Add xorShuffle obfuscator (#85)

* Refactoring

* Rename Xor2 to XorShuffle

internal/literals/obfuscators.go

@@ -20,6 +20,7 @@ var (
 		xor{},
 		swap{},
 		split{},
+		xorShuffle{},
 	}
 	envGarbleSeed = os.Getenv("GARBLE_SEED")
 )

internal/literals/xor_shuffle.go

@@ -0,0 +1,62 @@
+package literals
+
+import (
+	"go/ast"
+	"go/token"
+	mathrand "math/rand"
+
+	ah "mvdan.cc/garble/internal/asthelper"
+)
+
+type xorShuffle struct{}
+
+// check that the obfuscator interface is implemented
+var _ obfuscator = xorShuffle{}
+
+func (x xorShuffle) obfuscate(data []byte) *ast.BlockStmt {
+	key := make([]byte, len(data))
+	genRandBytes(key)
+
+	fullData := make([]byte, len(data)+len(key))
+	for i, b := range key {
+		fullData[i], fullData[i+len(data)] = data[i]^b, b
+	}
+
+	shuffledIdxs := mathrand.Perm(len(fullData))
+
+	shuffledFullData := make([]byte, len(fullData))
+	for i, b := range fullData {
+		shuffledFullData[shuffledIdxs[i]] = b
+	}
+
+	args := []ast.Expr{ah.Ident("data")}
+	for i := range data {
+		args = append(args, &ast.BinaryExpr{
+			X:  ah.IndexExpr("fullData", ah.IntLit(shuffledIdxs[i])),
+			Op: token.XOR,
+			Y:  ah.IndexExpr("fullData", ah.IntLit(shuffledIdxs[len(data)+i])),
+		})
+	}
+
+	return ah.BlockStmt(
+		&ast.AssignStmt{
+			Lhs: []ast.Expr{ah.Ident("fullData")},
+			Tok: token.DEFINE,
+			Rhs: []ast.Expr{ah.DataToByteSlice(shuffledFullData)},
+		},
+		&ast.DeclStmt{
+			Decl: &ast.GenDecl{
+				Tok: token.VAR,
+				Specs: []ast.Spec{&ast.ValueSpec{
+					Names: []*ast.Ident{ah.Ident("data")},
+					Type:  &ast.ArrayType{Elt: ah.Ident("byte")},
+				}},
+			},
+		},
+		&ast.AssignStmt{
+			Lhs: []ast.Expr{ah.Ident("data")},
+			Tok: token.ASSIGN,
+			Rhs: []ast.Expr{ah.CallExpr(ah.Ident("append"), args...)},
+		},
+	)
+}

testdata/scripts/literals.txt

@@ -45,6 +45,9 @@ grep '^\s+\w+ := \[\.{3}\](byte|uint16|uint32|uint64)\{[0-9\s,]+\}$' .obf-src/ma
 # Split obfuscator. Detect decryptKey ^= i * counter
 grep '^\s+\w+ \^= \w+ \* \w+$' .obf-src/main/z0.go
 
+# XorShuffle obfuscator. Detect data = append(data, x ^ y...)
+grep '^\s+\w+ = append\(\w+,(\s+\w+\[\d+\]\^\w+\[\d+\],?)+\)$' .obf-src/main/z0.go
+
 
 -- go.mod --
 module test/main