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91 lines
2.4 KiB
Go
91 lines
2.4 KiB
Go
// Copyright (c) 2020, The Garble Authors.
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// See LICENSE for licensing information.
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package literals
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import (
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"go/ast"
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"go/token"
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mathrand "math/rand"
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ah "mvdan.cc/garble/internal/asthelper"
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)
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type shuffle struct{}
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// check that the obfuscator interface is implemented
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var _ obfuscator = shuffle{}
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func (shuffle) obfuscate(obfRand *mathrand.Rand, data []byte) *ast.BlockStmt {
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key := make([]byte, len(data))
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obfRand.Read(key)
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const (
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minIdxKeySize = 2
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maxIdxKeySize = 16
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)
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idxKeySize := minIdxKeySize
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if tmp := obfRand.Intn(len(data)); tmp > idxKeySize {
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idxKeySize = tmp
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}
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if idxKeySize > maxIdxKeySize {
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idxKeySize = maxIdxKeySize
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}
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idxKey := make([]byte, idxKeySize)
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obfRand.Read(idxKey)
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fullData := make([]byte, len(data)+len(key))
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operators := make([]token.Token, len(fullData))
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for i := range operators {
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operators[i] = randOperator(obfRand)
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}
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for i, b := range key {
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fullData[i], fullData[i+len(data)] = evalOperator(operators[i], data[i], b), b
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}
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shuffledIdxs := obfRand.Perm(len(fullData))
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shuffledFullData := make([]byte, len(fullData))
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for i, b := range fullData {
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shuffledFullData[shuffledIdxs[i]] = b
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}
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args := []ast.Expr{ast.NewIdent("data")}
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for i := range data {
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keyIdx := obfRand.Intn(idxKeySize)
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k := int(idxKey[keyIdx])
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args = append(args, operatorToReversedBinaryExpr(
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operators[i],
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ah.IndexExpr("fullData", &ast.BinaryExpr{X: ah.IntLit(shuffledIdxs[i] ^ k), Op: token.XOR, Y: ah.CallExprByName("int", ah.IndexExpr("idxKey", ah.IntLit(keyIdx)))}),
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ah.IndexExpr("fullData", &ast.BinaryExpr{X: ah.IntLit(shuffledIdxs[len(data)+i] ^ k), Op: token.XOR, Y: ah.CallExprByName("int", ah.IndexExpr("idxKey", ah.IntLit(keyIdx)))}),
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))
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}
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return ah.BlockStmt(
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&ast.AssignStmt{
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Lhs: []ast.Expr{ast.NewIdent("fullData")},
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Tok: token.DEFINE,
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Rhs: []ast.Expr{ah.DataToByteSlice(shuffledFullData)},
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},
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&ast.AssignStmt{
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Lhs: []ast.Expr{ast.NewIdent("idxKey")},
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Tok: token.DEFINE,
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Rhs: []ast.Expr{ah.DataToByteSlice(idxKey)},
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},
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&ast.AssignStmt{
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Lhs: []ast.Expr{ast.NewIdent("data")},
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Tok: token.DEFINE,
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Rhs: []ast.Expr{ah.CallExpr(ast.NewIdent("make"), &ast.ArrayType{Elt: ast.NewIdent("byte")}, ah.IntLit(0), ah.IntLit(len(data)+1))},
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},
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&ast.AssignStmt{
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Lhs: []ast.Expr{ast.NewIdent("data")},
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Tok: token.ASSIGN,
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Rhs: []ast.Expr{ah.CallExpr(ast.NewIdent("append"), args...)},
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},
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)
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}
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