1002. XOR Decryption: Single-Byte Key

Hard · String

A message has been XOR-encrypted with a single repeated byte key. Recover the plaintext.

Strategy: try every possible key byte (0–255). Score each candidate by the fraction of printable ASCII characters it produces. Return the candidate with the highest printable ratio.

Input (stdin, JSON): { "ciphertextHex": "1b3733331b6e2331..." }

Output (stdout): the recovered plaintext string.

Hint: this is the foundational primitive behind many CTF crypto challenges.

Examples

Example 1
Input: {"ciphertextHex":"1b37373331363f78151b7f2b783431333d78397828372d363c78373e783a393b3736"}
Output: Cooking MC's like a pound of bacon
Explanation: Cryptopals classic — single-byte XOR.

Constraints

• Hex input, length 2..2048.
• Plaintext is printable ASCII.