Serpent (cipher) facts for kids

Serpent is a special type of secret code, also known as a block cipher. Think of it like a very strong lock that uses a secret key to protect information. It was created by three smart people: Ross Anderson, Eli Biham, and Lars Knudsen.

Serpent was one of the top choices in a big worldwide competition called the Advanced Encryption Standard (AES) contest. This contest was held to find the best new way to keep digital information safe. Serpent came in second place, right after another code called Rijndael.

This secret code works by taking information in chunks, called "blocks," which are 128 bits long. It can use different secret keys that are 128, 192, or 256 bits long. The longer the key, the harder it is to break the code! Serpent uses a special method called a "substitution-permutation network" and does its work in 32 steps, or "rounds," to make sure the information is very secure.

One cool thing about Serpent is that it was designed to do many things at once, like working on 32 small pieces of information at the same time. This makes it very efficient and strong against attacks. The people who designed Serpent wanted it to be super secure, so they added extra steps. They thought 16 rounds would be enough, but they put in 32 rounds just to be extra safe!

The Serpent code is completely free for anyone to use. It has not been patented, which means no one owns it, and it's available for everyone in the public domain.

Serpent vs. Rijndael: Which is Better?

In the AES contest, Serpent was compared to Rijndael. Both are excellent ways to protect information, but they have some differences:

• Serpent uses 32 steps (rounds) to scramble information. It also has a starting and ending step to make it work smoothly.
• Rijndael uses fewer steps, usually 10, 12, or 14 rounds, depending on the key size. It can also handle different block sizes, not just 128 bits.

How They Scramble Information

Both codes use different ways to mix up the data:

• The main scrambling part in Rijndael mixes things up, moves them around, and combines them with the secret key using a special math trick called XOR.
• The main scrambling part in Serpent first mixes with the key using XOR. Then, it uses 32 small "S-boxes" (think of these as tiny secret lookup tables) at the same time. After that, it does a linear transformation, which is another way to mix the data. In the very last step, it just uses XOR with the key again.

Different S-boxes

• Rijndael uses one big 8x8 S-box to scramble information.
• Serpent uses 8 different 4x4 S-boxes. This means it has more variety in how it scrambles the data.

Because Serpent uses 32 rounds, it is generally considered more secure than Rijndael. However, Rijndael, with its fewer rounds, is faster and easier to use, especially for smaller devices or systems. This is why Rijndael was chosen as the winner of the AES competition.

How Secure is Serpent?

Some people have talked about a type of attack called the XSL attack that might make Serpent (and Rijndael) less secure. However, many experts believe that this attack would be very hard to do. It would likely be even harder than trying every possible key until you find the right one, which is called a brute force attack. So, Serpent is still considered a very strong and secure way to protect information.

See also

In Spanish: Serpent para niños