garble

GO111MODULE=on go get mvdan.cc/garble

Obfuscate Go code by wrapping the Go toolchain. Requires Go 1.15.x; note that support for Go 1.16 is a work in progress.

garble build [build flags] [packages]

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 deobfuscate 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
• Obfuscate literals, if the -literals flag is given
• Remove extra information if the -tiny flag is given

Options

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 module-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 1.15.8:

$ go get golang.org/dl/go1.15.8
$ go1.15.8 download
$ PATH=$(go1.15.8 env GOROOT)/bin:${PATH} garble build

You can also declare a function to make multiple uses simpler:

$ withgo() {
        local gocmd=go${1}
        shift

        PATH=$(${gocmd} env GOROOT)/bin:${PATH} "$@"
}
$ withgo 1.15.8 garble build

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.

• Functions implemented outside Go, such as assembly, aren't obfuscated since we currently only transform the input Go source.

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

• There are cases where garble is a little too agressive with obfuscation, this may lead to identifiers getting obfuscated which are needed for reflection, e.g. to parse JSON into a struct; see #162. To work around this you can pass a hint to garble, that an type is used for reflection via passing it to reflect.TypeOf or reflect.ValueOf in the same file:

  // this is used for parsing json
  type Message struct {
      Command string
      Args    string
  }
  
  // never obfuscate the Message type
  var _ = reflect.TypeOf(Message{})
  

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 the prints panics, fatal errors, and trace/debug info. All in all this can make binaries 6-10% smaller in our testing.

Note: if -tiny is passed, no panics, fatal 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.

Contributing

We actively seek new contributors, if you would like to contribute to garble use the CONTRIBUTING.md as a starting point.