diff --git a/src/lib/hash/md5block.go b/src/lib/hash/md5block.go
new file mode 100644
index 00000000000..a885e63c501
--- /dev/null
+++ b/src/lib/hash/md5block.go
@@ -0,0 +1,178 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// MD5 block step.
+// In its own file so that a faster assembly or C version
+// can be substituted easily.
+
+package md5
+
+import "md5"
+
+// T[i] = int((1<<32) * abs(sin(i+1 radians))).
+var T = []uint32 {
+	// round 1
+	0xd76aa478,	
+	0xe8c7b756,
+	0x242070db,	
+	0xc1bdceee,	
+	0xf57c0faf,	
+	0x4787c62a,	
+	0xa8304613,	
+	0xfd469501,	
+	0x698098d8,	
+	0x8b44f7af,	
+	0xffff5bb1,	
+	0x895cd7be,	
+	0x6b901122,	
+	0xfd987193,	
+	0xa679438e,	
+	0x49b40821,
+
+	// round 2
+	0xf61e2562,	
+	0xc040b340,	
+	0x265e5a51,	
+	0xe9b6c7aa,	
+	0xd62f105d,	
+	0x2441453,	
+	0xd8a1e681,	
+	0xe7d3fbc8,	
+	0x21e1cde6,	
+	0xc33707d6,	
+	0xf4d50d87,	
+	0x455a14ed,	
+	0xa9e3e905,	
+	0xfcefa3f8,	
+	0x676f02d9,	
+	0x8d2a4c8a,
+
+	// round3
+	0xfffa3942,	
+	0x8771f681,	
+	0x6d9d6122,	
+	0xfde5380c,	
+	0xa4beea44,	
+	0x4bdecfa9,	
+	0xf6bb4b60,	
+	0xbebfbc70,	
+	0x289b7ec6,	
+	0xeaa127fa,	
+	0xd4ef3085,	
+	0x4881d05,	
+	0xd9d4d039,	
+	0xe6db99e5,	
+	0x1fa27cf8,	
+	0xc4ac5665,	
+
+	// round 4
+	0xf4292244,	
+	0x432aff97,	
+	0xab9423a7,	
+	0xfc93a039,	
+	0x655b59c3,	
+	0x8f0ccc92,	
+	0xffeff47d,	
+	0x85845dd1,	
+	0x6fa87e4f,	
+	0xfe2ce6e0,	
+	0xa3014314,	
+	0x4e0811a1,	
+	0xf7537e82,	
+	0xbd3af235,	
+	0x2ad7d2bb,	
+	0xeb86d391,	
+}
+
+var shift1 = []uint { 7, 12, 17, 22 };
+var shift2 = []uint { 5, 9, 14, 20 };
+var shift3 = []uint { 4, 11, 16, 23 };
+var shift4 = []uint { 6, 10, 15, 21 };
+
+package func Block(dig *Digest, p *[]byte) int {
+	a := dig.s[0];
+	b := dig.s[1];
+	c := dig.s[2];
+	d := dig.s[3];
+	n := 0;
+	var X [16]uint32;
+	for len(p) >= Chunk {
+		aa, bb, cc, dd := a, b, c, d;
+	
+		for i := 0; i < 16; i++ {
+			j := i*4;
+			X[i] = uint32(p[j]) | uint32(p[j+1])<<8 | uint32(p[j+2])<<16 | uint32(p[j+3])<<24;
+		}
+
+		// If this needs to be made faster in the future,
+		// the usual trick is to unroll each of these
+		// loops by a factor of 4; that lets you replace
+		// the shift[] lookups with constants and,
+		// with suitable variable renaming in each
+		// unrolled body, delete the a, b, c, d = d, a, b, c
+		// (or you can let the optimizer do the renaming).
+
+		// Round 1.
+		for i := 0; i < 16; i++ {
+			x := i;
+			t := i;
+			s := shift1[i%4];
+			f := ((c ^ d) & b) ^ d;
+			a += f + X[x] + T[t];
+			a = a<<s | a>>(32-s);
+			a += b;
+			a, b, c, d = d, a, b, c;
+		}
+	
+		// Round 2.
+		for i := 0; i < 16; i++ {
+			x := (1+5*i)%16;
+			t := 16+i;
+			s := shift2[i%4];
+			g := ((b ^ c) & d) ^ c;
+			a += g + X[x] + T[t];
+			a = a<<s | a>>(32-s);
+			a += b;
+			a, b, c, d = d, a, b, c;
+		}
+	
+		// Round 3.
+		for i := 0; i < 16; i++ {
+			x := (5+3*i)%16;
+			t := 32+i;
+			s := shift3[i%4];
+			h := b ^ c ^ d;
+			a += h + X[x] + T[t];
+			a = a<<s | a>>(32-s);
+			a += b;
+			a, b, c, d = d, a, b, c;
+		}
+		
+		// Round 4.
+		for i := 0; i < 16; i++ {
+			x := (7*i)%16;
+			s := shift4[i%4];
+			t := 48+i;
+			ii := c ^ (b | ^d);
+			a += ii + X[x] + T[t];
+			a = a<<s | a>>(32-s);
+			a += b;
+			a, b, c, d = d, a, b, c;
+		}
+
+		a += aa;
+		b += bb;
+		c += cc;
+		d += dd;
+		
+		p = p[Chunk:len(p)];
+		n += Chunk;
+	}
+	
+	dig.s[0] = a;
+	dig.s[1] = b;
+	dig.s[2] = c;
+	dig.s[3] = d;
+	return n;
+}