Our current ratchet key pair (hex-encoded).
Our current ratchet public key (hex-encoded).
Their current ratchet public key (hex).
Root key (hex, 32 bytes).
Sending chain key (hex, 32 bytes).
Receiving chain key (hex, 32 bytes).
Number of messages sent in current sending chain.
Number of messages received in current receiving chain.
Previous sending chain length (for header).
Skipped message keys: Map<"pubkey:messageNum", messageKeyHex>.
Serializable state of a Double Ratchet session.