Ease Me Into Cryptography Part 2: Symmetric Ciphers

In the first article in this series on the basics of crypto, “Ease Me Into Cryptography Part 1: Buzzwords and Hash Function“, we learned some lingo and talked about the different aspects of hash functions. Remember that hash functions are one-way — we cannot reverse them algorithmically. We talked about why this is useful, however let’s get to something that we can encrypt AND decrypt. In cryptography, we call these ciphers. Just like in the last section, and in true “Explain Like I’m Five” fashion, let’s break this down. What is a cipher? What are symmetric ciphers? How are they useful? Are there any weaknesses?

More Terms

First, let’s introduce a few more terms that will come into play in this article:

• A key is a piece of information used as input into an encryption or decryption algorithm in addition to the data that needs to be transformed. The data cannot properly be transformed without the proper key data.
• Symmetric Ciphers are a family of ciphers that uses the same key to encrypt as it does to decrypt; these are sometimes referred to as secret key algorithms because if the key is the same on both sides, it needs to be kept secret so that not just anyone can decrypt it.
• Asymmetric Ciphers are a family of ciphers that uses a different key to encrypt than it did to decrypt; these are sometimes referred to as public key algorithms because when the encrypting and decrypting keys are different, that allows for one to be public without compromising the correctness/privacy of decryption.
• Block Size refers to the size of chunks that an algorithm will chop data into in order to process it.
• Padding is a process that adds to data of an improper size (i.e. not a multiple (Read more...)