feature: randomize anti-tamper feedback + CFG multiplier constants (#69 level 2) (#98)

* feature: randomize anti-tamper feedback constant per run (#69)

Phase 2 of #69 (Level 2 identity). The anti-tamper method-body cipher used a
hardcoded feedback constant 0x3dbb2819 in both the obfuscator (encrypt) and the
injected runtime (decrypt) — a value de4dot signature-matches to identify
ConfuserEx.

Normal and Anti modes now generate a random per-run feedback value, use it in the
encryption loop, and inject it into the runtime via a new Mutation key (KeyI5),
exactly like the existing z/x/c/v hash constants (KeyI1-4). Obfuscator and runtime
stay in sync automatically because the same generated value is both used and
injected.

JIT mode is intentionally left unchanged — its runtime component is already broken
and its test is skipped, so a crypto change there cannot be validated.

Validated by AntiTamper.Test: the obfuscated app decrypts its own method bodies at
runtime and produces correct output (exit 42) for both Normal and Anti modes.

* feature: randomize CFG state multiplier constant per run (#69)

The Constants protection's control-flow encoding baked the fixed
multiplier 0x21412321 into both the obfuscator-side CFGState and the
injected runtime CFGCtx constructor, giving de4dot a stable signature.

Generate a random odd (invertible mod 2^32) multiplier per module when
the CFG state type is injected, rewrite the literal in the runtime ctor
IL, and thread the same value through the obfuscator CFGState so both
sides stay in sync. Validated end-to-end by the constants protection
tests (obfuscate -> run -> assert output).

---------

Co-authored-by: RandomCrocodile <mawi@polosab.com>

Author: mcpolo99

.gitignore

@@ -1,5 +1,6 @@
 # Visual Studio Cache files (starting with VS 2015)
 .vs/
+.temp
 
 # Launch Settings
 launchSettings.json

Confuser.Protections/AntiTamper/AntiMode.cs

@@ -16,6 +16,7 @@
 namespace Confuser.Protections.AntiTamper {
 	internal class AntiMode : IModeHandler {
 		uint c;
+		uint feedback;
 		IKeyDeriver deriver;
 
 		List<MethodDef> methods;
@@ -31,6 +32,7 @@ public void HandleInject(AntiTamperProtection parent, ConfuserContext context, P
 			x = random.NextUInt32();
 			c = random.NextUInt32();
 			v = random.NextUInt32();
+			feedback = random.NextUInt32();
 			name1 = random.NextUInt32() & 0x7f7f7f7f;
 			name2 = random.NextUInt32() & 0x7f7f7f7f;
 
@@ -77,8 +79,8 @@ public void HandleInject(AntiTamperProtection parent, ConfuserContext context, P
 				initMethod.Body.Instructions.Add(instr);
 
 			MutationHelper.InjectKeys(initMethod,
-									  new[] { 0, 1, 2, 3, 4 },
-									  new[] { (int)(name1 * name2), (int)z, (int)x, (int)c, (int)v });
+									  new[] { 0, 1, 2, 3, 4, 5 },
+									  new[] { (int)(name1 * name2), (int)z, (int)x, (int)c, (int)v, (int)feedback });
 
 			var name = context.Registry.GetService<INameService>();
 			var marker = context.Registry.GetService<IMarkerService>();
@@ -219,7 +221,7 @@ void EncryptSection(ModuleWriterBase writer) {
 			for (uint i = 0; i < encSize; i++) {
 				uint data = reader.ReadUInt32();
 				result[i] = data ^ key[i & 0xf];
-				key[i & 0xf] = (key[i & 0xf] ^ data) + 0x3dbb2819;
+				key[i & 0xf] = (key[i & 0xf] ^ data) + feedback;
 			}
 			var byteResult = new byte[encSize << 2];
 			Buffer.BlockCopy(result, 0, byteResult, 0, byteResult.Length);

Confuser.Protections/AntiTamper/NormalMode.cs

@@ -16,6 +16,7 @@
 namespace Confuser.Protections.AntiTamper {
 	internal class NormalMode : IModeHandler {
 		uint c;
+		uint feedback;
 		IKeyDeriver deriver;
 
 		List<MethodDef> methods;
@@ -31,6 +32,7 @@ public void HandleInject(AntiTamperProtection parent, ConfuserContext context, P
 			x = random.NextUInt32();
 			c = random.NextUInt32();
 			v = random.NextUInt32();
+			feedback = random.NextUInt32();
 			name1 = random.NextUInt32() & 0x7f7f7f7f;
 			name2 = random.NextUInt32() & 0x7f7f7f7f;
 
@@ -77,8 +79,8 @@ public void HandleInject(AntiTamperProtection parent, ConfuserContext context, P
 				initMethod.Body.Instructions.Add(instr);
 
 			MutationHelper.InjectKeys(initMethod,
-									  new[] { 0, 1, 2, 3, 4 },
-									  new[] { (int)(name1 * name2), (int)z, (int)x, (int)c, (int)v });
+									  new[] { 0, 1, 2, 3, 4, 5 },
+									  new[] { (int)(name1 * name2), (int)z, (int)x, (int)c, (int)v, (int)feedback });
 
 			var name = context.Registry.GetService<INameService>();
 			var marker = context.Registry.GetService<IMarkerService>();
@@ -220,7 +222,7 @@ void EncryptSection(ModuleWriterBase writer) {
 			for (uint i = 0; i < encSize; i++) {
 				uint data = reader.ReadUInt32();
 				result[i] = data ^ key[i & 0xf];
-				key[i & 0xf] = (key[i & 0xf] ^ data) + 0x3dbb2819;
+				key[i & 0xf] = (key[i & 0xf] ^ data) + feedback;
 			}
 			var byteResult = new byte[encSize << 2];
 			Buffer.BlockCopy(result, 0, byteResult, 0, byteResult.Length);

Confuser.Protections/Constants/CEContext.cs

@@ -35,6 +35,7 @@ internal class CEContext {
 		public TypeDef CfgCtxType;
 		public MethodDef CfgCtxCtor;
 		public MethodDef CfgCtxNext;
+		public uint CfgCtxMultiplier;
 		public Dictionary<MethodDef, List<Tuple<Instruction, uint, IMethod>>> ReferenceRepl;
 	}
 

Confuser.Protections/Constants/ReferenceReplacer.cs

@@ -51,11 +51,11 @@ struct CFGState {
 			public uint C;
 			public uint D;
 
-			public CFGState(uint seed) {
-				A = seed *= 0x21412321;
-				B = seed *= 0x21412321;
-				C = seed *= 0x21412321;
-				D = seed *= 0x21412321;
+			public CFGState(uint seed, uint mult) {
+				A = seed *= mult;
+				B = seed *= mult;
+				C = seed *= mult;
+				D = seed *= mult;
 			}
 
 			public void UpdateExplicit(int id, uint value) {
@@ -136,6 +136,15 @@ static void InjectStateType(CEContext ctx) {
 				ctx.CfgCtxCtor = ctx.CfgCtxType.FindMethod(".ctor");
 				ctx.CfgCtxNext = ctx.CfgCtxType.FindMethod("Next");
 
+				// Randomize the CFG state multiplier so the baked-in 0x21412321 literal
+				// no longer fingerprints the output. Must stay odd (invertible mod 2^32) and
+				// match the obfuscator-side CFGState computation (see CFGState.ctor).
+				ctx.CfgCtxMultiplier = ctx.Random.NextUInt32() | 1;
+				foreach (var instr in ctx.CfgCtxCtor.Body.Instructions) {
+					if (instr.OpCode == OpCodes.Ldc_I4 && (int)instr.Operand == 0x21412321)
+						instr.Operand = (int)ctx.CfgCtxMultiplier;
+				}
+
 				ctx.Name.MarkHelper(ctx.CfgCtxType, ctx.Marker, ctx.Protection);
 				foreach (var def in ctx.CfgCtxType.Fields)
 					ctx.Name.MarkHelper(def, ctx.Marker, ctx.Protection);
@@ -212,7 +221,7 @@ static void InsertEmptyStateUpdate(CFGContext ctx, ControlFlowBlock block) {
 				if (!ctx.StatesMap.TryGetValue(key.ExitState, out exit)) {
 					// Create new exit state from random seed
 					var seed = ctx.Random.NextUInt32();
-					exit = new CFGState(seed);
+					exit = new CFGState(seed, ctx.Ctx.CfgCtxMultiplier);
 					body.Instructions.Insert(targetIndex++, first = Instruction.Create(OpCodes.Ldloca, ctx.StateVariable));
 					body.Instructions.Insert(targetIndex++, Instruction.Create(OpCodes.Ldc_I4, (int)seed));
 					body.Instructions.Insert(targetIndex++, Instruction.Create(OpCodes.Call, ctx.Ctx.CfgCtxCtor));
@@ -301,7 +310,7 @@ static uint InsertStateGetAndUpdate(CFGContext ctx, ref int index, BlockKeyType
 				if (targetState == null) {
 					// Create new exit state from random seed
 					var seed = ctx.Random.NextUInt32();
-					currentState = new CFGState(seed);
+					currentState = new CFGState(seed, ctx.Ctx.CfgCtxMultiplier);
 					body.Instructions.Insert(index++, Instruction.Create(OpCodes.Ldloca, ctx.StateVariable));
 					body.Instructions.Insert(index++, Instruction.Create(OpCodes.Dup));
 					body.Instructions.Insert(index++, Instruction.Create(OpCodes.Ldc_I4, (int)seed));
@@ -398,7 +407,7 @@ static void ReplaceCFG(MethodDef method, List<Tuple<Instruction, uint, IMethod>>
 
 					// Create new entry state
 					uint blockSeed = ctx.Random.NextUInt32();
-					currentState = new CFGState(blockSeed);
+					currentState = new CFGState(blockSeed, ctx.CfgCtxMultiplier);
 					cfgCtx.StatesMap[key.EntryState] = currentState;
 
 					var index = graph.Body.Instructions.IndexOf(graph[blockRef.Key].Header);

Confuser.Runtime/AntiTamper.Anti.cs

@@ -27,6 +27,7 @@ static unsafe void Initialize() {
 			uint l = 0;
 			var r = (uint*)(p + 0x18 + o);
 			uint z = (uint)Mutation.KeyI1, x = (uint)Mutation.KeyI2, c = (uint)Mutation.KeyI3, v = (uint)Mutation.KeyI4;
+			uint fb = (uint)Mutation.KeyI5;
 
 			CheckRemoteDebuggerPresent(Process.GetCurrentProcess().Handle, ref isDebuggerPresent);
 			if (isDebuggerPresent) Environment.FailFast(null);
@@ -80,7 +81,7 @@ static unsafe void Initialize() {
 			uint h = 0;
 			for (uint i = 0; i < l; i++) {
 				*e ^= y[h & 0xf];
-				y[h & 0xf] = (y[h & 0xf] ^ (*e++)) + 0x3dbb2819;
+				y[h & 0xf] = (y[h & 0xf] ^ (*e++)) + fb;
 
 				CheckRemoteDebuggerPresent(Process.GetCurrentProcess().Handle, ref isDebuggerPresent);
 				if (isDebuggerPresent) Environment.FailFast(null);

Confuser.Runtime/AntiTamper.Normal.cs

@@ -20,6 +20,7 @@ static unsafe void Initialize() {
 			uint l = 0;
 			var r = (uint*)(p + 0x18 + o);
 			uint z = (uint)Mutation.KeyI1, x = (uint)Mutation.KeyI2, c = (uint)Mutation.KeyI3, v = (uint)Mutation.KeyI4;
+			uint fb = (uint)Mutation.KeyI5;
 			for (int i = 0; i < s; i++) {
 				uint g = (*r++) * (*r++);
 				if (g == (uint)Mutation.KeyI0) {
@@ -60,7 +61,7 @@ static unsafe void Initialize() {
 			uint h = 0;
 			for (uint i = 0; i < l; i++) {
 				*e ^= y[h & 0xf];
-				y[h & 0xf] = (y[h & 0xf] ^ (*e++)) + 0x3dbb2819;
+				y[h & 0xf] = (y[h & 0xf] ^ (*e++)) + fb;
 				h++;
 			}
 		}