Above you see a picture of Bob. He has just received the encrypted
message you can see in the form above, and he is wondering where it came
from. You will be able to help him, because authenticity can be proven with
the aid of cryptography. This is how:
Bob knows that the message can come from one of three senders: Alice, Amy or
Anna. The cryptographic keys they use for communication with Bob are shown
above. If you enter a key in the box below, and press the "Decrypt" button,
Bob's crypto system will deliver the decrypted version of the message to him.
By experimenting with different keys, you should be able to determine who
sent the message. Press the correct button and you will progress to the next
stage of the demo...