From 082f53429af8eea2b06275e9e8fbdcb3ffdd90bc Mon Sep 17 00:00:00 2001
From: Pagran <67878280+pagran@users.noreply.github.com>
Date: Mon, 27 Jul 2020 15:09:59 +0300
Subject: [PATCH] Implement swap obfuscator

---
 internal/literals/obfuscators.go |  13 ++++
 internal/literals/swap.go        | 108 +++++++++++++++++++++++++++++++
 2 files changed, 121 insertions(+)
 create mode 100644 internal/literals/swap.go

diff --git a/internal/literals/obfuscators.go b/internal/literals/obfuscators.go
index bd86bf6..80a8747 100644
--- a/internal/literals/obfuscators.go
+++ b/internal/literals/obfuscators.go
@@ -19,6 +19,7 @@ var (
 	// obfuscators contains all types which implement the obfuscator Interface
 	obfuscators = []obfuscator{
 		xor{},
+		swap{},
 	}
 	envGarbleSeed = os.Getenv("GARBLE_SEED")
 )
@@ -58,3 +59,15 @@ func genRandBytes(buffer []byte) {
 func genRandInt() int {
 	return mathrand.Int()
 }
+
+func genRandIntn(max int) int {
+	return mathrand.Intn(max)
+}
+
+func generateIntSlice(max, count int) []int {
+	indexes := make([]int, count)
+	for i := 0; i < count; i++ {
+		indexes[i] = genRandIntn(max)
+	}
+	return indexes
+}
diff --git a/internal/literals/swap.go b/internal/literals/swap.go
new file mode 100644
index 0000000..fde773e
--- /dev/null
+++ b/internal/literals/swap.go
@@ -0,0 +1,108 @@
+package literals
+
+import (
+	"go/ast"
+	"go/token"
+	"strconv"
+)
+
+type swap struct{}
+
+// check that the obfuscator interface is implemented
+var _ obfuscator = swap{}
+
+func dataToIntSlice(data []int) *ast.CompositeLit {
+	arr := &ast.CompositeLit{
+		Type: &ast.ArrayType{
+			Len: &ast.Ellipsis{}, // Performance optimization
+			Elt: &ast.Ident{
+				Name: "int",
+			},
+		},
+		Elts: []ast.Expr{},
+	}
+	for _, data := range data {
+		arr.Elts = append(arr.Elts, intLiteral(strconv.Itoa(data)))
+	}
+	return arr
+}
+
+func (x swap) obfuscate(data []byte) *ast.BlockStmt {
+	maxJunkIdxCount := len(data) / 2
+	if maxJunkIdxCount == 0 {
+		maxJunkIdxCount = 1
+	}
+	count := len(data) + genRandIntn(maxJunkIdxCount)
+	if count%2 != 0 {
+		count++
+	}
+	indexes := generateIntSlice(len(data), count)
+	for i := len(indexes) - 2; i >= 0; i -= 2 {
+		data[indexes[i]], data[indexes[i+1]] = data[indexes[i+1]], data[indexes[i]]
+	}
+
+	return &ast.BlockStmt{List: []ast.Stmt{
+		&ast.AssignStmt{
+			Lhs: []ast.Expr{ident("data")},
+			Tok: token.DEFINE,
+			Rhs: []ast.Expr{dataToByteSlice(data)},
+		},
+		&ast.AssignStmt{
+			Lhs: []ast.Expr{
+				ident("indexes"),
+			},
+			Tok: token.DEFINE,
+			Rhs: []ast.Expr{
+				dataToIntSlice(indexes),
+			},
+		},
+		&ast.ForStmt{
+			Init: &ast.AssignStmt{
+				Lhs: []ast.Expr{
+					ident("i"),
+				},
+				Tok: token.DEFINE,
+				Rhs: []ast.Expr{
+					intLiteral("0"),
+				},
+			},
+			Cond: &ast.BinaryExpr{
+				X:  ident("i"),
+				Op: token.LSS,
+				Y:  intLiteral(strconv.Itoa(len(indexes))),
+			},
+			Post: &ast.AssignStmt{
+				Lhs: []ast.Expr{
+					ident("i"),
+				},
+				Tok: token.ADD_ASSIGN,
+				Rhs: []ast.Expr{
+					intLiteral("2"),
+				},
+			},
+			Body: &ast.BlockStmt{
+				List: []ast.Stmt{
+					&ast.AssignStmt{
+						Lhs: []ast.Expr{
+							indexExpr("data", indexExpr("indexes", ident("i"))),
+							indexExpr("data", indexExpr("indexes", &ast.BinaryExpr{
+								X:  ident("i"),
+								Op: token.ADD,
+								Y:  intLiteral("1"),
+							})),
+						},
+						Tok: token.ASSIGN,
+						Rhs: []ast.Expr{
+							indexExpr("data", indexExpr("indexes", &ast.BinaryExpr{
+								X:  ident("i"),
+								Op: token.ADD,
+								Y:  intLiteral("1"),
+							})),
+							indexExpr("data", indexExpr("indexes", ident("i"))),
+						},
+					},
+				},
+			},
+		},
+	}}
+}