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Also known as: CSPRNG, DRBG
A pseudorandom number generator suitable for cryptographic use due to unpredictability and resistance to attacks.
DESCRIPTION
A cryptographically secure pseudorandom number generator produces numbers that are computationally indistinguishable from true randomness for adversaries, given appropriate entropy and seeding. CSPRNGs underpin key generation, nonces, salts, and secure tokens. Standards such as NIST SP 800-90A define approved deterministic random bit generators. Using non-cryptographic PRNGs for security threatens confidentiality and integrity.
ALTERNATIVE DEFINITIONS
NIST SP 800-90A Rev. 1
A DRBG is a deterministic algorithm that, given an initial seed, outputs a sequence of bits that are computationally indistinguishable from random bits to an observer without knowledge of the seed.
Formalizes deterministic generation and indistinguishability under standard assumptions.
IETF RFC 4086
For security, random numbers must be unpredictable; cryptographic applications require generators that produce bits lacking any predictable patterns to adversaries.
Stresses unpredictability requirements for security-sensitive contexts.
Microsoft Learn
Represents a cryptographic random number generator, which generates random numbers suitable for use in cryptography.
Vendor API definition focused on secure random usage.
RELATED TERMS
Entropy Seed NIST SP 800-90A RFC 4086 Random Number Generator Key Generation Nonce
COMPETING TERMS
Pseudorandom Number Generator Hardware Random Number Generator
RELATIONS
- Broader: Pseudorandom Number Generator
- Narrower: Blum Blum Shub
KNOWLEDGE AREAS
Data Security Mathematics Software Engineering
TARGET AUDIENCE
Cybersecurity Engineer Security Architect Software Developer DevOps Engineer Chief Information Security Officer
EXTERNAL SOURCES
- Wikipedia - Cryptographically secure pseudorandom number generator
- NIST - DRBG specifications and guidance
- OWASP - Secure randomness and storage guidance
- IETF - Randomness requirements for security
TOP QUESTIONS
Why use a CSPRNG instead of a PRNG?
CSPRNGs resist prediction and attack, ensuring secure keys and tokens, unlike typical PRNGs designed for simulation or performance.
Category: Misunderstanding
What makes a CSPRNG secure?
Proper entropy sources, strong seeding, vetted algorithms, and adherence to standards like NIST SP 800-90A ensure security.
Category: Requirements
What are common mistakes using CSPRNGs?
Reusing seeds, inadequate entropy, rolling your own generator, or using non-crypto PRNGs for security tasks.
Category: Mistakes
How do operating systems provide CSPRNGs?
APIs like /dev/urandom, CryptGenRandom, and RandomNumberGenerator supply secure randomness to applications.
Category: Overview
What is the risk of weak randomness?
Predictable keys and tokens enable breaches, impersonation, and data compromise.
Category: Risks
How to test randomness quality?
Use statistical test suites and compliance checks, but rely on vetted algorithms rather than custom designs.
Category: HowTo
Are hardware RNGs better than CSPRNGs?
Hardware RNGs provide entropy; CSPRNGs scale and manage distribution. Combine them for robust randomness.
Category: Opinion
Where to start learning about CSPRNGs?
Read NIST 800-90A, RFC 4086, and OWASP guidance; review OS-level APIs.
Category: Overview
What is a DRBG in NIST terminology?
A deterministic random bit generator—a standardized CSPRNG producing pseudo-random bits from a seed.
Category: Definition