core/crypto/shake: Support cSHAKE

core/crypto/_sha3/sha3.odin

@@ -20,9 +20,7 @@ import "core:mem"
 
 ROUNDS :: 24
 
-RATE_SHAKE_128 :: 168
-RATE_SHAKE_256 :: 136
-
+RATE_128 :: 1344 / 8 // ONLY for SHAKE128.
 RATE_224 :: 1152 / 8
 RATE_256 :: 1088 / 8
 RATE_384 :: 832 / 8

core/crypto/_sha3/sp800_185.odin

@@ -0,0 +1,130 @@
+package _sha3
+
+import "core:encoding/endian"
+import "core:math/bits"
+
+init_cshake :: proc(ctx: ^Context, n, s: []byte, sec_strength: int) {
+	rate: int
+	switch sec_strength {
+	case 128:
+		rate = RATE_128
+	case 256:
+		rate = RATE_256
+	case:
+		panic("crypto/sha3: invalid security strength")
+	}
+
+	ctx.mdlen = sec_strength / 8
+
+	// No domain separator is equivalent to vanilla SHAKE.
+	if len(n) == 0 && len(s) == 0 {
+		ctx.dsbyte = DS_SHAKE
+		init(ctx)
+		return
+	}
+
+	ctx.dsbyte = DS_CSHAKE
+	init(ctx)
+	bytepad(ctx, [][]byte{n, s}, rate)
+}
+
+// right_encode and left_encode are defined to support 0 <= x < 2^2040
+// however, the largest value we will ever need to encode is `max(int) * 8`.
+//
+// This is unfortunate as the extreme upper edge is larger than
+// `max(u64)`.  While such values are impractical at present,
+// they are possible (ie: https://arxiv.org/pdf/quant-ph/9908043.pdf).
+//
+// Thus we support 0 <= x < 2^128.
+
+@(private)
+_PAD: [RATE_128]byte // Biggest possible value of w per spec.
+
+bytepad :: proc(ctx: ^Context, x_strings: [][]byte, w: int) {
+	// 1. z = left_encode(w) || X.
+	z_hi: u64
+	z_lo := left_right_encode(ctx, 0, u64(w), true)
+	for x in x_strings {
+		// All uses of bytepad in SP 800-185 use the output from
+		// one or more encode_string values for `X`.
+		hi, lo := encode_string(ctx, x)
+
+		carry: u64
+		z_lo, carry = bits.add_u64(z_lo, lo, 0)
+		z_hi, carry = bits.add_u64(z_hi, hi, carry)
+
+		// This isn't actually possible, at least with the currently
+		// defined SP 800-185 routines.
+		if carry != 0 {
+			panic("crypto/sha3: bytepad input length overflow")
+		}
+	}
+
+	// We skip this step as we are doing a byte-oriented implementation
+	// rather than a bit oriented one.
+	//
+	// 2. while len(z) mod 8 ≠ 0:
+	//    z = z || 0
+
+	// 3. while (len(z)/8) mod w ≠ 0:
+	//    z = z || 00000000
+	z_len := u128(z_hi) << 64 | u128(z_lo)
+	z_rem := int(z_len % u128(w))
+	pad := _PAD[:w - z_rem]
+
+	// We just add the padding to the state, instead of returning z.
+	//
+	// 4. return z.
+	update(ctx, pad)
+}
+
+encode_string :: #force_inline proc(ctx: ^Context, s: []byte) -> (u64, u64) {
+	l := encode_byte_len(ctx, len(s), true) // left_encode
+	update(ctx, s)
+
+	lo, hi := bits.add_u64(l, u64(len(s)), 0)
+
+	return hi, lo
+}
+
+encode_byte_len :: #force_inline proc(ctx: ^Context, l: int, is_left: bool) -> u64 {
+	hi, lo := bits.mul_u64(u64(l), 8)
+	return left_right_encode(ctx, hi, lo, is_left)
+}
+
+@(private)
+left_right_encode :: proc(ctx: ^Context, hi, lo: u64, is_left: bool) -> u64 {
+	HI_OFFSET :: 1
+	LO_OFFSET :: HI_OFFSET + 8
+	RIGHT_OFFSET :: LO_OFFSET + 8
+	BUF_LEN :: RIGHT_OFFSET + 1
+
+	buf: [BUF_LEN]byte // prefix + largest uint + postfix
+
+	endian.unchecked_put_u64be(buf[HI_OFFSET:], hi)
+	endian.unchecked_put_u64be(buf[LO_OFFSET:], lo)
+
+	// 2. Strip leading `0x00` bytes.
+	off: int
+	for off = HI_OFFSET; off < RIGHT_OFFSET - 1; off = off + 1 {// Note: Minimum size is 1, not 0.
+		if buf[off] != 0 {
+			break
+		}
+	}
+	n := byte(RIGHT_OFFSET - off)
+
+	// 3. Prefix (left_encode) or postfix (right_encode) the length in bytes.
+	b: []byte
+	switch is_left {
+	case true:
+		buf[off - 1] = n // n | x
+		b = buf[off - 1:RIGHT_OFFSET]
+	case false:
+		buf[RIGHT_OFFSET] = n // x | n
+		b = buf[off:]
+	}
+
+	update(ctx, b)
+
+	return u64(len(b))
+}