Use of RSA Algorithm without OAEP

Description

Padding schemes are often used with cryptographic algorithms to make the plaintext less predictable and complicate attack efforts. The OAEP scheme is often used with RSA to nullify the impact of predictable common text.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The example below attempts to build an RSA cipher.

public Cipher getRSACipher() {
  Cipher rsa = null;
  try {
    rsa = javax.crypto.Cipher.getInstance("RSA/NONE/NoPadding");
  }
  catch (java.security.NoSuchAlgorithmException e) {
    log("this should never happen", e);
  }
  catch (javax.crypto.NoSuchPaddingException e) {
    log("this should never happen", e);
  }
  return rsa;
}

While the previous code successfully creates an RSA cipher, the cipher does not use padding. The following code creates an RSA cipher using OAEP.

public Cipher getRSACipher() {
  Cipher rsa = null;
  try {
    rsa = javax.crypto.Cipher.getInstance("RSA/ECB/OAEPWithMD5AndMGF1Padding");
  }
  catch (java.security.NoSuchAlgorithmException e) {
    log("this should never happen", e);
  }
  catch (javax.crypto.NoSuchPaddingException e) {
    log("this should never happen", e);
  }
  return rsa;
}

See Also