Breaking any code involves
four basic steps:

1. determining the language used;
2. determining the system used;
3. reconstructing the key; and
4. reconstructing the plaintext.

Consider this cipher: Nffu nf bu uif qbsl bu oppo.

Now apply the four steps:

1. Determining the language allows you to compare the cipher text to the suspected language. Our cryptanalysts usually start with English.

2. Determining the system: Is this cipher using rearranged words, replaced words, or perhaps letter substitution? In this case, it’s letter substitution.

3. Reconstructing the key: This step answers the question of how the code maker changed the letters. In our example, every character shifted one letter to the right in the alphabet.

4. Reconstructing the plaintext: By applying the key from the previous step, you now have a solution: Meet me at the park at noon.