- We define True-Random Number Bugs (TRN) as:
- The software generated output does not satisfy all
use-specifictrue-randomness requirements.
- Note that the output sequence is of random bits, where values are obtained from one
or more sources of entropy.
- See also the BF Model of
Cryptographic Store or Transfer.
- High (semantic).
- Fig. 1 depicts TRN causes, attributes and consequences.
Fig 1. True-Random Number Bugs (TRN) Class - click on image for detailed view.
- Function – Health Test, Conditioning, Mixing, Output, Converting.
- Algorithm – Hash Function, Block Cipher, XOR, etc.
- Used For –Seeding, Generation.
- This is what the output sequence is used for. It could be used as a seed for a PRNG
or for generation of passwords or cryptographic keying material (keys, nonces).
- Randomness Requirement –Sufficient Entropy, Sufficient Space Size, Non-Inferable.
- This is the failed requirement.
- The notion of entropy used here is min-entropy, as the negative logarithm of the probability
of the most likely outcome. Let X be a random variable such that the set of possible
values that it can have is finite. Let
P be the set of probabilities of X having those values.
The min-entropy of X is defined as –log2max(P), where
max()finds the largest value in a set. The min-entropy is a measure of how difficult it
is to guess the most likely entropy source output.- Space size is the number of elements of the space of possible outputs. If the number
of different outputs is not sufficiently large, there is a vulnerability to a brute
force attack. Non-inferable means one cannot recover from known (guessed) information
anything about the TRBG output (CVE-2008-0141). TRBGs used for cryptography/security
must satisfy the Non-Inferable randomness requirement.
- CWEs related to TRN are: CWE-330, CWE-331, CWE-332, CWE-333, CWE-334,CWE-337, CWE-339, CWE-340, CWE-341, CWE-342, CWE-343.
- The only related SFP cluster is SFP Primary Cluster: Predictability.
- BF Descriptions of TRN Related CWEs are provided here.
- Application examples are provided here.