42 lines
2.9 KiB
JavaScript
42 lines
2.9 KiB
JavaScript
// Browser WebAuthn and secret encryption helpers. The host verifies every proof.
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const bytes = text => Uint8Array.from(atob(text.replace(/-/g, '+').replace(/_/g, '/')), c => c.charCodeAt(0));
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const encoded = buffer => btoa(String.fromCharCode(...new Uint8Array(buffer))).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
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const post = async (path, body) => {
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const response = await fetch('/api/' + path.replace(/^\//, ''), {method: 'POST', headers: {'content-type': 'application/json'}, body: JSON.stringify(body)});
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const result = await response.json();
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if (!response.ok) throw new Error(result.message);
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return result;
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};
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function options(challenge) {
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const value = challenge.options;
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value.publicKey.challenge = bytes(value.publicKey.challenge);
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if (value.publicKey.user) value.publicKey.user.id = bytes(value.publicKey.user.id);
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for (const key of ['allowCredentials', 'excludeCredentials']) {
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for (const credential of value.publicKey[key] || []) credential.id = bytes(credential.id);
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}
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return value;
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}
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function serialize(credential) {
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const response = {};
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for (const key of ['clientDataJSON', 'attestationObject', 'authenticatorData', 'signature', 'userHandle']) {
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if (credential.response[key]) response[key] = encoded(credential.response[key]);
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}
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return {id: credential.id, rawId: encoded(credential.rawId), type: credential.type, response, clientExtensionResults: credential.getClientExtensionResults()};
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}
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async function assertion(challenge) {
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return {challenge_id: challenge.id, assertion: serialize(await navigator.credentials.get(options(challenge)))};
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}
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async function encrypt(publicKey, secret) {
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const host = await crypto.subtle.importKey('raw', new Uint8Array(publicKey), {name: 'ECDH', namedCurve: 'P-256'}, false, []);
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const pair = await crypto.subtle.generateKey({name: 'ECDH', namedCurve: 'P-256'}, true, ['deriveBits']);
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const shared = await crypto.subtle.deriveBits({name: 'ECDH', public: host}, pair.privateKey, 256);
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const material = await crypto.subtle.importKey('raw', shared, 'HKDF', false, ['deriveKey']);
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const key = await crypto.subtle.deriveKey({name: 'HKDF', hash: 'SHA-256', salt: new Uint8Array(), info: new TextEncoder().encode('sausage/secret-entry/v1')}, material, {name: 'AES-GCM', length: 256}, false, ['encrypt']);
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const iv = crypto.getRandomValues(new Uint8Array(12));
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const ciphertext = await crypto.subtle.encrypt({name: 'AES-GCM', iv}, key, new TextEncoder().encode(secret));
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const ephemeral_public_key = new Uint8Array(await crypto.subtle.exportKey('raw', pair.publicKey));
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const envelope = {ephemeral_public_key: [...ephemeral_public_key], iv: [...iv], ciphertext: [...new Uint8Array(ciphertext)]};
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const hash = new Uint8Array(await crypto.subtle.digest('SHA-256', new Uint8Array([...envelope.ephemeral_public_key, ...envelope.iv, ...envelope.ciphertext])));
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return {envelope, ciphertext_sha256: [...hash].map(byte => byte.toString(16).padStart(2, '0')).join('')};
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}
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