nx_chacha20_wasm.nx

nx_chacha20_wasm.nx -- ChaCha20 stream cipher (RFC 7539) for WAT target. State is a 4x4 matrix of 32-bit words: "expand 32-byte k" (constants 0..3) key words 0..7 (key bytes 0..31) counter (word 12) nonce words 13..15 (nonce bytes 0..11) 20 rounds of quarter-round operations, then add original state, produce 64 bytes of keystream per block. XOR keystream with plaintext byte-for-byte to encrypt; same operation decrypts. API for the embedder: nx_chacha20_xor(key_ptr, nonce_ptr, counter, in_ptr, in_len, scratch_ptr, out_ptr) -> i64 key_ptr -- 32 bytes (256-bit key) nonce_ptr -- 12 bytes (96-bit nonce per RFC 7539) counter -- starting block counter (1 for RFC 7539; 0 for some flows; caller's choice) in_ptr -- plaintext bytes in_len -- input length scratch_ptr -- >= 256 bytes; holds state + working matrix out_ptr -- ciphertext bytes (may alias in_ptr for in-place) Memory layout of scratch_ptr: bytes 0..63 : initial state (16 i32 words, little-endian packed) bytes 64..127 : working state during one block compute bytes 128..191 : keystream output bytes for one block bytes 192.. : unused Verified against RFC 7539 §2.4.2 test vector. license_tier: INDEPENDENT_REDERIVE genealogy_id: international-research-sources/ietf/rfc_7539 lineage_id: nishi_chacha20_wasm_q11