Encrypt and decrypt data using ChaCha20-Poly1305 AEAD cipher with authenticated encryption and nonce management.
ChaCha20-Poly1305 Encryption converts plaintext into authenticated ciphertext, or verifies and decrypts an existing result. The operation combines ChaCha20 encryption with a Poly1305 authentication tag, using a 256-bit key and a 96-bit nonce. The common mistake is treating the nonce as an optional random decoration. It need not be secret, but it must not be reused with the same key. Because keys and plaintext are sensitive, performing the operation entirely in the browser also avoids uploading them.
Encryption uses a 32-byte secret key and a 12-byte nonce. ChaCha20 transforms the plaintext into ciphertext, while Poly1305 produces a 16-byte authentication tag. The result therefore includes both encrypted bytes and evidence that the ciphertext has not been altered. Displayed text may be encoded as hexadecimal or Base64, which is a representation of the bytes rather than additional encryption.
Decryption requires the original key and nonce together with the complete ciphertext and authentication tag. If associated data was included during encryption, the identical bytes must also be supplied. A changed key, nonce, ciphertext, tag, or associated-data value causes authentication to fail. Plaintext from a failed verification must not be treated as valid.
No. ChaCha20-Poly1305 decryption needs the same nonce used for encryption, as well as the correct key, ciphertext, tag, and any associated data. The nonce does not need confidentiality, so it is normally retained with the encrypted result. Guessing a missing 96-bit nonce is not a practical recovery method.
At least one required byte differs from the encryption inputs. Check the key, nonce, ciphertext, authentication tag, associated data, and their encodings. Even a one-bit change should make verification fail. Authentication failure does not identify which field is wrong, and there is no valid partial plaintext to accept from that result.
The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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