CB-MPC v0.2.1

Security & Bug Fixes

• Harden Paillier validation: create_pub now validates the modulus (odd, >1, within bit_size) and returns error_t, preventing acceptance of malicious moduli from counterparties.
• Enforce Paillier modulus size bounds in ECDSA 2PC keygen/refresh to prevent potential buffer overflows in constant-time decryption.
• Fix use-after-free in buf_t: operator= and operator+= with an aliasing mem_t view would read zeroed/freed memory.
• Fix out-of-bounds write in HD key derivation: resize derived_keys inside derive_keys() rather than relying on caller pre-allocation.
• Fix const-correctness in secp256k1 point conversion to avoid undefined behavior from casting away const on Jacobian coordinates.

Other

• Add vartime_scope_t to paillier_t::verify_cipher for correct side-channel annotation.
• Add bits_t::ref_t copy assignment operator for correct value semantics.