Category: Pseudorandom permutations
Key scheduling – Block Ciphers and Their Modes of Operation
14.3.3 Key scheduling As a round key is added to the 128-bit plaintext block before the first encryption round and at the end of each encryption round, the AES key k needs to be expanded into r + 1 different round keys ki, where each round key has 128 bits and r ∈{10,12,14}. Suppose k…
Read MoreModes of operation – Block Ciphers and Their Modes of Operation
14.4 Modes of operation In the previous sections, we have discussed in detail how a block cipher encrypts a single block of plaintext data. But how should we proceed when faced with a large number of blocks? There are several possible answers to this question, each coming with its own advantages and disadvantages. The different…
Read MoreCBC mode – Block Ciphers and Their Modes of Operation
14.4.2 CBC mode Cipher Block Chaining (CBC), illustrated in Figure 14.9, is a mode of operation that chains the ciphertext blocks. CBC encryption is probabilistic, meaning that two identical plaintext blocks will result in two different ciphertext blocks: Figure 14.9: Working principle of the CBC mode of operation The initial ciphertext block c0 is set…
Read MoreCBC-MAC – Block Ciphers and Their Modes of Operation
14.4.3 CBC-MAC Looking closely at Figure 14.9 again, we can see that the last cipher block c3 depends on all plaintext blocks m1,m2,m3. Of course this is also true for an arbitrary number of plaintext blocks. Therefore, one can construct a message authentication code over some plaintext message m called the CBC-MAC by encrypting m…
Read More