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\section*{Ethical Considerations}
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<h2>Ethical Considerations</h2>
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This work presents a verifiable data structure for managing hash
algorithm lifecycles in append-only logs. It involves no human subjects,
no collection of personal data, and no interaction with vulnerable
populations. No Institutional Review Board (IRB) approval was required.
The EML is a defensive construction: it enables systems to migrate away
from weakened hash algorithms without fracturing their audit history or
incurring prohibitive recomputation costs. We anticipate a net positive
societal impact by reducing the systemic risk associated with hash
algorithm deprecation in critical infrastructure such as Certificate
Transparency, software supply chain attestation, and identity state
trees. The post-quantum transition currently underway in the TLS
ecosystem underscores the urgency of this capability.
We identify no plausible dual-use concerns. The EML does not weaken
existing cryptographic guarantees, introduce new attack surfaces, or
enable surveillance capabilities. It strictly extends the verification
capabilities available to auditors and end users.
The empirical evaluation was conducted entirely on synthetic test data
generated by the property-based testing and fuzz harnesses. No
real-world log data or production systems were involved.