8.8. Multiplication by Cofactor in Verification

8.8. Multiplication by Cofactor in Verification

The given verification formulas for both Ed25519 and Ed448 multiply points by the cofactor. While this is not strictly necessary for security (in fact, any signature that meets the non-multiplied equation will satisfy the multiplied one), in some applications it is undesirable for implementations to disagree about the exact set of valid signatures. Such disagreements could open up, e.g., fingerprinting attacks.