Small Seed Space in PRNG

Opis

A Pseudo-Random Number Generator (PRNG) uses a relatively small seed space, which makes it more susceptible to brute force attacks.

PRNGs are entirely deterministic once seeded, so it should be extremely difficult to guess the seed. If an attacker can collect the outputs of a PRNG and then brute force the seed by trying every possibility to see which seed matches the observed output, then the attacker will know the output of any subsequent calls to the PRNG. A small seed space implies that the attacker will have far fewer possible values to try to exhaust all possibilities.

Skutki

• Other

  Varies by Context

Zapobieganie

• Architecture and Design

  Use well vetted pseudo-random number generating algorithms with adequate length seeds. Pseudo-random number generators can produce predictable numbers if the generator is known and the seed can be guessed. A 256-bit seed is a good starting point for producing a "random enough" number.

• Architecture and Design, Requirements · Libraries or Frameworks

  Use products or modules that conform to FIPS 140-2 [REF-267] to avoid obvious entropy problems, or use the more recent FIPS 140-3 [REF-1192] if possible.

Przykłady podatności

• CVE-2019-10908 product generates passwords via org.apache.commons.lang.RandomStringUtils, which uses java.util.Random internally. This PRNG has only a 48-bit seed.

Słabość nadrzędna

• CWE-335 Incorrect Usage of Seeds in Pseudo-Random Number Generator (PRNG)

Pokrewna

• CWE-341 Predictable from Observable State

Kiedy powstaje

• Implementation — REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Dotyczy

Not Language-Specific

Uwagi

This entry may have a chaining relationship with predictable from observable state (CWE-341).

As of CWE 4.5, terminology related to randomness, entropy, and predictability can vary widely. Within the developer and other communities, "randomness" is used heavily. However, within cryptography, "entropy" is distinct, typically implied as a measurement. There are no commonly-used definitions, even within standards documents and cryptography papers. Future versions of CWE will attempt to define these terms and, if necessary, distinguish between them in ways that are appropriate for different communities but do not reduce the usability of CWE for mapping, understanding, or other scenarios.

Źródła

1. FIPS PUB 140-2: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES — Information Technology Laboratory, National Institute of Standards and Technology, Annex C, Approved Random Number Generators, 2001
2. FIPS PUB 140-3: SECURITY REQUIREMENTS FOR CRYPTOGRAPHIC MODULES — Information Technology Laboratory, National Institute of Standards and Technology, 2019