A very primitive but popular type of encryption cipher is called what?

The correct answer is the rotation cipher, also known as a Caesar cipher. This type of encryption cipher is quite primitive, relying on a simple method of shifting the letters of the alphabet by a fixed number. For instance, using a rotation of three would mean that A becomes D, B becomes E, and so on. This simplicity makes it easy to understand, but also extremely easy to break with modern computational techniques.

In the context of encryption methods, the rotation cipher offers a foundation for understanding more complex ciphers. While it was widely used in ancient times, it is not considered secure today. In contrast, substitution and transposition ciphers involve more complex processes of altering the arrangement or replacement of characters, while block ciphers manage data in fixed-size blocks and utilize more sophisticated algorithms for security.