nx_rsa_pkcs1_v1_5_sha256_4096.nx

nx_rsa_pkcs1_v1_5_sha256_4096.nx -- RSA-PKCS#1 v1.5 signature verify with SHA-256 hash, for RSA-4096 keys. Parallel to nx_rsa_pkcs1_v1_5_sha256 (the RSA-2048 variant); kept as a separate module rather than parameterizing the existing module so the existing 2048 callers continue to compile unchanged. RFC 8017 §8.2.2 RSASSA-PKCS1-v1_5-VERIFY (k=512 bytes for RSA-4096): 1. s -> m = s^e mod n (4096-bit RSA modular exponentiation) 2. Encode message into EM_test: EM_test = 0x00 || 0x01 || PS (FF*458) || 0x00 || T || H where T = SHA-256 DigestInfo DER prefix (19 bytes): 30 31 30 0d 06 09 60 86 48 01 65 03 04 02 01 05 00 04 20 and H = SHA-256(message) (32 bytes). PS_LEN = 512 - 3 - 19 - 32 = 458 bytes of 0xFF. 3. Convert m to 512-byte big-endian EM. 4. Compare EM == EM_test byte-by-byte. API: rsa_pkcs1_v1_5_sha256_4096_verify(msg, msg_len, sig_bytes, n_4096, e_i64) -> verdict Sealed verdict (parallel to 2048-variant; same shape so cert-chain verifier can map verdicts uniformly): NX_RSA_PKCS1_V15_4096_OK valid signature NX_RSA_PKCS1_V15_4096_S_OUT_OF_RANGE s_int >= n NX_RSA_PKCS1_V15_4096_BAD_PAD padding mismatch NX_RSA_PKCS1_V15_4096_HASH_MISMATCH trailing 32 bytes != SHA-256(msg) Composes: - sha256_digest (already shipped) - u4096_load_be / u4096_store_be (stone 1) - rsa4096_mod_exp (stone 3) - rsa_pkcs1_sha256_di_byte (shared with 2048 variant) Unblocks: L11 step 2d -> 2e (LE E7 -> ISRG Root X1 chain validates; nx_acme daemon can drive state machine end-to-end against LE). license_tier: INDEPENDENT_REDERIVE genealogy_id: international-research-sources/ietf/rfc_8017 + nist/fips_180_4 lineage_id: nishi_rsa_pkcs1_v1_5_sha256_4096_q1