ihtc

Local HTTP forward proxy for bypassing SNI-based DPI censorship. Splits the TLS ClientHello across multiple TCP packets to evade deep packet inspection.

Quick Start

go build -o ihtc ./cmd/ihtc/
./ihtc --auto-proxy

This binds 127.0.0.1:8080, serves a PAC file, and configures macOS auto proxy for all network services. Browsers route traffic through ihtc automatically.

On Ctrl+C, the proxy is disabled and browsers fall back to direct connections.

Usage

ihtc [flags]

  --listen string    Address to bind (default "127.0.0.1:8080")
  --min-chunk int    Minimum bytes per fragment (default 3)
  --max-chunk int    Maximum bytes per fragment (default 8)
  --delay-us int     Max microsecond delay between fragments (default 500)
  --refrag int       Dummy TLS records before ClientHello (default 1, disabled)
  --regex string     Only fragment hosts matching this regex
  --verbose          Enable debug logging
  --auto-proxy       Set macOS auto proxy configuration

Without --auto-proxy, point your browser/app at 127.0.0.1:8080 as an HTTP proxy manually.

How It Works

When a browser opens an HTTPS connection through the proxy:

1. The browser sends a TLS ClientHello containing the target hostname (SNI)
2. ihtc reads the complete ClientHello, then writes it in small random chunks (2-8 bytes by default) with microsecond delays between each
3. TCP sends each chunk as its own segment — simple DPIs see only fragments, not the hostname
4. After the handshake, ihtc relays data transparently in both directions

Limitations

• TCP only (no QUIC/HTTP3)
• Not effective against DPIs that perform TCP stream reassembly
  • For reassembling DPIs, see re-fragmentation
• No authentication (local-only, trusted environment)

Advanced

Fragmenting only blocked domains

Use --regex to limit fragmentation to specific hosts. All other traffic passes through unfragmented:

./ihtc --auto-proxy --regex 'discord\.com|discord\.gg|twitter\.com'

Re-fragmentation

For DPIs that reassemble TCP streams, enable re-fragmentation with --refrag N:

./ihtc --refrag 3

This inserts N-1 deliberately invalid TLS records before the real ClientHello, each in its own TCP segment. A reassembling DPI must inspect multiple nearly-identical records and choose the correct one — while the TLS server ignores the invalid records and processes only the final valid one.

Set N based on DPI aggressiveness (2-5 is typical). Higher values add latency with diminishing returns.

License

MIT — see LICENSE.