The example in the introduction used the same key for encryption and decryption. This is called Symmetric Cryptography. It is very fast, but Jack and Jones need to find a way to exchange their secret keys without Jane listening.
The advantages of symmetric cryptography are the high encryption and decryption speed. It is easy to calculate the decryption key with the knowledge of the encryption key, but the encryption key must be shared in a secure way, which is not possible with symmetric cryptography (thats the downside).
There are two kinds of symmetric cryptography systems, mono alphabetic ones and poly alphabetical ones. In mono alphabetic ones every element of the public vocabulary will always be represented with the same element of the private vocabulary.
There are several different symmetric cryptography systems available. The next few articles will explain a few of them.
- Permutation Cryptography
- Shift Cryptography
- Vigenere Cryptosystem
- Hill Cryptosystem