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132 lines
5.3 KiB
Markdown
132 lines
5.3 KiB
Markdown
# garble
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GO111MODULE=on go get mvdan.cc/garble
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Obfuscate Go code by wrapping the Go toolchain. Requires Go 1.16 or later.
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garble build [build flags] [packages]
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The tool also supports `garble test` to run tests with obfuscated code,
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and `garble reverse` to de-obfuscate text such as stack traces.
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See `garble -h` for up to date usage information.
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### Purpose
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Produce a binary that works as well as a regular build, but that has as little
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information about the original source code as possible.
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The tool is designed to be:
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* Coupled with `cmd/go`, to support modules and build caching
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* Deterministic and reproducible, given the same initial source code
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* Reversible given the original source, to de-obfuscate panic stack traces
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### Mechanism
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The tool wraps calls to the Go compiler and linker to transform the Go build, in
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order to:
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* Replace as many useful identifiers as possible with short base64 hashes
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* Replace package paths with short base64 hashes
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* Remove all [build](https://golang.org/pkg/runtime/#Version) and [module](https://golang.org/pkg/runtime/debug/#ReadBuildInfo) information
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* Strip filenames and shuffle position information
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* Strip debugging information and symbol tables via `-ldflags="-w -s"`
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* [Obfuscate literals](#literal-obfuscation), if the `-literals` flag is given
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* Remove [extra information](#tiny-mode), if the `-tiny` flag is given
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By default, the tool obfuscates the packages under the current module. If not
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running in module mode, then only the main package is obfuscated. To specify
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what packages to obfuscate, set `GOPRIVATE`, documented at `go help private`.
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Note that commands like `garble build` will use the `go` version found in your
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`$PATH`. To use different versions of Go, you can
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[install them](https://golang.org/doc/manage-install#installing-multiple)
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and set up `$PATH` with them. For example, for Go 1.16.1:
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```sh
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$ go get golang.org/dl/go1.16.1
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$ go1.16.1 download
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$ PATH=$(go1.16.1 env GOROOT)/bin:${PATH} garble build
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```
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### Literal obfuscation
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Using the `-literals` flag causes literal expressions such as strings to be
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replaced with more complex variants, resolving to the same value at run-time.
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This feature is opt-in, as it can cause slow-downs depending on the input code.
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Literal expressions used as constants cannot be obfuscated, since they are
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resolved at compile time. This includes any expressions part of a `const`
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declaration.
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### Tiny mode
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When the `-tiny` flag is passed, extra information is stripped from the resulting
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Go binary. This includes line numbers, filenames, and code in the runtime that
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prints panics, fatal errors, and trace/debug info. All in all this can make binaries
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2-5% smaller in our testing, as well as prevent extracting some more information.
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With this flag, no panics or fatal runtime errors will ever be printed, but they
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can still be handled internally with `recover` as normal. In addition, the
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`GODEBUG` environmental variable will be ignored.
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Note that this flag can make debugging crashes harder, as a panic will simply
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exit the entire program without printing a stack trace, and all source code
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positions are set to line 1. Similarly, `garble reverse` is generally not useful
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in this mode.
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### Speed
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`garble build` should take about twice as long as `go build`, as it needs to
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complete two builds. The original build, to be able to load and type-check the
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input code, and finally the obfuscated build.
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Go's build cache is fully supported; if a first `garble build` run is slow, a
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second run should be significantly faster. This should offset the cost of the
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double builds, as incremental builds in Go are fast.
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### Determinism and seeds
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Just like Go, garble builds are deterministic and reproducible if the inputs
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remain the same: the version of Go, the version of Garble, and the input code.
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This has significant benefits, such as caching builds or being able to use
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`garble reverse` to de-obfuscate stack traces.
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However, it also means that an input package will be obfuscated in exactly the
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same way if none of those inputs change. If you want two builds of your program
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to be entirely different, you can use `-seed` to provide a new seed for the
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entire build, which will cause a full rebuild.
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If any open source packages are being obfuscated, providing a custom seed can
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also provide extra protection. It could be possible to guess the versions of Go
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and garble given how a public package was obfuscated without a seed.
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### Caveats
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Most of these can improve with time and effort. The purpose of this section is
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to document the current shortcomings of this tool.
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* Exported methods are never obfuscated at the moment, since they could
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be required by interfaces and reflection. This area is a work in progress.
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* It can be hard for garble to know what types will be used with
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[reflection](https://golang.org/pkg/reflect), including JSON encoding or
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decoding. If your program breaks because a type's names are obfuscated when
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they should not be, you can add an explicit hint:
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```go
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type Message struct {
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Command string
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Args string
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}
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// Never obfuscate the Message type.
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var _ = reflect.TypeOf(Message{})
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```
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* Go plugins are not currently supported; see [#87](https://github.com/burrowers/garble/issues/87).
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### Contributing
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We welcome new contributors. If you would like to contribute, see
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[CONTRIBUTING.md](CONTRIBUTING.md) as a starting point.
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