Introduction to Cryptography and its History Quiz

Answer: mlqa

J is replaced by m since m is three letters after j. Similarly, i is replaced by l and n by q. To go three letters after x, we loop around and get back to a.

Answer: Somebody help me

If you encode a message by going 3 letters later in the alphabet, you decode it by undoing that and going back 3 letters. V goes back to S, R goes back to O and so on. To go back 3 letters from B, you wrap back around the alphabet.

Answer: The fort is under attack

The key is to look at one of the short words ... trying some common three letter words as aol, we see that if "the" is moved forward 7 letters, we get aol. After that, decryption is fairly easy.

Answer: about 4 times 10 to the 26th (400 septillion American, 400 quadrillion European)

Obviously, it is no longer possible for the enemy to simply try every possible method of decoding the message. Nevertheless... (see next answer)

Answer: False

This may seem surprising, until you think about it. The key is to use what is called frequency analysis. Some letters are used more in any language than others are (In english, for example, e is used more often than any other letter). If e is always replaced by the same letter, than the letter which occurs most often in the coded message is probably the one that e is replaced by.

Many letters don't appear as double letters, further narrowing things down. Finally, if a 3 letter word appears 25 or 30 times a page, odds are its "the".

Answer: U

It is likely that C represents the letter Q, both because it occurs so rarely and because it is always followed by the same letter. Given that, the M simply has to represent the U. This code isn't nearly as secure as it seems at first glance! To counteract this, some mathematicians in the 15th to 16th century created codes which change over the course of a message. M may represent U in one sentence, but it may represent T in the sentence after it.

This makes the code much more difficult to break, though not impossible.

Answer: Telegraph

Telegraphs enabled people to send messages at a much faster rate over much longer distances than horses and riders. Unfortunately, they were also much more vulnerable to eavesdropping. If military commanders were to use this new method of communication, they needed a way to make sure their secret plans stayed secret.

Answer: Enigma

This also marked one of the first uses of (primitive) computers to break codes ... Alan Turing was one of the chief mathematicians on site. Even though the British knew a method of breaking the code, the Germans were able to thwart their efforts somewhat by changing the code slightly each day.

It would take the British and their computers half a morning (or sometimes more) to break the new code, so messages were safe ... for an hour or two, at least.

Answer: Prime Numbers

Basically RSA works as follows: Each person published what is known as a public key, a number that is known to everyone. Messages are converted to series of numbers, and each number is taken to the power of the public key. The only (practical) way to undo this operation is to take the numbers in the coded message to a certain other power.

The only way you can know this number is by knowing the factorization of the public key. What makes this code special is that even the person who encodes this message doesn't know how to decode it.

It is (for now) secure in that even eavesdroppers can't decode it.

Answer: Quantum Computer

Quantum computers were first suggested by Richard Feynmann (of "Surely you're joking!" and bongo drum fame). Shor's method relies on a quantum computer being able to store much more information at a time (as a superposition of a large number of what are known as "Quantum states"). All is not lost, however.

Other people have suggested methods of using quantum mechanics to create even more secure codes. The battle goes on!