ed25519-dalek PK Oracle

[pinkforest]

EDIT: This issue was about both the PK oracle in pub API as well as mainenance issue - Maintenace status was / has been resolved but older versions still have PK oracle where we should nudge people to bump.

NOTE: This does NOT necessarily mean the crypto on ed25519-dalek is inherently broken or insecure as of now

e.g. Depending on how we classify / see broken / insecure - people often see crypto-failure where pub API was not misused

Nonetheless facts -

6,821,009 downloads all time - 12k per day

Major downstream include ed25519, libp2p-core, solana-runtime, solana-sdk, signatory, lettre, ..

Crate has not had new publish in two years - EDIT: Release imminent.
https://crates.io/crates/ed25519-dalek

There may be a potential PrivateKey exposure that relies on public API misuse:

• Potential Signature Exploit dalek-cryptography/ed25519-dalek#209
• w/ PoC at https://github.com/MystenLabs/ed25519-unsafe-libs
• PR restrict ExpandedSK::sign visibility to avoid pk oracle dalek-cryptography/ed25519-dalek#205 from 30 June

Considering the above alone it might be feasible to flag Notice on this at least.

Crates ed25519 and Signatory are downstream high level / proxies for this

[tarcieri]

It’s maintained now

[pinkforest]

This is also a notice about older versions being vulnerable, not just a maintenance issue.
I wil keep open until the fix and advisory is merged to track it.
I've also edited to reflect the issue that it is solely now for the PK oracle which probably still should have a notice.