Archive/brook/protocol/brook-wsserver-protocol.md

brook wsserver protocol

Terminology

• DST Address: The address that the application actually wants to request, address contains IP/domain and port

  ATYP + IP/Domain + PORT
  

  • ATYP: 1 byte
    • 0x01: IPv4
    • 0x03: Domain
    • 0x04: IPv6
  • IP/Domain: 4/n/16 bytes
    • If ATYP is 0x01, then this is IPv4, 4 bytes
    • If ATYP is 0x03, then this is domain, n bytes, and the first byte is the domain length
    • If ATYP is 0x04, then this is IPv6, 16 bytes
  • Port: 2 bytes
    • Big Endian 16-bit unsigned integer

• KEY: AES key, 32 bytes

  • KEY: HKDF_SHA256(Password, Nonce, Info)
    • Password: User-defined password
    • Nonce: 12 bytes
    • Info: [0x62, 0x72, 0x6f, 0x6f, 0x6b]. Note that this can be overwrite by brook link --clientHKDFInfo and brook link --serverHKDFInfo

• HKDF: Defined in RFC 5869

• SHA256: Defined in FIPS 180-4

• AES: Defined in U.S. Federal Information Processing Standards Publication 197

• AES-GCM: Defined in RFC 5246, 5869

Client --TCP--> Server

[Standard WebSocket Protocol Header] + Client Nonce + [AES_GCM(Fragment Length) + AES_GCM(Fragment)]...

The maximum length of AES_GCM(Fragment Length) + AES_GCM(Fragment) is 2048 bytes

• Client Nonce: 12 bytes, randomly generated
  • The nonce should be recalculated when it is not used for the first time, the calculation method: add 1 to the first 8 bytes according to the Little Endian 64-bit unsigned integer
• Fragment Length: Big Endian 16-bit unsigned integer
• Fragment: Actual data being proxied
  • The first Fragment should be:

    Unix Timestamp + DST Address
    

    • Unix Timestamp: If it is not even, it should be increased by 1. Big Endian 32-bit unsigned integer

Server --TCP--> Client

[Standard WebSocket Protocol Header] + Server Nonce + [AES_GCM(Fragment Length) + AES_GCM(Fragment)]...

The maximum length of AES_GCM(Fragment Length) + AES_GCM(Fragment) is 2048 bytes

• Server Nonce: 12 bytes, randomly generated
  • The nonce should be recalculated when it is not used for the first time, the calculation method: add 1 to the first 8 bytes according to the Little Endian 64-bit unsigned integer
• Fragment Length: Big Endian 16-bit unsigned integer
• Fragment: Actual data being proxied

Client --UDP(UDP over TCP)--> Server

[Standard WebSocket Protocol Header] + Client Nonce + [AES_GCM(Fragment Length) + AES_GCM(Fragment)]...

The maximum length of AES_GCM(Fragment Length) + AES_GCM(Fragment) is 65507 bytes, but the maximum length if the first one is 2048 bytes

• Client Nonce: 12 bytes, randomly generated
  • The nonce should be recalculated when it is not used for the first time, the calculation method: add 1 to the first 8 bytes according to the Little Endian 64-bit unsigned integer
• Fragment Length: Big Endian 16-bit unsigned integer
• Fragment: Actual data being proxied
  • The first Fragment should be:

    Unix Timestamp + DST Address
    

    • Unix Timestamp: If it is not odd, it should be increased by 1. Big Endian 32-bit unsigned integer

Server --UDP(UDP over TCP)--> Client

[Standard WebSocket Protocol Header] + Server Nonce + [AES_GCM(Fragment Length) + AES_GCM(Fragment)]...

The maximum length of AES_GCM(Fragment Length) + AES_GCM(Fragment) is 65507 bytes

• Server Nonce: 12 bytes, randomly generated
  • The nonce should be recalculated when it is not used for the first time, the calculation method: add 1 to the first 8 bytes according to the Little Endian 64-bit unsigned integer
• Fragment Length: Big Endian 16-bit unsigned integer
• Fragment: Actual data being proxied