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import {Resources} from "../resources/main.js";
import {SRPProtocol} from "../resources/network-types.js";
/**
* The 2048-bit group used by Apple's SRP implementation (RFC 5054, Appendix A)
*/
const SRP_GROUP = {
N: BigInt(`0x` + [
`AC6BDB41 324A9A9B F166DE5E 1389582F AF72B665 1987EE07 FC319294 3DB56050`,
`A37329CB B4A099ED 8193E075 7767A13D D52312AB 4B03310D CD7F48A9 DA04FD50`,
`E8083969 EDB767B0 CF609517 9A163AB3 661A05FB D5FAAAE8 2918A996 2F0B93B8`,
`55F97993 EC975EEA A80D740A DBF4FF74 7359D041 D5C33EA7 1D281E44 6B14773B`,
`CA97B43A 23FB8016 76BD207A 436C6481 F1D2B907 8717461A 5B9D32E6 88F87748`,
`544523B5 24B0D57D 5EA77A27 75D2ECFA 032CFBDB F52FB378 61602790 04E57AE6`,
`AF874E73 03CE5329 9CCC041C 7BC308D8 2A5698F3 A8D0C382 71AE35F8 E9DBFBB6`,
`94B5C803 D89F7AE4 35DE236D 525F5475 9B65E372 FCD68EF2 0FA7111F 9E4AFF73`,
].join(``).replace(/\s/g, ``)),
g: 2n,
/**
* Byte length of N, used to pad values
*/
length: 256,
};
/**
* @param parts - The byte arrays to hash
* @returns The SHA-256 hash of the concatenated parts
*/
function hash(...parts: Uint8Array[]): Buffer {
const sha = crypto.createHash(`sha256`);
parts.forEach(part => sha.update(part));
return sha.digest();
}
/**
* @param value - The value to convert
* @returns The minimal big-endian byte representation of the value
*/
function toBytes(value: bigint): Buffer {
const hex = value.toString(16);
return Buffer.from(hex.length % 2 === 0 ? hex : `0${hex}`, `hex`);
}
/**
* @param value - The value to convert
* @returns The big-endian byte representation of the value, left-padded with zeros to the byte length of N
*/
function pad(value: bigint): Buffer {
const bytes = toBytes(value);
return Buffer.concat([Buffer.alloc(SRP_GROUP.length - bytes.length), bytes]);
}
/**
* @param bytes - The big-endian byte representation
* @returns The value as bigint
*/
function toBigint(bytes: Uint8Array): bigint {
return bytes.length === 0 ? 0n : BigInt(`0x${Buffer.from(bytes).toString(`hex`)}`);
}
/**
* @returns base^exponent mod modulus
*/
function modPow(base: bigint, exponent: bigint, modulus: bigint): bigint {
let result = 1n;
base %= modulus;
while (exponent > 0n) {
if (exponent & 1n) {
result = result * base % modulus;
}
exponent >>= 1n;
base = base * base % modulus;
}
return result;
}
/**
* This class handles the GSA SRP-6a protocol required for authentication
* The implementation mirrors Apple's iCloud web client (webSRPClientWorker.js): A, g and S are padded to the length of N, B is used as received and the account name is lowercased when hashed
*/
export class iCloudCrypto {
/**
* The account name used within the SRP protocol
*/
accountName: string;
/**
* The client's private ephemeral value (a)
*/
privateValue: bigint;
/**
* The client's public ephemeral value (A = g^a mod N)
*/
publicValue: bigint;
/**
* The shared session key (K) - only available after the proof values have been generated
*/
sessionKey?: Buffer;
/**
* Creates a new crypto object and initiates the ephemeral values for this session
* @param accountName - The account name used within the SRP protocol - defaults to the configured username. The escrow flow uses an empty account name.
* @param privateValue - The client's private ephemeral value - randomly generated by default, parameterized for testing purposes
*/
constructor(accountName: string = Resources.manager().username, privateValue: bigint = toBigint(crypto.randomBytes(SRP_GROUP.length))) {
this.accountName = accountName;
this.privateValue = privateValue;
this.publicValue = modPow(SRP_GROUP.g, privateValue, SRP_GROUP.N);
}
/**
* @returns A Promise that will resolve to the clients's ephemeral challenge used in the SRP protocol, formatted as a base64 string
*/
async getClientEphemeral(): Promise<string> {
return pad(this.publicValue).toString(`base64`);
}
/**
* This function will use the PBKDF2 algorithm to derive the password key
* @param protocol - The protocol to use for hashing the password
* @param salt - The salt value to use for password hashing as a base64 string
* @param iterations - Number of iterations to use for key derivation
* @returns A Promise that will resolve to the derived password key
*/
async derivePassword(protocol: SRPProtocol, salt: string, iterations: number): Promise<Uint8Array> {
let passHash: Buffer = hash(Buffer.from(Resources.manager().password, `utf8`));
if (protocol === `s2k_fo`) {
passHash = Buffer.from(passHash.toString(`hex`));
}
const imported = await crypto.subtle.importKey(
`raw`,
new Uint8Array(passHash),
{name: `PBKDF2`},
false,
[`deriveBits`],
);
const derived = await crypto.subtle.deriveBits({
name: `PBKDF2`,
hash: `SHA-256`,
salt: Buffer.from(salt, `base64`),
iterations,
}, imported, 256);
return new Uint8Array(derived);
}
/**
* Generates the proof values required for authentication
* @param derivedPassword - The PBKDF2 derived password key
* @param serverPublicValue - The public value shared by the server - base64 encoded string
* @param salt - The salt value shared by the server - base64 encoded string
* @returns A tuple containing the proof values m1 and m2, formatted as base64 strings
* @throws An error, if the server's public value is invalid
*/
async getProofValues(derivedPassword: Uint8Array, serverPublicValue: string, salt: string): Promise<[m1: string, m2: string]> {
const {N, g} = SRP_GROUP;
const saltBytes = Buffer.from(salt, `base64`);
const serverPublicBytes = Buffer.from(serverPublicValue, `base64`);
const B = toBigint(serverPublicBytes);
if (B % N === 0n) {
throw new Error(`Invalid server public value`);
}
const A = pad(this.publicValue);
const u = toBigint(hash(A, pad(B)));
if (u === 0n) {
throw new Error(`Invalid server public value`);
}
const k = toBigint(hash(toBytes(N), pad(g)));
// GSA: The account name is not part of the private key
const x = toBigint(hash(saltBytes, hash(Buffer.from(`:`), derivedPassword)));
const base = ((B - (k * modPow(g, x, N))) % N + N) % N;
const S = modPow(base, this.privateValue + (u * x), N);
this.sessionKey = hash(pad(S));
const hN = hash(toBytes(N));
const hG = hash(pad(g));
const hNxorHg = Buffer.from(hN.map((byte, i) => byte ^ hG[i]));
const hI = hash(Buffer.from(this.accountName.toLowerCase(), `utf8`));
const m1 = hash(hNxorHg, hI, saltBytes, A, serverPublicBytes, this.sessionKey);
const m2 = hash(A, m1, this.sessionKey);
return [m1.toString(`base64`), m2.toString(`base64`)];
}
/**
* The shared session key, which is required by the escrow flow - only available after the proof values have been generated
* @returns A Promise that will resolve to the session key K, formatted as base64 string
* @throws An error, if the proof values have not been generated yet
*/
async getSessionKey(): Promise<string> {
if (!this.sessionKey) {
throw new Error(`Session key not available before generating proof values`);
}
return this.sessionKey.toString(`base64`);
}
}
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