Gotatun WireGuard Backend

Overview

NymVPN uses mullvad/gotatun, a pure Rust userspace WireGuard implementation, for its tunnel backend. This replaces both wireguard-go (Go FFI) and kernel WireGuard modules.

Location: nym-vpn-core/crates/nym-wg-gotatun/

Why Gotatun?

Approach	Problem
Kernel WireGuard (kmod-wireguard)	Not available on all devices, requires kernel module management
wireguard-go (nym-wg-go)	Go cross-compilation with MUSL is painful, especially for MIPS
gotatun	Pure Rust, single toolchain, works everywhere with kmod-tun

Modules

• lib.rs — Public API: PrivateKey, PublicKey, PresharedKey, PeerConfig, PeerEndpointUpdate
• wireguard_go.rs — Tunnel struct wrapping gotatun; start(), stop(), update_peers()
• amnezia.rs — AmneziaConfig with 9 obfuscation parameters
• amnezia_udp.rs — UDP transport layer obfuscation (504 lines)

Key Design Decisions

• PrivateKey derives Zeroize, ZeroizeOnDrop for secure key handling
• AmneziaConfig::rand() returns Result instead of panicking
• Feature-gated: nym-vpn-lib enables the amnezia feature

AmneziaWG Obfuscation

AmneziaWG defeats deep packet inspection that identifies and blocks standard WireGuard traffic.

How it works:

The obfuscation layer wraps gotatun's UDP socket factory:

1. AmneziaUdpFactory<F> — wraps the socket factory
2. AmneziaSend<S> — remaps WireGuard message headers and prepends junk packets during handshakes
3. AmneziaRecv<R> — strips junk and reverses header remapping on receive

When the config is OFF or absent, the layer operates in passthrough mode with zero overhead.

Obfuscation Parameters

Parameter	Field	Description
Jc	junk_pkt_count	Number of junk packets before handshake
Jmin	junk_pkt_min_size	Minimum junk packet size
Jmax	junk_pkt_max_size	Maximum junk packet size
S1	init_pkt_junk_size	Junk padding on handshake init
S2	response_pkt_junk_size	Junk padding on handshake response
H1	init_pkt_magic_header	Header remap for init messages
H2	response_pkt_magic_header	Header remap for response messages
H3	under_load_pkt_magic_header	Header remap for under-load messages
H4	transport_pkt_magic_header	Header remap for transport data