18.095 Lecture Notes - Lecture 1: Transport Layer Security, Block Cipher Mode Of Operation, Forward Secrecy
Document Summary
Completely secure if used properly; acts as a random mapping. Extremely insecure if used improperly, such as using a two-times pad. Key distribution and synchronization is a big problem. Can be vied as a generalization of a one time pad. The key steam is typically a pseudo-random sequence generally from a (reasonably short) seed. Security depends on how good the pseudo-random generator is. Key speci es a bijective function (a permutation) from the set of all pain text blocks to the set of all ciphertext blocks. Identical plaintext blocks always have identical ciphertext blocks. Symmetric encryption uses a shared secret key k = k. Typically the decryption key is secret, but the encryption key is not, making k public solves the key distribution problem. Initialization vector is a random block that need not be secret. Chaining allows a block cipher to behave like a stream cipher. Let n = pq be the product of two distinct primes.
