• 08/20/2021

Overall structure – Block Ciphers and Their Modes of Operation

14.3.1 Overall structure AES has a fixed block length of 128 bits and, as required by the initial call for algorithms, a flexible key length of 128, 192, or 256 bits. AES is a substitution-permutation network consisting of 10, 12, or 14 rounds, depending on the key length. The 128 plaintext bits are arranged in…

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Modes 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…

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CBC 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…

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CBC-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…

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