_PKCS1);

        // Set weak elliptic curve
        $rsa->setHash('md5');
        $rsa->setMGFHash('md5');
        $rsa->setEncryptionMode(RSA::ENCRYPTION_PKCS1);

        $plaintext = $request->input('plaintext');

        $ciphertext = $rsa->encrypt($plaintext);

        return response()->json(['ciphertext' => base64_encode($ciphertext)]);
    }
}

The code above is a controller in Laravel that handles data encryption. The encryptData function receives a plaintext input from a request, encrypts it using RSA encryption, and returns the ciphertext.

The vulnerability lies in the usage of a weak hashing algorithm md5 in the encryption process. The setHash and setMGFHash functions are used to set the hashing algorithm for the RSA encryption. MD5 is considered weak due to its susceptibility to collision attacks, which means two different inputs can produce the same hash. This significantly reduces the security of the encryption.

The setEncryptionMode function is used to set the encryption mode to PKCS1. While PKCS1 is not inherently insecure, when used with a weak hashing algorithm like MD5, it can make the encryption process vulnerable.

This insecure encryption algorithm vulnerability could allow an attacker to decrypt the sensitive data by exploiting the weak MD5 hash. To fix this vulnerability, a stronger hashing algorithm like SHA-256 should be used instead.

Steps​

  • Replace the weak elliptic curve with a stronger one. The MD5 hash function is considered weak and should not be used for cryptographic purposes.
  • Use a stronger hash function for the setHash and setMGFHash methods. SHA-256 or SHA-3 are recommended.
  • Ensure that the encryption mode is set to a secure mode. RSA::ENCRYPTION_OAEP is a more secure mode than RSA::ENCRYPTION_PKCS1.
  • Regularly update the cryptographic libraries to the latest versions to benefit from the latest security patches and improvements.

Compliant code​

<?php

namespace App\\Http\\Controllers;

use Illuminate\\Http\\Request;
use phpseclib\\Crypt\\RSA;
use phpseclib\\Math\\BigInteger;

class EncryptionController extends Controller
{
    public function encryptData(Request $request)
    {
        $rsa = new RSA();
        $rsa->setPublicKeyFormat(RSA::PUBLIC_FORMAT_OPENSSH);
        $rsa->setPrivateKeyFormat(RSA::PRIVATE_FORMAT_PKCS1);

        // Set strong elliptic curve
        $rsa->setHash('sha256');
        $rsa->setMGFHash('sha256');
        $rsa->setEncryptionMode(RSA::ENCRYPTION_OAEP);

        $plaintext = $request->input('plaintext');

        $ciphertext = $rsa->encrypt($plaintext);

        return response()->json(['ciphertext' => base64_encode($ciphertext)]);
    }
}

The original code was using the MD5 hash function, which is considered weak for cryptographic purposes. This could lead to vulnerabilities where an attacker could potentially break the encryption.

In the fixed code, we have replaced the MD5 hash function with SHA-256, which is a much stronger hash function and is currently recommended for cryptographic purposes. This significantly reduces the risk of an attacker being able to break the encryption.

Additionally, we have changed the encryption mode from RSA::ENCRYPTION_PKCS1 to RSA::ENCRYPTION_OAEP. OAEP (Optimal Asymmetric Encryption Padding) is a more secure mode than PKCS1 and is recommended for new applications.

By making these changes, we have significantly improved the security of the encryption in the application. It is also recommended to regularly update the cryptographic libraries to the latest versions to benefit from the latest security patches and improvements.

References​

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