core/crypto/chacha20: Use 128-bit/256-bit SIMD

core/crypto/_chacha20/chacha20.odin

@@ -0,0 +1,123 @@
+package _chacha20
+
+import "base:intrinsics"
+import "core:encoding/endian"
+import "core:math/bits"
+import "core:mem"
+
+// KEY_SIZE is the (X)ChaCha20 key size in bytes.
+KEY_SIZE :: 32
+// NONCE_SIZE is the ChaCha20 nonce size in bytes.
+NONCE_SIZE :: 12
+// XNONCE_SIZE is the XChaCha20 nonce size in bytes.
+XNONCE_SIZE :: 24
+
+// MAX_CTR_IETF is the maximum counter value for the IETF flavor ChaCha20.
+MAX_CTR_IETF :: 0xffffffff
+// BLOCK_SIZE is the (X)ChaCha20 block size in bytes.
+BLOCK_SIZE :: 64
+// STATE_SIZE_U32 is the (X)ChaCha20 state size in u32s.
+STATE_SIZE_U32 :: 16
+// Rounds is the (X)ChaCha20 round count.
+ROUNDS :: 20
+
+// SIGMA_0 is sigma[0:4].
+SIGMA_0: u32 : 0x61707865
+// SIGMA_1 is sigma[4:8].
+SIGMA_1: u32 : 0x3320646e
+// SIGMA_2 is sigma[8:12].
+SIGMA_2: u32 : 0x79622d32
+// SIGMA_3 is sigma[12:16].
+SIGMA_3: u32 : 0x6b206574
+
+// Context is a ChaCha20 or XChaCha20 instance.
+Context :: struct {
+	_s:              [STATE_SIZE_U32]u32,
+	_buffer:         [BLOCK_SIZE]byte,
+	_off:            int,
+	_is_ietf_flavor: bool,
+	_is_initialized: bool,
+}
+
+// init inititializes a Context for ChaCha20 with the provided key and
+// nonce.
+//
+// WARNING: This ONLY handles ChaCha20.  XChaCha20 sub-key and nonce
+// derivation is expected to be handled by the caller, so that the
+// HChaCha call can be suitably accelerated.
+init :: proc "contextless" (ctx: ^Context, key, nonce: []byte, is_xchacha: bool) {
+	if len(key) != KEY_SIZE || len(nonce) != NONCE_SIZE {
+		intrinsics.trap()
+	}
+
+	k, n := key, nonce
+
+	ctx._s[0] = SIGMA_0
+	ctx._s[1] = SIGMA_1
+	ctx._s[2] = SIGMA_2
+	ctx._s[3] = SIGMA_3
+	ctx._s[4] = endian.unchecked_get_u32le(k[0:4])
+	ctx._s[5] = endian.unchecked_get_u32le(k[4:8])
+	ctx._s[6] = endian.unchecked_get_u32le(k[8:12])
+	ctx._s[7] = endian.unchecked_get_u32le(k[12:16])
+	ctx._s[8] = endian.unchecked_get_u32le(k[16:20])
+	ctx._s[9] = endian.unchecked_get_u32le(k[20:24])
+	ctx._s[10] = endian.unchecked_get_u32le(k[24:28])
+	ctx._s[11] = endian.unchecked_get_u32le(k[28:32])
+	ctx._s[12] = 0
+	ctx._s[13] = endian.unchecked_get_u32le(n[0:4])
+	ctx._s[14] = endian.unchecked_get_u32le(n[4:8])
+	ctx._s[15] = endian.unchecked_get_u32le(n[8:12])
+
+	ctx._off = BLOCK_SIZE
+	ctx._is_ietf_flavor = !is_xchacha
+	ctx._is_initialized = true
+}
+
+// seek seeks the (X)ChaCha20 stream counter to the specified block.
+seek :: proc(ctx: ^Context, block_nr: u64) {
+	assert(ctx._is_initialized)
+
+	if ctx._is_ietf_flavor {
+		if block_nr > MAX_CTR_IETF {
+			panic("crypto/chacha20: attempted to seek past maximum counter")
+		}
+	} else {
+		ctx._s[13] = u32(block_nr >> 32)
+	}
+	ctx._s[12] = u32(block_nr)
+	ctx._off = BLOCK_SIZE
+}
+
+// reset sanitizes the Context.  The Context must be re-initialized to
+// be used again.
+reset :: proc(ctx: ^Context) {
+	mem.zero_explicit(&ctx._s, size_of(ctx._s))
+	mem.zero_explicit(&ctx._buffer, size_of(ctx._buffer))
+
+	ctx._is_initialized = false
+}
+
+check_counter_limit :: proc(ctx: ^Context, nr_blocks: int) {
+	// Enforce the maximum consumed keystream per nonce.
+	//
+	// While all modern "standard" definitions of ChaCha20 use
+	// the IETF 32-bit counter, for XChaCha20 most common
+	// implementations allow for a 64-bit counter.
+	//
+	// Honestly, the answer here is "use a MRAE primitive", but
+	// go with "common" practice in the case of XChaCha20.
+
+	ERR_CTR_EXHAUSTED :: "crypto/chacha20: maximum (X)ChaCha20 keystream per nonce reached"
+
+	if ctx._is_ietf_flavor {
+		if u64(ctx._s[12]) + u64(nr_blocks) > MAX_CTR_IETF {
+			panic(ERR_CTR_EXHAUSTED)
+		}
+	} else {
+		ctr := (u64(ctx._s[13]) << 32) | u64(ctx._s[12])
+		if _, carry := bits.add_u64(ctr, u64(nr_blocks), 0); carry != 0 {
+			panic(ERR_CTR_EXHAUSTED)
+		}
+	}
+}