ML-KEM refactor

[dkostic]

Issues:

CryptoAlg-2614

Description of changes:

Previous to this change, ML-KEM was implemented such that the code for a parameter set was selected by defining the correct C pre-processor flag (for example, if you want to compile the code for ML-KEM 512 parameter set you would #define KYBER_K 2). The consequence of this was that we had to compile the code three times for three ML-KEM parameter sets. We do this by adding a C file for each parameter set where we first define the corresponding KYBER_K value and then include all the ML-KEM C files. Besides being an awkward way to handle multiple parameter sets, this will not work for the FIPS module where we bundle all C files inside bcm.c and compile it as a single compilation unit.

In this change we refactor ML-KEM by parametrizing all functions that depend on values that are specific to a parameter set, i.e., that directly or indirectly depend on the value of KYBER_K. To do this, in params.h we define a structure that holds those ML-KEM parameters and functions that initialize a given structure with values corresponding to a parameter set. This structure can then be passed to every function that requires it. For example, polyvec_ntt function was previously implemented like this:

void polyvec_ntt(polyvec *r) {
  unsigned int i;
  for(i=0;i<KYBER_K;i++)
    poly_ntt(&r->vec[i]);
}

We now change that to:

void polyvec_ntt(ml_kem_params *params, polyvec *r) {
  unsigned int i;
  for(i=0;i<params->k;i++)
    poly_ntt(&r->vec[i]);
}

Of course, now we have to change all callers of polyvec_ntt to also have ml_kem_params as an input argument, and then callers of the caller, etc. These changes bubble up to the highest level API defined in kem.h where we now have:

int crypto_kem_keypair(ml_kem_params *params, ...);
int crypto_kem_enc(ml_kem_params * params, ...);
int crypto_kem_dec(ml_kem_params * params, ...);
int crypto_kem_keypair_derand(ml_kem_params *params, ...);
int crypto_kem_enc_derand(ml_kem_params * params, ...);

Then we can easily implement these functions for specific parameter sets, which can be seen in ml_kem.c file. For example:

int ml_kem_512_ipd_keypair(...) {
  ml_kem_params params;
  ml_kem_512_params_init(&params);
  return ml_kem_keypair_ref(&params, ...);
}
int ml_kem_768_ipd_keypair(...) {
  ml_kem_params params;
  ml_kem_768_params_init(&params);
  return ml_kem_keypair_ref(&params, ...);
}

Call-outs:

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Testing:

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 78.32%. Comparing base (79d5d16) to head (9c591df). Report is 18 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1763 +/- ## ========================================== - Coverage 78.44% 78.32% -0.13% ========================================== Files 580 581 +1 Lines 96780 97176 +396 Branches 13863 13930 +67 ========================================== + Hits 75921 76113 +192 - Misses 20243 20440 +197 - Partials 616 623 +7 ```

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