But now we're going to talk about what are called "block ciphers."

So those block ciphers are not considered secure enough for, like, way into the future.

Now, that's a perfect example of a very simple block cipher.

RC2 is a 64-bit block cipher with a variable size key.

For example, p might be the number of bits in a block cipher's key.

And older block ciphers had sometimes, for example, 64 bits was popular.

So 64-bit block ciphers are really no longer considered secure enough for industrial work.

In 2004, a fault attack was published on the block cipher.

RC2 is a 64-bit block cipher with a variable key size and using 18 rounds.

So but in terms of a symmetric block cipher, we've never looked inside one.