Go build obfuscator.

Daniel Martí c76c4196af prepare changelog for 0.4.0 2 years ago
.github b3101b252f github: add an issue template 2 years ago
internal 6b632d07e2 Fix minor typo in RecordUsedAsConstants docstring 2 years ago
scripts 5e3ba2fc09 update the list of runtime-related packages for 1.16 (#246) 3 years ago
testdata 5c70681fee detect more std API calls which use reflection 2 years ago
.gitattributes ab560ff007 start testing on GitHub Actions 4 years ago
.gitignore f1bf6f91ee skip literals used in constant expressions 3 years ago
AUTHORS 805c895d59 set up an AUTHORS file to attribute copyright 3 years ago
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CONTRIBUTING.md 5d49955998 README: document commands 2 years ago
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README.md c77bc9e5e1 start using "go install pkg@version" in docs 2 years ago
bench_test.go 091f8239c0 rework the build benchmarks 3 years ago
go.mod 816954b9ba mod: update direct deps 2 years ago
go.sum 816954b9ba mod: update direct deps 2 years ago
hash.go c9b0b07853 hash field names equally in all packages 2 years ago
main.go 0eba9c210c document version command in help text 2 years ago
main_test.go 680e5624e9 speed up tests by 20-30% by using GOGC=off 2 years ago
position.go 8edde922ee remove unused code spotted by -coverprofile 2 years ago
reverse.go 7fc424ca26 make "garble command -h" give command-specific help 2 years ago
runtime_strip.go 5f8bae06b7 small improvements towards obfuscating the runtime 2 years ago
shared.go c77bc9e5e1 start using "go install pkg@version" in docs 2 years ago

README.md

garble

go install mvdan.cc/garble@latest

Obfuscate Go code by wrapping the Go toolchain. Requires Go 1.16 or later.

garble build [build flags] [packages]

The tool also supports garble test to run tests with obfuscated code, and garble reverse to de-obfuscate text such as stack traces. See garble -h for up to date usage information.

Purpose

Produce a binary that works as well as a regular build, but that has as little information about the original source code as possible.

The tool is designed to be:

  • Coupled with cmd/go, to support modules and build caching
  • Deterministic and reproducible, given the same initial source code
  • Reversible given the original source, to de-obfuscate panic stack traces

Mechanism

The tool wraps calls to the Go compiler and linker to transform the Go build, in order to:

  • Replace as many useful identifiers as possible with short base64 hashes
  • Replace package paths with short base64 hashes
  • Remove all build and module information
  • Strip filenames and shuffle position information
  • Strip debugging information and symbol tables via -ldflags="-w -s"
  • Obfuscate literals, if the -literals flag is given
  • Remove extra information, if the -tiny flag is given

By default, the tool obfuscates the packages under the current module. If not running in module mode, then only the main package is obfuscated. To specify what packages to obfuscate, set GOPRIVATE, documented at go help private.

Note that commands like garble build will use the go version found in your $PATH. To use different versions of Go, you can install them and set up $PATH with them. For example, for Go 1.16.1:

$ go install golang.org/dl/go1.16.1@latest
$ go1.16.1 download
$ PATH=$(go1.16.1 env GOROOT)/bin:${PATH} garble build

Literal obfuscation

Using the -literals flag causes literal expressions such as strings to be replaced with more complex variants, resolving to the same value at run-time. This feature is opt-in, as it can cause slow-downs depending on the input code.

Literal expressions used as constants cannot be obfuscated, since they are resolved at compile time. This includes any expressions part of a const declaration.

Tiny mode

When the -tiny flag is passed, extra information is stripped from the resulting Go binary. This includes line numbers, filenames, and code in the runtime that prints panics, fatal errors, and trace/debug info. All in all this can make binaries 2-5% smaller in our testing, as well as prevent extracting some more information.

With this flag, no panics or fatal runtime errors will ever be printed, but they can still be handled internally with recover as normal. In addition, the GODEBUG environmental variable will be ignored.

Note that this flag can make debugging crashes harder, as a panic will simply exit the entire program without printing a stack trace, and all source code positions are set to line 1. Similarly, garble reverse is generally not useful in this mode.

Speed

garble build should take about twice as long as go build, as it needs to complete two builds. The original build, to be able to load and type-check the input code, and finally the obfuscated build.

Go's build cache is fully supported; if a first garble build run is slow, a second run should be significantly faster. This should offset the cost of the double builds, as incremental builds in Go are fast.

Determinism and seeds

Just like Go, garble builds are deterministic and reproducible if the inputs remain the same: the version of Go, the version of Garble, and the input code. This has significant benefits, such as caching builds or being able to use garble reverse to de-obfuscate stack traces.

However, it also means that an input package will be obfuscated in exactly the same way if none of those inputs change. If you want two builds of your program to be entirely different, you can use -seed to provide a new seed for the entire build, which will cause a full rebuild.

If any open source packages are being obfuscated, providing a custom seed can also provide extra protection. It could be possible to guess the versions of Go and garble given how a public package was obfuscated without a seed.

Caveats

Most of these can improve with time and effort. The purpose of this section is to document the current shortcomings of this tool.

  • Exported methods are never obfuscated at the moment, since they could be required by interfaces and reflection. This area is a work in progress; see #3.

  • It can be hard for garble to know what types will be used with reflection. Its detection will improve over time with #162 Until then, if your program breaks due to the obfuscation of field names, you can add an explicit hint:

    type Message struct {
        Command string
        Args    string
    }
    
    // Never obfuscate the Message type.
    var _ = reflect.TypeOf(Message{})
    
  • Go declarations exported for cgo via //export are not obfuscated.

  • Go plugins are not currently supported; see #87.

Contributing

We welcome new contributors. If you would like to contribute, see CONTRIBUTING.md as a starting point.