Is my data uploaded anywhere?

No. All processing happens locally in your browser with no server round-trip.

Does this tool work offline?

Yes. Once the page loads, the tool runs entirely client-side and needs no network connection.

Is this real ChaCha20 encryption?

Yes. It implements RFC 8439 exactly and is verified byte-for-byte against the RFC's official test vectors (quarter round §2.1.1, block function §2.3.2, encryption §2.4.2, Appendix A.1), cross-checked with OpenSSL.

What key and nonce sizes are required?

The key must be exactly 32 bytes and the nonce exactly 12 bytes, entered as UTF-8 text; other lengths are rejected with an explicit error. Never reuse a nonce with the same key — reusing the keystream makes the plaintext recoverable.

TOOL

ChaCha20 Decryptor

Decrypt ChaCha20 ciphertext (RFC 8439) — a real algorithm verified byte-for-byte against official RFC test vectors. Key must be exactly 32 bytes, nonce exactly 12 bytes, and the block counter must match the value used for encryption. Ciphertext input format follows the output format option (hex or base64). Free, private, and 100% client-side.

KeyNonceInitial counterOutput format

Input

Try an example:

Output

Local only

Recent history

No history yet

How to use

Paste the ChaCha20 ciphertext (hex or base64) into the input box.
Set the same key (exactly 32 bytes) and nonce (exactly 12 bytes) used for encryption.
Set the same initial block counter and choose the matching ciphertext format.
Copy the recovered plaintext.

Frequently asked questions

Is my data uploaded anywhere?: No. All processing happens locally in your browser with no server round-trip.
Does this tool work offline?: Yes. Once the page loads, the tool runs entirely client-side and needs no network connection.
Is this real ChaCha20 encryption?: Yes. It implements RFC 8439 exactly and is verified byte-for-byte against the RFC's official test vectors (quarter round §2.1.1, block function §2.3.2, encryption §2.4.2, Appendix A.1), cross-checked with OpenSSL.
What key and nonce sizes are required?: The key must be exactly 32 bytes and the nonce exactly 12 bytes, entered as UTF-8 text; other lengths are rejected with an explicit error. Never reuse a nonce with the same key — reusing the keystream makes the plaintext recoverable.

Glossary terms

ChaCha20

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