@spec aead_decrypt(binary(), key(), nonce(), binary(), tag()) :: binary() | :error

authenticated encryption with additional data - decryption

• encrypted message
• shared secret key
• one-time use nonce
• additional authenticated data
• MAC

On success, returns the plaintext message. If the message cannot be authenticated :error is returned.

@spec aead_encrypt(binary(), key(), nonce(), binary()) :: {binary(), tag()}

authenticated encryption with additional data - encryption

• message to be encrypted
• shared secret key
• one-time use nonce
• additional authenticated data

The return value will be a tuple of {ciphertext, MAC}

The algorithm is applied as described in RFC7539:

• The key and nonce are used to encrypt the message with ChaCha20.
• The one-time MAC key is derived from the cipher key and nonce.
• The ciphertext and additional data are authenticated with the MAC

@spec hmac(binary(), key()) :: tag()

Compute a Message authentication code

The one-time key should never be reused.

@spec same_hmac?(binary(), binary()) :: boolean()

compare two HMACs in constant time