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docs: enhance documentation with threat model, limitations, air-gapped guidance
- Update version to v1.4.4 - Add explicit threat model documentation - Document known limitations prominently - Include air-gapped usage recommendations - Polish all documentation for clarity and examples - Update README, DEVELOPMENT.md, GEMINI.md, RECOVERY_PLAYBOOK.md
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LC mac
331
src/lib/krux.ts
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331
src/lib/krux.ts
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// src/lib/krux.ts
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// Krux KEF (Krux Encryption Format) implementation
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// Compatible with Krux firmware (AES-GCM, label as salt, hex QR)
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// Currently implements version 20 (AES-GCM without compression)
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// Version 21 (AES-GCM +c) support can be added later with compression
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// KEF version definitions (matches Python reference)
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export const VERSIONS: Record<number, {
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name: string;
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compress?: boolean;
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auth: number; // GCM tag length (4 for version 20, full 16 for v1?)
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}> = {
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20: { name: "AES-GCM", auth: 4 },
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// Version 21 would be: { name: "AES-GCM +c", compress: true, auth: 4 }
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};
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// IV length for GCM mode
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const GCM_IV_LENGTH = 12;
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/**
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* Convert data to a proper ArrayBuffer for Web Crypto API.
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* Ensures it's not a SharedArrayBuffer.
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*/
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function toArrayBuffer(data: Uint8Array): ArrayBuffer {
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// Always create a new ArrayBuffer and copy the data
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const buffer = new ArrayBuffer(data.length);
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new Uint8Array(buffer).set(data);
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return buffer;
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}
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/**
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* Wrap data into KEF envelope format (matches Python exactly)
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* Format: [1 byte label length][label bytes][1 byte version][3 bytes iterations][payload]
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*/
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export function wrap(label: string, version: number, iterations: number, payload: Uint8Array): Uint8Array {
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const labelBytes = new TextEncoder().encode(label);
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if (!(0 <= labelBytes.length && labelBytes.length <= 252)) {
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throw new Error("Label too long (max 252 bytes)");
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}
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const lenId = new Uint8Array([labelBytes.length]);
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const versionByte = new Uint8Array([version]);
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let itersBytes = new Uint8Array(3);
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// Krux firmware expects iterations in multiples of 10000 when possible
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if (iterations % 10000 === 0) {
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const scaled = iterations / 10000;
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if (!(1 <= scaled && scaled <= 10000)) {
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throw new Error("Iterations out of scaled range");
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}
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itersBytes[0] = (scaled >> 16) & 0xff;
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itersBytes[1] = (scaled >> 8) & 0xff;
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itersBytes[2] = scaled & 0xff;
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} else {
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if (!(10000 < iterations && iterations < 2**24)) {
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throw new Error("Iterations out of range");
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}
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itersBytes[0] = (iterations >> 16) & 0xff;
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itersBytes[1] = (iterations >> 8) & 0xff;
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itersBytes[2] = iterations & 0xff;
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}
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return new Uint8Array([...lenId, ...labelBytes, ...versionByte, ...itersBytes, ...payload]);
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}
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/**
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* Unwrap KEF envelope to extract components (matches Python exactly)
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*/
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export function unwrap(envelope: Uint8Array): {
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label: string;
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version: number;
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iterations: number;
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payload: Uint8Array
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} {
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if (envelope.length < 5) {
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throw new Error("Invalid KEF envelope: too short");
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}
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const lenId = envelope[0];
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if (!(0 <= lenId && lenId <= 252)) {
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throw new Error("Invalid label length in KEF envelope");
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}
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if (1 + lenId + 4 > envelope.length) {
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throw new Error("Invalid KEF envelope: insufficient data");
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}
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const labelBytes = envelope.subarray(1, 1 + lenId);
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const label = new TextDecoder().decode(labelBytes);
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const version = envelope[1 + lenId];
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const iterStart = 2 + lenId;
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let iters = (envelope[iterStart] << 16) | (envelope[iterStart + 1] << 8) | envelope[iterStart + 2];
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const iterations = iters <= 10000 ? iters * 10000 : iters;
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const payload = envelope.subarray(5 + lenId);
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return { label, version, iterations, payload };
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}
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/**
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* Krux Cipher class for AES-GCM encryption/decryption
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*/
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export class KruxCipher {
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private keyPromise: Promise<CryptoKey>;
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constructor(passphrase: string, salt: string, iterations: number) {
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const encoder = new TextEncoder();
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this.keyPromise = (async () => {
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// Import passphrase as raw key material
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const passphraseBytes = encoder.encode(passphrase);
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const passphraseBuffer = toArrayBuffer(passphraseBytes);
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const baseKey = await crypto.subtle.importKey(
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"raw",
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passphraseBuffer,
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{ name: "PBKDF2" },
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false,
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["deriveKey"]
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);
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// Derive AES-GCM key using PBKDF2
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const saltBytes = encoder.encode(salt);
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const saltBuffer = toArrayBuffer(saltBytes);
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return crypto.subtle.deriveKey(
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{
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name: "PBKDF2",
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salt: saltBuffer,
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iterations: Math.max(1, iterations),
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hash: "SHA-256"
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},
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baseKey,
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{ name: "AES-GCM", length: 256 },
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false,
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["encrypt", "decrypt"]
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);
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})();
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}
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/**
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* Encrypt plaintext using AES-GCM
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*/
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async encrypt(plaintext: Uint8Array, version = 20, iv?: Uint8Array): Promise<Uint8Array> {
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const v = VERSIONS[version];
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if (!v) {
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throw new Error(`Unsupported KEF version: ${version}`);
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}
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// Note: No compression for version 20
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// For version 21, we would add compression here
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// Ensure ivBytes is a fresh Uint8Array with its own ArrayBuffer (not SharedArrayBuffer)
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let ivBytes: Uint8Array;
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if (iv) {
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// Copy the iv to ensure we have our own buffer
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ivBytes = new Uint8Array(iv.length);
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ivBytes.set(iv);
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} else {
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// Create new random IV with a proper ArrayBuffer
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ivBytes = new Uint8Array(GCM_IV_LENGTH);
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crypto.getRandomValues(ivBytes);
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}
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const key = await this.keyPromise;
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const plaintextBuffer = toArrayBuffer(plaintext);
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const ivBuffer = toArrayBuffer(ivBytes);
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// Use auth length from version definition (in bytes, convert to bits)
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const tagLengthBits = v.auth * 8;
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const encrypted = await crypto.subtle.encrypt(
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{
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name: "AES-GCM",
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iv: ivBuffer,
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tagLength: tagLengthBits
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},
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key,
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plaintextBuffer
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);
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// For GCM, encrypted result includes ciphertext + tag
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// Separate ciphertext and tag
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const authBytes = v.auth;
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const encryptedBytes = new Uint8Array(encrypted);
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const ciphertext = encryptedBytes.slice(0, encryptedBytes.length - authBytes);
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const tag = encryptedBytes.slice(encryptedBytes.length - authBytes);
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// Combine IV + ciphertext + tag (matches Python format)
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const combined = new Uint8Array(ivBytes.length + ciphertext.length + tag.length);
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combined.set(ivBytes, 0);
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combined.set(ciphertext, ivBytes.length);
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combined.set(tag, ivBytes.length + ciphertext.length);
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return combined;
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}
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/**
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* Decrypt payload using AES-GCM
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*/
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async decrypt(payload: Uint8Array, version: number): Promise<Uint8Array> {
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const v = VERSIONS[version];
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if (!v) {
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throw new Error(`Unsupported KEF version: ${version}`);
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}
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const ivLen = GCM_IV_LENGTH;
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const authBytes = v.auth;
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// Payload is IV + ciphertext + tag
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if (payload.length < ivLen + authBytes) {
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throw new Error("Payload too short for AES-GCM");
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}
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// Extract IV, ciphertext, and tag
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const iv = payload.slice(0, ivLen);
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const ciphertext = payload.slice(ivLen, payload.length - authBytes);
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const tag = payload.slice(payload.length - authBytes);
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const key = await this.keyPromise;
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try {
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// For Web Crypto, we need to combine ciphertext + tag
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const ciphertextWithTag = new Uint8Array(ciphertext.length + tag.length);
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ciphertextWithTag.set(ciphertext, 0);
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ciphertextWithTag.set(tag, ciphertext.length);
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const ciphertextBuffer = toArrayBuffer(ciphertextWithTag);
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const ivBuffer = toArrayBuffer(iv);
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const decrypted = await crypto.subtle.decrypt(
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{
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name: "AES-GCM",
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iv: ivBuffer,
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tagLength: authBytes * 8
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},
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key,
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ciphertextBuffer
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);
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return new Uint8Array(decrypted);
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} catch (error) {
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// Web Crypto throws generic errors for decryption failure
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// Convert to user-friendly message
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throw new Error("Krux decryption failed - wrong passphrase or corrupted data");
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}
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}
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}
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/**
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* Convert hex string to bytes
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*/
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export function hexToBytes(hex: string): Uint8Array {
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// Remove any whitespace and optional KEF: prefix
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const cleaned = hex.trim().replace(/\s/g, '').replace(/^KEF:/i, '');
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if (!/^[0-9a-fA-F]+$/.test(cleaned)) {
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throw new Error("Invalid hex string");
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}
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if (cleaned.length % 2 !== 0) {
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throw new Error("Hex string must have even length");
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}
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const bytes = new Uint8Array(cleaned.length / 2);
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for (let i = 0; i < bytes.length; i++) {
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bytes[i] = parseInt(cleaned.substr(i * 2, 2), 16);
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}
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return bytes;
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}
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/**
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* Convert bytes to hex string
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*/
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export function bytesToHex(bytes: Uint8Array): string {
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return Array.from(bytes)
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.map(b => b.toString(16).padStart(2, '0'))
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.join('')
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.toUpperCase();
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}
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/**
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* Encrypt mnemonic to KEF format
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*/
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export async function encryptToKrux(params: {
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mnemonic: string;
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passphrase: string;
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label?: string;
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iterations?: number;
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version?: number;
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}): Promise<{ kefHex: string; label: string; version: number; iterations: number }> {
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const label = params.label || "Seed Backup";
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const iterations = params.iterations || 200000;
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const version = params.version || 20;
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if (!params.passphrase) {
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throw new Error("Passphrase is required for Krux encryption");
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}
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const mnemonicBytes = new TextEncoder().encode(params.mnemonic);
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const cipher = new KruxCipher(params.passphrase, label, iterations);
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const payload = await cipher.encrypt(mnemonicBytes, version);
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const kef = wrap(label, version, iterations, payload);
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return {
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kefHex: bytesToHex(kef),
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label,
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version,
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iterations
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};
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}
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/**
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* Decrypt KEF hex to mnemonic
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*/
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export async function decryptFromKrux(params: {
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kefHex: string;
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passphrase: string;
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}): Promise<{ mnemonic: string; label: string; version: number; iterations: number }> {
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if (!params.passphrase) {
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throw new Error("Passphrase is required for Krux decryption");
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}
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const bytes = hexToBytes(params.kefHex);
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const { label, version, iterations, payload } = unwrap(bytes);
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const cipher = new KruxCipher(params.passphrase, label, iterations);
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const decrypted = await cipher.decrypt(payload, version);
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const mnemonic = new TextDecoder().decode(decrypted);
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return { mnemonic, label, version, iterations };
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}
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