@turnkey/react-native-passkey-stamper/dist/util.mjs

Passkey stamper for React Native

import { Buffer } from 'buffer';
import { createHash } from 'sha256-uint8array';

// Buffer is available in Node and react-native contexts but needs to be imported
// Needs to return a base64-encoded string
function getChallengeFromPayload(payload) {
    const hexString = createHash().update(payload).digest("hex");
    const hexBuffer = Buffer.from(hexString, "utf8");
    return hexBuffer.toString("base64");
}
// Function to return 32 random bytes encoded as hex
// (e.g "5e4c2c235fc876a9bef433506cf596f2f7db19a959e3e30c5a2d965ec149d40f")
// ----
// Important note: this function doesn't return strong cryptographic randomness (Math.random is a PRNG),
// but this is good enough for registration challenges.
// If the challenge was not random at all the risk is that someone can replay a previous
// signature to register an authenticator they don't own. However:
// - we are creating a brand new authenticator here, which means keygen is happening right as we call this library
//   (this makes the replay attack hard-to-impossible)
// - even if a replay attack went through, the authenticator wouldn't be usable given Turnkey has anti-replay in place in activity payloads
//   (there is a `timestampMs` in activity payloads, see https://docs.turnkey.com/api-introduction#queries-and-submissions)
// ----
// As for "why Math.random in the first place?": it lets us avoid a dependency on webcrypto + associated polyfills
// (in react-native webcrypto isn't available)
function getRandomChallenge() {
    let randomHexChars = [];
    const hexChars = [
        "0",
        "1",
        "2",
        "3",
        "4",
        "5",
        "6",
        "7",
        "8",
        "9",
        "a",
        "b",
        "c",
        "d",
        "e",
        "f",
    ];
    for (let i = 0; i < 64; i++) {
        randomHexChars.push(hexChars[Math.floor(Math.random() * 16)]);
    }
    return randomHexChars.join("");
}

export { getChallengeFromPayload, getRandomChallenge };
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