[TLS] Re: WG Last Call: draft-ietf-tls-mlkem-08 (Ends 20 26-07-08) (was Re: Re: Response to CoI Complaints)

Hi Jacob,

I see you have had enough free time to write several long messages.
Do you have enough time to write a short one? In particular, I asked you a few days ago
what I believe to be a question of vital importance. Does pre-hashing m do anything?
In particular, if any RFC that leverages a ML-KEM variant included pre-hashing, would you be
comfortable setting your system random to DUAL_EC_DRBG? Or even the RNG used in solely your TLS stack.

I would not be comfortable with this. I doubt many on this mailing list would think this is a sensible idea.
I imagine since you are devoting so much time to the subject of pre-hashing, you think that it will give a concrete benefit.
In particular, in the setting you have been highlighting as the relevant attack vector (a backdoored RNG, a la DUAL_EC_DRBG),
I would *hope* you think that pre-hashing ML-KEM would meaningfully prevent an attack on TLS.

If you would not be comfortable with this, I can’t see the point of debating pre-hashing.
It would be (in my eyes) a “defense in depth” countermeasure that does not defend against the attack scenario that justifies it.
This sounds useless to me personally, and is precisely what I mean when I said that “defense in depth” appears to be consistent with the definition of “arbitrary protocol modifications of questionable cryptographic value”.

Is this the case? As others have expressed, it would be nice if you could keep any reply short, as this is a very simple question, so hopefully it has a simple answer.

Best,

Mark

> On Jul 18, 2026, at 9:48 AM, Jacob Appelbaum <[email protected]> wrote:
> 
> Hi Nico,
> 
> On 7/17/26 07:35, Nico Williams wrote:
> > On Fri, Jul 17, 2026 at 12:52:05AM +0200, Jacob Appelbaum wrote:
>>> On 7/16/26 21:57, Nico Williams wrote:
>>>> The objective answer is that the horse left the barn two decades
>>>> ago when the IETF decided to get out of fighting about national
>>>> cryptographic standards, therefore Deb's 37 years at the NSA are
>>>> irrelevant in this case, and you're fighting the wrong battle if
>>>> you want to change that two-decade-old decision.
>>> That is not correct and the ISE could easily publish the drafts under discussion without consensus as Rob suggested more than a week ago.
>> Has that not been opposed too? / The relevant decision-makers would be the authors and the Independent Submission Editor. I have not seen a definitive objection from either, and I understood Eliot to be open to considering the idea.
>> 
>> Would that not be opposed too? It could certainly be opposed. What kind of opposition do you mean?
> 
> Rob's (it was Rob, right?) suggestion appears to be a viable fallback.
> The Independent Stream does not require IETF rough consensus, although
> it is not an automatic bypass: the authors and ISE would have to pursue
> it, and the IESG would still conduct the RFC 5742 conflict review
> [0][1]. I note that the authors have largely not engaged in discussion.
> 
>> I swear I've seen arguments that users of RFCs don't really understand these subtle differences in track and editor queues,
>> that they take any RFC as a 'standard'.
> 
> Yes. Many readers treat any RFC number as a standard despite the stream
> boilerplate. That is a real drawback, but it is also why the distinction
> matters for _us_: Independent Stream publication would not assert IETF
> consensus. In practice, I suspect very few outside of the IETF would
> care about the distinction. It would allow us to provide clarity when
> the matter is raised.
> 
> I still prefer resolving the issues in the working group. I am not
> opposed to publication; I am trying to identify text that makes
> publication responsible.
> 
>>>> What you're really litigating is a social death penalty for the NSA -- something we *could* do, but shouldn't.  We really, really shouldn't do that for at least several reasons, such as:
>>> You may be surprised but I very strongly agree with you. We should
>>> not litigate a social death penalty. I do not advocate for removing Deb from the IETF. No one should be harassing her. No one
>>> should be making threats. No one should be giving her a hard time.
>>> No one should be mocking her on social media. No one should be
>>> sending threatening or slanderous or libelous emails.
>> It's not just the invectives against Deb.  It's also the invectives against the I-D authors and those who have voiced support for the I-
>> D.
> 
> I extend that to everyone: Deb, the authors, supporters, opponents,
> and other participants. We need more technical communication, not
> threats, harassment, ostracism, or censorship.
> 
> I have received several reports of troubling off-list conduct. That
> should be handled through the appropriate conduct process rather than
> mixed into the technical disposition of the drafts. It is unclear to me
> if those reports will by sent by those persons to the IETF out of
> (expressed to me) fear of retaliation.
> 
>> The incessant urging to not publish anything that might be tainted by the NSA *is* very much akin to a social death penalty for the NSA.
> 
> I do not oppose publication because NSA personnel were involved.
> 
> The immediate concern is a documented NIST design decision: FIPS 203
> removed Kyber's `m <- H(m)` step, whose stated purpose was protection
> against flawed randomness, because FIPS 203 requires approved randomness
> generation [2][3]. The question is whether IETF documents should repeat
> that assumption silently or not, describe and explain the peer-
> recoverable value, and preserve a cheap local safeguard for deployments
> that do not satisfy the full FIPS model.
> 
> It is indisputable that NIST removed the hash over `m`, ignored all
> pushback, ignored official comments on the matter, and unrelated to much
> of the discussion they then also declared that non FIPS-certified
> settings are expected to simply fail catastrophically if the RNG has an
> issue. So you see, removing the hash and qualatatively weakening the
> design of Kyber, they assert is fine. That they accept this outcome and
> state that they are correct was explictly stated by NIST on this very
> list. They additionally also push this without a hybrid construction,
> also over the express concerns of the authors of Kyber. Those two things
> together and my ability to exploit ML-KEM in the Dual_EC_DRBG setting
> correctly raise eyebrows.
> 
> NSA involvement is relevant historical context, but it is not a social
> veto. NIST is not the final technical authority for the IETF, any more
> than BSI, CSE, ETSI, ISO, IEEE, or a corporation would be. Former NIST
> people dropping by to argue that the world should adopt their public
> security posture is unreasonable. They have a traditionally had the
> Suite A and Suite B security postures and we're being offered the B
> option by another name, again. The IETF should have a stronger security
> posture and wihtout being in a FIPS-certified setting. The same
> scrutiny should apply to every source: examine the design, assumptions,
> evidence, and consequences for the end user.
> 
> The still-incomplete public record concerning NIST/NSA coordination and
> the answers given in this discussion make careful review more, not less,
> appropriate. I would also welcome explicit clarification of the IPR
> position, although the current drafts do not resolve it.
> 
> Comments that are not made by NIST have not brought clarity because any
> such analysis carries no weight about NIST's actual position. If NIST
> makes clear that we are free to hash `m` and retain the IPR waiver, we
> would be able to resolve the issue of excess authority preventing a
> stronger security posture, if it is desired. Do you see that they are
> unwilling to bring this clarity? If they were gagged as John Kelsey was,
> I would expect that bringing this clarity would be out of bounds. NIST
> is free to say otherwise and what they did say on the matter is
> contridicted by the public record. It could be credibly explained but
> NIST did not deem it worthy of their time.
> 
> The American cliché "good enough for government" is the phrase that comes to mind here. Is that good enough for the IETF? No, it is not.
> 
>>> People should *especially* not be punished for the worst thing they are suspected of doing, and especially if they did not do it.
>>> Even if they are guilty, they deserve a chance at redemption.
>>> Everyone deserves a fair shot at re-integration.
>> For those who say TL;DR, the summary is that: IMO the ML-KEM I-D - and all I-Ds specifying KEMs- should normatively state which DRBGs are acceptable, and they should include informative text about the unfortunate risk of RNG-based kleptography when using KEMs outside DH hybrids.
> 
> I broadly agree, with the qualification if 'acceptable' is stated as a
> 'MUST' or a 'requirement imposed by NIST to achieve security' and that a
> hybrid does not help if both components depend on the same recovered RBG
> lineage.
> 
>> Ok then, here's my take:
>> * Ideally we should have a practical, strong PQ Diffie-Hellman.  We do not. I agree in the strongest terms. Practical post-quantum constructions with genuine Diffie-Hellman-like contributory
>> behavior remain an important research goal.
> 
> MIKE seems interesting but I have not analyzed it, evaluated it, used an
> implementation in a deployment.
> 
> CTIDH is somewhat more familar to me and while there is literature that
> is relevant for the security in the quantum setting, I find it to be
> extremely promising.
> 
> CTIDH and related commutative group-action work are interesting in that
> respect. I help maintain an implementation released by an academic
> group, but I did not design CTIDH and make no claim that it is ready to
> replace standardized KEMs. In my own experimental use I combine it with
> X25519.
> 
> More generally, I would not deploy a comparatively young post-quantum
> construction without an independently generated classical component
> today. On balance I have decided that in at least two protocol withs no
> other PQC option available, a hybrid X25519 and CTIDH-512 or CTIDH-1024
> were better than X25519 alone. This protects against CTIDH failures
> today, and hedges against a future with quantum computers.
> 
>> * All KEMs are going to have this `m` problem in some fashion.  Is that a correct statement?  That makes all of them suitable for RNG- based kleptography. I do not think that all KEMs necessarily have the same problem. We need a precise property: can an adversarial recipient recover an unchanged, sufficiently large, ordered sample of the sender's RBG output?
> 
> ML-KEM clearly exposes that shape in the most risky way possible and it
> is unnecessary risk. To recap before we en-and-de-cap: `ML-KEM.Encaps`
> samples a 32-byte `m`, and a decapsulating peer that controls its
> implementation can retain the reconstructed `m'`. Third-round Kyber
> instead hashed `m` before using it [2][3]. Other KEMs and their uses
> have to be analyzed construction by construction; a ciphertext carrying
> a recoverable secret is not necessarily carrying raw generator bytes.
> 
> In addition to Kyber where everything is essentially equal except the
> hash in our discussion, sntrup761 is a useful contrast. It uses a
> structured fixed-weight ternary polynomial `r`, not a raw 32-byte `m`.
> In the reference sampler, many 32-bit random words are masked, sorted,
> and mapped into the ternary polynomial before `r` is used, and the
> shared key is derived by hashing its encoding [4]. The recipient can
> recover `r`, but `r` is not an unchanged contiguous generator block. The
> difference is extremely stark.
> 
> That does not prove immunity to every malicious or specially shaped
> RBG. It means only that the direct ML-KEM argument does not transfer
> unchanged. I made a preliminary attempt to recover a Dual_EC_DRBG block
> through this sampler and did not succeed. I would welcome a better
> analysis, especially from the sntrup761 authors: do you see a practical
> method for reconstructing a full Dual_EC output block from the existing
> fixed-weight sampler? The sntrup761 authors and implementations could
> also hash the RNG as Kyber did to make the comparison even easier.
> Regardless, NIST and a couple of other people may discuss the
> construction of `m` and KEMs in a way that would lead a reasonable
> person to believe a KEM always has this issue. However, it is simply not
> true. A KEM does not imply an `m`  must be composed of contiguous sample
> of the system RNG without transformation, otherwise. It is misleading
> and it is dangerous as I have shown with Dual_EC_DRBG as an example. In
> TLS this can lead to decryption of the connection, and future sessions.
> This is acceptable to NIST, and it should not be to the IETF.
> 
> This difference is one reason I remain comfortable with sntrup761x25519
> as a conservative OpenSSH option. The ML-KEM SSH exchange, like TLS,
> gives an unauthenticated client an opportunity to supply the
> encapsulation key and recover the server-generated `m` pre-auth; the
> actual risk still depends on the implementation's RBG, state separation,
> and generation order. This is a kind of landmine where it increases
> analysis work and where implementations may get it wrong. It is not the
> conservative choice that I would expect from the professionally prudent
> securtiy minds that brought us OpenBSD and OpenSSH.
> 
> It however entirely makes sense if OpenSSH needs to provide ML-KEM. I
> hope that they will ensure that `m` is hashed in practice but if not, it
> only further underscores why the NIST's decision process and their
> conclusion is unreasonable. OpenSSH is not only used in a FIPS-certified
> setting, and I highly doubt that NIST will promote the various DRBGs
> used by GNU/Linux, FreeBSD, NetBSD, and OpenBSD as qualified designs. I
> would welcome it as long as they did not impose unreasonable changes as
> they did with Kyber for `m` since those designs are what the world uses.
> 
>> For this reason I think we should have no RECOMMENDED=Y non-hybrid KEMs.  But I don't see why not have RECOMMENDED=N KEMs.
>> Interesting. I support hybrids as the conservative default, but the
>> hybrid label alone is not sufficient for this issue.
> 
> If the ML-KEM interaction permits recovery of an RBG state before the
> same state lineage generates the X25519 scalar, both components may be
> predictable. If the X25519 scalar was generated first and the RBG
> resists backtracking, that component may remain independent. Reseeding,
> per-connection state, buffering, and call order all matter.
> 
> A compact version of my current classification is therefore:
> 
> scheme       recoverable value            raw RBG block?
> ML-KEM       32-byte `m`                   yes
> Kyber r3     `H(m)`                        no
> sntrup761    fixed-weight ternary `r`      no
> 
> That table is deliberately narrow. I would not label every randomized
> signature, OAEP seed, DH exponent, or structured KEM secret as a "raw
> leak" merely because it depends on randomness; the transformation and
> recoverability must be analyzed. I have done most of that analysis on
> other IETF primitives but that is for a different email.
> 
>> * TLS 1.3 has insanely large nonces ('random'), and that's enough for RNG-based kleptography.
> 
> Agreed. TLS `Random` fields already create a broader public-output
> problem, and I regret not addressing it while TLS 1.3 was being written.
> I am preparing separate work on public and peer-recoverable RBG outputs
> across TLS, QUIC, MLS, SSH, IKE, and other protocols. That broader work
> should not prevent fixing an additional clean oracle now.
> 
>> therefore ML-KEM adds nothing much new *except* that when using a FIPS-140-3 validated module then ML-KEM can sneak a Dual_EC-style DRBG in through the back door even when the TLS 1.3 implementation would not otherwise use such a DRBG.
> 
> The word "except" is doing substantial work in your sentence. ML-KEM can
> expose an additional sample of the randomness used for secret generation
> even when an implementation separates or conditions other TLS-visible
> fields.
> 
> A successful sabotage mechanism should be reliable, economical, and
> plausibly deniable. The protocol should not make that job easier when a
> wire-compatible hash removes the direct structured sample.
> 
>> * We can insist that the choice of DRBG to use MUST be one of a set we approve of, and, impliedly, none of the ones we don't approve of.
>> Agreed in principle. We should state the actual requirement rather
>> than invent combined algorithm names. FIPS 203 requires fresh
>> randomness from an approved RBG, with the required security strength, under the SP 800-90 framework [2]. Hash_DRBG, HMAC_DRBG, and CTR_DRBG are the SP 800-90A mechanisms, but the requirement
>> also includes the entropy source and construction requirements in
>> SP 800-90B and SP 800-90C.
> 
> I would then state the separate `m` issue. The approved-RBG requirement
> is the primary layer; hashing `m` is a local layer that prevents this
> consumer from returning algebraically structured output to a peer when
> the primary assumption fails.
> 
> NIST and some of the IETF, such as myself, appear to have different risk
> tolerances on that point. NIST has publicly acknowledged the limited
> claim: hashing protected the KEM, while a broken RBG could still
> compromise the wider system. That is not an argument that the KEM-level
> protection has zero value but NIST agreeing that it has value, and that
> it is not valuable to _them_. Okay! I am glad that they did not present
> an attack as their original motivation to remove the hash. It is not a
> security issue to have the hash. It is good that we do not disagree on
> that point. The performance was also not a relevant concern. Their
> expressed concern is how they logically separate things in a FIPS-
> certified setting, and outside of that setting, they qualatiatively
> weakened the design and accept the consequences. This tells us their
> security posture, and it is less than the IETF should accept. These
> kinds of "logical" separations are how we had IPsec failures with
> Dual_EC_DRBG on the internet that allowed for full passive decryption
> through nonce leakage. This was reportedly exploited by the NSA and it
> is not in dispute. Juniper engineers probably deeply regret being
> tricked by that kind of mistaken protocol and implementation design.
> 
> The public record concerning NIST/NSA coordination is, and remains,
> incomplete. Materials produced through litigation appear relevant to
> statements made during this discussion. My understanding is that the
> litagion is ongoing and that production of documented related to NIST/
> NSA collaboration remains unfinished. I do not need to resolve that
> institutional history in this email. I do think NIST should answer
> concrete questions and publish enough of the record for independent
> evaluation. We could also wait for the lawsuit to finish but that is likely to take a long time, so NIST could really help speed things up by either stating their intention to 1) immediately and proactively produce the documents in question and/or 2) directly engage here with the understanding that if the documents later contridict them, they will be on the hook. Both of those seem incredibly unlikely and that is why an independent court has been involved to _force_ NIST to produce the facts.
> 
> Does it not concern you that the facts _already_ produced in that lawsuit do not match the claims made by NIST on this very list?
> 
> If not, what would be the line for you? I ask so that when the lawsuit is finished, we may do a proper retrospective analysis.
> 
>> The AES counter DRBG is plenty good enough. Which implementation?
> 
> CTR_DRBG can be a sound construction, but naming it does not guarantee a
> side-channel-resistant implementation. Cohney et al. demonstrated cache-
> based recovery against vulnerable table-based AES CTR_DRBG code in SGX,
> including state recovery, loss of forward security, and an end-to-end TLS compromise [5]. This was an implementation attack, not a universal break of CTR_DRBG. These kinds of failures are possible because NIST's standards are below the security and the quality of the IETF's standards. There are examples worth considering such as the constraints described in NIST SP 800-90a.
> 
> The distinction matters. FIPS 197 specifies AES, but does not by itself
> require a constant-time implementation or test for secret-indexed table
> lookups. SP 800-90A specifies the DRBG construction, but cannot make a
> leaky AES implementation safe. Hardware instructions can reduce this
> particular risk, while introducing their own hardware and microcode
> assumptions. Would you believe that one of the findings in [5] as presented in 2020 ( https://rwc.iacr.org/2020/slides/Cohney.pdf ) included an OpenSSL FIPS module, the NetBSD kernel systemwide PRG (!), mbedTLS _inside_ SGX, and also the nist_rng library. That includes a FIPS-certified setting. Perhaps the FIPS-certified setting is not as strong as the NIST advertising would have us believe?
> 
> NIST has not updated the corresponding standards in response to the publication [5] as far as I am aware. I am happy to be corrected on this point but if even NIST is able to get it right, maybe we should consider this as a factor in their security posture?
> 
> I want to note as a matter of honesty that here, hashing `m` does not save a system after the attacker has extracted the CTR_DRBG key; the attacker can reproduce the hash. It does, however, address a different failure class: algebraic structure in output that is otherwise handed directly to the peer. Therefore the correct guidance is not "CTR_DRBG is broken" or "the hash fixes everything." It is:
> 
> * exclude Dual_EC_DRBG and analogous structured generators;
> * require a securely implemented, prediction-resistant RBG;
> * require side-channel-resistant primitives and sound reseeding/state
>  management;
> * retain the local hash to avoid exporting raw structure;
> * even NIST's standards and certified FIPS modules get this wrong;
> * NIST updated their threat model in 2019;
> * NIST did not update the actual standards to require safe defaults!
> 
> The longer document should review Hash_DRBG, HMAC_DRBG, and CTR_DRBG,
> including side channels, fault attacks, entropy failure, reseeding, and
> state compromise, rather than treating an approved algorithm name as an
> implementation proof. The authors of [5] note that CTR_DRBG is not provably secure, they note that Woodage and Shumow found problems with HMAC_DRBG, and they encourage the use of Hash_DRBG.
> 
> Note that the authors in addition to the "Dual_EC Backdoor" they raise the "Juniper Dual_EC Incident" they also raise the DUHK Attack on ANSI X9.31.
> 
> So - lets recap that into some conclusions:
> - No: Dual_EC_DRBG (withdrawn (!))
> - No: CTR_DRBG (FIPS certifiable (!!) does not mean not exploitable)
> - No: HMAC_DRBG (see Woodage and Shumow's related work, and others)
> 
> Meanwhile, NIST says they are working on an updated SP 800-90A where they announced a comment period ( https://csrc.nist.gov/pubs/sp/800/90/a/r2/iprd ) which closed in late 2025:
> 
>  Date Published: September 4, 2025
>  Comments Due: November 4, 2025 (public comment period is CLOSED)
> 
> Aside from the absurdly short comment period, NIST says that public comments will be posted after the closing date. Nearly a year later, that statement remains true as someday they may be posted. As of today, the public comments have not been posted as far as I am aware.
> 
> Do you want to make a prediction about Hash_DRBG?
> 
>> This, however, may run into a problem where FIPS-140-3 validated cryptographic modules might not be configurable as to DRBG choice. However, it is enough to state this requirement.  We do not have a Protocol Police function.
> 
> Agreed. Accurately summarizing the NIST requirement and adding the
> right cross-references is sufficient for that part of the issue.
> 
>> * As long as there is one acceptable DRBG that can be selected, we can state a normative requirement and give useful advice regarding the dangers of RNG-based kleptography.
> 
> Agreed. I would list the approved constructions as examples, state
> the required properties, and explain the kleptographic failure mode.
> 
>> * I do suspect that all KEMs enable Dual_EC-style kleptography. And yet ML-KEM should be published.  Not because that's a good thing, but because -once more- the horse left the barn when the nonces (`Random`) were made more than large enough and when the codepoint registries were made Specification Required. I do not think the general conclusion about all KEMs follows, but I also do not think this is a reason to withhold ML-KEM indefinitely. My request concerns an avoidable, wire-compatible footgun and accurate
>> Security Considerations, not ML-KEM's lattice hardness assumptions.
> 
>> But also I'd have to see how recovering *one* `m` value would allow a kleptographer to steal *many* other clients' `m` values.
> 
> For Dual_EC_DRBG, the result depends on truncation and state
> management. With an untruncated 32-byte output, one `m` may be enough for the trapdoor holder to recover the next state. With the standardized
> P-256 truncation, the attacker normally enumerates the missing bits and
> uses another output or other state information to identify the correct
> candidate [8]. Once a long-lived shared state is recovered, later
> outputs may be predicted until reseeding or separation defeats
> synchronization.
> 
> Or put simply: you draw 32 bytes from the sabotaged RNG, you transmit it, you then draw 32 more bytes.
> 
> An adversary with the Dual_EC_DRBG trapdoor/secretkey(s) that receives your first 32 bytes is able to predict the 32 bytes of the second draw, even if you do not send them.
> 
> Would you like me to send you an implementation of this where you control the trapdoor/secretkey(s)?
> 
>> * The large size of `Random` is still problematic.
> 
> Agreed. I call these public or peer-recoverable wire oracles. TLS 1.1,
> 1.2, and 1.3 all expose large `Random` fields, and other protocols can inherit related risks through TLS or their own public randomness.
> 
> My broader survey remains preliminary because implementation choices,
> state sharing, sequencing, and authentication phase change the answer.
> If this attack class is deployed, however, the strategic value for mass
> collection and real-time decryption could be substantial.
> 
>> [Heavy trimming follows.]
> 
> Thank you for tolerating my verbosity. I will try to return the favor.
> 
>>>> * If the NSA wants to get burned again by playing the Dual_EC game again, let them!
>>> This is frankly, reckless. We should not be used unwittingly or be
>>> party to such folly.
>> My personal advice: sometimes that is the smart play -- if you never
>> engage in tactical retreats thus badly losing some battles, you'll
>> exhaust yourself and lose the war.
> 
> I take the advice. My claim here is bounded: we should learn from
> Dual_EC_DRBG and treat it as the canonical public example of strategic
> cryptographic sabotage. The tactical compromise I can support is to
> publish after adding accurate RBG requirements and the `m` guidance,
> while moving the larger analysis to separate work.
> 
> I am exhausted, but that is another reason to turn the dispute into
> specific text rather than continue repeating it.
> 
>>>> * The NSA is not likely the monolith a social death penalty for it would have to presume.
>>> I do not understand this point but I agree that the NSA is not a monolith. Part of asking the questions that I asked is that there are NSA people I have directly spoken to who answered almost all of those questions without a problem. I am not only talking about whistleblowers but people whose job never involved cryptographic sabotage.
>> But you and/or others in these threads are treating all involved with NSA in regards to ML-KEM as monolithically motivated by the same interest in kleptography.  That amounts to treating the NSA as a monolith.  "It's supported by NSA pEoPlE!!" is basically the backup singers' line.
> 
> Thank you for clarifying. I do not infer a common motive from NSA
> affiliation, nor do I want an institutional blacklist. I would apply the
> same skepticism to Edward Snowden, Bill Binney, Thomas Drake, an NSA
> engineer, a NIST employee, a defense contractor, or an independent
> academic: examine what they propose, what assumptions they bring, how
> they answer questions, and what outcomes their position produces. Most of all, I would want to examine their security posture.
> 
> Institutional background can still be relevant without making the
> institution a monolith. People with access to classified systems may
> know constraints or attacks that they cannot describe publicly. That can
> create blind spots even without malicious intent. Suite A is the obvious
> example: public reviewers cannot reason from secret knowledge they do not possess, and a person who possesses it may be unable to explain why or even _that_ a public design is unsafe.
> 
> Furthermore, they may feel that even if they _could_ do so, they do not agree with thwarting large-scale adversaries if it would thwart their favorite, civil-liberties respecting, honest, law-abiding, large-scale adversary... who they consider more as a friend in any case.
> 
> The solution is not personal exclusion. It is transparent threat models,
> conflict disclosure where applicable, independent review, explicit
> assumptions, and technical mitigations that do not depend on trusting a
> person's institutional role. It is also important to look at the results. NIST's modified Kyber grants a cryptographic oracle in over a dozen protocols where the protocols are layered.
> 
> Example: your Signal client uses ML-KEM in TLS, and again in the Signal e2ee ratchet. Neither are required to be FIPS-certified, to put it mildly.
> 
> My own principle is simple: I will not support cryptographic sabotage or
> an accommodation designed to preserve it or that allows for it as an acceptable consequence of an imposed change against the express wishes of the cryptographic primitive's designer(s). I will support technically
> sound protections even when they protect people or institutions hostile
> to me. RFC 7258 says pervasive monitoring is an attack; the relevant IETF value is to reduce harm to the end user [12].
> 
>>>> * There is no technical content regarding ML-KEM to back this up.
>>> I could easily believe that you were aware of these issues before the discussions on this list. Were you?
>> Some of them.
> 
> Agreed. As exhausting as it has been, the discussion has produced a
> clearer technical record and some real convergence.
>>> For example, were you aware that you could do this kind of thing, including recovering `m`?
>> I believe my earlier response (and the above) should make it clear that I am.  Above is a fuller treatment of this issue.
> 
> 
> Yes, now it is clearer. I was asking about before the discussion
> because the point is subtle and was absent from the drafts' Security
> Considerations and from several early responses. That suggests a gap in
> our protocol-analysis process worth fixing.
>>> Do you think that the removal of a hash function to enable it is not "technical content" when that single design choice was made exactly to counter this kind of thing?
>> Not sufficient to stop publication.  Instead it is sufficient to argue that the choice of DRBG must be limited.
> 
> 
> Then we agree that it is technical content. I am not asking for nonpublication as an end in itself. If the DRBG restriction includes the reason for it, the recoverability of `m`, and the Appendix C.1 tradeoff, we are close to agreement.
>>> Are you really buying the argument from NIST where they made it worse and accept that as a fact, over what, ~300-1500 cycles?
>> With a non-kleptographic DRBG it seems fine.
> 
> Does that still hold with the cited research showing that the current (not even including Dual_EC_DRBG!) NIST DRBG have non-trivial security failures?
> 
> Does it concern you at all that a practical full state recovery over the network against TLS was shown for CTR_DRBG in a FIPS-certified setting and NIST has so far only updated their _threat model_? If the authors did not catch that two month call for comments _five years later_, will NIST even address these issues?
> 
> Regardless, as of now, it does not seem fine to me. Updating the threat model is absolutely hilarious, I am sure that is very reassuring to impacted parties.
> 
>> I agree that the risk of inserting a kleptographic DRBG is real, but not publishing is not
>> really a good answer.
> 
> 
> We agree that the kleptographic-RBG risk is real, and I agree that
> nonpublication is not the only answer.
> 
> I still would not call the unhashed design equally safe. It is
> qualitatively weaker than the same construction with one additional
> hash because it relies entirely on the RBG and its implementation. The
> hash was present specifically to tolerate one class of upstream failure.
> 
> CTR_DRBG illustrates the distinction between an algorithm and a deployed
> system. The Cohney et al. work used cache leakage in a vulnerable AES
> implementation to recover DRBG state and compromise TLS [5]. That does
> not show that CTR_DRBG is kleptographic, but it does show that "use an
> approved DRBG" is incomplete implementation guidance. Similar questions
> exist for Hash_DRBG and HMAC_DRBG. What the relevant research literature
> says about side channels, fault injection, entropy failure, reseeding, (RNG) state compromise, and malicious implementation all deserve
> systematic analysis.
> 
> We should define the attack classes carefully. Young and Yung's SETUP
> model is a natural starting point for deliberate kleptography, while
> side-channel and fault attacks may belong in adjacent categories. The
> engineering response can still be systematic:
> 
> * write down each attack strategy and the required capabilities;
> * distinguish design, implementation, supply-chain, and compulsion
>  failures;
> * test whether each construction and implementation resists it;
> * record mitigations and residual risk; and
> * set a minimum profile for protocol use.
> 
> Hardware acceleration is not a magic boundary. AES instructions, RDRAND,
> and SHA extensions reduce some software-side channels but add
> assumptions about hardware, microcode, firmware signing, and update channels. Those assumptions can fail through ordinary bugs or sophisticated compromise.
> 
> The point is not that every extreme scenario is occurring; it is that
> protocol guidance should not confuse a standardized algorithm with an
> immutable, side-channel-free implementation. Also, IETF should not push a standard that requires FIPS-certified setting as a general matter when the general case was made weaker and imposed a new dependency to acheive security: the FIPS-certified setting!
> 
> I have preliminary experiments in which an ML-KEM interaction supplies a
> useful observation point against a deliberately vulnerable table-based
> CTR_DRBG implementation. I do not present that as a general break or a
> finished result. The research from 2019/2020 still generally applies.
> 
> The immediate conclusion remains modest: require a defensible RBG,
> require secure implementation and state management, and hash `m` so this
> particular peer interface does not export raw structure. The longer-term
> work can determine what additional requirements are needed for each
> SP 800-90 construction.
> 
> Also just to restate the obvious: we are really discussing some text in a text file that is _advice_ to implemnters who are not building in a NIST-certified setting. Those implementers better understand the situation and are required to diligently follow NIST's standards. Yes, that still leads to certified implementations being broken in some cases and that is _also_ NIST's problem, not the core concern that we face.
> 
>>>> There is only the 1DES key weakening and the Dual_EC adventure,
>>> This is not a fair or accurate accounting of the history. Even if you skip the Clipper Chip, export cryptography and all related attacks in SSL/TLS, and many other related matters, the issue of Dual_EC_DRBG amazingly *still* ships today in one of the most popular Java libraries in the world. It also ships ML-KEM. We agree about 1DES, of course.
>> Clipper was an overt attack on the public. There are at least two distinct issues.
> 
> Clipper was an overt policy attack, but policy opposition was not the
> whole story.
> 
> From memory, Prof. Dr. Matt Blaze had to find a novel technical failure in the Escrowed Encryption Standard: the 16-bit LEAF authentication check could be searched so that a device retained strong Skipjack encryption while bypassing the escrow mechanism [9]. This was not a cryptanalytic break of Skipjack itself; it was a break of the key-escrow protocol surrounding it. That distinction strengthens, rather than weakens, the lesson that expert technical review can defeat a government-mandated access design. Skipjack itself followed the 1DES pattern with the 80-bit key and 64 bit block choices by the way.
> 
>> The 512-bit modular DH group precomputation thing was not a covert attack on the standards process.
> 
> It is not only about 512-bit DH, of course.
> 
> I understand the perspective that export controls and weak 512-bit groups were not, by themselves, covert manipulation of the standards process.
> 
> Noteworthy however is that "covert" depends on a lot of assumptions about people's understanding of what certain technical framing means in a given context. The GSM cryptographic weaknesses may well have been understood by some telecom technician but most non-technical users of the phones most certainly did not always understand.
> 
> They were nevertheless policy-created weaknesses whose practical consequences were not understood by most users of products marketed as secure. We should classify the history precisely without minimizing the harm.
> 
>> Perhaps only Dual_EC was a covert attack on the standards process.
> 
> I do not think Dual_EC_DRBG exhausts the documented history of
> SIGINT enabling or weakened communications standards.
> 
> GSM is one example. TETRA is another important case: the secret TEA1 algorithm,  used in critical-communications systems, reduced an advertised 80- bit key to 32 effective bits and was only publicly understood after reverse engineering [10]. The researchers did not establish who inserted the weakening or whether it was exploited, but the result is directly relevant to how we evaluate secret or nationally
> constrained cryptographic designs. TETRA is highly relevant to European security.
>> ML-KEM might be a covert attack, but not on the standards process because the codepoints were always going to be assigned, and of course we're discussing the possibility that ML-KEM is kleptography so much that everyone who needs to know that it could be, does.
> 
> The public, undeniable fact is that FIPS 203 removed the hash that
> Kyber said protected against flawed randomness [2][3]. I am not claiming
> that ML-KEM is itself a covert attack. I am saying that the change opens
> a direct hidden-structure failure mode and that an approved algorithm
> name does not eliminate implementation or side-channel risk and that is when we are speaking about the FIPS-certified setting. Outside of that NIST's change makes our lives harder which is not something that we are required to accept and to pass on to others. The NetBSD kernel wide DRBG CTR_DRBG example from [5] was impressive.
> 
>> Clipper being an overt attack, and ML-KEM maybe a covert attack, you
>> can see that Clipper would be easier to defeat -- the whole public
>> could see it.
> 
> Agreed: the removal is not covert. Appendix C.1 records it. The
> technical effect is also public: relative to third-round Kyber, ML-KEM
> no longer has that local safeguard against flawed randomness. Experts
> therefore have a responsibility to explain the tradeoff and the
> assumption that replaced it.
> 
>>>> And again, if your fears turn out to be true, then you win a big
>>>> prize: more egg on the NSA's face.
>>> This does not follow. It took over a decade for John Kelsey to come out with his public apology tour. It only happened because one person blew the whistle and essentially killed himself for us to know about it.
>> But the egg landed on their face much earlier.  Apologies and non- apologies are merely the acknowledgement
> 
> Agreed that the reputational damage began earlier but it was also
> paid in disrespect to people who raised the findings as a concern.
> That pattern repeats here as a variation on the theme but this time,
> the attack may be a fact to some but now instead of being in doubt,
> it is dismissed as old news or as irrelevent or unexploitable, and so on.
> 
> The important point is not whether an institution eventually apologizes; it is how long users remain exposed before the technical problem is acknowledged and fixed. Shumow and Ferguson's 2007 rump-session observation, and Blaze's Clipper work, are reminders that early warnings deserve serious technical treatment.
>>>> Thus I don't think there is anything we can do regarding `m` other than give advice for non-FIPS implementations -- perhaps we should do that much,
>>> That sounds like the discussions have moved you!
>> Then you might like the above.  Except you might not because it doesn't move the needle as much as you seem to want.
> 
> I will take the movement and thank you for several intense but useful
> days of discussion.
> 
>>>> but that seems like something TLS and IETF should say much more generally in a BCP rather than in each Internet protocol RFC that somehow needs RNGs.
>>> Or maybe, not? I guess I also agree with you that we need a draft about the overall issue. Would you be interested in co-authoring such a draft?
>> I cannot easily co-author I-Ds [for reasons], not with celerity.  I can comment and suggest text.
> 
> Thank you. Comments and suggested text would be genuinely useful; I
> could take responsibility for an updated draft but I think the draft authors should resolve the outstanding technical issues that they see as valid. That tells us about the security posture that they wish to advance in the IETF. That applies _equally_ to the hybrid and the pure ML-KEM drafts.
> 
>>>> * You and others are destroying your credibility and good will towards yourselves and towards the IETF by really reaching in your arguments against ML-KEM.
>>> That is a fair point. [...]
>> That sounds like the discussions have moved you as well :)
> 
> Yes. The discussion has moved me toward a narrower, more actionable
> position where now I see that NIST's current DRBG offerings are _exceeding dangerous_ in the TLS context. Simply presenting them
> without qualification seriously misrepresents the risks as a general
> solution. I remain concerned that credibility and tone sometimes
> displace technical disposition, but I should also make my own arguments easier to assess and harder to dismiss.
> 
>>> I observed an intense desire for conformity and harmonization in the form of a popularity contest. There are a few people in the discussion who broke through that wall. Quite a few people demonstrated that when it came down to a factual point that they have a duty to the truth. I personally respect that a lot more than the parasocial shaming behavior and the foot dragging.
>> Last October I was on DJB's side.  His pounding the table got me to abandon that side -- there were no real arguments other than "they've done it before" and "of course they'd do it again".  Now there's the `m` matter, and regarding that see the above.
> 
> The cases for and against pure PQC and hybrids are broader than those
> two slogans. I also understand why perceptions of repetitive or abrasive presentation can cause readers to disengage. This is in part a big
> structural failing of the NIST process and it is a problem in the IETF
> as well.
> 
> At the same time, process cannot substitute reaction to style for a
> technical disposition. NIST's participation raised factual questions
> about the history and rationale of the change, and the answers did not
> resolve all of them. My earlier comments also waited years for a partial
> response. That history helps explain the frustration, although it does
> not excuse unnecessary heat from any participant.
> 
> I will focus this reply on the concrete convergence: define the RBG
> requirements, explain `m`, record the Kyber/FIPS change, and state the
> mitigation.
> 
>> I really want to emphasize that DJB's manner of argument is a tremendous turn-off.
> 
> 
> I hear you. It should not determine whether a reproducible technical
> claim is true. The working group needs both professional communication and a process that tracks substantive objections to a clear disposition.
>>> We should still try to do good things for the betterment of all people, even if they're unappreciative.
>> Some people, when faced with a difficult war, choose a hill to die on, then die on it.  Others fight until it's time to retreat to live
>> to fight another day.  Martyrs don't win wars.
> I understand. The useful response is not martyrdom but converting the
> issue into durable text and reproducible work. While it remains in our
> power, we should endeavor to create that centered around the End User's security. The End User that is not in the FIPS-certified setting especially as NIST has the FIPS-certified setting covered. It does not exactly inspire confidence that in the FIPS-certified setting the certified CTR_DRBG could be exploited to remotely extract the CTR_DRBG AES keys over a network through TLS. They have it covered alright! That security posture is their choice.
> 
>>> This mistake by NIST should be undone in so much as we should not go along with something when the research data shows that it is dangerous.
>> Look at it from NIST's point of view: that hash merely extends the DRBG, and via FIPS they mandate DRBGs, so if the hash is important then it should be included in the DRBG or the DRBG should be designed so it's not needed because the DRBG is not necessary.
> 
> I understand that position. But a protocol-level hash is not merely
> "more DRBG." It enforces a property at a separate boundary: the peer
> receives `H(x)` rather than the DRBG output `x`. That matters precisely
> when the upstream RBG assumption fails, and not every TLS deployment is
> inside the FIPS validation model.
> 
>> Thus my [new] position is that we should limit the set of acceptable
>> DRBGs.
> 
> We may agree on limiting acceptable RBGs if phrased as NIST's requirements that must be imposed to acheive their notion of security.
> Because approved construction names do not by themselves guarantee a
> safe implementation, I would add implementation guidance here and
> develop the broader requirements in a separate document. I was shocked
> when I realized that the literature piles up but the FIPS standards do not keep pace, rather the _threat model_ is updated! TLS should become stronger and stronger as we learn new things, and the threat model should become _stronger_ as adversary capabilities improve. The purpose of TLS is to provide _security_ not a false sense of security, after all.
>>> Yes, I understand the criticism that this appears to be contrived because you do not use /dev/hwrng or similar interfaces but I wonder what would change your mind?
>> The `m` issue did change my mind, as you noted.  Just not to the point of opposing publication.  Rather, I propose normatively limiting the choice of DRBGs to ones we believe are not kleptographic.
> 
> I do not oppose publication once the immediate issues are written down
> or referenced accurately.
> 
>>> For example, the Cavium SIGINT enabling - Cavium has a kernel driver for their hwrng and it presents as /dev/hwrng which does not transform the output. This kind of CPU is used in "security" devices.
>>> Please consider that NSA claims it as a SIGINT Enabling Success.
>> If you have a TLA-in-the-box attack, you have bigger problems.  And by you I mean we, naturally.
> 
> My question is whether "if" is the right prior and what evidence would
> change it.
> 
> The Cavium reporting shows a knowledge-and-choice problem: users may rely on hardware and firmware they cannot meaningfully audit, and hardware RNG interfaces can feed operating-system entropy pools or be consumed directly. A compromised source is a system-wide problem, but that is not a reason to remove cheap local barriers at protocol boundaries. The reason for the removal is not required for security and
> it re-introduces an entire class of security failures. Some large-scale deployments could easily remove that hash and no one will know, so in my view those kinds of deployments should not impose their extreme privilege on the rest of us. Most people, unlike the large defense contractors who mentioned hashing was going to impact their bottom line or the environment, do not have thousands of engineers working from the top to the bottom on their systems. Most people do not have absolute confidence in their full computing systems, they must make assumptions about trust which will change in a big way with this PQC transition.
> 
>>> Would you believe that someone does the wrong thing with that kind
>>> of stack and does so in a way that harms security?
>> Certainly possible, even likely.
> 
> I am glad we agree.
> 
>>>> * We know they will go to IEEE if we don't publish.  IETF is much more open, so if we abdicate our remit to more closed SDOs,
>>>> what will you have achieved with this social death penalty?
>>> I do not understand this part - the draft can go to the ISE if consensus can't be reached. Deb should not be pushed out of the IETF, and no one should be ostracizing her. This holds for anyone in these discussions, even convicted felons.
>> See above (at the very top).
> 
> Understood.
> 
>>> That said - if the authors of the draft want to take it elsewhere and publish it, especially because the WG won't rubberstamp something and want to add some basic security considerations, I would say that is their right. I note that they are welcome to integrate the text and then I think most objections would be handled. Most of us can't edit the draft by merging a pull request. I have the sneaking suspicion that that if I open the pull request that it would not be merged. If I am wrong, I would do the work.
>> Would you settle for publishing with a normative requirement that the DRBG used to generate `m` be one we approve of?
> 
> Almost. I would settle on publication with a normative RBG requirement
> plus text that explains why `m` matters and recommends restoring the
> hash. The RBG restriction and the hash address different layers. The
> same is true of CTR_DRBG: choosing the construction does not excuse a
> leaky table-based AES implementation. That leaky table-based AES situation is catastrophic and that is for a current NIST DRBG. At the very least we should also normatively cite the (ever weaker?) NIST threat model!
> 
>>>> Really, pick your fights carefully!
>>> I take your point(s) and I respectfully submit that I observe what
>>> appear to be some oversight in a few of your priors. I appreciate
>>> many of your points though.
>> Have I covered all points now?
> 
> Probably, yes. Remaining is some discussion above as well as the task to produce the exact text.
> 
>>> We all have a duty to resist and none of us have a duty to obey. We
>> I agree with this.
> 
> Good to know, I am glad.
> 
>>> have no requirement to simply go along with such things, especially if we think will lead to harm to the End User. With deep respect to the actual Indigenous people of the world: we the Indigenous Cryptographers of the Internet SHOULD help the End User
>>> to resist targeted and mass surveillance and indeed, we MUST treat
>>> pervasive monitoring as an attack [0].
>>> To paraphrase Bill Hicks: there is a war on your privacy and each time that you protect your privacy with strong encryption, you're winning it.
>> On so many fronts.  The whole age verification stuff is clearly aimed at ending anonymous and pseudonymous posting so as to force self-censorship on people.
> 
> Agreed. The claimed benefit of broad age-verification mandates does
> not justify the resulting surveillance, identity linkage, and chilling
> of anonymous or pseudonymous expression.
> 
>>> [0] A term the NSA has given *us* and we should claim it, and wear
>>> it with pride to stand in solidarity with other Indigenous peoples
>>> of the world.  Note: "the fact that NSA/CSS makes cryptographic
>>> modifications to commercial or indigenous cryptographic
>>> information security devices or systems in order to make them
>>> exploitable" is "Top Secret" - https://www.spiegel.de/ international/germany/inside-the-nsa-s-war-on-internet-security- a-1010361.html
>> But also public.  And something we basically knew to expect.
> 
> Yes. The history is public enough that surprise is no longer a
> reasonable response. The standards question is which concrete
> engineering lessons we apply now.
> 
> Kind regards,
> Jacob Appelbaum
> 
> [0] https://datatracker.ietf.org/doc/html/rfc8730
> 
> [1] https://datatracker.ietf.org/doc/html/rfc5742
> 
> [2] https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.203.pdf
> 
> [3] https://pq-crystals.org/kyber/data/kyber-specification-
> round3-20210804.pdf
> 
> [4] https://ntruprime.cr.yp.to/nist/ntruprime-20201007.pdf
> 
> [5] https://eprint.iacr.org/2019/996
> 
> [6] https://datatracker.ietf.org/doc/html/rfc4086
> 
> [7] https://datatracker.ietf.org/doc/html/rfc8937
> 
> [8] https://hovav.net/ucsd/dist/juniper.pdf
> 
> [9] https://www.mattblaze.org/papers/eesproto.pdf
> 
> [10] https://www.midnightblue.nl/research/tetraburst
> 
> [11] https://cr.yp.to/antiforgery/cachetiming-20050414.pdf
> 
> [12] https://datatracker.ietf.org/doc/html/rfc7258
> 
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