Caesar Cipher

Encryption here goes as follows: take the plain text, and shift every letter in it by a constant number of letters. For example, if a shift size is 3, then every instance of the letter A will be replaced D, the letter B will be replaced by E, etc., in a circular manner (Z will be replaced by C.)

To decrypt such text, one needs to know that the shift size is 3, and simply perform the opposite operation: 'subtract' 3 from every letter (A will be replaced by X, B will be replaced by Y, etc.,) which will return the plain text.

For example, given the cipher text: uryyb jbeyq, if you know that the original shift size was 13, you can decrypt this text back to plain text by subtracting 13 from each letter, thereby getting: hello world.

Because there are only 26 letters in the English alphabet, there are only 26 possible shift sizes. This means anyone is able to manually check against each one of the shifts within a few minutes to 'crack' the plain text even without being told what the shift size is. As you might guess, it means that the Caesar Cipher is weak.