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+**Title:** Investigate Ed25519 clamping behavior</br>
+**Date:** 2021-12-09 </br>
+
+# Summary
+Ed25519 signatures have three bits that should be zero due to clamping.  What
+happens when verifying a signature that has these three bits set to something
+else?  Sigsum requires that such a signature is rejected.
+
+# Description
+First confirm that Ed25519 signatures are clamped as described in the summary,
+then investigate how `Verify()` is implemented in `"crypto/ed25519"`.  The
+assumed sigsum-log-go behavior is that `Verify()` is strict.  In other words, a
+signature that is not clamped correctly should be rejected and not "fixed".
+
+If a signature is "fixed" it would be possible to replay add-leaf requests.  A
+replay is bad for the log due to overhead.  A replay is also bad for the
+legitimate submitter because it eats into their rate limit (DoS vector).
+
+The following part of Go's implementation might be a good place to start:
+- https://cs.opensource.google/go/go/+/refs/tags/go1.16.4:src/crypto/ed25519/ed25519.go;l=208