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OSTP — Ospab Stealth Transport Protocol

Русский язык · Wiki · Contributing · Releases · Migration Guide

OSTP (Ospab Stealth Transport Protocol) is an encrypted transport protocol written in Rust. It implements a custom ARQ transport over UDP and a UDP-over-TCP (UoT) mode. The protocol uses cryptographic masking for all packet headers and payloads to resist traffic classification by Deep Packet Inspection (DPI) systems.

[!IMPORTANT] Upgrading from v0.2.x? Please read the v0.3.1 Configuration Migration Guide.

Technical Capabilities

Capability	Description
Traffic Masking	Header and payload encryption using per-packet HMAC-derived keys. Indistinguishable from random noise.
Noise Protocol	`Noise_NNpsk0_25519_ChaChaPoly_BLAKE2s` — PSK-authenticated, forward-secret key exchange.
Reliable UDP (ARQ)	Selective ACK/NACK with rate-limited retransmission, configurable reorder buffer, and exponential backoff.
Multiplexed Streams	Multiple logical TCP streams over a single encrypted UDP session with per-stream flow control.
Session Roaming	Connection persistence across IP changes via session ID tracking.
UoT Mode	UDP-over-TCP encapsulation with length-prefixing to bypass UDP blocking.
Fallback Server	TCP proxying to a legitimate web server to resist active probing.
TUN Mode	Native network stack integration (`smoltcp`) for full-system routing without external dependencies.
Management API	Built-in REST API for server administration, metrics, and key generation.
TURN Relay	RFC 5766 TURN support for NAT traversal.

Architecture

flowchart LR
    Apps[Local Apps] -->|SOCKS5 / TUN| CoreC

    subgraph Client [Client Node]
        CoreC[OSTP Client] -.->|Encrypt & Mask| NetC[Transport Layer]
    end

    NetC <==>|Encrypted UDP / UoT| NetS

    subgraph Server [Server Node]
        NetS[Transport Layer] -.->|Decrypt & Auth| CoreS[OSTP Server]
        NetS -->|Unauthenticated| Fallback[Fallback Server]
    end

    CoreS -->|Relay| WWW((Internet))
    Fallback -->|Forward| Web((Web / NGINX))

Quick Start

1. Installation

Linux:

bash <(curl -Ls https://raw.githubusercontent.com/ospab/ostp/master/scripts/install.sh)

Windows (PowerShell as Administrator):

irm https://raw.githubusercontent.com/ospab/ostp/master/scripts/install.ps1 | iex

2. Configuration

Initialize the configuration files for the server and client:

# On the server:
./ostp --init server

# On the client:
./ostp --init client

Server Example (config.json):

{
  "mode": "server",
  "listen": "0.0.0.0:50000",
  "access_keys": ["YOUR_SECRET_KEY"]
}

Client Example (config.json):

{
  "mode": "client",
  "version": "0.3.1",
  "inbounds": [
    { "type": "local_proxy", "tag": "socks-in", "protocol": "socks", "listen": "127.0.0.1", "port": 1088 }
  ],
  "outbounds": [
    {
      "type": "ostp",
      "tag": "proxy",
      "server": "YOUR_SERVER_IP",
      "port": 50000,
      "access_key": "YOUR_SECRET_KEY",
      "transport": { "type": "udp" }
    }
  ]
}

3. Execution

# Run with default config.json
./ostp

# Run with a specific config path
./ostp --config /path/to/config.json

Or connect via a one-line share link on the client:

./ostp "ostp://YOUR_SECRET_KEY@YOUR_SERVER_IP:50000?transport=udp"

Protocol Specification

Layer	Mechanism
Key Exchange	Noise NNpsk0 (X25519 + ChaChaPoly + BLAKE2s) zero-RTT
Encryption	ChaCha20-Poly1305 AEAD per-packet
Header Masking	HMAC-SHA256 derived per-packet mask
Reliability	Selective ACK with cumulative + SACK ranges
Retransmission	Rate-limited NACK + exponential backoff RTO
Keepalive	Ping/Pong with RTT measurement every 5s

Building from Source

# Requires Rust 1.75+
cargo build --release

# Cross-compile for Linux
cross build --release --target x86_64-unknown-linux-gnu

Documentation

License

GNU Affero General Public License v3.0 (AGPL-3.0). See LICENSE for more details.

Contacts

Telegram: @ospab0
Email: gvoprgrg@gmail.com

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