Hawkynt

JSF

JSF (Jenkins Small Fast) is a compact, high-speed pseudo-random number generator by Bob Jenkins with 128-bit state. It uses simple operations (rotate, add, XOR) to achieve good statistical properties and passes PractRand testing. Widely used as a baseline for evaluating small fast RNGs.

Properties

Property	Value
Category	Random Number Generators
Sub-category	Deterministic PRNG
Security status	🎓 Educational Only
Complexity	Intermediate
Inventor	Bob Jenkins
Year	2007
Origin	🇺🇸 United States
Source	algorithms/random/jsf.js

Parameters

Parameter	Supported values
Seed sizes	1 byte (8 bits) to 4 bytes (32 bits)

Capabilities

Flag	Value
IsDeterministic	Yes
IsCryptographicallySecure	No

Security

Status: 🎓 Educational Only

No vulnerabilities are recorded for this implementation.

Documentation

• Original Specification: A small noncryptographic PRNG
• PractRand Analysis: Bob Jenkins’s Small PRNG
• C++ Implementation by Melissa O’Neill
• Wikipedia: Jenkins hash function

References

• PractRand Statistical Testing Suite
• Bob Jenkins’ Website: Hash and PRNG algorithms

Test vectors

5 vectors ship with this algorithm and run in the test suite. Byte values are hexadecimal.

Vector 1 — Seed 0x00000000: First 10 outputs (40 bytes) - verified against reference C implementation

Field	Value
seed	00000000
outputSize	40
input	null
expected	1a9b6c079a550895f12be8760902ba19 20f1a244832bc5d20bfdb9a17384175a 96a0f7e5470ad8f6

Vector 2 — Seed 0x00000001: First 10 outputs (40 bytes) - reference implementation

Field	Value
seed	00000001
outputSize	40
input	null
expected	a25132f41efa0761332b56b3d1aedb87 4c4d7156b663157a9b0a0c8a973762fe dde060ec17e08dec

Vector 3 — Seed 0xDEADBEEF: First 10 outputs - test with common debug value

Field	Value
seed	deadbeef
outputSize	40
input	null
expected	fa65a416addcc8e093bc44ac7abd07e5 19cbdd754b2dc24764721eef1216e1bf fdcaec4e4dd17fb7

Vector 4 — Seed 0x12345678: First 10 outputs - test with sequential byte pattern

Field	Value
seed	12345678
outputSize	40
input	null
expected	4324435b28203161e6d195a631e53a77 7c50cdfb1849d8708acf3d19b11c67e4 22bac8877c58e3e7

Vector 5 — Seed 0xCAFEBABE: First 8 outputs (32 bytes) - test with another common value

Field	Value
seed	cafebabe
outputSize	32
input	null
expected	c722b02e94af7b4bad16571e1f2632d3faa708acc7a955c6227b814437a4f519

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