nx_ed25519_sign_bisect_test.nx

nx_ed25519_sign_bisect_test.nx -- bisection diagnostic for the known Ed25519 sign byte-1 mismatch reported by nx_ed25519_signature_smoke (FAIL at assertion #1). Walks the RFC 8032 §7.1 test vector 1 (empty message) step by step and returns a non-zero exit code at the FIRST step whose output diverges from the published reference. This identifies which Ed25519 sub-primitive is broken so the fix can target the actual root cause instead of the symptom. Step-by-step check sequence (each step returns its own assertion code so the failure surface is unambiguous): Step 1 (assertion 1..32): H = SHA-512(priv) byte-by-byte vs the RFC 8032 reference H_priv (precomputed offline -- the SHA-512 of the known priv is itself a known value) Step 2 (assertion 100): s_scalar = H[0..32] clamped == expected s_scalar (precomputed offline) Step 3 (assertion 200+i): A = s_scalar * G; compress(A) == known pub byte-by-byte (this catches scalar_mul OR compress bugs) Step 4 (assertion 300): if A_enc matches pub then scalar_mul works for this scalar -- so any R_enc mismatch is sc_reduce's fault. Continue. Step 5 (assertion 400): r_h = SHA-512(prefix || empty) == expected (precomputed offline) Step 6 (assertion 500+i): r_scalar = sc_reduce(r_h) bytes match expected r_scalar (precomputed offline) Step 7 (assertion 600+i): R = r_scalar * G; compress(R) matches expected R_enc (= first 32 bytes of expected sig) expect_exit: 0 license_tier: ORIGINAL