This represents the individual block of plaintext. The size depends on the specific block cipher being used. For instance, if DES is being used, the size of each block will be 64 bits. - Block of plaintext, This symbol fittingly represents the encryption key, which again is based on the specific cipher being used. - Key Symbol, This represents the encryption or cipher process, i.e., where the key is applied to encipher inputs. - Encryption Function, This represents an initialization vector (IV) used to incorporate randomness. With CTR mode you will see an alternative method to achieve this annotated by similar green boxes. - IV Symbol, This symbol annotates the exclusive or (X-OR) function. - ⊕ Circle with plus sign , This represents the resultant ciphertext output from a given stage. - Ciphertext, Most basic, weak, and unsecure mode. Each block is processed separately. No Salt or IV is used and the same key will be used to encrypt each block. This means if a given plaintext is encrypted in ECB and results in a given ciphertext, that same ciphertext will be output EVERY TIME the same plaintext is encrypted. - Electronic Code Book (ECB), Minor step up from ECB with the incorporation of an initialization vector for the first block. Results of encryption from previous block is input into to encryption process of the current block. - Cipher Block Chaining (CBC), Converts the block cipher into a self-synchronizing stream cipher. Current block takes output of the XOR ⊕ process vs from the cipher stage of the previous block (difference between CFB and OFB). - Cipher Feedback (CFB), Converts the block cipher to a synchronous stream output. Current block takes output from the cipher stage vs from the output of the XOR process of the previous block (difference between CFB and OFB). The first stage takes the data blocks and X-ORs it with the encrypted version of the IV value. The output of the first stage encryption is then feed into the next stage, and encrypted, with the output being X-OR’ed with the second block.  - Output Feedback (OFB), Converts the block cipher into a stream cipher. Generates a counter value and a nonce, and encrypts this, in order to EX-OR with the plain text block. The advantage of CTR that each block is processed independent of the others, facilitating ability to conduct parallel processing of blocks. i.e., feedback from other stages to feed into the current one is not required. - Counter Mode (CTR),

D334-Chapter 2 Block Cipher Modes Basic Components

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