Executive summary — MILCODEC Receiver is a zero-install browser demonstration that detects the repository's chirp-spread-spectrum packet format, checks a shared-key packet envelope, and displays decoded text locally. It is intended for codec development, interoperability experiments, and browser audio testing.
Technical demonstration utility. Not authenticated operational intelligence.
Shared demo key verifies packet integrity only; it does not authenticate sender identity.
- Data-over-sound reception in the 14–17 kHz near-ultrasonic band — no radios, no pairing, no network. The air gap is the channel.
- Chirp Spread Spectrum ("The Dolphin") modulation — binary chirp keying (up-chirp = 1, down-chirp = 0) at 20 baud, decoded with a matched-filter correlation receiver for robustness against ambient noise.
- Shared-key packet integrity via TweetNaCl
secretbox(XSalsa20-Poly1305), with no claim of sender identity. - Forward error correction — 3× repetition coding with majority-vote bit recovery, plus a preamble + 16-bit sync word + length-prefixed framing protocol for reliable packet recovery.
- Military message precedence — decoded traffic is tagged
FLASH/IMMEDIATE/ROUTINE, with audible alerting on high-priority receipt. - Direct, accessible receiver UI with keyboard-operable controls, inline permission errors, a live spectrum, and a decoded-message inbox.
- Real-time spectral visualizer — Web Audio FFT spectrum and signal-strength indicator for live link assessment.
MILCODEC Receiver is the receive-side demonstration for this repository's acoustic packet format. A compatible test sender can play an encoded waveform through a speaker; this page listens through the microphone, recovers a candidate bitstream, opens its shared-key envelope, and displays valid text.
End-to-end signal flow:
PC Sender → Speaker → Air (acoustic) → Device Mic → Milcodec Receiver → Decode → Decrypt → Inbox
The decoder generates linear up- and down-chirp templates (14 kHz ⇄ 17 kHz over a 50 ms symbol) and slides them across the captured audio as a correlation receiver. It locates the U-U-D-D preamble by spaced peak detection, locks to a 16-bit sync word, reads a 16-bit payload-length field, then recovers each payload bit by majority vote across three transmitted copies before reassembling bytes.
Recovered payloads are NaCl secretbox frames (24-byte nonce + ciphertext). On successful open, the inner packet is parsed as 1-byte type + 64-byte signature field + JSON body, yielding the message text and its precedence. Failed opens are rejected and never displayed.
The console runs entirely on the Web Audio API — getUserMedia capture, an AnalyserNode spectrum, and a bounded local buffer passed to the decoder. The page requests microphone access only when the start button is activated. It exposes receiver status, decoded messages, and a local diagnostic log without a hidden passcode flow.
This is an analytical tool, not a data feed — but Monarch Castle doctrine still governs every message it surfaces: evidence before assertion.
- Input: live acoustic audio from the device microphone (mono, 44.1 kHz), captured only after explicit user permission.
- Output: decoded messages, each stamped at the point of receipt with:
- collected_at — local reception timestamp on the receiving device,
- priority — military precedence (
FLASH/IMMEDIATE/ROUTINE), - method —
MILCODEC CSS · 14–17 kHz · secretbox(XSalsa20-Poly1305), - verification — authentication status of the sender / packet.
- Auditability: a live debug log records preamble locks, extracted bit counts, payload lengths, and decrypt outcomes so every displayed message is traceable from raw audio to plaintext.
- Language: vanilla JavaScript (no framework, no build step) · HTML5 · CSS3
- DSP / capture: Web Audio API —
AudioContext,AnalyserNode,ScriptProcessorNode,getUserMedia; HTML5<canvas>spectrum rendering - Cryptography: TweetNaCl (
nacl-fast) +tweetnacl-util, loaded via jsDelivr CDN - Modulation: custom Chirp Spread Spectrum codec ("The Dolphin") with repetition-code FEC
- Hosting: GitHub Pages (static, HTTPS — required for microphone access);
.nojekyllfor raw asset serving - Test harnesses:
test_crypto.html,test_file.html— in-browser round-trip checks for the crypto and end-to-end paths
Use the live build (recommended):
- Open https://monarchcastletech.github.io/milcodec-receiver/ on a modern browser (Chrome, Safari, or Firefox) — HTTPS is required for microphone access.
Operate the receiver:
- The interface opens as an FM radio tuner (cover mode).
- Activate Start microphone receiver and grant microphone permission.
- Play a compatible MILCODEC test waveform near the device microphone.
- Press POWER, then grant microphone permission when prompted.
- Decoded transmissions appear in the INBOX, tagged by precedence; high-priority traffic triggers an audible alert.
Run locally:
git clone https://github.com/monarchcastletech/milcodec-receiver.git
cd milcodec-receiver
python -m http.server 8080
# open http://localhost:8080Deployment: Legacy GitHub Pages is deliberately preserved from main at the repository root. No Actions workflow has replaced it because an identical-artifact migration has not been proven.
Security boundary. This build ships with a hardcoded shared demo key. It does not provide key exchange, participant identity, replay prevention, traffic analysis resistance, or a trusted operational workflow. Audio buffers are capped at 30 seconds and decoded packets at 1,024 bytes; message text is inserted through
textContent.
A product of Defense Intelligence · Monarch Castle Technologies — an operating company of Monarch Castle Holdings. Sister companies: Monarch Castle Technologies · Strategic Data Company of Ankara
See LICENSE. © 2026 Monarch Castle Holdings · Ankara, Türkiye.
Browser-based acoustic data link that demodulates and decrypts MILCODEC chirp-spread-spectrum signals over sound — a Monarch Castle Technologies / Defense Intelligence receiver.
Lifecycle: Active. The badge and this statement describe maintenance status, not service availability.
The preview is maintained as a repository asset; the live interface or generated output remains authoritative.
These repository-specific sources define the methodology or provenance boundary. Source dates, transformation steps, and known gaps must travel with analytical outputs.
Release-driven; the receiver has no background data feed.
python -m http.server 8080Run only in a trusted development environment and review repository-specific prerequisites before using networked or hardware features.
decoder.js— repository-specific implementation, data, or configuration boundary.crypto.js— repository-specific implementation, data, or configuration boundary.app.js— repository-specific implementation, data, or configuration boundary.
node --test tests/repository-hygiene.test.mjsOriginal software history is maintained in Git. External datasets, reports, trademarks, screenshots, and assets are not relicensed by this repository; see THIRD_PARTY_NOTICES.md before reuse.
This repository does not publish a guaranteed forecast. Any scenarios, scores, or forward-looking language are analytical aids, not facts or advice; review source dates and methodology before use.
Do not publish vulnerabilities in an issue. Use GitHub's private vulnerability-reporting flow when available, or follow the organization security policy.
Original repository code and documentation are available under MIT; see LICENSE. That license does not override third-party terms documented in THIRD_PARTY_NOTICES.md.
Use the machine-readable CITATION.cff. Cite the specific commit and, for analytical use, record the data or model snapshot date.
MILCODEC Receiver is a Monarch Castle Technologies project. Part of Monarch Castle Technologies.