Description

This detector identifies hardcoded nonces used with AEAD (Authenticated Encryption with Associated Data) ciphers in Elixir code. Using a fixed nonce with AEAD encryption compromises the security guarantees of the cipher, potentially allowing attackers to recover plaintext or forge authenticated messages.

Detection Strategy

• The detector scans for specific function calls that match a predefined AEAD encryption pattern (likely functions like :aes_gcm.encrypt or similar)

• It examines the cipher argument at a specific position to verify it's an AEAD cipher type (such as :aes_256_gcm)

• It checks the initialization vector (IV/nonce) argument at another specific position to determine if it contains a hardcoded value

• A vulnerability is flagged when both conditions are met: the function uses an AEAD cipher AND the nonce/IV parameter is a hardcoded literal value rather than a dynamically generated one

Vulnerable code example

defmodule VulnerableAead do
  def encrypt_with_hardcoded_nonce(key, data, aad) do
    # Hardcoded nonce breaks AEAD security - nonces must be unique per encryption
    :crypto.crypto_one_time_aead(:aes_256_gcm, key, "000000000000", data, aad, true)
  end

  def encrypt_with_static_nonce(key, data, aad) do
    nonce = "000000000000" # Static nonce allows attacks on encrypted data...

✅ Secure code example

defmodule SecureAead do
  def encrypt_with_random_nonce(key, data, aad) do
    nonce = :crypto.strong_rand_bytes(12) # Generate unique nonce per encryption
    :crypto.crypto_one_time_aead(:aes_256_gcm, key, nonce, data, aad, true)
  end

  def encrypt_with_parameter_nonce(key, nonce, data, aad) do
    # Nonce from caller ensures uniqueness responsibility is external...