FCMP++ Integration Audit Overview

[j-berman]

I'm proposing a 4-phase audit, where each subsequent phase builds off the blocks of the prior.

Audit 1: Crypto

We want the functions from the following PR's audited for this phase:

• Faster transparent amount commitments
  • rct::zeroCommitVartime
• Batch inverse
  • fe_batch_invert
  • fe_equals
• Torsion clearing
  • clear_torsion
  • get_valid_torsion_cleared_point
  • rct::verPointsForTorsion
  • mul8_is_identity
• Unbiased key image generator
  • unbiased_hash_to_ec
  • derive_key_image_generator
  • Review that this new function achieves the stated goal of not having expected bias. Unbiased hash to point safety (and is expected collision resistant).
• ed25519 -> wei conversion
  • point_to_ed_derivatives
  • ed_derivatives_to_wei_x_y
  • fe_ed_derivatives_to_wei_x_y
  • fe_reduce

Review: safety, constant timedness in crypto functions (excluding rct).

Out of scope (slated for future optional audit):

• Torsion check
  • torsion_check_vartime
  • get_valid_torsion_cleared_point_fast

Audit 2: Integrated Crypto

• output_to_tuple
• output_to_pre_leaf_tuple
• selene_scalar_from_bytes
• set_valid_leaves
• hash_grow
• hash_init_point
• point_to_cycle_scalar
• from_bytes / to_bytes

Audit 3: Curve Tree Building

• get_tree_extension
• get_leaf_layer_grow_instructions
• hash_children_chunks
• set_next_layer_extension
• get_grow_layer_instructions
• get_next_layer_extension

Audit 4: Consensus Integration

advance_tree
grow_tree
trim_block
trim_tree
get_last_path
handle_fcmp_tree
batch_verify_fcmp_pp_txs

• batchVerifyFcmpPpProofs
  // Make sure the block uses the correct FCMP++ tree root and n tree layers