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