Cryptographic Operations are run Before Supporting Units are Ready

Description

Many cryptographic hardware units depend upon other hardware units to supply information to them to produce a securely encrypted result. For example, a cryptographic unit that depends on an external random-number-generator (RNG) unit for entropy must wait until the RNG unit is producing random numbers. If a cryptographic unit retrieves a private encryption key from a fuse unit, the fuse unit must be up and running before a key may be supplied.

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 following pseudocode illustrates the weak encryption resulting from the use of a pseudo-random-number generator output.

If random_number_generator_self_test_passed() == TRUE
then Seed = get_random_number_from_RNG()
else Seed = hardcoded_number

In the example above, first a check of RNG ready is performed. If the check fails, the RNG is ignored and a hard coded value is used instead. The hard coded value severely weakens the encrypted output.

If random_number_generator_self_test_passed() == TRUE
then Seed = get_random_number_from_RNG()
else enter_error_state()

See Also