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XOR Cipher — Encode/Decode With a Repeating Key

XOR each byte of your text against a repeating key to encode or decode — a fast, simple cipher built from the same XOR operation cryptographers actually use inside real algorithms. The catch: it is only unbreakable in the specific case of a truly random key as long as the message, used exactly once (a one-time pad); a short repeating key, which is what most practical use of this tool means, is breakable through frequency analysis once the key length is found.

How to use XOR Cipher

  1. Paste your text.
  2. Enter your key.
  3. Read the encoded or decoded result.
  4. Use the same key to reverse the operation — XOR is its own inverse.

Frequently asked questions

Why is XOR encoding its own inverse?
XOR-ing the same value twice with the same key returns the original — a core property of the XOR operation, which is exactly why the same tool handles both encoding and decoding with no mode switch needed.
Is a repeating-key XOR cipher actually secure?
No — a short repeating key creates a periodic pattern that frequency analysis can exploit once the key length is deduced (similar to how the Vigenère cipher is broken), which is very different from the one-time-pad case where the key is truly random and as long as the message.
Where is real XOR encryption used?
XOR is a genuine building block inside real ciphers like AES, combined with far more sophisticated key scheduling and multiple rounds of transformation — it is the simplistic standalone repeating-key version that is weak, not the operation itself.

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