Block Cipher Modes

Each block cipher consists of an algorithm for encryption and an algorithm for decryption. The mode of a block cipher describes the manner in which the algorithms will perform the encryption/decryption of blocks.

Multiple modes were invented:

• Providing confidentiality only: ECB, CBC, CTR, etc.
• Provide confidentiality and authentication: GCM, CCM, OCB, EAX, etc.
• Created for special purposes: CMC, EME, etc.

In these lecture notes, we will look into the ECB and CBC modes.

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ECB (Electronic Code Book) is the simplest mode: each block is encrypted separately by plugging the block plaintext into an encryption function that is given to you. Blocks can be encrypted in parallel (such as by using threads).