RSTR-CRY-004 — ECB cipher mode

Summary

Electronic Codebook (ECB) encrypts every plaintext block independently with the same key. Identical plaintext blocks therefore produce identical ciphertext blocks — patterns in the plaintext (the famous ECB-penguin image) are visible in the ciphertext regardless of how strong the underlying cipher is.

ECB provides confidentiality of single blocks at best; it is never the right mode for application data.

Severity

High.

Languages

Java, Kotlin, Python.

What rastray flags

Java/Kotlin: Cipher.getInstance("AES/ECB/..."), Cipher.getInstance("DES/ECB/..."), etc.
Python: Crypto.Util.Cipher.MODE_ECB or AES.new(key, AES.MODE_ECB).

What rastray deliberately does not flag

GCM, CCM, CBC, CTR modes.
Stream ciphers (ChaCha20).

How to fix it

Use AES-GCM. It provides authenticated encryption (AEAD): confidentiality and integrity in one primitive, with a single per-message nonce:

// Java
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
cipher.init(Cipher.ENCRYPT_MODE, key,
    new GCMParameterSpec(128, nonce));
byte[] ct = cipher.doFinal(plaintext);

# Python (cryptography)
from cryptography.hazmat.primitives.ciphers.aead import AESGCM

aesgcm = AESGCM(key)
ct = aesgcm.encrypt(nonce, plaintext, aad)

Never reuse a (key, nonce) pair with GCM — generate the nonce from a counter or os.urandom(12) per message.

rastray rules