Top all-time · #6665
Henry de Valence
Personal blog · hdevalence.ca/blog · on HN as hdevalencesecuritymathprogramming
Henry de Valence's personal blog at hdevalence.ca covers security, math and programming. Since 2013, 12 different Hacker News readers have linked it 16 times, most often “It’s 255:19AM. Do you know what your validation criteria are?”. It is still writing: the last post was on 2025-07-08, and you can follow it by feed.
Too few sampled comments (10) to say how often HN recommends it.?
Why HN links it
HN readers link Henry de Valence's posts on Ed25519 signature validation inconsistencies ("It's 25519am") as a reference on implementations disagreeing about valid signatures. Another post covers the djb/Tor/TU/e dispute.
Summarised by Claude from a sample of 10 HN comments that link here. Each comment is marked recommending, critical or neutral (citing without judging); how this works.
Most-linked posts?
- It’s 255:19AM. Do you know what your validation criteria are?7 people · 7 mentions · first linked 2020-10-05
- /blog/2020-10-04-its-25519am/2 people · 3 mentions · first linked 2025-11-24
- /etc/34de2f3c2a48f7da/EmAiLs.txt2 people · 3 mentions · first linked 2017-03-17
What Hacker News says?
Is there consensus on what signature validation is correct? https://hdevalence.ca/blog/2020-10-04-its-25519am
Comment linking /blog/2020-10-04-its-25519am
on “Willow, Our Quantum Chip”Submitted It’s 255:19AM. Do you know what your validation criteria are? as a story · 199 points
HN discussionIt's not exactly what you're looking for, but clang can give you record dumps of C and C++ structs and classes. (In general, clang has lots of interesting tooling for C and C++, and I highly recommend looking into using it). I wrote here [1] about using it in a KDE program (KStars) to cut 10% off the memory usage. In particular you can also use this tool to see some of the many bad effects of deeply nested classes:…
Comment linking /blog/2013-12-22-better-living-through-clangistry
on “The Lost Art of C Structure Packing”Submitted It’s 255:19AM. Do you know what your validation criteria are? as a story · 5 points
HN discussionGiven the emphasis on reliability of implementations of an algorith, it's ironic that the Curve 25519-based Ed25519 digital signature standard was itself specified and originally implemented in such a way as to lead to implementation divergence on what a valid and invalid signature actually was. See https://hdevalence.ca/blog/2020-10-04-its-25519am/ Not a criticism, if anything it reinforces DJB's point. But it make…
Comment linking /blog/2020-10-04-its-25519am/
on “NSA and IETF, part 3: Dodging the issues at hand”Submitted Curved-Fold Origami as a story · 2 points
HN discussionFrom the article: "Dan has written at some length about the importance of “due process”, both internally to the research group and externally to the world. But it’s telling to notice that in every such discussion, Dan carefully avoided any mention of concrete processes: he did not define the “different procedures” suddenly required for him to take action, nor what “proper procedures” should be followed." This is pat…
Comment linking /etc/34de2f3c2a48f7da/EmAiLs.txt
on “When ‘he’ll be kept on payroll, somewhere’ is where you are”Submitted Incompatible Validation Criteria for Ed25519 as a story · 1 points
HN discussionSince this post casts djb in an unfavorable light, I feel it's important to post some of his emails here, so that his words can stand alone, uncolored. From https://www.hdevalence.ca/etc/34de2f3c2a48f7da/EmAiLs.txt "Hi everybody, As most of you know, we hired Jake for a 5-year PhD program, starting with a 50-50 split between Tor and TU/e, and increasing TU/e percentage assuming that the first year goes well. The Tor…
Comment linking /etc/34de2f3c2a48f7da/EmAiLs.txt
on “When ‘he’ll be kept on payroll, somewhere’ is where you are”> I would love to hear his side of the story. Some of his side of the story has been told in the leaked emails: https://www.hdevalence.ca/etc/34de2f3c2a48f7da/EmAiLs.txt
Comment linking /etc/34de2f3c2a48f7da/EmAiLs.txt
on “When ‘he’ll be kept on payroll, somewhere’ is where you are”EdDSA is also quite a mess, see e.g. https://hdevalence.ca/blog/2020-10-04-its-25519am/ . Almost no two implementations that aren't the same code base can agree on what is and isn't a valid signature. ECDSA isn't nearly as bad, there's only two forms of the same signature possible and implementations seem to generate either of the two at random (this makes for a great subliminal channel to leak the private key if yo…
Comment linking /blog/2020-10-04-its-25519am/
on “RSA-260 Factorized”> It uses ed25519 but doesn't do anything about inconsistent validation criteria ( https://hdevalence.ca/blog/2020-10-04-its-25519am ), different implementations consider non-overlapping sets of signatures valid. If you want to have automated klaxons on signature failures, this ought to be addressed for the same reason as "repositories do not fail for a subset of users". (though it's not fatal in this application as…
Comment linking /blog/2020-10-04-its-25519am
on “Ditching OpenPGP, a new approach to signing APT repositories”Doesn't appear to have any domain separation. This means that if a common private key is reused in another application you may be able to use that application as an oracle to produce signatures it doesn't intend to use. Say you later want to have packagers sign with the same keys for security announcements. Obviously not reusing keys is good but there are reasons people do that (e.g. to share the trust of an existin…
Comment linking /blog/2020-10-04-its-25519am
on “Ditching OpenPGP, a new approach to signing APT repositories”Did you also check all of the libraries that implement the check differently to libsodium? That's one problem with the near-universal cargo-culting of ref10, it never did any of the checking so everyone has to reinvent it themselves in different ways. It might be useful to have a single known-good check for both x25519 and ed25519 that people could integrate into their own ref10-derived code. For people not familiar…
Comment linking /blog/2020-10-04-its-25519am/
on “A Vulnerability in Libsodium”25519 just brings in a different set of problems though, see for example https://hdevalence.ca/blog/2020-10-04-its-25519am , and @mmsc's post above which barely scratches the surface.
Comment linking /blog/2020-10-04-its-25519am
on “We found cryptography bugs in the elliptic library using Wycheproof”
