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+# Ed25519 clamping behavior
+Reported by: rgdd
+
+If I recall correctly an Ed25519 signature has 3 bits that should always be
+zero. What happens if any of the 3 bits are not zero during signature
+verification? It probably depends on the implementation. I would expect that the
+signature is rejected. However, a possible behavior that I would not expect is
+that the three bits are zeroed ("fixed").
+
+We need the signature to be rejected; not fixed. Otherwise it is possible to
+replay a logged entry several times by enumerating the remaining bit patterns.
+Replays are bad for the log (overhead).  Replays are also bad for the legitimate
+submitter because it will eat into their rate limit (DoS vector).
+
+It would be great if anyone could:
+- Confirm if I recall correctly. And if so, confirm if the behavior of
+`crypto/ed25519` is to reject signatures if any of the three bits are set.
+- After a quick look this might be the place to understand:
+https://cs.opensource.google/go/go/+/refs/tags/go1.16.4:src/crypto/ed25519/ed25519.go;l=208