helpers.js

const hexToBytes = (hex: string): Array<number> => {
  const bytes = [];
  for (let c = 0; c < hex.length; c += 2) {
    bytes.push(parseInt(hex.substr(c, 2), 16));
  }
  return bytes;
};

export const SHA256 = async (doc: ArrayBuffer): Promise<string> => (
  crypto ?
    crypto.createHash('sha256').update(doc).digest('hex') :
    Buffer.from(await window.crypto.subtle.digest('SHA-256', doc)).toString('hex')
);

export const getOtsFromCertificate = (certificate: string) =>
  OTS.DetachedTimestampFile.fromHash(
    new OTS.Ops.OpSHA256(),
    hexToBytes(await SHA256(Buffer.from(certificate, 'base64'))),
  );

export const encodeOts = (ots: Object): string =>
  Buffer.from(ots.serializeToBytes()).toString('base64');
export const decodeOts = (ots: string): Object =>
  OTS.DetachedTimestampFile.deserialize(Buffer.from(ots, 'base64'));