GameHandshakeResponse (0xA301)

This packet is sent in response to a GameHandshakeRequest, and is responsible for informing the client of the encryption mode to be used.

Payload

Data type	Name	Description
u8	status	The status of the handshake. A value of 0 indicates a success.
u8	encryptionMode	More research needed - the Ep4 PDB always specifies a value of 2.
u8[16]	expandedKeySeed	The seed to use for the XOR encryption used later in the game.

XOR Encryption

Upon handshaking with the client, the game server provdes an expandedKeySeed. This isn’t used straight away, but is instead used upon receiving the XorEncryptionSignal packet. The key is then used like so:

digest = SHA256(initial_aes_key)
expandedKey = expandedKeySeed.append(digest)

for (i = 1; i < 128; i++)
    // create a hash of the last 16 bytes of the expanded key
    len = expandedKey.length
    hash = SHA256(expandedKey[len - 16..len])
    expandedKey.append(hash)

for (i = 0; i < packet.length; i++)
    packet[i] ^= expandedKey[i]