feat(companion): fipssh — ssh to a mesh node by npub (Termux helper)
Verified against the fips crate source: the mesh ULA is a pure function of the PUBLIC key — fd || sha256(x-only pubkey)[0..15] — so the npub is the durable address and needs no resolver. Android/tools/fipssh wraps ssh for Termux: 'fipssh user@npub1…' derives the ULA (pure-python bech32 + sha256, checksum-validated, typo protection) and execs ssh over the companion's split tunnel; --resolve prints the ULA alone. The derivation is pinned by a new Rust test (npub_derives_the_same_mesh_ula_as_the_fips_identity, 3 seeds against fips::Identity) and the helper's output was verified byte-identical against a live fips identity pair. SSH-over-mesh handover updated with an addendum: node docs/UI can advertise npub-based addressing, no node-side DNS needed for this case.
This commit is contained in:
Dorian
@@ -795,4 +795,30 @@ mod tests {
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);
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assert!(secret_from_nsec("npub1").is_err());
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}
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/// The mesh ULA is a PURE function of the node's public key:
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/// `fd ‖ sha256(x-only pubkey)[0..15]` (fips identity/node_addr.rs →
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/// identity/address.rs). That is what makes "address by npub" work —
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/// Termux's fipssh helper, and any future DNS-style resolver, just
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/// computes what the fips daemon's DNS answers.
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#[test]
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fn npub_derives_the_same_mesh_ula_as_the_fips_identity() {
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for seed in [0x42u8, 0x07, 0x31] {
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// 0xff… would exceed the curve order — secret keys must be valid scalars.
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let secret = [seed; 32];
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let id = fips::Identity::from_secret_bytes(&secret).unwrap();
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let npub = id.npub();
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let expected = id.address().to_ipv6().to_string();
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let pubkey_hex = pubkey_from_any(&npub).unwrap();
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let pk = hex::decode(&pubkey_hex).unwrap();
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let mut hasher = Sha256::new();
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hasher.update(&pk);
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let hash = hasher.finalize();
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let mut ula = [0u8; 16];
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ula[0] = 0xfd;
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ula[1..].copy_from_slice(&hash[..15]);
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assert_eq!(std::net::Ipv6Addr::from(ula).to_string(), expected, "npub {npub}");
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}
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}
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}
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Executable
+145
@@ -0,0 +1,145 @@
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#!/data/data/com.termux/files/usr/bin/sh
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# fipssh — SSH to an Archipelago FIPS mesh node BY NPUB.
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#
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# The mesh ULA is a pure function of the node's public key (verified against
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# the fips crate itself — archy-fips-core's npub_derives_the_same_mesh_ula
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# test, and the Android tools commit that shipped this script):
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#
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# ula = fd || sha256(x-only pubkey)[0..15]
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#
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# so the npub IS the address: no DNS server, no mesh query, works offline.
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# The node's fips daemon answers the same question through its DNS resolver
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# (core/archipelago/src/fips/dial.rs) — this is the phone-side equivalent.
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#
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# Setup (Termux): pkg install python openssh
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# Usage:
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# fipssh <user>@npub1… [ssh args…] connect
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# fipssh npub1… connect as $FIPSSH_USER
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# fipssh --resolve npub1… print the ULA and exit
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#
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# The companion's split tunnel carries the connection (fd00::/8 routes the
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# whole device while the mesh is up) — at home on LAN, away via the anchors.
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# The node still has to allow port 22 through its fips0 firewall: see
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# docs/HANDOFF-2026-08-31-ssh-over-mesh.md (the interim 90-ssh.nft drop-in,
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# restricted to your phone's ULA, until the node-side toggle ships).
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set -eu
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usage() {
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sed -n '2,20p' "$0" | sed 's/^# \{0,1\}//'
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exit 1
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}
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RESOLVE_ONLY=0
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if [ "${1:-}" = "--resolve" ]; then
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RESOLVE_ONLY=1
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shift
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fi
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[ $# -ge 1 ] || usage
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TARGET="$1"
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shift 2>/dev/null || true
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case "$TARGET" in
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*npub1*)
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case "$TARGET" in
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*@npub1*) USER_PART="${TARGET%%@*}"; N_PUB="${TARGET#*@}" ;;
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npub1*)
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USER_PART="${FIPSSH_USER:-}"
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N_PUB="$TARGET"
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if [ -z "$USER_PART" ] && [ "$RESOLVE_ONLY" = 0 ]; then
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echo "fipssh: no user given (use user@npub… or set FIPSSH_USER)" >&2
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exit 1
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fi
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;;
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*) echo "fipssh: expected [user@]npub1…, got '$TARGET'" >&2; exit 1 ;;
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esac
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;;
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*) echo "fipssh: '$TARGET' is not an npub (expected [user@]npub1…)" >&2; exit 1 ;;
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esac
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command -v python3 >/dev/null 2>&1 || {
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echo "fipssh: python3 not found — run: pkg install python" >&2
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exit 1
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}
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ULA=$(python3 - "$N_PUB" <<'PYEOF'
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import hashlib, ipaddress, sys
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CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
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def bech32_polymod(values):
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gen = [0x3B6A57B2, 0x26508E6D, 0x1EA119FA, 0x3D4233DD, 0x2A1462B3]
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chk = 1
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for value in values:
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top = chk >> 25
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chk = (chk & 0x1FFFFFF) << 5 ^ value
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for i in range(5):
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chk ^= gen[i] if ((top >> i) & 1) else 0
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return chk
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def bech32_hrp_expand(hrp):
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return [ord(c) >> 5 for c in hrp] + [0] + [ord(c) & 31 for c in hrp]
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def bech32_verify_checksum(hrp, data):
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return bech32_polymod(bech32_hrp_expand(hrp) + data) == 1
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def bech32_decode(s):
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if any(ord(c) < 33 or ord(c) > 126 for c in s):
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raise ValueError("bad character")
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if s.lower() != s and s.upper() != s:
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raise ValueError("mixed case")
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s = s.lower()
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pos = s.rfind("1")
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if pos < 1 or pos + 7 > len(s) or len(s) > 90:
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raise ValueError("bad separator")
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hrp = s[:pos]
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data = [CHARSET.find(c) for c in s[pos + 1:]]
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if -1 in data:
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raise ValueError("bad data character")
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if not bech32_verify_checksum(hrp, data):
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raise ValueError("bad checksum — typo in the npub?")
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return hrp, data[:-6]
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def convertbits(data, frombits, tobits):
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acc = 0
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bits = 0
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ret = bytearray()
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maxv = (1 << tobits) - 1
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for value in data:
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if value < 0 or (value >> frombits):
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raise ValueError("bad value")
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acc = (acc << frombits) | value
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bits += frombits
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while bits >= tobits:
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bits -= tobits
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ret.append((acc >> bits) & maxv)
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if bits >= frombits or ((acc << (tobits - bits)) & maxv):
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raise ValueError("bad padding")
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return bytes(ret)
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npub = sys.argv[1]
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hrp, data = bech32_decode(npub)
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if hrp != "npub":
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raise ValueError(f"expected hrp 'npub', got '{hrp}'")
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pubkey = convertbits(data, 5, 8)
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if len(pubkey) != 32:
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raise ValueError(f"npub data must be 32 bytes, got {len(pubkey)}")
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# ula = fd || sha256(pubkey)[0..15] — mirrors fips identity/node_addr.rs +
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# identity/address.rs (FIPS_ADDRESS_PREFIX = 0xfd).
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ula = bytes([0xFD]) + hashlib.sha256(pubkey).digest()[:15]
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print(ipaddress.IPv6Address(ula).compressed)
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PYEOF
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) || exit 1
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if [ "$RESOLVE_ONLY" = 1 ]; then
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echo "$ULA"
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exit 0
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fi
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exec ssh "${USER_PART}@${ULA}" "$@"
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@@ -87,6 +87,25 @@ the node UI**, default **off**. Sketch:
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- [ ] Settings UI survives a page reload; RPC has a vitest like
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`TransportPrefsCard.test.ts`.
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## Addendum (2026-08-31, same day): the npub IS the address
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While wiring this up we confirmed the mesh ULA is a **pure function of the
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public key** — `fd ‖ sha256(x-only pubkey)[0..15]` (`fips/src/identity/node_addr.rs`
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`from_pubkey` → `identity/address.rs` `from_node_addr`,
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`FIPS_ADDRESS_PREFIX = 0xfd`). The daemon's DNS resolver (`fips/dial.rs`) just
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answers what anyone can compute. Consequences for the node side:
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- Docs/UI can advertise `ssh <user>@npub1…`-style addressing: Termux's
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`Android/tools/fipssh` (shipped with the companion work) derives the ULA
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from the npub with zero infrastructure, verified byte-identical against
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the fips crate (`archy-fips-core` test
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`npub_derives_the_same_mesh_ula_as_the_fips_identity`).
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- If the settings toggle from this handover ever grows a "copy command"
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affordance, `fipssh <user>@<npub>` is the natural shape (npub, not ULA —
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it is the durable identity; the ULA follows from it).
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- No node-side DNS surface is required for the SSH case; the resolver stays
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what it is today (the node's own peer dials).
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## Working rules
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Same as the queue handoffs: small commits, tracker issue for this feature
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