Updates for CGGMP'24

[fjarri]

Fixes #157

• Updated paper references in PAPER.md, removed obsolete items.
• Updated to the new range definition (±2^l now means [-2^(l-1)+1, 2^(l-1)] instead of the previous [-2^l, 2^l]). This caused a bit of a chain reaction:
  • SecretSigned::assert_exponent_range() logic changed.
  • SecretSigned::random_in_exp_range*() logic changed, and also exp was changed to exponent to match the assertion name.
  • PublicSigned::from_xof_reader_bounded() changed its behavior to produce the number according to the new range definition, and was renamed to from_xof_reader_in_range().
  • PublicSigned::in_range_bits() changed its behavior according to the new range definition, and was renamed to is_in_exponent_range().
  • Wherever scalars are passed to proofs and Ciphertext constructor they are passed as SecretSigned, to comply with the range requirements in the proofs.
  • conversions::secret_unsigned_from_scalar() removed.
  • Added SecretSigned::new_modulo() constructor to make a signed number in range [-N/2, N/2] from an Uint in range [0, N).
  • Removed Ciphertext::new() and decrypt() (which took unsigned plaintexts), renamed new_signed() and decrypt_signed() to new() and decrypt().
  • Ciphertext::new_with_randomizer() was renamed to new_with_randomizer_unsigned(), since it's now a special one, only used in P_mul. Renamed new_with_randomizer_signed() to new_with_randomizer(), and new_public_with_randomizer_signed() to new_public_with_randomizer().
• Following that, wherever in the paper e <-- ±q is used, we are sampling the challenge as a Scalar using the new Scalar::from_xof_reader() method (and using that in П^sch as well).
• Updated paper references and notation in aff-g proof.
• Updated paper references in prm proof, and started using BitVec for its commitment.
• Updated dec proof (there were significant changes). Temporarily, it is located in dec_new.rs, will be moved to dec.rs when Presigning is updated.
• Added elog proof.
• Added enc-elg proof.
• Added aff-g* proof.
• Updated paper references and notation in fac proof, and implemented necessary changes to the algorithm (some variables are calculated differently, and the challenge is now a signed Uint and not a Scalar)
• Updated paper references and notation in mod proof, and enforced invertibility conditions that were added in '24
• Updated paper references and notation sch proof
• Encapsulated the invertibility check in an IsInvertible trait, documenting the choice between GCD and invert()

[codecov]

Codecov Report

Attention: Patch coverage is 88.18505% with 166 lines in your changes missing coverage. Please review.

Project coverage is 92.38%. Comparing base (423f1b5) to head (e0565ce).

Files with missing lines	Patch %	Lines
synedrion/src/cggmp21/key_init.rs	15.17%	95 Missing ⚠️
synedrion/src/cggmp21/interactive_signing.rs	65.51%	10 Missing ⚠️
synedrion/src/cggmp21/aux_gen.rs	0.00%	9 Missing ⚠️
synedrion/src/cggmp21/key_refresh.rs	18.18%	9 Missing ⚠️
synedrion/src/www02/key_resharing.rs	10.00%	9 Missing ⚠️
synedrion/src/cggmp21/sigma/aff_g_star.rs	96.42%	7 Missing ⚠️
synedrion/src/cggmp21/sigma/enc_elg.rs	96.55%	6 Missing ⚠️
synedrion/src/cggmp21/sigma/dec_new.rs	97.26%	5 Missing ⚠️
synedrion/src/cggmp21/sigma/elog.rs	96.58%	4 Missing ⚠️
synedrion/src/cggmp21/sigma/fac.rs	93.47%	3 Missing ⚠️
... and 6 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #170      +/-   ##
==========================================
- Coverage   93.06%   92.38%   -0.69%     
==========================================
  Files          36       40       +4     
  Lines        7012     7734     +722     
==========================================
+ Hits         6526     7145     +619     
- Misses        486      589     +103     

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