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Security Fundamentals & Crypto · Foundational

Ciphertext

The unreadable, encrypted output of a cipher that requires the correct key to decrypt.

Definition

Ciphertext should reveal no useful information about the plaintext other than possibly its length. Strong ciphers produce ciphertext that is indistinguishable from random data. Ciphertext integrity must be protected separately or by using authenticated encryption.

Example

Encrypting 'HELLO' with AES-GCM yields a string of random-looking bytes plus an authentication tag.

Exam tip

Encryption without authentication can allow undetected ciphertext tampering; prefer AEAD modes.

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