1 files changed, 137 insertions, 0 deletions
diff --git a/web/js/crypto.js b/web/js/crypto.js
new file mode 100644
index 0000000..5c12a2c
--- /dev/null
+++ b/web/js/crypto.js
@@ -0,0 +1,137 @@
+'use strict';
+
+// taken from fxa
+function hexToUint8(str) {
+    const HEX_STRING = /^(?:[a-fA-F0-9]{2})+$/;
+    if (!HEX_STRING.test(str)) {
+        throw new Error(`invalid hex string: ${str}`);
+    }
+    const bytes = str.match(/[a-fA-F0-9]{2}/g);
+    return new Uint8Array(bytes.map((byte) => parseInt(byte, 16)));
+}
+function uint8ToHex(array) {
+    return array.reduce((str, byte) => str + ('00' + byte.toString(16)).slice(-2), '');
+}
+function uint8ToBase64(array) {
+    return btoa(String.fromCharCode(...array));
+}
+function uint8ToBase64Url(array) {
+    return uint8ToBase64(array).replace(/=/g, '').replace(/\+/g, '-').replace(/\//g, '_');
+}
+
+export function urlatob(s) {
+    return atob(s.replace(/-/g, '+').replace(/_/g, "/"));
+}
+
+export async function deriveScopedKey(kB, uid, identifier, key_rotation_secret, key_rotation_timestamp) {
+    async function importKey(k) {
+        return await crypto.subtle.importKey('raw', hexToUint8(k), 'HKDF', false, ['deriveBits']);
+    }
+
+    async function derive(salt, k, info, len) {
+        let params = {
+            name: 'HKDF',
+            salt,
+            info: new TextEncoder().encode(info),
+            hash: 'SHA-256',
+        };
+        return new Uint8Array(await crypto.subtle.deriveBits(params, await importKey(k), len * 8));
+    }
+
+    if (identifier == "https://identity.mozilla.com/apps/oldsync") {
+        const bits = await derive(
+            new Uint8Array(),
+            kB,
+            "identity.mozilla.com/picl/v1/oldsync",
+            64);
+        const kHash = await crypto.subtle.digest("SHA-256", hexToUint8(kB));
+        const kid = key_rotation_timestamp.toString() + "-" +
+              uint8ToBase64Url(new Uint8Array(kHash.slice(0, 16)));
+        return {
+            k: uint8ToBase64Url(bits),
+            kty: "oct",
+            kid,
+            scope: identifier,
+        };
+    } else {
+        const bits = await derive(
+            hexToUint8(uid),
+            kB + key_rotation_secret,
+            "identity.mozilla.com/picl/v1/scoped_key\n" + identifier,
+            16 + 32);
+        const fp = new Uint8Array(bits.slice(0, 16));
+        const key = new Uint8Array(bits.slice(16));
+        const kid = key_rotation_timestamp.toString() + "-" + uint8ToBase64Url(fp);
+        return {
+            k: uint8ToBase64Url(key),
+            kty: "oct",
+            kid,
+            scope: identifier,
+        };
+    }
+}
+
+export async function encryptScopedKeys(bundle, to, local_key, iv) {
+    let encode = s => new TextEncoder().encode(s);
+
+    let peer_key = await crypto.subtle.importKey(
+        "jwk",
+        JSON.parse(urlatob(to)),
+        { name: "ECDH", namedCurve: "P-256" },
+        false,
+        ['deriveKey']);
+    local_key = local_key || await crypto.subtle.generateKey(
+        { name: "ECDH", namedCurve: "P-256" },
+        true,
+        ['deriveKey']);
+    iv = iv || new Uint8Array(await crypto.subtle.exportKey(
+        "raw",
+        await crypto.subtle.generateKey({ name: "AES-CBC", length: 128 }, true, ['encrypt'])
+    )).slice(0, 12);
+
+    let key =  await crypto.subtle.deriveKey(
+        { name: "ECDH", public: peer_key },
+        local_key.privateKey,
+        { name: "AES-GCM", length: 256 },
+        true,
+        ['encrypt']);
+    key = new Uint8Array(await crypto.subtle.exportKey("raw", key));
+    key = await crypto.subtle.digest(
+        "SHA-256",
+        new Uint8Array([
+            0, 0, 0, 1, // rounds
+            ...key,
+            0, 0, 0, 7, ...encode("A256GCM"),
+            0, 0, 0, 0, // apu
+            0, 0, 0, 0, // apv
+            0, 0, 1, 0, // key size
+        ]));
+    key = await crypto.subtle.importKey("raw", key, { name: "AES-GCM" }, false, ['encrypt']);
+
+    let exported_key = await crypto.subtle.exportKey("jwk", local_key.publicKey);
+    let header = {
+        "alg": "ECDH-ES",
+        "enc": "A256GCM",
+        "epk": {
+            crv: "P-256",
+            kty: "EC",
+            x: exported_key.x,
+            y: exported_key.y
+        }
+    };
+
+    let ciphered = await crypto.subtle.encrypt(
+        { name: "AES-GCM", iv, additionalData: encode(uint8ToBase64Url(encode(JSON.stringify(header)))) },
+        key,
+        encode(JSON.stringify(bundle)));
+    let tag = ciphered.slice(-16);
+    ciphered = ciphered.slice(0, -16);
+
+    return (uint8ToBase64Url(encode(JSON.stringify(header))) +
+            ".." +
+            uint8ToBase64Url(new Uint8Array(iv)) +
+            "." +
+            uint8ToBase64Url(new Uint8Array(ciphered)) +
+            "." +
+            uint8ToBase64Url(new Uint8Array(tag)));
+}