@spec decrypt(binary(), binary()) :: {:ok, String.t()} | {:error, atom()}

Decrypts a payload using a pre-computed conversation key.

Parameters

• payload: Base64-encoded encrypted payload
• conversation_key: 32-byte conversation key (raw bytes)

Returns

• {:ok, plaintext} on success
• {:error, reason} on failure

@spec decrypt(binary(), binary(), binary()) :: {:ok, String.t()} | {:error, atom()}

Decrypts a payload using the recipient's secret key.

Parameters

• payload: Base64-encoded encrypted payload
• seckey: Recipient's secret key (hex-encoded)
• pubkey: Sender's public key (hex-encoded, x-only)

Returns

• {:ok, plaintext} on success
• {:error, reason} on failure

@spec encrypt(String.t(), binary()) :: binary()

Encrypts plaintext using a pre-computed conversation key.

Parameters

• plaintext: The message to encrypt (1-65535 bytes)
• conversation_key: 32-byte conversation key (raw bytes)

Returns

Base64-encoded encrypted payload

@spec encrypt(String.t(), binary(), binary()) :: binary()

Encrypts plaintext for a recipient using their public key.

Parameters

• plaintext: The message to encrypt (1-65535 bytes)
• seckey: Sender's secret key (hex-encoded)
• pubkey: Recipient's public key (hex-encoded, x-only)

Returns

Base64-encoded encrypted payload

@spec encrypt_with_nonce(String.t(), binary(), binary()) :: binary()

Encrypts plaintext using a conversation key and specific nonce.

This function is primarily for testing with deterministic nonces. In production, use encrypt/2 or encrypt/3 which generate random nonces.

Parameters

• plaintext: The message to encrypt (1-65535 bytes)
• conversation_key: 32-byte conversation key (raw bytes)
• nonce: 32-byte nonce (raw bytes)

Returns

Base64-encoded encrypted payload

@spec get_conversation_key(binary(), binary()) :: binary()

Computes the conversation key between two parties.

The conversation key is symmetric: get_conversation_key(a, B) == get_conversation_key(b, A)

Parameters

• seckey: Secret key (hex-encoded)
• pubkey: Public key (hex-encoded, x-only)

Returns

32-byte conversation key (raw bytes)

@spec get_message_keys(binary(), binary()) :: {binary(), binary(), binary()}

Derives message-specific keys from conversation key and nonce.

Parameters

• conversation_key: 32-byte conversation key (raw bytes)
• nonce: 32-byte nonce (raw bytes)

Returns

Tuple of {chacha_key, chacha_nonce, hmac_key}