h1 = function(b) {
    return new e2e.hash.Sha1().hash([b].concat(secbytes));
  }
h1 function as defined in OTR spec.
@param {number} b The input byte.
@return {!e2e.ByteArray} The 160-bit output of the SHA-1 hash of the
    (5+len) bytes consisting of the byte b, followed by secbytes.