diff --git a/const.go b/const.go
index 836ad7d..45b1bfd 100644
--- a/const.go
+++ b/const.go
@@ -1,4 +1,34 @@
 package keccak
 
-var RC = [24]uint64{0x0000000000000001, 0x0000000000008082, 0x800000000000808a, 0x8000000080008000, 0x000000000000808b, 0x0000000080000001, 0x8000000080008081, 0x8000000000008009, 0x000000000000008a, 0x0000000000000088, 0x0000000080008009, 0x000000008000000a, 0x000000008000808b, 0x800000000000008b, 0x8000000000008089, 0x8000000000008003, 0x8000000000008002, 0x8000000000000080, 0x000000000000800a, 0x800000008000000a, 0x8000000080008081, 0x8000000000008080, 0x0000000080000001, 0x8000000080008008}
-var rotc = [5][5]uint{[5]uint{0x0, 0x1, 0x3e, 0x1c, 0x1b}, [5]uint{0x24, 0x2c, 0x6, 0x37, 0x14}, [5]uint{0x3, 0xa, 0x2b, 0x19, 0x27}, [5]uint{0x29, 0x2d, 0xf, 0x15, 0x8}, [5]uint{0x12, 0x2, 0x3d, 0x38, 0xe}}
+var roundc = [24]uint64{
+	0x0000000000000001,
+	0x0000000000008082,
+	0x800000000000808a,
+	0x8000000080008000,
+	0x000000000000808b,
+	0x0000000080000001,
+	0x8000000080008081,
+	0x8000000000008009,
+	0x000000000000008a,
+	0x0000000000000088,
+	0x0000000080008009,
+	0x000000008000000a,
+	0x000000008000808b,
+	0x800000000000008b,
+	0x8000000000008089,
+	0x8000000000008003,
+	0x8000000000008002,
+	0x8000000000000080,
+	0x000000000000800a,
+	0x800000008000000a,
+	0x8000000080008081,
+	0x8000000000008080,
+	0x0000000080000001,
+	0x8000000080008008,
+}
+var rotc = [5][5]uint{[5]uint{0x0, 0x1, 0x3e, 0x1c, 0x1b},
+	[5]uint{0x24, 0x2c, 0x6, 0x37, 0x14},
+	[5]uint{0x3, 0xa, 0x2b, 0x19, 0x27},
+	[5]uint{0x29, 0x2d, 0xf, 0x15, 0x8},
+	[5]uint{0x12, 0x2, 0x3d, 0x38, 0xe},
+}
diff --git a/keccak_test.go b/keccak_test.go
index a582e6d..cfbb022 100644
--- a/keccak_test.go
+++ b/keccak_test.go
@@ -5,24 +5,47 @@ import (
 	"testing"
 )
 
-var vector = []byte{
+var vector256 = []byte{
 	0xc5, 0xd2, 0x46, 0x01, 0x86, 0xf7, 0x23, 0x3c,
 	0x92, 0x7e, 0x7d, 0xb2, 0xdc, 0xc7, 0x03, 0xc0,
 	0xe5, 0x00, 0xb6, 0x53, 0xca, 0x82, 0x27, 0x3b,
 	0x7b, 0xfa, 0xd8, 0x04, 0x5d, 0x85, 0xa4, 0x70,
 }
 
-func TestKeccak(t *testing.T) {
-	h := New()
+var vector512 = []byte{
+	0x0e, 0xab, 0x42, 0xde, 0x4c, 0x3c, 0xeb, 0x92,
+	0x35, 0xfc, 0x91, 0xac, 0xff, 0xe7, 0x46, 0xb2,
+	0x9c, 0x29, 0xa8, 0xc3, 0x66, 0xb7, 0xc6, 0x0e,
+	0x4e, 0x67, 0xc4, 0x66, 0xf3, 0x6a, 0x43, 0x04,
+	0xc0, 0x0f, 0xa9, 0xca, 0xf9, 0xd8, 0x79, 0x76,
+	0xba, 0x46, 0x9b, 0xcb, 0xe0, 0x67, 0x13, 0xb4,
+	0x35, 0xf0, 0x91, 0xef, 0x27, 0x69, 0xfb, 0x16,
+	0x0c, 0xda, 0xb3, 0x3d, 0x36, 0x70, 0x68, 0x0e,
+}
+
+func TestKeccak256(t *testing.T) {
+	h := newKeccak256()
 	sum := h.Sum(nil)
-	if !reflect.DeepEqual(sum, vector) {
-		t.Errorf("\"\": want % x, got % x", vector, sum)
+	if !reflect.DeepEqual(sum, vector256) {
+		t.Errorf("\"\": want % x, got % x", vector256, sum)
+	}
+}
+
+func TestKeccak512(t *testing.T) {
+	h := newKeccak512()
+	sum := h.Sum(nil)
+	if !reflect.DeepEqual(sum, vector512) {
+		t.Errorf("\"\": want % x, got % x", vector512, sum)
 	}
 }
 
 func Benchmark256(b *testing.B) {
 	var tmp [Size]byte
-	h := New()
+	h := New256()
+	var msg [BlockSize]byte
+	if len(msg) != h.BlockSize() {
+		b.Fatalf("message length does not match block size: want %d got %d", h.BlockSize(), len(msg))
+	}
 	b.SetBytes(BlockSize)
 	for i := 0; i < b.N; i++ {
 		h.Sum(tmp[:])
diff --git a/sponge.go b/sponge.go
index 1d659e7..d43914e 100644
--- a/sponge.go
+++ b/sponge.go
@@ -11,28 +11,36 @@ var round = roundGo
 // digest implements hash.Hash
 type digest struct {
 	a   [5][5]uint64 // a[y][x][z]
-	buf [BlockSize]byte
+	buf [200]byte
+	dsbyte byte
 	len int
+	size int
 }
 
-func New() hash.Hash {
-	return &digest{}
-}
+func New256() hash.Hash { return &digest{size: 256/8, dsbyte: 0x06} }
+func New512() hash.Hash { return &digest{size: 512/8, dsbyte: 0x06} }
 
-func (d *digest) Size() int      { return Size }
-func (d *digest) BlockSize() int { return BlockSize }
+func newKeccak256() hash.Hash { return &digest{size: 256/8, dsbyte: 0x01} }
+func newKeccak512() hash.Hash { return &digest{size: 512/8, dsbyte: 0x01} }
+
+func (d *digest) Size() int      { return d.size }
+func (d *digest) BlockSize() int { return 200 - d.size*2 }
 
 func (d *digest) Reset() {
-	*d = digest{}
+	//fmt.Println("resetting")
+	d.a = [5][5]uint64{}
+	d.buf = [200]byte{}
+	d.len = 0
 }
 
 func (d *digest) Write(b []byte) (int, error) {
 	written := len(b)
+	bs := d.BlockSize()
 	for len(b) > 0 {
-		n := copy(d.buf[d.len:], b)
+		n := copy(d.buf[d.len:bs], b)
 		d.len += n
 		b = b[n:]
-		if d.len == BlockSize {
+		if d.len == bs  {
 			d.flush()
 		}
 	}
@@ -40,7 +48,8 @@ func (d *digest) Write(b []byte) (int, error) {
 }
 
 func (d *digest) flush() {
-	b := d.buf[:]
+	//fmt.Printf("Flushing with %d bytes\n", d.len)
+	b := d.buf[:d.len]
 loop:
 	for y := range d.a {
 		for x := range d.a[0] {
@@ -58,23 +67,24 @@ loop:
 func keccakf(a *[5][5]uint64) {
 	for i := 0; i < 24; i++ {
 		round(a)
-		a[0][0] ^= RC[i]
+		a[0][0] ^= roundc[i]
 	}
 }
 
 func (d0 *digest) Sum(b []byte) []byte {
 	d := *d0
-	d.buf[d.len] = 0x01
-	for i := d.len + 1; i < BlockSize; i++ {
+	d.buf[d.len] = d.dsbyte
+	bs := d.BlockSize()
+	for i := d.len + 1; i < bs; i++ {
 		d.buf[i] = 0
 	}
-	d.buf[BlockSize-1] |= 0x80
+	d.buf[bs-1] |= 0x80
+	d.len = bs
 	d.flush()
 
-	b = le64enc(b, d.a[0][0])
-	b = le64enc(b, d.a[0][1])
-	b = le64enc(b, d.a[0][2])
-	b = le64enc(b, d.a[0][3])
+	for i := 0; i < d.size/8; i++ {
+		b = le64enc(b, d.a[i/5][i%5])
+	}
 	return b
 }