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Task/The-ISAAC-Cipher/C-sharp/the-isaac-cipher.cs

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+using System;
+
+namespace cipher {
+
+static class Cipher {
+
+// external results
+static uint[] randrsl = new uint[256];
+static uint randcnt;
+// internal state
+static uint[] mm = new uint[256];
+static uint aa=0, bb=0, cc=0;
+
+
+static void isaac() {
+   uint i,x,y;
+   cc++;    // cc just gets incremented once per 256 results
+   bb+=cc;   // then combined with bb
+
+   for (i=0; i<=255; i++) {
+     x = mm[i];
+     switch (i & 3) {
+      case 0: aa = aa ^ (aa << 13); break;
+      case 1: aa = aa ^ (aa >> 6); break;
+      case 2: aa = aa ^ (aa << 2); break;
+      case 3: aa = aa ^ (aa >> 16); break;
+     }
+     aa = mm[(i+128) & 255] + aa;
+     y  = mm[(x >> 2) & 255] + aa + bb;
+     mm[i] = y; 	
+     bb = mm[(y >> 10) & 255] + x;
+     randrsl[i]= bb;
+   }
+}
+
+
+// if (flag==TRUE), then use the contents of randrsl[] to initialize mm[].
+static void mix(ref uint a, ref uint b, ref uint c, ref uint d, ref uint e, ref uint f, ref uint g, ref uint h) {
+   a = a ^ b << 11; d+=a; b+=c;
+   b = b ^ c >> 2;  e+=b; c+=d;
+   c = c ^ d << 8;  f+=c; d+=e;
+   d = d ^ e >> 16; g+=d; e+=f;
+   e = e ^ f << 10; h+=e; f+=g;
+   f = f ^ g >> 4;  a+=f; g+=h;
+   g = g ^ h << 8;  b+=g; h+=a;
+   h = h ^ a >> 9;  c+=h; a+=b;
+}
+
+
+static void Init(bool flag) {
+  short i; uint a,b,c,d,e,f,g,h;
+
+   aa=0; bb=0; cc=0;
+   a=0x9e3779b9; b=a; c=a; d=a;
+   e=a; f=a; g=a; h=a;
+
+   for (i=0; i<=3; i++)           // scramble it
+        mix(ref a,ref b,ref c,ref d,ref e,ref f,ref g,ref h);
+
+   i=0;
+   do  { // fill in mm[] with messy stuff
+          if (flag) {     // use all the information in the seed
+            a+=randrsl[i  ]; b+=randrsl[i+1]; c+=randrsl[i+2]; d+=randrsl[i+3];
+            e+=randrsl[i+4]; f+=randrsl[i+5]; g+=randrsl[i+6]; h+=randrsl[i+7];
+          } // if flag
+
+      mix(ref a,ref b,ref c,ref d,ref e,ref f,ref g,ref h);
+      mm[i  ]=a; mm[i+1]=b; mm[i+2]=c; mm[i+3]=d;
+      mm[i+4]=e; mm[i+5]=f; mm[i+6]=g; mm[i+7]=h;
+      i+=8;
+      }
+   while (i<255);
+
+   if (flag) {
+   // do a second pass to make all of the seed affect all of mm
+     i=0;
+     do {
+      a+=mm[i  ]; b+=mm[i+1]; c+=mm[i+2]; d+=mm[i+3];
+      e+=mm[i+4]; f+=mm[i+5]; g+=mm[i+6]; h+=mm[i+7];
+      mix(ref a,ref b,ref c,ref d,ref e,ref f,ref g,ref h);
+      mm[i  ]=a; mm[i+1]=b; mm[i+2]=c; mm[i+3]=d;
+      mm[i+4]=e; mm[i+5]=f; mm[i+6]=g; mm[i+7]=h;
+      i+=8;
+        }
+     while (i<255);
+   }
+   isaac();           // fill in the first set of results
+   randcnt=0;       // prepare to use the first set of results
+}
+
+
+// Seed ISAAC with a string
+static void Seed(string seed, bool flag) {
+	for (int i=0; i<256; i++) mm[i]=0;
+	for (int i=0; i<256; i++) randrsl[i]=0;
+	int m = seed.Length;
+	for (int i=0; i<m; i++) {
+        randrsl[i] = seed[i];
+	}
+	// initialize ISAAC with seed
+	Init(flag);
+}
+
+
+// Get a random 32-bit value
+static uint Random() {
+    uint result = randrsl[randcnt];
+    randcnt++;
+    if (randcnt>255) {
+         isaac(); randcnt=0;
+    }
+    return result;
+}
+
+
+// Get a random character in printable ASCII range
+static byte RandA() {	
+	return (byte)(Random() % 95 + 32);
+}
+
+
+// XOR encrypt on random stream. Output: ASCII byte array
+static byte[] Vernam(string msg)
+	{
+		int n,l;
+		byte[] v = new byte[msg.Length];
+		l = msg.Length;
+		// XOR message
+		for (n=0; n<l; n++) {
+			v[n] = (byte) (RandA() ^ (byte)msg[n]);
+		}	
+		return v;
+	}
+
+	
+	public static void Main() {
+		string msg = "a Top Secret secret";
+		string key = "this is my secret key";
+		byte[] xctx= new byte[msg.Length];
+		byte[] xptx= new byte[msg.Length];
+		string xtcx= "*******************";
+		string xtpx= "*******************";
+		Seed(key,true);
+		// XOR encrypt
+		xctx = Vernam(msg);
+		xtcx = System.Text.Encoding.ASCII.GetString(xctx);
+		// XOR decrypt
+		Seed(key,true);
+		xptx = Vernam(xtcx);
+		xtpx = System.Text.Encoding.ASCII.GetString(xptx);
+		Console.WriteLine("Message: "+msg);
+		Console.WriteLine("Key    : "+key);
+		Console.Write    ("XOR    : ");
+		// output ciphertext as a string of hexadecimal digits
+		for (int n=0; n<xctx.Length; n++) Console.Write("{0:X2}", xctx[n]);
+		Console.WriteLine("\nXOR dcr: "+xtpx);
+	}
+}
+}