Understanding AES Modi von Operation

问题

You brauchen in select ein AES Modus aber sind unsure wie ECB, CBC, CTR, und GCM differ in Sicherheit und performance.

Voraussetzungen

• Understanding of AES block cipher
• Knowledge of IVs and padding

Schritte

1. 1. Review the mode characteristics

   ECB encrypts each block independently and leaks patterns. CBC chains blocks with an IV and requires padding. CTR turns AES into a stream cipher and needs no padding. GCM adds authentication on top of CTR. Each mode has different security properties and performance trade-offs.

   Eingabe

   modes: ECB, CBC, CTR, GCM

   输出

   GCM recommended for most uses

2. 2. Evaluate authentication needs

   If you need to detect tampering, use an authenticated mode like GCM or ChaCha20-Poly1305. CBC and CTR provide confidentiality only; an attacker can modify the ciphertext undetected. Adding an HMAC over the ciphertext is an alternative for non-GCM modes.

   Eingabe

   need integrity?

   输出

   use GCM or Encrypt-then-MAC

3. 3. Choose based on constraints

   For most modern applications, GCM is the default choice: it provides authenticated encryption and is hardware-accelerated. Use CTR for streaming contexts where authentication is handled separately. Never use ECB for more than a single block.

   Eingabe

   general purpose

   输出

   AES-256-GCM

Erwartetes Ergebnis

Ein informed choice von AES Modus das provides der needed Sicherheit Eigenschaften für your verwenden case.

Häufige Fehler

Using ECB for multi-block data

ECB leaks patterns. The famous ECB penguin image demonstrates how identical plaintext blocks produce identical ciphertext blocks. Use CBC or GCM instead.

Using CBC without authenticating the ciphertext

CBC is malleable. Apply an HMAC over the IV and ciphertext (encrypt-then-MAC) or switch to GCM.

Troubleshooting指引

• If performance is critical, GCM is hardware-accelerated on modern CPUs via AES-NI.
• If you need a stream cipher without padding, CTR mode is the right choice.

Sicherheitsgrenzen

• Always prefer authenticated encryption (GCM). Non-authenticated modes allow ciphertext manipulation.