code: function RSADecrypt(ctext) {
    var c = parseBigInt(ctext, 16);
    var m = this.doPrivate(c);
    if(m == null) return null;
    return pkcs1unpad2(m, (this.n.bitLength()+7)>>3);
  }
docs: Return the PKCS#1 RSA decryption of "ctext". "ctext" is an even-length hex string and the output is a plain string.