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Informational 24 Bitcoin

Better testing of kef compression to prove importance of wbits=-10 (#728)

Public commit record

What the developer wrote

Authored by Jean Do

91/100 · Strong
Better testing of kef compression to prove importance of wbits=-10 (#728)

* better testing of kef compression (same as bbqr) to prove that wbits=-10
demanded in KEF Specifications is truly a necessary detail.
See unit-test test_brute_force_compression_check()'s docstring
to provoke errors w/ bad wbits values during compression.

* Emphasize that KEF is strict about wbits=-10 for compress,
but that implementations may use larger windows during decompress.
* expressed in tests comments (as well as by-hand tests of decompressing
with wbits=-11 to -15, for 100K samples, each having size greater than
wbits.
* expressed in `On compressed versions` section of KEF Specifications
✓ Specific, descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context✓ Mentions testing or verification✓ Links an issue, advisory, or supporting reference
The short version

What changed, and why it matters

This commit is a documentation and testing-only change for Krux's encrypted backup format (KEF). It adds unit tests and clarifies in the specification that compression must use a very specific deflate window size (wbits=-10). The change itself does not alter any production encryption or compression code; it only makes the existing requirement stricter to document and proves with tests why that exact setting matters. There is no direct security vulnerability being patched here, but it guards against a future interoperability or data-recovery failure if an implementer used a larger compression window.

Recommended action

No immediate action is required for end users. Developers and third-party implementers of KEF should ensure their compression code uses zlib.compress(..., wbits=-10) and should run the new unit tests to validate compliance. Review any forks or alternative KEF implementations for correct wbits usage.

Security signals we found

01

Specification tightening around compression window size (wbits=-10)

02

New test cases demonstrating decompression failures with non-compliant wbits values

03

No runtime code changes; defensive hardening via documentation and tests

Risk score

Why this scored 24/100

Our methodology →
Potential impact 5/30
Exploitability 3/25
Stealth signal 2/15
Affected reach 4/15
Confidence 7/10
Evidence quality 3/5
Human-validated context

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