Lecture 5:DES & Rivest-Shamir-Adelman (Feb 3)

We began the lecture by discussing how DES came to be unreasonable for encrypting messages when it was easy enough to crack it. Then, triple DES was introduced to cover this weakness. Triple DES is used with two separate keys. The first is used to encrypt, the second is used to decrypt, and finally the first is used to encrypt again. This creates a better encryption because these two keys need to be ordered the right way to decrypt the message, creating an exponential increase in the encryption. We then went over computational complexity and what P, NP, NP-Hard, and NP-Complete problems. Finally, we went over what is behind the Rivest-Shamir-Adelman encryption which uses two large prime numbers.

Lecture 4: Data Encryption Standard (DES) (Feb 1)

In today’s lecture we discussed the Data Encryption Standard. The DES algorithm is a combination of substitutions and transpositions. Product ciphers are created by the combination of two weaker ciphers. DES uses an initial permutation followed by 16 cycles of different shifts and swaps that increase the cipher texts security. Most of the class was spent diving into the granular details of the steps in the algorithm. The algorithm uses a series of look up tables that are all published. DES is used on 64 bit blocks with 56 bit keys. Decryption is just the inverse of the encryption by applying the 16 cycles in reverse order. For more in depth information about the DES algorithm see the Lecture 4 Ppt. Also Wikipedia has a ton of great information about the standard.