* Re: [bitcoindev] P2QRH / BIP-360 Update
2025-02-19 15:40 [bitcoindev] P2QRH / BIP-360 Update Hunter Beast
@ 2025-02-19 17:23 ` Dustin Ray
2025-02-19 22:57 ` Hunter Beast
2025-02-20 22:11 ` Matt Corallo
2025-02-21 8:54 ` Jonas Nick
2 siblings, 1 reply; 8+ messages in thread
From: Dustin Ray @ 2025-02-19 17:23 UTC (permalink / raw)
To: Hunter Beast; +Cc: Bitcoin Development Mailing List
[-- Attachment #1: Type: text/plain, Size: 9276 bytes --]
Thanks for your work on this, it's exciting to watch it move along.
One item I have not yet addressed yet that is worth discussing is the
hierarchical deterministic seed characteristic of private keys for any of
the post quantum schemes you have mentioned so far. At present, if FALCON
is shortlisted, how do you propose to backup private keys? Must a new
wallet backup be made for each new public key that is generated?
Per your comment on security levels, I agree that your previous proposal
was absolutely overkill. My personal thought is that we will be just fine
by matching the current security levels provided by ecdsa, many years of
scrutiny has shown that this is sufficient.
On Wed, Feb 19, 2025 at 7:57 AM Hunter Beast <hunter@surmount•systems>
wrote:
> Dear Bitcoin Dev Community,
>
> A bit over six months after introducing the P2QRH proposal (now BIP-360),
> I'm writing to share significant developments and request additional
> feedback on our post-quantum roadmap, and I'd also like to mention a
> potential P2TRH post-quantum mitigation strategy.
>
> First, now that there's a BIP number assigned, you can find the update BIP
> here:
>
> https://github.com/cryptoquick/bips/blob/p2qrh/bip-0360.mediawiki
>
> The revised BIP-360 draft reflects substantial changes since initial
> publication, particularly regarding algorithm selection. While we
> originally considered SQIsign, it has 15,000x slower verification compared
> to ECC [1]. If it takes 1 second to verify a fully ECC block, it would take
> 4 hours to validate a block filled with SQIsign transactions. This has
> obvious and concerning DDoS implications.
>
> While it would take a long time to sign many thousands of SQIsign
> transactions as well, the increased time needed to sign the transactions
> likely won’t affect the practicality of DDoS attacks-- another concern
> which has been brought to my attention. As such, I've decided to deprecate
> SQIsign from the BIP.
>
> It's worth mentioning because it was brought up in the PR, there's a new
> class of algorithms that support signature aggregation, but they generally
> result in signatures that are still quite large. Chipmunk and RACCOON are
> good examples [2], [3]. I do expect that to improve with time. It might be
> worthwhile to shorten the list by making signature aggregation a
> requirement, so as not to regress too far from Schnorr signatures. That
> said, I think those capabilities should be introduced in a separate BIP
> once they're more mature and worthwhile.
>
> Our current shortlist prioritizes FALCON for its signature aggregation
> potential, with SPHINCS+ and CRYSTALS-Dilithium as secondary candidates.
> However, major technical challenges remain, particularly BIP-32
> compatibility issues affecting xpub generation in watch-only wallets, as
> detailed by conduition in another mailing list discussion [4], and also,
> how we should handle multisig wallets.
>
> Additionally, I think it's worthwhile to restrict BIP-360 to NIST-approved
> algorithms to maintain FIPS compliance. That's because HSMs such as those
> provided by Securosys already have support for all three algorithms [5],
> which is essential for secure deployment of federated L2 treasuries.
>
> Presently, for multisigs, we have a merkle tree configuration defined for
> encumbering the output with multiple keys. While that's efficient, it's a
> novel construction. I'm not certain we should proceed with the merkle tree
> commitment scheme-- it needs more scrutiny. We could use a sort of P2SH
> approach, just modifying the semantics of OP_CHECKMULTISIG in a witness
> script to alias to public keys in the attestation. But that could introduce
> additional overhead in a signature scheme that already uses a lot more
> space. Without this, however, we do not yet have a way specified to
> indicate thresholds or a locking script for the attestation, as it is
> designed to be purposely limited, so as specified it is only capable of n/n
> multisig. I consider m/n multisigs to be the single largest obvious
> omission in the spec right now. It definitely needs more thought and I'm
> open to suggestions. Perhaps two additional bytes at the top level of the
> SegWit v3 output hash could be provided to indicate PQC signature threshold
> and total, and those would be hashed and committed to in the output, then
> provided in a field in the attestation once spent.
>
> While finalizing PQC selections, I've also drafted P2TRH as an interim
> solution to secure Taproot keypath spends without disabling them, as
> Matthew Corallo proposes in the aforementioned mailing list thread [4]. The
> P2TRH approach hashes public keys rather than exposing them directly,
> particularly benefiting:
>
> - MuSig2 Lightning channel implementations
>
> - FROST-based MPC vaults
>
> - High-value transactions using private pools that don't reveal the block
> template
>
> For those interested, take a look at the draft BIP for P2TRH here:
> https://github.com/cryptoquick/bips/blob/p2trh/bip-p2trh.mediawiki
>
> I have my hands full with P2QRH advocacy and development and would prefer
> to focus on that, but I wanted to introduce P2TRH in case that is
> attractive as the community's preferred solution-- at least for Taproot
> quantum security. The tradeoff is that it adds 8.25 vB of overhead per
> input, and key tweaking might have slightly less utility for some
> applications, and it also doesn't protect against short exposure quantum
> attacks as defined in BIP-360.
>
> Returning to P2QRH and what's needed to push it across the finish line...
>
> I still need to finish the test vectors. I'm implementing these using a
> fork of rust-bitcoin and modeling them after Steven Roose's work on
> BIP-346. I've been told that's not a blocker for merging the draft, but if
> it isn't merged by the time I'm finished, hopefully that will provide some
> additional impetus behind it.
>
> One concern Murch brought up is that introducing four new algorithms into
> the network was too many-- adding too much complexity to the network and to
> wallets and other applications-- and I agree.
>
> Hopefully this is addressed to some degree by removing SQIsign (especially
> in its current state lacking implementation maturity), and will help push
> the BIP below a certain complexity threshold, making it somewhat easier to
> review.
>
>
>
> I think it's still important to include multiple signature algorithm
> options for users to select their desired level of security. It's not 100%
> certain that all of these algorithms will remain quantum resistant for all
> time, so redundancy here is… key.
>
> Another concern is that NIST level V is overkill. I have less conviction
> on this since secp256k1 technically has 128 bits of security due to
> Pollard's rho attacks. But if the intention was for 256 bits of security,
> should level V security be the default? It's difficult for me to say.
> Perhaps both level V and level I implementations could be included, but
> this would be a deviation from the BIP as presently specified, which
> defaults to level V security. The disadvantage of including level I support
> for each algorithm is that it essentially doubles the complexity of
> libbitcoinpqc.
>
> Ultimately, I hope the default of NIST V and selection of 3 mature
> NIST-approved algorithms demonstrate a focused, polished, and conservative
> proposal.
>
> At this point, the major call to action I would like to highlight is
> simply the need for more feedback from the community. Please review and
> provide feedback here: https://github.com/bitcoin/bips/pull/1670
>
> I look forward to feedback and opinions on P2QRH and P2TRH.
>
> P.S. I'll be advocating for BIP-360 at OP_NEXT in VA, btc++ in Austin,
> Consensus in Toronto, and BTC 25 in Las Vegas, and later this year, TABConf
> in Atlanta.
>
>
> [1] https://pqshield.github.io/nist-sigs-zoo
>
> [2] https://eprint.iacr.org/2023/1820.pdf
>
> [3] https://eprint.iacr.org/2024/1291.pdf
>
> [4] https://groups.google.com/g/bitcoindev/c/8O857bRSVV8/m/7uu4dZNgAwAJ
>
> [5]
> https://docs.securosys.com/tsb/Tutorials/Post-Quantum-Cryptography/pqc-release-overview
>
> --
> You received this message because you are subscribed to the Google Groups
> "Bitcoin Development Mailing List" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to bitcoindev+unsubscribe@googlegroups•com.
> To view this discussion visit
> https://groups.google.com/d/msgid/bitcoindev/8797807d-e017-44e2-b419-803291779007n%40googlegroups.com
> <https://groups.google.com/d/msgid/bitcoindev/8797807d-e017-44e2-b419-803291779007n%40googlegroups.com?utm_medium=email&utm_source=footer>
> .
>
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [bitcoindev] P2QRH / BIP-360 Update
2025-02-19 17:23 ` Dustin Ray
@ 2025-02-19 22:57 ` Hunter Beast
0 siblings, 0 replies; 8+ messages in thread
From: Hunter Beast @ 2025-02-19 22:57 UTC (permalink / raw)
To: Bitcoin Development Mailing List
[-- Attachment #1.1: Type: text/plain, Size: 10103 bytes --]
> HD wallets
libbitcoinpqc will require key entropy to be provided, so it should
maintain compatibility with that feature of HD wallets, so that's not a
concern. The larger problem is for full BIP-32 support, I'm not really sure
how xpubs or watch-only wallets will work.
> Security levels
You're not the first person to say that NIST V is overkill... I'll update
the spec for NIST I. If more security is desired, they can use all three
algorithms, plus Schnorr.
On Wednesday, February 19, 2025 at 11:47:04 AM UTC-7 Dustin Ray wrote:
> Thanks for your work on this, it's exciting to watch it move along.
>
> One item I have not yet addressed yet that is worth discussing is the
> hierarchical deterministic seed characteristic of private keys for any of
> the post quantum schemes you have mentioned so far. At present, if FALCON
> is shortlisted, how do you propose to backup private keys? Must a new
> wallet backup be made for each new public key that is generated?
>
> Per your comment on security levels, I agree that your previous proposal
> was absolutely overkill. My personal thought is that we will be just fine
> by matching the current security levels provided by ecdsa, many years of
> scrutiny has shown that this is sufficient.
>
>
> On Wed, Feb 19, 2025 at 7:57 AM Hunter Beast <hun...@surmount•systems>
> wrote:
>
>> Dear Bitcoin Dev Community,
>>
>> A bit over six months after introducing the P2QRH proposal (now BIP-360),
>> I'm writing to share significant developments and request additional
>> feedback on our post-quantum roadmap, and I'd also like to mention a
>> potential P2TRH post-quantum mitigation strategy.
>>
>> First, now that there's a BIP number assigned, you can find the update
>> BIP here:
>>
>> https://github.com/cryptoquick/bips/blob/p2qrh/bip-0360.mediawiki
>>
>> The revised BIP-360 draft reflects substantial changes since initial
>> publication, particularly regarding algorithm selection. While we
>> originally considered SQIsign, it has 15,000x slower verification compared
>> to ECC [1]. If it takes 1 second to verify a fully ECC block, it would take
>> 4 hours to validate a block filled with SQIsign transactions. This has
>> obvious and concerning DDoS implications.
>>
>> While it would take a long time to sign many thousands of SQIsign
>> transactions as well, the increased time needed to sign the transactions
>> likely won’t affect the practicality of DDoS attacks-- another concern
>> which has been brought to my attention. As such, I've decided to deprecate
>> SQIsign from the BIP.
>>
>> It's worth mentioning because it was brought up in the PR, there's a new
>> class of algorithms that support signature aggregation, but they generally
>> result in signatures that are still quite large. Chipmunk and RACCOON are
>> good examples [2], [3]. I do expect that to improve with time. It might be
>> worthwhile to shorten the list by making signature aggregation a
>> requirement, so as not to regress too far from Schnorr signatures. That
>> said, I think those capabilities should be introduced in a separate BIP
>> once they're more mature and worthwhile.
>>
>> Our current shortlist prioritizes FALCON for its signature aggregation
>> potential, with SPHINCS+ and CRYSTALS-Dilithium as secondary candidates.
>> However, major technical challenges remain, particularly BIP-32
>> compatibility issues affecting xpub generation in watch-only wallets, as
>> detailed by conduition in another mailing list discussion [4], and also,
>> how we should handle multisig wallets.
>>
>> Additionally, I think it's worthwhile to restrict BIP-360 to
>> NIST-approved algorithms to maintain FIPS compliance. That's because HSMs
>> such as those provided by Securosys already have support for all three
>> algorithms [5], which is essential for secure deployment of federated L2
>> treasuries.
>>
>> Presently, for multisigs, we have a merkle tree configuration defined for
>> encumbering the output with multiple keys. While that's efficient, it's a
>> novel construction. I'm not certain we should proceed with the merkle tree
>> commitment scheme-- it needs more scrutiny. We could use a sort of P2SH
>> approach, just modifying the semantics of OP_CHECKMULTISIG in a witness
>> script to alias to public keys in the attestation. But that could introduce
>> additional overhead in a signature scheme that already uses a lot more
>> space. Without this, however, we do not yet have a way specified to
>> indicate thresholds or a locking script for the attestation, as it is
>> designed to be purposely limited, so as specified it is only capable of n/n
>> multisig. I consider m/n multisigs to be the single largest obvious
>> omission in the spec right now. It definitely needs more thought and I'm
>> open to suggestions. Perhaps two additional bytes at the top level of the
>> SegWit v3 output hash could be provided to indicate PQC signature threshold
>> and total, and those would be hashed and committed to in the output, then
>> provided in a field in the attestation once spent.
>>
>> While finalizing PQC selections, I've also drafted P2TRH as an interim
>> solution to secure Taproot keypath spends without disabling them, as
>> Matthew Corallo proposes in the aforementioned mailing list thread [4]. The
>> P2TRH approach hashes public keys rather than exposing them directly,
>> particularly benefiting:
>>
>> - MuSig2 Lightning channel implementations
>>
>> - FROST-based MPC vaults
>>
>> - High-value transactions using private pools that don't reveal the block
>> template
>>
>> For those interested, take a look at the draft BIP for P2TRH here:
>> https://github.com/cryptoquick/bips/blob/p2trh/bip-p2trh.mediawiki
>>
>> I have my hands full with P2QRH advocacy and development and would prefer
>> to focus on that, but I wanted to introduce P2TRH in case that is
>> attractive as the community's preferred solution-- at least for Taproot
>> quantum security. The tradeoff is that it adds 8.25 vB of overhead per
>> input, and key tweaking might have slightly less utility for some
>> applications, and it also doesn't protect against short exposure quantum
>> attacks as defined in BIP-360.
>>
>> Returning to P2QRH and what's needed to push it across the finish line...
>>
>> I still need to finish the test vectors. I'm implementing these using a
>> fork of rust-bitcoin and modeling them after Steven Roose's work on
>> BIP-346. I've been told that's not a blocker for merging the draft, but if
>> it isn't merged by the time I'm finished, hopefully that will provide some
>> additional impetus behind it.
>>
>> One concern Murch brought up is that introducing four new algorithms into
>> the network was too many-- adding too much complexity to the network and to
>> wallets and other applications-- and I agree.
>>
>> Hopefully this is addressed to some degree by removing SQIsign
>> (especially in its current state lacking implementation maturity), and will
>> help push the BIP below a certain complexity threshold, making it somewhat
>> easier to review.
>>
>>
>>
>> I think it's still important to include multiple signature algorithm
>> options for users to select their desired level of security. It's not 100%
>> certain that all of these algorithms will remain quantum resistant for all
>> time, so redundancy here is… key.
>>
>> Another concern is that NIST level V is overkill. I have less conviction
>> on this since secp256k1 technically has 128 bits of security due to
>> Pollard's rho attacks. But if the intention was for 256 bits of security,
>> should level V security be the default? It's difficult for me to say.
>> Perhaps both level V and level I implementations could be included, but
>> this would be a deviation from the BIP as presently specified, which
>> defaults to level V security. The disadvantage of including level I support
>> for each algorithm is that it essentially doubles the complexity of
>> libbitcoinpqc.
>>
>> Ultimately, I hope the default of NIST V and selection of 3 mature
>> NIST-approved algorithms demonstrate a focused, polished, and conservative
>> proposal.
>>
>> At this point, the major call to action I would like to highlight is
>> simply the need for more feedback from the community. Please review and
>> provide feedback here: https://github.com/bitcoin/bips/pull/1670
>>
>> I look forward to feedback and opinions on P2QRH and P2TRH.
>>
>> P.S. I'll be advocating for BIP-360 at OP_NEXT in VA, btc++ in Austin,
>> Consensus in Toronto, and BTC 25 in Las Vegas, and later this year, TABConf
>> in Atlanta.
>>
>>
>> [1] https://pqshield.github.io/nist-sigs-zoo
>>
>> [2] https://eprint.iacr.org/2023/1820.pdf
>>
>> [3] https://eprint.iacr.org/2024/1291.pdf
>>
>> [4] https://groups.google.com/g/bitcoindev/c/8O857bRSVV8/m/7uu4dZNgAwAJ
>>
>> [5]
>> https://docs.securosys.com/tsb/Tutorials/Post-Quantum-Cryptography/pqc-release-overview
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "Bitcoin Development Mailing List" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to bitcoindev+...@googlegroups•com.
>> To view this discussion visit
>> https://groups.google.com/d/msgid/bitcoindev/8797807d-e017-44e2-b419-803291779007n%40googlegroups.com
>> <https://groups.google.com/d/msgid/bitcoindev/8797807d-e017-44e2-b419-803291779007n%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [bitcoindev] P2QRH / BIP-360 Update
2025-02-19 15:40 [bitcoindev] P2QRH / BIP-360 Update Hunter Beast
2025-02-19 17:23 ` Dustin Ray
@ 2025-02-20 22:11 ` Matt Corallo
2025-02-23 20:33 ` Hunter Beast
2025-02-21 8:54 ` Jonas Nick
2 siblings, 1 reply; 8+ messages in thread
From: Matt Corallo @ 2025-02-20 22:11 UTC (permalink / raw)
To: Hunter Beast, Bitcoin Development Mailing List
If we want to do something like this in the short to medium term, IMO we should strip out all the
signature schemes that are anything more than quite straightforward in their security assumptions
(i.e. only keep hash-based signatures, maybe just SPHINCS+), only embed them in a taproot leaf, and
call it a day.
BIP 32 compatibility isn't a really huge deal if we're talking about an "emergency break glass"
kinda setup - most wallets are set up with a root key and can just embed the same PQ pubkey in all
of their outputs. The privacy cost is only realized in a break glass case, and long before then
hopefully whatever we do today is replaced with something better, with the knowledge that we'll gain
on the way to "then". We'd still want to do it in an opcode so that we can do multisig, though.
Matt
On 2/19/25 10:40 AM, Hunter Beast wrote:
> Dear Bitcoin Dev Community,
>
>
> A bit over six months after introducing the P2QRH proposal (now BIP-360), I'm writing to share
> significant developments and request additional feedback on our post-quantum roadmap, and I'd also
> like to mention a potential P2TRH post-quantum mitigation strategy.
>
>
> First, now that there's a BIP number assigned, you can find the update BIP here:
>
> https://github.com/cryptoquick/bips/blob/p2qrh/bip-0360.mediawiki <https://github.com/cryptoquick/
> bips/blob/p2qrh/bip-0360.mediawiki>
>
>
> The revised BIP-360 draft reflects substantial changes since initial publication, particularly
> regarding algorithm selection. While we originally considered SQIsign, it has 15,000x slower
> verification compared to ECC [1]. If it takes 1 second to verify a fully ECC block, it would take 4
> hours to validate a block filled with SQIsign transactions. This has obvious and concerning DDoS
> implications.
>
>
> While it would take a long time to signmany thousands of SQIsign transactions as well, the increased
> time needed to sign the transactions likely won’t affect the practicality of DDoS attacks-- another
> concern which has been brought to my attention. As such, I've decided to deprecate SQIsign from the BIP.
>
>
> It's worth mentioning because it was brought up in the PR, there's a new class of algorithms that
> support signature aggregation, but they generally result in signatures that are still quite large.
> Chipmunk and RACCOON are good examples [2], [3]. I do expect that to improve with time. It might be
> worthwhile to shorten the list by making signature aggregation a requirement, so as not to regress
> too far from Schnorr signatures. That said, I think those capabilities should be introduced in a
> separate BIP once they're more mature and worthwhile.
>
>
> Our current shortlist prioritizes FALCON for its signature aggregation potential, with SPHINCS+ and
> CRYSTALS-Dilithium as secondary candidates. However, major technical challenges remain, particularly
> BIP-32 compatibility issues affecting xpub generation in watch-only wallets, as detailed by
> conduition in another mailing list discussion [4], and also, how we should handle multisig wallets.
>
>
> Additionally, I think it's worthwhile to restrict BIP-360 to NIST-approved algorithms to maintain
> FIPS compliance. That's because HSMs such as those provided by Securosys already have support for
> all three algorithms [5], which is essential for secure deployment of federated L2 treasuries.
>
>
> Presently, for multisigs, we have a merkle tree configuration defined for encumbering the output
> with multiple keys. While that's efficient, it's a novel construction. I'm not certain we should
> proceed with the merkle tree commitment scheme-- it needs more scrutiny. We could use a sort of P2SH
> approach, just modifying the semantics of OP_CHECKMULTISIG in a witness script to alias to public
> keys in the attestation. But that could introduce additional overhead in a signature scheme that
> already uses a lot more space. Without this, however, we do not yet have a way specified to indicate
> thresholds or a locking script for the attestation, as it is designed to be purposely limited, so as
> specified it is only capable of n/n multisig. I consider m/n multisigs to be the single largest
> obvious omission in the spec right now. It definitely needs more thought and I'm open to
> suggestions. Perhaps two additional bytes at the top level of the SegWit v3 output hash could be
> provided to indicate PQC signature threshold and total, and those would be hashed and committed to
> in the output, then provided in a field in the attestation once spent.
>
>
> While finalizing PQC selections, I've also drafted P2TRH as an interim solution to secure Taproot
> keypath spends without disabling them, as Matthew Corallo proposes in the aforementioned mailing
> list thread [4]. The P2TRH approach hashes public keys rather than exposing them directly,
> particularly benefiting:
>
>
> - MuSig2 Lightning channel implementations
>
> - FROST-based MPC vaults
>
> - High-value transactions using private pools that don't reveal the block template
>
>
> For those interested, take a look at the draft BIP for P2TRH here: https://github.com/cryptoquick/
> bips/blob/p2trh/bip-p2trh.mediawiki <https://github.com/cryptoquick/bips/blob/p2trh/bip-p2trh.mediawiki>
>
>
> I have my hands full with P2QRH advocacy and development and would prefer to focus on that, but I
> wanted to introduce P2TRH in case that is attractive as the community's preferred solution-- at
> least for Taproot quantum security. The tradeoff is that it adds 8.25 vB of overhead per input, and
> key tweaking might have slightly less utility for some applications, and it also doesn't protect
> against short exposure quantum attacks as defined in BIP-360.
>
>
> Returning to P2QRH and what's needed to push it across the finish line...
>
>
> I still need to finish the test vectors. I'm implementing these using a fork of rust-bitcoin and
> modeling them after Steven Roose's work on BIP-346. I've been told that's not a blocker for merging
> the draft, but if it isn't merged by the time I'm finished, hopefully that will provide some
> additional impetus behind it.
>
>
> One concern Murch brought up is that introducing four new algorithms into the network was too many--
> adding too much complexity to the network and to wallets and other applications-- and I agree.
>
>
> Hopefully this is addressed to some degree by removing SQIsign (especially in its current state
> lacking implementation maturity), and will help push the BIP below a certain complexity threshold,
> making it somewhat easier to review.
>
> I think it's still important to include multiple signature algorithm options for users to select
> their desired level of security. It's not 100% certain that all of these algorithms will remain
> quantum resistant for all time, so redundancy here is… key.
>
>
> Another concern is that NIST level V is overkill. I have less conviction on this since secp256k1
> technically has 128 bits of security due to Pollard's rho attacks. But if the intention was for 256
> bits of security, should level V security be the default? It's difficult for me to say. Perhaps both
> level V and level I implementations could be included, but this would be a deviation from the BIP as
> presently specified, which defaults to level V security. The disadvantage of including level I
> support for each algorithm is that it essentially doubles the complexity of libbitcoinpqc.
>
>
> Ultimately, I hope the default of NIST V and selection of 3 mature NIST-approved algorithms
> demonstrate a focused, polished, and conservative proposal.
>
>
> At this point, the major call to action I would like to highlight is simply the need for more
> feedback from the community. Please review and provide feedback here: https://github.com/bitcoin/
> bips/pull/1670 <https://github.com/bitcoin/bips/pull/1670>
>
>
> I look forward to feedback and opinions on P2QRH and P2TRH.
>
>
> P.S. I'll be advocating for BIP-360 at OP_NEXT in VA, btc++ in Austin, Consensus in Toronto, and BTC
> 25 in Las Vegas, and later this year, TABConf in Atlanta.
>
>
>
> [1] https://pqshield.github.io/nist-sigs-zoo
>
> [2] https://eprint.iacr.org/2023/1820.pdf
>
> [3] https://eprint.iacr.org/2024/1291.pdf
>
> [4] https://groups.google.com/g/bitcoindev/c/8O857bRSVV8/m/7uu4dZNgAwAJ
>
> [5] https://docs.securosys.com/tsb/Tutorials/Post-Quantum-Cryptography/pqc-release-overview
>
>
> --
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [bitcoindev] P2QRH / BIP-360 Update
2025-02-20 22:11 ` Matt Corallo
@ 2025-02-23 20:33 ` Hunter Beast
0 siblings, 0 replies; 8+ messages in thread
From: Hunter Beast @ 2025-02-23 20:33 UTC (permalink / raw)
To: Bitcoin Development Mailing List
[-- Attachment #1.1: Type: text/plain, Size: 11054 bytes --]
Hi Matt,
The only problem with that approach is that SLH-DSA signatures are quite
large. NIST has also approved ML-DSA and FN-DSA, which, while both are
based on lattice cryptography, they're not only standardized, but becoming
widely supported. One consideration is hardware acceleration, and I believe
those three algorithms will have the best chance of having hardware
implementations as PQC extensions are added to CPUs and SoCs.
As for gating P2TR, the problem with that approach is that keypath spends
would need to be disabled and that has a confiscatory effect that I'm
seeking to avoid in this BIP.
An additional opcode should not be necessary if multisig capability is
built into the attestation.
I agree with your statement on full BIP-32 compatibility. BIP-360 is just a
starting point, and maybe you're right, it's best thought of as a "break
glass" implementation. It's not ideal, it's full of compromises, not
everyone is 100% happy with it, and that's probably okay, because bitcoin
isn't perfect-- but it doesn't have to be in order to work.
Thank you for your thoughts.
Hunter
On Friday, February 21, 2025 at 3:18:21 AM UTC-7 Matt Corallo wrote:
If we want to do something like this in the short to medium term, IMO we
should strip out all the
signature schemes that are anything more than quite straightforward in
their security assumptions
(i.e. only keep hash-based signatures, maybe just SPHINCS+), only embed
them in a taproot leaf, and
call it a day.
BIP 32 compatibility isn't a really huge deal if we're talking about an
"emergency break glass"
kinda setup - most wallets are set up with a root key and can just embed
the same PQ pubkey in all
of their outputs. The privacy cost is only realized in a break glass case,
and long before then
hopefully whatever we do today is replaced with something better, with the
knowledge that we'll gain
on the way to "then". We'd still want to do it in an opcode so that we can
do multisig, though.
Matt
On 2/19/25 10:40 AM, Hunter Beast wrote:
> Dear Bitcoin Dev Community,
>
>
> A bit over six months after introducing the P2QRH proposal (now BIP-360),
I'm writing to share
> significant developments and request additional feedback on our
post-quantum roadmap, and I'd also
> like to mention a potential P2TRH post-quantum mitigation strategy.
>
>
> First, now that there's a BIP number assigned, you can find the update
BIP here:
>
> https://github.com/cryptoquick/bips/blob/p2qrh/bip-0360.mediawiki <
https://github.com/cryptoquick/
> bips/blob/p2qrh/bip-0360.mediawiki>
>
>
> The revised BIP-360 draft reflects substantial changes since initial
publication, particularly
> regarding algorithm selection. While we originally considered SQIsign, it
has 15,000x slower
> verification compared to ECC [1]. If it takes 1 second to verify a fully
ECC block, it would take 4
> hours to validate a block filled with SQIsign transactions. This has
obvious and concerning DDoS
> implications.
>
>
> While it would take a long time to signmany thousands of SQIsign
transactions as well, the increased
> time needed to sign the transactions likely won’t affect the practicality
of DDoS attacks-- another
> concern which has been brought to my attention. As such, I've decided to
deprecate SQIsign from the BIP.
>
>
> It's worth mentioning because it was brought up in the PR, there's a new
class of algorithms that
> support signature aggregation, but they generally result in signatures
that are still quite large.
> Chipmunk and RACCOON are good examples [2], [3]. I do expect that to
improve with time. It might be
> worthwhile to shorten the list by making signature aggregation a
requirement, so as not to regress
> too far from Schnorr signatures. That said, I think those capabilities
should be introduced in a
> separate BIP once they're more mature and worthwhile.
>
>
> Our current shortlist prioritizes FALCON for its signature aggregation
potential, with SPHINCS+ and
> CRYSTALS-Dilithium as secondary candidates. However, major technical
challenges remain, particularly
> BIP-32 compatibility issues affecting xpub generation in watch-only
wallets, as detailed by
> conduition in another mailing list discussion [4], and also, how we
should handle multisig wallets.
>
>
> Additionally, I think it's worthwhile to restrict BIP-360 to
NIST-approved algorithms to maintain
> FIPS compliance. That's because HSMs such as those provided by Securosys
already have support for
> all three algorithms [5], which is essential for secure deployment of
federated L2 treasuries.
>
>
> Presently, for multisigs, we have a merkle tree configuration defined for
encumbering the output
> with multiple keys. While that's efficient, it's a novel construction.
I'm not certain we should
> proceed with the merkle tree commitment scheme-- it needs more scrutiny.
We could use a sort of P2SH
> approach, just modifying the semantics of OP_CHECKMULTISIG in a witness
script to alias to public
> keys in the attestation. But that could introduce additional overhead in
a signature scheme that
> already uses a lot more space. Without this, however, we do not yet have
a way specified to indicate
> thresholds or a locking script for the attestation, as it is designed to
be purposely limited, so as
> specified it is only capable of n/n multisig. I consider m/n multisigs to
be the single largest
> obvious omission in the spec right now. It definitely needs more thought
and I'm open to
> suggestions. Perhaps two additional bytes at the top level of the SegWit
v3 output hash could be
> provided to indicate PQC signature threshold and total, and those would
be hashed and committed to
> in the output, then provided in a field in the attestation once spent.
>
>
> While finalizing PQC selections, I've also drafted P2TRH as an interim
solution to secure Taproot
> keypath spends without disabling them, as Matthew Corallo proposes in the
aforementioned mailing
> list thread [4]. The P2TRH approach hashes public keys rather than
exposing them directly,
> particularly benefiting:
>
>
> - MuSig2 Lightning channel implementations
>
> - FROST-based MPC vaults
>
> - High-value transactions using private pools that don't reveal the block
template
>
>
> For those interested, take a look at the draft BIP for P2TRH here:
https://github.com/cryptoquick/
> bips/blob/p2trh/bip-p2trh.mediawiki <
https://github.com/cryptoquick/bips/blob/p2trh/bip-p2trh.mediawiki>
>
>
> I have my hands full with P2QRH advocacy and development and would prefer
to focus on that, but I
> wanted to introduce P2TRH in case that is attractive as the community's
preferred solution-- at
> least for Taproot quantum security. The tradeoff is that it adds 8.25 vB
of overhead per input, and
> key tweaking might have slightly less utility for some applications, and
it also doesn't protect
> against short exposure quantum attacks as defined in BIP-360.
>
>
> Returning to P2QRH and what's needed to push it across the finish line...
>
>
> I still need to finish the test vectors. I'm implementing these using a
fork of rust-bitcoin and
> modeling them after Steven Roose's work on BIP-346. I've been told that's
not a blocker for merging
> the draft, but if it isn't merged by the time I'm finished, hopefully
that will provide some
> additional impetus behind it.
>
>
> One concern Murch brought up is that introducing four new algorithms into
the network was too many--
> adding too much complexity to the network and to wallets and other
applications-- and I agree.
>
>
> Hopefully this is addressed to some degree by removing SQIsign
(especially in its current state
> lacking implementation maturity), and will help push the BIP below a
certain complexity threshold,
> making it somewhat easier to review.
>
> I think it's still important to include multiple signature algorithm
options for users to select
> their desired level of security. It's not 100% certain that all of these
algorithms will remain
> quantum resistant for all time, so redundancy here is… key.
>
>
> Another concern is that NIST level V is overkill. I have less conviction
on this since secp256k1
> technically has 128 bits of security due to Pollard's rho attacks. But if
the intention was for 256
> bits of security, should level V security be the default? It's difficult
for me to say. Perhaps both
> level V and level I implementations could be included, but this would be
a deviation from the BIP as
> presently specified, which defaults to level V security. The disadvantage
of including level I
> support for each algorithm is that it essentially doubles the complexity
of libbitcoinpqc.
>
>
> Ultimately, I hope the default of NIST V and selection of 3 mature
NIST-approved algorithms
> demonstrate a focused, polished, and conservative proposal.
>
>
> At this point, the major call to action I would like to highlight is
simply the need for more
> feedback from the community. Please review and provide feedback here:
https://github.com/bitcoin/
> bips/pull/1670 <https://github.com/bitcoin/bips/pull/1670>
>
>
> I look forward to feedback and opinions on P2QRH and P2TRH.
>
>
> P.S. I'll be advocating for BIP-360 at OP_NEXT in VA, btc++ in Austin,
Consensus in Toronto, and BTC
> 25 in Las Vegas, and later this year, TABConf in Atlanta.
>
>
>
> [1] https://pqshield.github.io/nist-sigs-zoo
>
> [2] https://eprint.iacr.org/2023/1820.pdf
>
> [3] https://eprint.iacr.org/2024/1291.pdf
>
> [4] https://groups.google.com/g/bitcoindev/c/8O857bRSVV8/m/7uu4dZNgAwAJ
>
> [5]
https://docs.securosys.com/tsb/Tutorials/Post-Quantum-Cryptography/pqc-release-overview
>
>
> --
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [bitcoindev] P2QRH / BIP-360 Update
2025-02-19 15:40 [bitcoindev] P2QRH / BIP-360 Update Hunter Beast
2025-02-19 17:23 ` Dustin Ray
2025-02-20 22:11 ` Matt Corallo
@ 2025-02-21 8:54 ` Jonas Nick
2025-02-23 20:58 ` Hunter Beast
2 siblings, 1 reply; 8+ messages in thread
From: Jonas Nick @ 2025-02-21 8:54 UTC (permalink / raw)
To: bitcoindev
Hi Hunter,
Thanks for your work on BIP 360. I think now is a good time to develop and
discuss concrete PQ proposals. I have a few questions and comments regarding
some aspects of the proposal:
Selective disclosure
---
From, the output contains a root of a Merkle tree of public key hashes and
spending from this output requires revealing the public keys and their
corresponding valid signatures. More concretely, if the user creates root
R = MerkleRoot([hash(public_key_falcon_1024), hash(public_key_secp256k1)]),
they can spend from R by revealing both public keys and corresponding signatures.
The BIP also mentions that the public keys can be selectively disclosed:
> When spending, if a public key hash is provided in the attestation with an
> empty signature, that hash will be used directly in the merkle tree computation
> rather than hashing the full public key.
What prevents an quantum adversary, upon observing a spend from R, from breaking
public_key_secp256k1 and then spending from R by providing
[
hash(public_key_falcon_1024),
empty string,
public_key_secp256k1,
a secp256k1 signature forgery
]?
Attestation structure
---
The BIP proposes to an attestation structure alongside the witness which is
supposed to contain BIP 360 public keys and signatures (instead having them in
the witness). The purpose of this structure is to assign a higher weight
discount than the witness. The "Rationale" and "Output Mechanics" sections the
BIP describe that, since the attestation structure only contains public keys and
signatures, storage of arbitrary data ("inscriptions") is prevented.
Leaving aside that there may be creative ways to embed arbitrary data in public
keys and signatures as well, selective disclosure of the Merkle tree appears to
allow embedding arbitrary data. For instance, a user can create root
R = MerkleRoot(data, hash(public_key_secp256k1)]),
where data is an arbitrary 256-bit string. What prevents the user from
pretending that data is the hash of a public key and providing
[
data,
empty string,
public_key_secp256k1,
a secp256k1 signature forgery
]
in the attestation structure to spend from R?
Multi-signature 256-bit security
---
The BIP briefly discusses multi-signature scenarios in the script validation
section, but the details seem incomplete. From what I can infer, the current
specification fails to achieve the claimed 256-bit security.
The potential attack would work as follows:
1. The victim provides their public key pk to the adversary.
2. The adversary finds two public keys pk' and pk'' such that
MerkleRoot(MultiSig[pk, pk']) = MerkleRoot([pk''])
3. The adversary convinces the victim to send coins to MerkleRoot(MultiSig[pk,
pk']) and then steals the coins by opening the Merkle tree root to [pk''] and
providing a signature for pk''.
Since the Merkle root is the 256-bit output of SHA256, the adversary can find
this collision with about 2^128 operations.
If I remember correctly, this attack was discussed on the mailing list in the
context of segwit and it's the reason why P2WSH (unlike P2PKH) requires 256-bit
hashes.
General comments
---
I think one of the main questions that the BIP does not currently address is how
it affects the worst-case validation cost of a block.
Regarding your question:
> But if the intention was for 256 bits of security, should level V security be
> the default?
I don't know what Satoshi's intentions were, but the secp256k1 specification
clearly indicates 128-bit "strength" ([0], Table 1). I believe that's fairly
well known in the technical Bitcoin space.
I am not quite convinced that adding three PQ schemes to the Bitcoin consensus
protocol is a great solution to the problem of not being sure which exact scheme
to pick. Offloading this decision to users does not really solve this problem.
Moreover, this adds massive complexity and new cryptographic assumptions to the
protocol. Remember that one of the main motivations behind libsecp256k1, was
that general purpose cryptographic libraries are not well suited for consensus
systems. So all new cryptographic schemes added to the consensus protocol need
to be exceptionally well specified and implemented. That said, it makes a lot of
sense to design a hybrid scheme that also provides security against a classic
attacker through an established signature scheme (as BIP 360 proposes).
Lastly, I agree that non-interactive aggregation of PQ schemes might be
promising, as it could mitigate about signature size and verification cost if
aggregation is applied on the transaction level. Recently, there has been
progress on the security of aggregating hash-based signatures [1] and Falcon
[2].
[0] https://www.secg.org/sec2-v2.pdf
[1] https://eprint.iacr.org/2025/055
[2] https://eprint.iacr.org/2024/311 (Unfortunately, this only beats trivial
aggregation (concatenation of signatures) when the number of signatures is
greater than about 110)
Jonas
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^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [bitcoindev] P2QRH / BIP-360 Update
2025-02-21 8:54 ` Jonas Nick
@ 2025-02-23 20:58 ` Hunter Beast
2025-02-24 13:17 ` Jonas Nick
0 siblings, 1 reply; 8+ messages in thread
From: Hunter Beast @ 2025-02-23 20:58 UTC (permalink / raw)
To: Bitcoin Development Mailing List
[-- Attachment #1.1: Type: text/plain, Size: 8496 bytes --]
Hi Jonas,
On Selective Disclosure,
I think we're going to need to add simple multisig semantics to the
attestation due to its lack of script capability. Would that help? Separate
multisig semantics like quorum and total would be needed for each class of
key, so that even if Schnorr signatures can be broken (or one or two of the
other PQC signatures even), they don't count towards the quorum of the
other signature types.
On Attestation structure,
What prevents arbitrary data being hashed and then included in the
attestation is, each signature public key pair must be able to verify the
transaction message in order to be considered a valid transaction. In other
words, each public key and signature pair is validated against the
transaction message upon transaction verification.
On Multisignature 256-bit security,
To be honest, I've read this a couple of times and I will admit I don't
understand this attack. Can you provide more details on how it works, and
how it might be possible to mitigate?
On General comments,
I agree with the worst-case transaction verification concern. I'll need to
put some work into detailing NIST I variants and their signature
verification times, and then computing worst-case scenarios for different
discount constants.
On 128-bit security... Yes, I'm coming to realize that too. It's been a
common point of feedback.
On adding three schemes, there are a couple of advantages of this. First,
wallets can automatically decide how many signatures to add based on the
amount being spent. This then acts as a sort of MEV opportunity for miners,
because the higher the value of the transaction, the more signatures might
be included, which increases fee revenue. Also, it addresses Matt's concern
about security assumptions. There's a strong desire for SLH-DSA support,
even though it's so large. However, from a practicality standpoint
(thinking of plebs), it will make sense to include the smaller ML-DSA and
FN-DSA also. While it does increase complexity, I believe that a
libbitcoinpqc library, as mentioned in the BIP, will serve as a useful
analogue to libsecp256k1. It's also worth noting that in my position at
Anduro, I have resources to put into building such a library. Hopefully
this can help meet the expectation of a well specified and implemented
consensus level library.
On signature aggregation, yes, I'm excited to see those developments in
FN-DSA, and maybe we can see that filter into SLH-DSA as well. Hopefully
those improvements will be ready once the time comes to activate.
On Friday, February 21, 2025 at 3:18:35 AM UTC-7 Jonas Nick wrote:
> Hi Hunter,
>
> Thanks for your work on BIP 360. I think now is a good time to develop and
> discuss concrete PQ proposals. I have a few questions and comments
> regarding
> some aspects of the proposal:
>
> Selective disclosure
> ---
>
> From, the output contains a root of a Merkle tree of public key hashes and
> spending from this output requires revealing the public keys and their
> corresponding valid signatures. More concretely, if the user creates root
>
> R = MerkleRoot([hash(public_key_falcon_1024), hash(public_key_secp256k1)]),
>
> they can spend from R by revealing both public keys and corresponding
> signatures.
>
> The BIP also mentions that the public keys can be selectively disclosed:
>
> > When spending, if a public key hash is provided in the attestation with
> an
> > empty signature, that hash will be used directly in the merkle tree
> computation
> > rather than hashing the full public key.
>
> What prevents an quantum adversary, upon observing a spend from R, from
> breaking
> public_key_secp256k1 and then spending from R by providing
>
> [
> hash(public_key_falcon_1024),
> empty string,
> public_key_secp256k1,
> a secp256k1 signature forgery
> ]?
>
>
> Attestation structure
> ---
>
> The BIP proposes to an attestation structure alongside the witness which is
> supposed to contain BIP 360 public keys and signatures (instead having
> them in
> the witness). The purpose of this structure is to assign a higher weight
> discount than the witness. The "Rationale" and "Output Mechanics" sections
> the
> BIP describe that, since the attestation structure only contains public
> keys and
> signatures, storage of arbitrary data ("inscriptions") is prevented.
>
> Leaving aside that there may be creative ways to embed arbitrary data in
> public
> keys and signatures as well, selective disclosure of the Merkle tree
> appears to
> allow embedding arbitrary data. For instance, a user can create root
>
> R = MerkleRoot(data, hash(public_key_secp256k1)]),
>
> where data is an arbitrary 256-bit string. What prevents the user from
> pretending that data is the hash of a public key and providing
>
> [
> data,
> empty string,
> public_key_secp256k1,
> a secp256k1 signature forgery
> ]
>
> in the attestation structure to spend from R?
>
>
> Multi-signature 256-bit security
> ---
>
> The BIP briefly discusses multi-signature scenarios in the script
> validation
> section, but the details seem incomplete. From what I can infer, the
> current
> specification fails to achieve the claimed 256-bit security.
>
> The potential attack would work as follows:
> 1. The victim provides their public key pk to the adversary.
> 2. The adversary finds two public keys pk' and pk'' such that
> MerkleRoot(MultiSig[pk, pk']) = MerkleRoot([pk''])
> 3. The adversary convinces the victim to send coins to
> MerkleRoot(MultiSig[pk,
> pk']) and then steals the coins by opening the Merkle tree root to [pk'']
> and
> providing a signature for pk''.
>
> Since the Merkle root is the 256-bit output of SHA256, the adversary can
> find
> this collision with about 2^128 operations.
>
> If I remember correctly, this attack was discussed on the mailing list in
> the
> context of segwit and it's the reason why P2WSH (unlike P2PKH) requires
> 256-bit
> hashes.
>
>
> General comments
> ---
>
> I think one of the main questions that the BIP does not currently address
> is how
> it affects the worst-case validation cost of a block.
>
> Regarding your question:
> > But if the intention was for 256 bits of security, should level V
> security be
> > the default?
>
> I don't know what Satoshi's intentions were, but the secp256k1
> specification
> clearly indicates 128-bit "strength" ([0], Table 1). I believe that's
> fairly
> well known in the technical Bitcoin space.
>
> I am not quite convinced that adding three PQ schemes to the Bitcoin
> consensus
> protocol is a great solution to the problem of not being sure which exact
> scheme
> to pick. Offloading this decision to users does not really solve this
> problem.
> Moreover, this adds massive complexity and new cryptographic assumptions
> to the
> protocol. Remember that one of the main motivations behind libsecp256k1,
> was
> that general purpose cryptographic libraries are not well suited for
> consensus
> systems. So all new cryptographic schemes added to the consensus protocol
> need
> to be exceptionally well specified and implemented. That said, it makes a
> lot of
> sense to design a hybrid scheme that also provides security against a
> classic
> attacker through an established signature scheme (as BIP 360 proposes).
>
> Lastly, I agree that non-interactive aggregation of PQ schemes might be
> promising, as it could mitigate about signature size and verification cost
> if
> aggregation is applied on the transaction level. Recently, there has been
> progress on the security of aggregating hash-based signatures [1] and
> Falcon
> [2].
>
> [0] https://www.secg.org/sec2-v2.pdf
> [1] https://eprint.iacr.org/2025/055
> [2] https://eprint.iacr.org/2024/311 (Unfortunately, this only beats
> trivial
> aggregation (concatenation of signatures) when the number of signatures is
> greater than about 110)
>
> Jonas
>
>
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^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [bitcoindev] P2QRH / BIP-360 Update
2025-02-23 20:58 ` Hunter Beast
@ 2025-02-24 13:17 ` Jonas Nick
0 siblings, 0 replies; 8+ messages in thread
From: Jonas Nick @ 2025-02-24 13:17 UTC (permalink / raw)
To: bitcoindev
> What prevents arbitrary data being hashed and then included in the attestation
> is, each signature public key pair must be able to verify the transaction
> message in order to be considered a valid transaction.
This appears to contradict the selective disclosure mechanism described in the
BIP and this sentence in the "Script Validation" section:
> Public keys that are not needed can be excluded by including their hash in the
> attestation accompanied with an empty signature
Even if the selective disclosure vulnerability is fixed by committing to the
multisig semantics in the P2QRH output, any unopened public key commitment could
still be "abused" for arbitrary data storage. Similar to the scenario in my
previous post, if the root R is MerkleRoot([leafhash1, leafhash2]) and the
multisig policy is "1-of-2", then we can set
leafhash1 := data
leafhash2 := hash(public_key_secp256k1)
and post the data to the chain by spending the output using an attestation
structure that includes leafhash1, an empty signature, public_key_secp256k1 and
the corresponding signature.
> I will admit I don't understand this attack. Can you provide more details on
> how it works, and how it might be possible to mitigate?
To give more context, this attack is intended as a concrete demonstration of how
breaking the collision resistance of the hash function used in the Merkle tree
can enable an adversary to steal coins. Here's a different explanation for
essentially the same attack in the context of P2SH vs. P2WSH:
https://bitcoin.stackexchange.com/a/54847/35586
The attack against the BIP's proposed signature scheme (where the Merkle tree is
constructed from public keys and then an ordinary signature scheme is applied to
one or more of the committed public keys) can be mitigated by using a hash
function with a larger output space (e.g., SHA-512).
However, I'm not suggesting to do this. My point is that while the BIP aims for
256 bits of security by using NIST strength level V parameters, it does not
actually achieve that security level (when the adversary can affect any of the
leaves as in multisignatures, for example).
The Bitcoin protocol relies heavily on collision-resistance of SHA-256, which is
pretty much the definition of NIST strength level II [0].
[0] https://csrc.nist.gov/projects/post-quantum-cryptography/post-quantum-cryptography-standardization/evaluation-criteria/security-(evaluation-criteria)
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