Add XorSeed obfuscator (#86)

Co-authored-by: lu4p <lu4p@pm.me>

internal/literals/obfuscators.go

@@ -21,6 +21,7 @@ var (
 		swap{},
 		split{},
 		xorShuffle{},
+		xorSeed{},
 	}
 	envGarbleSeed = os.Getenv("GARBLE_SEED")
 )

internal/literals/xor_seed.go

@@ -0,0 +1,117 @@
+package literals
+
+import (
+	"go/ast"
+	"go/token"
+
+	ah "mvdan.cc/garble/internal/asthelper"
+)
+
+type xorSeed struct{}
+
+// check that the obfuscator interface is implemented
+var _ obfuscator = xorSeed{}
+
+func (x xorSeed) obfuscate(data []byte) *ast.BlockStmt {
+	preSeed := make([]byte, 1)
+	genRandBytes(preSeed)
+
+	seed := preSeed[0]
+	originalSeed := seed
+
+	var callExpr *ast.CallExpr
+	for i, b := range data {
+		encB := b ^ seed
+		seed += encB
+
+		if i == 0 {
+			callExpr = ah.CallExpr(ah.Ident("fnc"), ah.IntLit(int(encB)))
+			continue
+		}
+
+		callExpr = ah.CallExpr(callExpr, ah.IntLit(int(encB)))
+	}
+
+	return ah.BlockStmt(
+		&ast.AssignStmt{
+			Lhs: []ast.Expr{ah.Ident("seed")},
+			Tok: token.DEFINE,
+			Rhs: []ast.Expr{ah.CallExpr(ah.Ident("byte"), ah.IntLit(int(originalSeed)))},
+		},
+		&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.DeclStmt{
+			Decl: &ast.GenDecl{
+				Tok: token.TYPE,
+				Specs: []ast.Spec{&ast.TypeSpec{
+					Name: ah.Ident("decFunc"),
+					Type: &ast.FuncType{
+						Params: &ast.FieldList{List: []*ast.Field{
+							{Type: ah.Ident("byte")},
+						}},
+						Results: &ast.FieldList{List: []*ast.Field{
+							{Type: ah.Ident("decFunc")},
+						}},
+					},
+				}},
+			},
+		},
+		&ast.DeclStmt{
+			Decl: &ast.GenDecl{
+				Tok: token.VAR,
+				Specs: []ast.Spec{&ast.ValueSpec{
+					Names: []*ast.Ident{ah.Ident("fnc")},
+					Type:  ah.Ident("decFunc"),
+				}},
+			},
+		},
+		&ast.AssignStmt{
+			Lhs: []ast.Expr{ah.Ident("fnc")},
+			Tok: token.ASSIGN,
+			Rhs: []ast.Expr{
+				&ast.FuncLit{
+					Type: &ast.FuncType{
+						Params: &ast.FieldList{
+							List: []*ast.Field{{
+								Names: []*ast.Ident{ah.Ident("x")},
+								Type:  ah.Ident("byte"),
+							}},
+						},
+						Results: &ast.FieldList{
+							List: []*ast.Field{{
+								Type: ah.Ident("decFunc"),
+							}},
+						},
+					},
+					Body: ah.BlockStmt(
+						&ast.AssignStmt{
+							Lhs: []ast.Expr{ah.Ident("data")},
+							Tok: token.ASSIGN,
+							Rhs: []ast.Expr{
+								ah.CallExpr(ah.Ident("append"), ah.Ident("data"), &ast.BinaryExpr{
+									X:  ah.Ident("x"),
+									Op: token.XOR,
+									Y:  ah.Ident("seed"),
+								}),
+							},
+						},
+						&ast.AssignStmt{
+							Lhs: []ast.Expr{ah.Ident("seed")},
+							Tok: token.ADD_ASSIGN,
+							Rhs: []ast.Expr{ah.Ident("x")},
+						},
+						ah.ReturnStmt(ah.Ident("fnc")),
+					),
+				},
+			},
+		},
+		ah.ExprStmt(callExpr),
+	)
+}

testdata/scripts/literals.txt

@@ -48,6 +48,9 @@ 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
 
+# XorSeed obfuscator. Detect type decFunc func(byte) decFunc
+grep '^\s+type \w+ func\(byte\) \w+$' .obf-src/main/z0.go
+
 
 -- go.mod --
 module test/main