*kryptos*, which means hidden. If a message is intercepted by a third party who has everything needed to decrypt the message, the code is broken.

Named after Julius Caesar, who used a code for his military messages, the Caesar cypher was simple, yet it took years to break. All you do is substitute each letter in the alphabet by shifting it right or left by a specific number of letters.

A cryptarithm is a mathematical cypher that Alexander learned today. You turn any addition, subtraction, multiplication, or division problem into a cryptarithm by replacing letters with numbers.

Here is a cryptarithm for SEND MORE MONEY. Imagine yourself to be a spy and you need more money.

Rules: the only digits allowed are 0 – 9 with one carry forward. A carry forward is what happens when you add numbers with digits in the ones, tens, hundreds place, etcetera, that result in the number 10 or larger.

Set up this way:

SEND

+

__MORE__

MONEY

Now turn the letters into numbers, column by column (an X on the arrow means wrong move):