From the course: Symmetric Cryptography Essential Training
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The Data Encryption Standard (DES)
From the course: Symmetric Cryptography Essential Training
The Data Encryption Standard (DES)
- [Instructor] We're gonna talk about our first actual block cipher. This is the Data Encryption Standard. Before we do that though, we should talk about some of the goals of modern cryptosystems and how this standard tried to accomplish them. The first thing is that we want one key to be used many times without compromising security. We don't wanna be stuck in the position of having a one time pad where when we use a key, we can't use it again. We also wanna be able to use short keys to be able to encrypt long messages rather than having keys that are the length of the entire message. Modern cryptosystems meet both of these goals. One of the ways that we measure whether a cryptosystems has met these goals is with the Strict Avalanche Criterion. Strict Avalanche is a common consideration when block ciphers are designed. Each ciphertext bit should have a 50/50 chance of changing when the plaintext changes. If this criterion is satisfied, it means that the block cipher does a good job…
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