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Insecure encryption algorithm - Cipher Block Chaining

Need​

Implementation of secure encryption algorithms with strong cipher block chaining

Context​

  • Usage of Go 1.16 for developing high-performance and efficient applications
  • Usage of crypto/aes for AES encryption and decryption
  • Usage of crypto/cipher for encryption and decryption operations
  • Usage of crypto/rand for generating random numbers and cryptographic operations
  • Usage of fmt for formatting strings and values
  • Usage of socket.io for real-time communication between client and server

Description​

Non compliant code​

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"fmt"
	"io"
)

func main() {
	text := []byte("This is a text that needs to be encrypted")
	key := []byte("mysecurepassword")

	block, err := aes.NewCipher(key)
	if err != nil {
		fmt.Println(err)
		return
	}

	ciphertext := make([]byte, aes.BlockSize+len(text))
	iv := ciphertext[:aes.BlockSize]
	if _, err := io.ReadFull(rand.Reader, iv); err != nil {
		fmt.Println(err)
		return
	}

	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(ciphertext[aes.BlockSize:], text)

	fmt.Printf("%x\\n", ciphertext)
}

In this code snippet, we are creating an AES cipher with a key and then using this cipher in Cipher Block Chaining (CBC) mode to encrypt some text.

The problem lies in the usage of the CBC mode. In CBC mode, each block of plaintext is XORed with the previous ciphertext block before being encrypted. This means that the encryption of each block depends on all the previous blocks. As a result, errors or manipulations in a block affect all subsequent blocks which can lead to serious security vulnerabilities.

Moreover, CBC mode is vulnerable to padding oracle attacks when used without a proper integrity check mechanism. A padding oracle attack allows an attacker to decrypt the ciphertext just by analyzing the server's responses to crafted ciphertexts.

To fix this vulnerability, it's recommended to use a more secure mode of operation like GCM (Galois/Counter Mode) which provides both confidentiality and integrity.

Steps​

  • Replace the insecure encryption algorithm with a secure one.
  • Use a secure mode of operation for the encryption algorithm.
  • Generate a strong and random initialization vector (IV) for each encryption operation.
  • Ensure that the encryption key used is strong and securely stored.
  • Implement proper error handling and logging for encryption operations.

Compliant code​

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"fmt"
	"io"
	"golang.org/x/crypto/chacha20poly1305"
)

func main() {
	text := []byte("This is a text that needs to be encrypted")
	key := []byte("mysecurepassword")

	aead, err := chacha20poly1305.NewX(key)
	if err != nil {
		fmt.Println(err)
		return
	}

	nonce := make([]byte, chacha20poly1305.NonceSizeX)
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		fmt.Println(err)
		return
	}

	ciphertext := aead.Seal(nil, nonce, text, nil)

	fmt.Printf("%x\\n", ciphertext)
}

The original code was using AES encryption in CBC mode, which is considered insecure due to its vulnerability to various attacks such as padding oracle attacks.

The updated code uses the ChaCha20-Poly1305 AEAD (Authenticated Encryption with Associated Data) cipher, which is currently considered to be secure. AEAD ciphers provide confidentiality, integrity, and authenticity, which makes them a good choice for many cryptographic applications.

The key used for the cipher is the same as before, but it should be noted that in a real-world application, this key should be securely generated and stored, and not hardcoded as it is here.

The initialization vector (IV), here called a nonce, is randomly generated for each encryption operation. This is important as reusing a nonce with the same key can completely break the security of the cipher.

Finally, the encryption operation itself is performed with the Seal method of the AEAD cipher. This method encrypts and authenticates the plaintext, and also authenticates any additional associated data (none in this case). The resulting ciphertext includes the authentication tag, which can be used to verify the integrity and authenticity of the data when decrypting.

The error handling in the code ensures that any issues with the encryption operation are caught and logged. This is important for diagnosing issues and for security, as it can help to identify any attempted attacks or other malicious activity.

References​

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