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Security Fundamentals & Crypto · Intermediate

Electronic Codebook (ECB)

Block cipher mode that encrypts each block independently, so identical plaintext blocks yield identical ciphertext.

Definition

ECB is the simplest mode but leaks patterns in the plaintext, as famously shown by the 'ECB penguin' image. It requires no IV and can be parallelized. It should not be used for more than one block of data.

Example

An image encrypted with AES-ECB still shows the outline of the original picture.

Exam tip

ECB is the wrong answer for any 'secure mode' question because it leaks patterns.

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