isthislegit? [v1.01]

Domain Impersonation & OSINT Triage Tool.

isthislegit compares a known-legitimate domain (target) against a suspect domain using DNS resolution, X.509 TLS certificates, and RDAP registration data to produce a deterministic risk score and verdict. DNS answers are cross-checked across the system resolver, 1.1.1.1, and 8.8.8.8 for split-brain or hijacking signals (state consistency only — raw addresses are never compared, so CDN/GeoDNS fronting stays quiet). Each unique domain is probed once and the outcomes reused; even identical target/suspect pairs run the full pipeline (verdict forced to legitimate). System-dark/public-live suppression splits score on the suspect, while split-horizon shapes stay display-only. It ships as a single static binary built on the Go standard library (plus golang.org/x/sync for the concurrent fetch pipeline) — no curl, openssl, jq, or dig required.

Features

• DNS pre-flight — NXDOMAIN / unresolvable domains abort early.
• X.509 classification — leaf certificate issuer, SANs, and validation level (EV / OV / IV / DV) from CA/Browser Forum policy OIDs.
• RDAP triage — creation date and registrar via https://rdap.org/domain/.
• Deterministic scoring — transparent point system with a four-tier verdict.
• Flexible output — human-readable report, --json for scripting, --verbose for raw OIDs, cert details, and RDAP payloads.

Prerequisites

• Go 1.24 or newer.
• Network access to DNS, remote port 443, and rdap.org.

Clone, build, run

git clone https://github.com/example/isthislegit.git
cd isthislegit
CGO_ENABLED=0 go build -ldflags="-s -w" -o isthislegit ./cmd/isthislegit
./isthislegit jdsoft.com jdsoftcareers.com

Run the test suite with:

go test ./...

Cross-compiling with compile.go

compile.go (repo root) is the supported build driver. It cross-compiles ./cmd/isthislegit for a platform/arch matrix, always with CGO_ENABLED=0, so every target builds without a cross C toolchain:

go run ./compile.go --platform=linux --arch=amd64

Flag	Default	Description
--platform	linux	Target OS (see vocabulary below).
--arch	amd64	Target arch (see vocabulary below).
--static	true	true for static (CGO_ENABLED=0), false for dynamic (CGO_ENABLED=1, host builds only unless CC points at a cross compiler). Both modes are stripped via -ldflags="-s -w".

Platform vocabulary (case-insensitive): linux; mac/macos/osx/darwin → darwin; windows/win → windows; bsd → all three of freebsd, openbsd, netbsd in one run (or name a single BSD explicitly).

Arch vocabulary: raw GOARCH names plus aliases — x64/x86-64 → amd64; x86/i386/32bit → 386; aarch64 → arm64; arm/armv7/armv6/armv5 → arm with matching GOARM. Unknown values exit 1, and combos the toolchain does not support (e.g. darwin/386) are refused with a clear error.

Output binaries are named isthislegit-<goos>-<goarch> (with a vGOARM suffix when applicable, e.g. isthislegit-linux-armv7, and .exe on Windows):

go run ./compile.go --platform=linux --arch=amd64
go run ./compile.go --platform=windows --arch=x64 --static=false
go run ./compile.go --platform=bsd --arch=x64
go run ./compile.go --platform=linux --arch=armv7   # embedded ARM (Miyoo Mini Plus)

Flags

Flag	Description
-v, --verbose	Append raw cert policy OIDs, TLS details, and RDAP JSON.
-j, --json	Output the result summary as JSON for scripting.
-k, --insecure	Skip TLS verification for RDAP
--timeout=DUR	Per-call deadline for DNS/TLS/RDAP (Go duration, default 5s).
--scale	Print the scoring scale reference table and exit.
-h, --help	Display usage and exit.

Examples:

isthislegit jdsoft.com jdsoftcareers.com
isthislegit -j example.com suspect-example.com
isthislegit --timeout=10s example.com suspect-example.com
isthislegit --scale

Embedded systems (no CA certificates)

isthislegit runs on embedded ARM devices (verified on a Miyoo Mini Plus), but minimal firmware images often ship without a CA certificate store. In that case DNS resolution and certificate inspection still work, while verified HTTPS (RDAP) fails — the fail-closed error will say so directly (x509: certificate signed by unknown authority). Prefer installing ca-certificates and fixing the system clock where possible; otherwise use insecure mode:

isthislegit -k jdsoft.com jdsoftcareers.com

--insecure prints a warning and weakens results, so treat it as a last resort for devices without stored CA certificates.

Example output

isthislegit? [v1.01]
Domain Impersonation & OSINT Triage Tool

[*] Comparing: example.com (Target) <---> example.org (Suspect)

[+] Target Domain: example.com
  |-- Creation Date : 1995-08-14
  |-- Registrar     : RESERVED-Internet Assigned Numbers Authority
  |-- Cert Issuer   : SSL Corporation
  |-- Validation    : DV (Domain Validated)
  |-- Cert SANs     : example.com, *.example.com

[-] Suspect Domain: example.org
  |-- Creation Date : 1995-08-31
  |-- Registrar     : ICANN
  |-- Cert Issuer   : SSL Corporation
  |-- Validation    : DV (Domain Validated)
  |-- Cert SANs     : example.org, *.example.org

----------------------------------------------------------------------
[!] RISK ANALYSIS (score: 30):
  [!] MISMATCH: Registrars do not align (RESERVED-Internet Assigned Numbers Authority vs ICANN).

VERDICT: LIKELY UNRELATED / MISCONFIGURED

Scoring scale

Signal	Points
Suspect < 30d (CRITICAL), stacked w/ signal	+80
Suspect < 30d (CRITICAL), isolated	+40
Suspect 30–89d (WARNING), stacked w/ signal	+40
Suspect 30–89d (WARNING), isolated	+20
Shared cert infrastructure (halves age tier)	x0.5
Identical target/suspect (forced LEGITIMATE)	+0
Resolution tampering: suppression split (suspect)	+50
DNS split-horizon / target-side (display only)	+0
Cert downgrade: target EV/OV vs suspect DV	+40
Registrar mismatch	+30
Same-class issuer difference (display only)	+0

Score	Verdict
0–14	LIKELY LEGITIMATE
15–39	LIKELY UNRELATED / MISCONFIGURED
40–50	SUSPICIOUS — MANUAL REVIEW RECOMMENDED
51+	LIKELY PHISHING / IMPERSONATION ATTEMPT

Lookups fail closed: if RDAP dates or TLS data cannot be retrieved for either domain, the tool errors out instead of printing a verdict built on missing data, and the message names the underlying cause(s) (e.g. a TLS verification failure, which on minimal devices usually means missing CA certificates or a wrong system clock). Fetches run concurrently under a 15s global budget with 5s per-call deadlines (3 attempts each, adjustable via --timeout); --insecure skips RDAP TLS verification as a last resort, with a warning.

Project layout

cmd/isthislegit   CLI parsing, fetch orchestration, output dispatch
internal/dns      Domain normalization, syntax checks, DNS pre-flight
internal/cert     TLS leaf fetch and validation-level classification
internal/rdap     RDAP client, creation date and registrar extraction
internal/score    Risk scoring and verdict mapping
internal/report   Human, JSON, scale, and verbose renderers

License

Copyright (C) 2026 Mark Robillard Jr (MARKMENTAL). isthislegit is free software licensed under the GNU General Public License v3 — see LICENSE for the full text.