Most things are done. Missing stuff

Alright: We have support for all our combined algos ky{768,1024}_bp{256,384,512}and ky{768,1024}_cv{25519,448} as well as test keys and encrypted test messages.

Here comes a new test key along with its 3 secret parts (one for the primary and two for the composite Kyber subkey).

Wit the test keys posted in T7014 it is now possible to decrypt the sample data. The test data has been slightly adjusted for the new format; see

A way to generated keys in the usual s-expression way has been added. This allows us to get the keygrip for the key.

FWIW, I posted some ideas at https://lists.gnupg.org/pipermail/librepgp-discuss/2024/000043.html . For official use in Germany we will very likely also add Brainpool curves as a replacement for the IETF curves.

Although, we don't use our usual s-expressions we need to add a way to derive a keygrip from Kyber et al and also to wrap the key into an s-expression to that it can be stored by gpg-agent in its usual files. An exported new API to get the keygrip of a KEM key would be good to avoid encapsulation but for other purposes an encapsulation is still required.

Regading Kyber in GnuPG, there are a couple of open questions. For example whether the implicit lengths used for the key parameters match well with the overall protocol structure. Thus, as soon as we have finished the Libgcrypt part we will address this and implement it in some way. Before we do this we have to do a couple of changes to GnuPG required for FIPS compliance.

I just saw that Niibe is already working on the integration of the ML-KEM code into the master branch of libgcrypt. Apparently, this is an entirely new code base. Currently we are working on the integration of our ML-KEM implementation in libgcrypt into GnuPG. But based on what I see now it seems that apparently another approach is planned and already underway for libgcrypt and probably later also for GnuPG. It would be helpful if you could give us a pointer what your exact plans are, this makes it easier for us to direct our efforts in the optimal way.

And another question: in the GnuPG code on the master branch I saw that algorithm identifiers for ML-KEM with Ed25519 and Ed448 are already defined in the code base. Do I understand correctly that the maintainers prefer the inclusion of these two algorithms and not necessarily the inclusion of the ones based on ML-KEM with ECDH using NIST or Brainpool curves?

We have addressed all comments regarding ML-KEM (Kyber) and KMAC. Currently I am working on the GnuPG integration of the the ML-KEM composites. For that purpose I will need a branch of libgcrypt with both ML-KEM and KMAC. I am not sure if you are considering to integrate the ML-KEM version already now before the final NIST standards are release. Some libraries do it, for instance Botan. Appropriate naming of the algorithms can ensure that there arises no confusion which version of the algorithm one is using.

In master, when fixing padding issue, libgcrypt/src/const-time.h is just introduced.
I will replace your functions.

In T6637#177217, @jukivili wrote:

Yes, int8_t/int16_t/int32_t/uint8_t/uint16_t/uint32_t should not be used. There is size-specific integer types defined in src/types.h which can be used instead (byte/u16/u32). This header does not yet have signed integer types, but those can be added (for example, s8/s16/s32).

In T6637#176910, @fse wrote:

OK, fine, however, in order to be able keep an overview of our tasks I would still keep track of them in our GitHub, where I can create a sub-issue from the list of tasks with one click. But we will post our comments and results here as well as far relevant for the purpose of documentation. I think most of the points Jussi raised are more or less clear to me anyway.

Yes, int8_t/int16_t/int32_t/uint8_t/uint16_t/uint32_t should not be used. There is size-specific integer types defined in src/types.h which can be used instead (byte/u16/u32). This header does not yet have signed integer types, but those can be added (for example, s8/s16/s32).

@jukivilli I have addressed a number of your comments now. You find my comments inline.

Yes, apparently I confused uint8_t and unsigned char here because the former appears in Simon's comments. We also kept to the use of unsigned char* in our implementations (that is even part of the GNU coding guidelines if I remember correctly).

Actually we never use uint8_t* because that is c99 and very uncommon except for some MCU projects. Instead we use unsigned char *. The use of void* is often used because this allows to pass arbitrary types to a function without requiring ugly and error-prone casting at the caller site.

You don't need a library but just one object file.

OK, fine, however, in order to be able keep an overview of our tasks I would still keep track of them in our GitHub, where I can create a sub-issue from the list of tasks with one click. But we will post our comments and results here as well as far relevant for the purpose of documentation. I think most of the points Jussi raised are more or less clear to me anyway.

With respect to the function signatures, I see the following issues with the API you reference via the provided link:

@fse: Github is not an option here. We don't use it and thus everything relevant to Libgcrypt needs to be documented here and not at some external platform.

For length information, we can find that Simon's patch (let me call it v1) has length argument:
https://gitlab.com/jas/libgcrypt/-/commit/3af635afca052a9575912b257fe7518a58bfe810

Hi Jussi,

• There's many functions that use buffers on stack. Do those contain secrets? Should those buffers be wiped before returning from function (with wipememory())? For example, "mlkem_check_secret_key" has two buffers "shared_secret_1" and "shared_secret_2" which are not wiped.
• mlkem.c: mlkem_check_secret_key: "memcmp" is used to compare shared secrets. Should this use constant time comparison instead?
• mlkem-common.c: _gcry_mlkem_mlkem_shake256_rkprf:
  • _gcry_md_hash_buffers_extract can be used here instead of _gcry_md_open&write&extract&close.
• mlkem-symmetric.c: _gcry_mlkem_shake256_prf:
  • _gcry_md_hash_buffers_extract can be used here instead of _gcry_md_open&write&extract&close. Temporary buffer usage can be avoided by passing input buffers through two IOV to _gcry_md_hash_buffers_extract.

Few comments on the patches.

Our own internal function signatures is not necessarily a good refernce. The main objection to all what you list above is the lack of explicit length information. For each uint8_t* there should also be a size_t ...len in my opinion. Otherwise the API will be highly prone to memory access errors.

@fse Thank you for your comment (quick ! :-).

The API that you quote at the end is indeed what is comonly understood as how a KEM functions and is exactly what fits to ML-KEM.

Please send us patches (to this branch).

One question on the future cooperation: is it from now on possible to directly commit to these branches or will we continue to work with uploading patches to this task?

Pushed the change into kem-kyber branch.
https://dev.gnupg.org/source/libgcrypt/history/kem-kyber/

I'll create a branch for this work. Then, I'll incorporate changes to master.

Uploading two patches for review: