nx_rsa_pkcs1_v1_5_k.nx

nx_rsa_pkcs1_v1_5_k.nx -- k-aware RSA-PKCS#1 v1.5 verify for RSA moduli whose byte-length k is NOT exactly 256 or 512 (e.g. RSA-3072 = 384 bytes, common on Sectigo/USERTrust intermediates like iana.org's chain). Mechanism: load the (zero-extended) k-byte signature into a u4096 and mod-exp under the (zero-extended) modulus. The recovered EM value is < n < 2^(8k), so its big-endian 512-byte form has the high (512-k) bytes = 0x00 and the real k-byte PKCS#1 EM (00 01 PS 00 T H) in the LOW k bytes, i.e. starting at offset zoff = 512-k. We verify the high zero-extension AND the EM structure at zoff with PS_LEN = k-3-19-hashlen. For k=512 this reduces to the existing RSA-4096 check (zoff=0); we only route here for k not in {256,512} so the proven 2048/4096 paths are untouched. Verdicts reuse the SHA-384 module's enum (same shape). license_tier: INDEPENDENT_REDERIVE genealogy_id: international-research-sources/ietf/rfc_8017 lineage_id: nishi_rsa_pkcs1_v1_5_k_q1