This is a message encrypted using the Caesar cipher. This encryption technique was used by Julius Caesar during the reign of the Roman Empire to “encrypt messages of military significance.” This is one of the oldest and simplest methods of encryption known to us today.
You can try this out yourself by moving some letters forward in the alphabet. An ‘A’ turns into a ‘B’, ‘B’ into ‘C’, ‘C’ into ‘D’, et cetera. In this case, “Hello!” would become “Ifmmp!” That is just using a shift of one. You can use a shift of seven, for example, and then you would shift letters like so:
A -> +7 -> H
Q -> +7 -> X
T -> +7 -> A
When you reach the end of the alphabet, wrap around to the beginning to find the encrypted letter.
Let’s setup a little story to illustrate the problems of encryption. We will have three characters:
Alice really likes Bob and wants to tell Bob her feelings, so she writes “I love you, Bob! Please eat healthier!” on a sticky note. She passes it to Eve, so Eve can pass it to Alice’s love interest. However, in an unfortunate turn of events Eve reads the note herself, and decides not to give it to Bob.
Oh the horror! Alice is without young love! How could she remedy this so that Bob can read her message, but evil Eve can not? Let’s use the Caesar cipher to fix this problem.
Let us assume that Alice and Bob already have a shared key, 7 for example. To encrypt this message, she should shift her letters seven letters forward in the alphabet—just like the example above.
Now Alice’s message reads “P svcl fvb, Ivi! Wslhzl lha olhsaoply!”
Now, when Alice sends her Romeo a little note, all he has to do is decrypt the text by shifting the letters down by 7. Here is a site which can do longer pieces of text for you instead of doing it manually.
Before the two love-birds start smooching on the branch of a big pine tree in the schoolyard, perhaps we should consider some problems with the Ceasar cipher.
Even Eve with her measly grade 4 math skills could easily start going through this message with pen and paper and figure out any combination in a couple hours at maximum. Imagine how easy this is for a computer? This could be broken in a few microseconds even on an older processor like the Intel Core 2 Duo.
We assumed in our previous example that Bob and Alice already have a shared key (seven) to encrypt and decrypt all of their messages. If Bob and Alice did not have a previous friendship and time to share secrets of this sort, there is no way to share their key with eachother without Eve also knowing. This would defeat the entire purpose of obscuring the message in the first place.
Every message sent between the two parties uses the same code to encrypt and decrypt. If someone finds out the code once, all previous communications are comprimised.
To combat the issues with easily breakable, shared-key cryptography, we can turn to the beautiful beast that is Asymetric Cryptography. I will discuss this more in another article, but for the technically inclined: