Late night ramblings about symmetric encryption…

Hello again,

This will be a shorter post today, I have several things I still need to get done and its getting late, but I wanted to get at least a little bit of what I have been studying down on paper, and hopefully have it make sense to anyone who reads it.

Tonight, I want to start talking about symmetric cryptography. As you can imagine, something that is “symmetric” is the same on both sides or mirrored if that makes more sense. The same principle applies with symmetric key cryptography, in that both the key to encrypt and the key to decrypt are the same key. This differs from asymmetric key cryptography, in that asymmetric key cryptography has a “key pair”, a private key, and a public key, but I will talk about that at a later point.

Symmetric encryption can be expressed mathematically as: C=E(k,p)

“C” stands for the ciphertext, “E” stands for the encryption function, “k” stands for the key, and “p” is the plaintext.

Symmetric decryption is expressed as: P=E(k,c)

An important topic to point out, that I think fits well here, is Kerckhoffs’s principle. Back in 1883, Aguste Kerckhoff proposed that a cryptography system should be so secure, that even if all parts of the system are public knowledge, if the key is secure (not public knowledge), then the system is secure.

Unfortunately, that is it for tonight. Next time I will talk about Horst Feistel, and the Feistel network. I will also go over a couple of the more well-known symmetric encryption standards (DES, 3DES, DESx, AES, etc.)