Global and Local Entropy Tests for STL Files Under IEEE-754 Validity Constraints
Researchers derive STL-specific entropy thresholds so valid ciphertexts are not falsely rejected.
The paper derives the exact mean and variance of Shannon entropy for STL files constrained to finite IEEE-754 single-precision values, with second-order expansions for large files. Under the valid-STL distribution, the global entropy limit is 7.99991479609 bits rather than 8. For local tests, the recommended block size is 1950 bytes instead of 1936, with an exact reference mean of 7.903106732975 bits. The authors say conventional intervals can falsely reject ideal valid-STL ciphertexts and report Monte Carlo agreement with the new references.
- Exact entropy mean and variance are derived for valid STL files.
- The global reference limit falls from 8 to 7.99991479609 bits.
- Local tests should use 1950-byte blocks rather than 1936.
- Unadjusted thresholds can falsely reject ideal valid-STL ciphertexts.
From the original article
1 min read at arxiv.orgShannon entropy is a standard measure of ciphertext randomness, evaluated either globally over the byte histogram of the entire ciphertext or locally as the average over non-overlapping blocks of ? xed size. While the global statistic captures only the overall byte distribution, the local statistic is also sensitive to non-randomness that is con?
By Tonislav Troev · arxiv.org
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