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Security Fundamentals & Crypto · Intermediate

Mode of Operation

A method that defines how a block cipher repeatedly applies its transformation to encrypt data longer than one block.

Definition

Modes of operation determine whether identical plaintext blocks produce identical ciphertext, whether encryption can be parallelized, and whether integrity is provided. Common modes include ECB, CBC, CTR, GCM, CCM, and XTS. Authenticated modes such as GCM and CCM are preferred for modern protocols.

Example

TLS 1.3 permits only AEAD modes such as AES-GCM and AES-CCM.

Exam tip

ECB is insecure for most data; GCM is the preferred general-purpose mode.

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