The Data Encryption Standard, or DES, is an historic encryption algorithm designed and implemented by IBM in the 1970s with the purpose of serving as a standard encryption algorithm for unclassified communication throughout the federal government. In this video, learn how DES implements encryption and decryption, as well as the flaws in this approach.
- [Instructor] Modern symmetric algorithms are much more complex than the simple substitution and transposition ciphers of years past. One of the most well-known symmetric algorithms is the Data Encryption Standard or DES. DES is a historic encryption algorithm designed and implemented by IBM in the 1970s with the purpose of serving as a standard encryption algorithm for unclassified communication throughout the federal government.
Up until that point, different agencies used different encryption algorithms. This caused issues with both security because all of those algorithms weren't thoroughly tested and interoperability because different agencies couldn't easily communicate with each other in a secure manner. Let's dig into how DES works because it serves as a great example of the complexity of modern cryptographic algorithms. This picture shows the basic functioning of DES.
It takes 64 bits of plain text as input in the top and then runs it through an encryption operation known as the Feistel function. Those are those yellow boxes with the F's inside of them. It uses the Feistel function 16 different times in order to produce the cipher text. And here's a view inside one of those F boxes. Each of these F boxes that implements the Feistel function takes half a block of input or 32 bits and combines it with a piece of the 56-bit encryption key.
That's happening at the red icon in the middle of this image. Then the output of that function is broken up into eight segments and fed into eight different functions called S boxes, these yellow boxes labeled S1 through S8 that just appeared on the screen. S stands for Substitution and each one of these boxes contains a different substitution cipher. The results of all of those substitutions are then combined back together again and fed into a P box, the green box that just appeared.
P stands for Permutation which is just another term for transposition. So the output of all of those S boxes is scrambled up to produce the cipher text. That's a pretty complex encryption operation. And don't forget, that complexity inside the F box is repeated 16 times on any block of input. DES was used widely throughout the government and the private sector for decades. But today, it is no longer considered secure.
Mathematicians and cryptologists have published papers containing several effective attacks against the DES algorithm and it is no longer recommended for use. You'll need to learn about many different encryption algorithms for the exam so let me sum up here with some key facts that you should know about DES. DES is a symmetric encryption algorithm. It is a block cipher that works on 64-bit blocks using a 56-bit key.
And DES is now considered insecure.
- Symmetric and asymmetric cryptography
- Reviewing the four major goals of cryptography
- Cryptographic math
- Choosing encryption algorithms
- Symmetric cryptography
- Common cipher modes
- Elliptic curve and quantum cryptography
- Public key infrastructure
- Creating and revoking a digital certificate
- Brute force and knowledge-based attacks
- Digital rights management