Re: IMA and PQC

[Coiby Xu <coxu@redhat.com>]

On Fri, Jan 30, 2026 at 09:31:26PM +0100, Johannes Wiesböck wrote:
>Hi all,

Hi Johannes,

>
>we conducted an evaluation regarding PQC use in IMA last year (see [1] for all
>details) where we also considered the interplay of different PQC signatures and
>file systems (ext4, btrfs, XFS, f2fs).

Thanks for sharing this comprehensive study! There are many nuances in
this research paper!

>
>Coiby Xu <coxu@redhat.com> wrote:
>
>>According to my experiments done so far, for verification speed,
>>ML-DSA-65 is consistently faster than ECDSA P-384 which is used by
>>current CentOS/RHEL to sign files in a package.
>
>Regarding performance, similar to Coiby, we found that all variants of ML-DSA
>consistently outperformed ECDSA P-256.

Glad to know ML-DSA is also faster than ECDSA P-256!

>
>>The size of a single ML-DSA-65 signature indeed increases dramatically
>>compared with ECDSA P-384 (3309 bytes vs ~100 bytes). But I'm not sure
>>it can be a big problem when considering the storage capacity. Take
>>latest fresh CentOS Stream 10 x86_64 KVM guest as example, without any
>>file system optimization, extra ~189MB disk space is needed if all files
>>in /usr signed using by ML-DSA-65 where the disk size is 50G. But I
>>don't have enough experience to tell how users will perceive it and I'll
>>try to collect more feedback.
>>
>>For the details of my experiments, you can check
>>https://gist.github.com/coiby/41cf3a4d59cd64fb19d35b9ac42e4cd7
>>And here's the tldr; version,
>>- Verification Speed: ML-DSA-65 is consistently ~10-12% faster
>>   at verification than ECDSA P-384 when verifying all files in /usr;
>>   ML-DSA-65 is 2.5x or 3x faster by "openssl speed"
>>
>>- Signing Speed: ML-DSA-65 appears ~25-30% slower when signing
>>   all files in /usr; ML-DSA-65 is 4x or 4.8x slower by "openssl speed"
>>
>>- Storage overhead: For ML-DSA-65, /usr will increase by 189MB and
>>   430MB when there are 27346 and 58341 files respectively. But total
>>   size of pure IMA signatures are estimated (files x (3309+20) bytes) to
>>   be ~87MB and ~185MB respectively.
>
>Two relevant aspects we discovered regard the signature size. TL;DR:
>
>1. Most file systems need to be tuned to support the larger extended attributes
>(signatures) if their size goes above a certain threshold (e.g. enable EA_INODE
>in ext4). This influences not only disk usage but overall compatibility between
>file systems and PQC signatures. A file system that would not provide the
>functionality to store larger extended attributes would be incompatible with
>large signatures.
>
>2. For most smaller signatures (like ML-DSA-44/65), we believe that the overhead
>of signatures is actually compensated by fragmentation within the file systems.
>For example, ext4 will allocate a full file system block for extended attributes.
>As long as the signature size is below this block size, we did not observe less
>free space on the file system despite the larger signatures.

I think this explains why I didn't see any disk overhead when using ECDSA P-384:)

>
>Overall, we concluded that ML-DSA-65 provides the best combination of disk
>overhead, performance and security level. Performace was good and for all
>algorithms with larger signatures than ML-DSA-65, file systems would need to be
>tuned.

Thanks for summarizing your findings regarding the signature size and
also sharing your evaluation!

>
>>According to
>>https://www.ietf.org/archive/id/draft-salter-lamps-cms-ml-dsa-00.html
>>ML-DSA-44 is intended to meet NIST's level 2 security category. Will
>>NIST level 2 meet users' security requirements?
>
>Regarding security levels:
>For security levels, we referred to NIST IR 8547 ipd [2].
>ECDSA P-256 has a classical security strength of 128bits (P-384: 192bits).
>According to [2] Table 3, these levels are met by the different ML-DSA variants.
>So, if you are migrating from ECDSA P-384, you need to use at least ML-DSA-65 to
>meet the same security strength.

This is helpful info! And thanks for sharing the perspective of
migration!

>
>Best regards,
>Johannes
>
>[1] https://www.wsbck.net/publications/pqc-ima.pdf
>[2] https://nvlpubs.nist.gov/nistpubs/ir/2024/NIST.IR.8547.ipd.pdf
>

-- 
Best regards,
Coiby