ChaCha20-Poly1305 decrypt

Decrypt a file produced by ChaCha20-Poly1305 encrypt, on your device.

ChaCha20-Poly1305 decrypt reverses ChaCha20-Poly1305 encrypt, reading the 16-byte salt and 12-byte nonce stored ahead of the ciphertext and rebuilding the same PBKDF2 key. A file shorter than 44 bytes, salt, nonce and Poly1305 tag combined, is refused outright. A wrong password and a tampered ciphertext produce the identical decryption-failed message, so the two causes cannot be told apart.

Questions

What does it read from the file?

The 16-byte salt and the 12-byte nonce stored at the start, then rebuilds the same PBKDF2 key from your password and that salt.

Why did I get "decryption failed"?

Either the password is wrong or the file is corrupted or was never encrypted with this tool; the message does not say which.

What is the minimum valid file size?

44 bytes: 16 for the salt, 12 for the nonce, and 16 for the Poly1305 authentication tag. Anything shorter is refused before decryption is attempted.

How is the output named?

By stripping the .chacha20p1305 suffix if present, or adding .dec otherwise.

Can I use this from the command line?

Yes, the same code runs on the page, the CLI and MCP.

Related Crypto tools

n→nAES-GCM encryptEncrypt a file with AES-256-GCM under a password.n→nAES-GCM decryptDecrypt a file produced by AES-GCM encrypt.n→nAES key wrap (RFC 3394)Wrap a raw key under a key-encrypting key (AES-KW).n→nAES key unwrap (RFC 3394)Unwrap a key that was wrapped with AES-KW.n→nRSA-OAEP encryptEncrypt a small file with an RSA public key (RSA-OAEP).n→nRSA-OAEP decryptDecrypt a file produced by RSA-OAEP encrypt, with the matching private key.n→nChaCha20-Poly1305 encryptEncrypt a file with ChaCha20-Poly1305 under a password.n→nXChaCha20-Poly1305 encryptEncrypt a file with XChaCha20-Poly1305 under a password.