@sphereon/oid4vci-common/lib/functions/RandomUtils.ts

OpenID 4 Verifiable Credential Issuance Common Types

import { defaultHasher } from '@sphereon/oid4vc-common';
import * as u8a from 'uint8arrays';
import { SupportedEncodings } from 'uint8arrays/to-string';

import { CodeChallengeMethod } from '../types';

import { randomBytes } from './randomBytes';

export const CODE_VERIFIER_DEFAULT_LENGTH = 128;
export const NONCE_LENGTH = 32;

export const generateRandomString = (length: number, encoding?: SupportedEncodings): string => {
  return u8a.toString(randomBytes(length), encoding).slice(0, length);
};

export const generateNonce = (length?: number): string => {
  return generateRandomString(length ?? NONCE_LENGTH);
};
export const generateCodeVerifier = (length?: number): string => {
  const codeVerifier = generateRandomString(length ?? CODE_VERIFIER_DEFAULT_LENGTH, 'base64url');
  assertValidCodeVerifier(codeVerifier);
  return codeVerifier;
};

export const createCodeChallenge = (codeVerifier: string, codeChallengeMethod?: CodeChallengeMethod): string => {
  if (codeChallengeMethod === CodeChallengeMethod.plain) {
    return codeVerifier;
  } else if (!codeChallengeMethod || codeChallengeMethod === CodeChallengeMethod.S256) {
    return u8a.toString(defaultHasher(codeVerifier, 'sha256'), 'base64url');
  } else {
    // Just a precaution if a new method would be introduced
    throw Error(`code challenge method ${codeChallengeMethod} not implemented`);
  }
};

export const assertValidCodeVerifier = (codeVerifier: string) => {
  const length = codeVerifier.length;
  if (length < 43) {
    throw Error(`code_verifier should have a minimum length of 43; see rfc7636`);
  } else if (length > 128) {
    throw Error(`code_verifier should have a maximum length of 128; see rfc7636`);
  }
};