Double Cipher Decryption
Decrypt a message that has been encrypted twice using two different letter substitution mappings applied in sequence. You must reverse both encryption layers to recover the original message.
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Late April, 2026
Input is two known plain text / cipher text pairs. Each pair is produced using a fixed shift Caesar cipher. First shift gives you A -> B, and second pair gives you B -> C. A final message C -> A was encrypted twice using the two previous shifts. Decrypt the final message.
Late January, 2026
In a classroom setting, students are passing ciphered messages. You have intercepted a message from Carol intended for Alice. However, Carol is one of the smartest pupils and has applied a double layer of encryption to her message to keep it secret. The Mechanism The encryption follows the communication chain established in the classroom: Alice to Bob (AB): Alice sends messages to Bob using a specific letter substitution mapping. Bob to Carol (BC): Bob sends messages to Carol using a different letter substitution mapping. Carol’s message to Alice was ciphered twice: Layer 1: It was first ciphered using the mapping used for Bob to Carol. Layer 2: That result was then ciphered a second time using the mapping used for Alice to Bob.
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