Double Public Key Signing Function Oracle Attack on ed25519-dalek
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.
See advisory page for additional details.
ed25519-dalek1.0.1>=2Versions of
ed25519-dalekprior to v2.0 model private and public keys asseparate types which can be assembled into a
Keypair, and also provide APIsfor 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 the
Rvalue. An adversary could somehow use the signing function asan oracle that allows arbitrary public keys as input can obtain two signatures
for the same message sharing the same
Rand 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 decoupledprivate/public keypair as signing input, except as part of specially labeled
"hazmat" APIs which are clearly labeled as being dangerous if misused.
See advisory page for additional details.