Description

This detector identifies Kotlin code that encrypts data with AES-GCM using an authentication tag shorter than 96 bits. A truncated tag lowers the cost of forging ciphertexts, so an attacker can tamper with encrypted data and have it accepted as authentic, compromising its integrity.

Detection Strategy

• The code must import the javax.crypto.spec package

• The detector examines Cipher init calls made in encrypt mode and resolves the parameter specification argument

• It checks that the specification is a GCMParameterSpec and examines its first argument, the tag length in bits

• A vulnerability is reported when the tag length is a literal, or a variable that resolves to one, below 96 bits

• Tag lengths received as function parameters, and specifications used in decrypt mode, are not reported

Vulnerable code example

import java.security.SecureRandom
import javax.crypto.Cipher
import javax.crypto.spec.GCMParameterSpec
import javax.crypto.spec.SecretKeySpec

fun encrypt(keySpec: SecretKeySpec, data: ByteArray): ByteArray {
    val iv = ByteArray(12)
    SecureRandom.getInstanceStrong().nextBytes(iv)...

✅ Secure code example

import java.security.SecureRandom
import javax.crypto.Cipher
import javax.crypto.spec.GCMParameterSpec
import javax.crypto.spec.SecretKeySpec

fun encrypt(keySpec: SecretKeySpec, data: ByteArray): ByteArray {
    val iv = ByteArray(12)
    SecureRandom.getInstanceStrong().nextBytes(iv)...