Question

We have intercepted a message that we need to decode. Luckily, we know that they use the letters A to Z, space, 0 to 9. We also know that when they encode messages they start by shifting the first letter once to the left, then shift the next two letters right twice, then the next three letters left 3 times, then the next four letters right 4 times, the next five letters left 5 times, and so on.

a. If the message intercepted was 9EGPXK3CW what was the original message?

b. What would we get if we encoded the phrase AGENT 007 (the 0s are zeros) using the given algorithm?

Answer 1

a.

For decrypting the message, we need to follow the reverse process of encryption, as follows :

• 9
  • each character 1 times to right
  • so we get A
• EG
  • each character 2 times to left
  • so we get CE

• PXK
  • each character 3 times to right
  • so we get S<space>N
• 3CW
  • each character 4 times to left
  • so we get <space>8S

Thus, the decrypted message is

ACES N 8S

b.

For encrypting the message, we proceed as follows :

• A
  • each character 1 times to left
  • so we get 9

• GE
  • each character 2 times to right
  • so we get IG
• NT<space>
  • each character 3 times to left
  • so we get KQX
• 007
  • each character 4 times to right
  • so we get 44B

Thus, the encrypted message is

9IGKQX44B