HandshakeExchangeRequest
Second E2EE handshake step: the client's wrapped AES key.
RSA-OAEP of a 32-byte key is one modulus long, 684 Base64 characters for a 4096-bit key, so 1024 bounds every key the server may hold.
Attributes
attributeencrypted_session_keystr= Field(max_length=1024)