Improper Handling of Insufficient Entropy in TRNG

Description

The rate at which true random numbers can be generated is limited. It is important that one uses them only when they are needed for security.

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

This code uses a TRNG to generate a unique session id for new connections to a server:

while (1){

  if (haveNewConnection()){
    if (hwRandom()){
      int sessionID = hwRandom();
      createNewConnection(sessionID);
    } } }

This code does not attempt to limit the number of new connections or make sure the TRNG can successfully generate a new random number. An attacker may be able to create many new connections and exhaust the entropy of the TRNG. The TRNG may then block and cause the program to crash or hang.

See Also