nx_rsa2048_mod.nx

nx_rsa2048_mod.nx -- bit-by-bit reduction mod 2048-bit modulus. Given a 4096-bit dividend (in a 128-limb wide buffer) and a 2048-bit modulus n (in a 64-limb u2048 buffer with the top bit set), compute the 2048-bit remainder. Algorithm (shift-and-subtract, MSB-first): rem = 0 (u2048; one extra "carry" bit kept separately) for i in 4095 down to 0: rem = (rem << 1) | bit_i(dividend) if (carry from shift) OR (rem >= n): rem -= n return rem O(4096 * 64) limb operations ~= O(262K) per reduction. Combined with 17 squarings/mul for RSA-2048 verify (e=65537), one verify is ~4-5M limb ops -- a few seconds in qemu-riscv64. API: rsa2048_mod(out_64, dividend_128, n_64) -- out_64 = dividend_128 mod n_64 license_tier: INDEPENDENT_REDERIVE genealogy_id: international-research-sources/ietf/rfc_8017 lineage_id: nishi_rsa2048_mod_q10