Versions of ed25519-dalek prior to v2.0 model private and public keys as separate types which can be assembled into a Keypair, and also provide APIs for serializing and deserializing 64-byte private/public keypairs.
Such APIs and serializations are inherently unsafe as the public key is one of the inputs used in the deterministic computation of the S part of the signature, but not in the R value. An adversary could somehow use the signing function as an oracle that allows arbitrary public keys as input can obtain two signatures for the same message sharing the same R and only differ on the S part.
Unfortunately, when this happens, one can easily extract the private key.
Revised public APIs in v2.0 of ed25519-dalek do NOT allow a decoupled private/public keypair as signing input, except as part of specially labeled "hazmat" APIs which are clearly labeled as being dangerous if misused.
References
Versions of
ed25519-dalekprior to v2.0 model private and public keys as separate types which can be assembled into aKeypair, and also provide APIs for serializing and deserializing 64-byte private/public keypairs.Such APIs and serializations are inherently unsafe as the public key is one of the inputs used in the deterministic computation of the
Spart of the signature, but not in theRvalue. An adversary could somehow use the signing function as an oracle that allows arbitrary public keys as input can obtain two signatures for the same message sharing the sameRand only differ on theSpart.Unfortunately, when this happens, one can easily extract the private key.
Revised public APIs in v2.0 of
ed25519-dalekdo NOT allow a decoupled private/public keypair as signing input, except as part of specially labeled "hazmat" APIs which are clearly labeled as being dangerous if misused.References