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Block cipher and modes of encryptions

Block cipher and modes of encryptions. Block cipher. Other name for fixed-length encryption scheme. Problem with just encrypting each block of the message using a randomized encryption scheme. Each block uses k bits of randomness If we have blocks, it requires bits of randomness.

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Block cipher and modes of encryptions

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  1. Block cipher and modes of encryptions

  2. Block cipher • Other name for fixed-length encryption scheme

  3. Problem with just encrypting each block of the message using a randomized encryption scheme • Each block uses k bits of randomness • If we have blocks, it requires bits of randomness. • Randomness is expensive

  4. Solution to minimize randomness • Create an initial state • May use some randomness (called Nonce or IV). • Encrypt the current block using the current state • Update the state after each use of the block cipher

  5. Goals (block cipher) • Security • Is it secure? • What level of security does it have? • Parallelizable: Can we encrypt/decrypt each block in parallel • We don’t need to wait for the previous part to encrypt the next part. • Forward: Do we need to use decryption operation • Better if we don’t • Error-resilient: If one block of the ciphertext becomes corrupted

  6. ECB mode

  7. Electronic codebook mode (ECB)

  8. Electronic codebook mode (ECB)

  9. Problem with ECB mode

  10. Counter mode (CM)

  11. Counter mode (CM)

  12. Counter mode

  13. Cipher block chaining

  14. Cipher block chaining (CBC)

  15. Cipher block chaining

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