nx_rsa4096_mod.nx

nx_rsa4096_mod.nx -- bit-by-bit reduction mod 4096-bit modulus. Given an 8192-bit dividend (in a 256-limb wide buffer) and a 4096-bit modulus n (in a 128-limb u4096 buffer with the top bit set), compute the 4096-bit remainder. Mirrors nx_rsa2048_mod with bit-width doubled (8191 iterations instead of 4095; reduction takes ~4x more limb operations). Algorithm (shift-and-subtract, MSB-first): rem = 0 (u4096; one extra "carry" bit kept separately) for i in 8191 down to 0: rem = (rem << 1) | bit_i(dividend) if (carry from shift) OR (rem >= n): rem -= n return rem O(8192 * 128) limb operations ~= O(1M) per reduction. Combined with 17 squarings/mul for RSA verify (e=65537), one verify is ~17M limb ops -- ~10-20 seconds in qemu-riscv64. API: rsa4096_mod(out_128, dividend_256, n_128) -- out = dividend mod n license_tier: INDEPENDENT_REDERIVE genealogy_id: international-research-sources/ietf/rfc_8017 lineage_id: nishi_rsa4096_mod_q1