What is RC4?
RC4 decryption recovers the original data by XORing the ciphertext with the same keystream used to encrypt — so it uses the same key and the same operation as encryption. RC4 is a broken cipher, so use this only for legacy compatibility or learning; choose AES for security. Runs entirely in your browser.
Legacy only: RC4 is insecure. Use the same key that encrypted the data. Runs locally in your browser.
How RC4 works
RC4 decryption is identical to encryption:
- The key regenerates the same 256-byte state and keystream.
- Each ciphertext byte is XORed with a keystream byte.
- Because XOR is its own inverse, this restores the original plaintext.
How to use
- Paste the RC4 ciphertext.
- Enter the same key and settings used to encrypt.
- The decrypted text appears in the output.
Options explained
- Key / passphrase — Must be the same key used to encrypt.
- Encoding — Match the encoding of the ciphertext (Hex, Base64).
Common uses
- Reading RC4-encrypted legacy data.
- Interoperability testing.
- Education.
Frequently asked questions
Why doesn't my RC4 decrypt?
The key or the input encoding does not match what was used to encrypt.
Is RC4 safe?
No, it is broken — use AES for anything that matters.
How do I encrypt instead?
Use the RC4 Encryption tool.