Awesome
garble
go install mvdan.cc/garble@latest
Obfuscate Go code by wrapping the Go toolchain. Requires Go 1.23 or later.
garble build [build flags] [packages]
The tool also supports garble test
to run tests with obfuscated code,
garble run
to obfuscate and execute simple programs,
and garble reverse
to de-obfuscate text such as stack traces.
Run garble -h
to see all available commands and flags.
You can also use go install mvdan.cc/garble@master
to install the latest development version.
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
- Replace filenames and position information with short base64 hashes
- Remove all build and module 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 all the packages being built.
You can manually specify which packages to obfuscate via GOGARBLE
,
a comma-separated list of glob patterns matching package path prefixes.
This format is borrowed from GOPRIVATE
; see 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 1.17.1:
$ go install golang.org/dl/go1.17.1@latest
$ go1.17.1 download
$ PATH=$(go1.17.1 env GOROOT)/bin:${PATH} garble build
Use cases
A common question is why a code obfuscator is needed for Go, a compiled language. Go binaries include a surprising amount of information about the original source; even with debug information and symbol tables stripped, many names and positions remain in place for the sake of traces, reflection, and debugging.
Some use cases for Go require sharing a Go binary with the end user. If the source code for the binary is private or requires a purchase, its obfuscation can help discourage reverse engineering.
A similar use case is a Go library whose source is private or purchased. Since Go libraries cannot be imported in binary form, and Go plugins have their shortcomings, sharing obfuscated source code becomes an option. See #369.
Obfuscation can also help with aspects entirely unrelated to licensing.
For example, the -tiny
flag can make binaries 15% smaller,
similar to the common practice in Android to reduce app sizes.
Obfuscation has also helped some open source developers work around
anti-virus scans incorrectly treating Go binaries as malware.
Literal obfuscation
Using the -literals
flag causes literal expressions such as strings to be
replaced with more complex expressions, resolving to the same value at run-time.
String literals injected via -ldflags=-X
are also replaced by this flag.
This feature is opt-in, as it can cause slow-downs depending on the input code.
Literals used in constant expressions cannot be obfuscated, since they are
resolved at compile time. This includes any expressions part of a const
declaration, for example.
Tiny mode
With the -tiny
flag, even more information is stripped from the Go binary.
Position information is removed entirely, rather than being obfuscated.
Runtime code which prints panics, fatal errors, and trace/debug info is removed.
Many symbol names are also omitted from binary sections at link time.
All in all, this can make binaries about 15% smaller.
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 source code
positions and many names are removed.
Similarly, garble reverse
is generally not useful in this mode.
Control flow obfuscation
See: CONTROLFLOW.md
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 then the obfuscated build.
Garble obfuscates one package at a time, mirroring how Go compiles one package
at a time. This allows Garble to fully support Go's build cache; incremental
garble build
calls should only re-build and re-obfuscate modified code.
Note that the first call to garble build
may be comparatively slow,
as it has to obfuscate each package for the first time. This is akin to clearing
GOCACHE
with go clean -cache
and running a go build
from scratch.
Garble also makes use of its own cache to reuse work, akin to Go's GOCACHE
.
It defaults to a directory under your user's cache directory,
such as ~/.cache/garble
, and can be placed elsewhere by setting GARBLE_CACHE
.
Determinism and seeds
Just like Go, garble builds are deterministic and reproducible in nature.
This has significant benefits, such as caching builds and being able to use
garble reverse
to de-obfuscate stack traces.
By default, garble will obfuscate each package in a unique way, which will change if its build input changes: the version of garble, the version of Go, the package's source code, or any build parameter such as GOOS or -tags. This is a reasonable default since guessing those inputs is very hard.
You can use the -seed
flag to provide your own obfuscation randomness seed.
Reusing the same seed can help produce the same code obfuscation,
which can help when debugging or reproducing problems.
Regularly rotating the seed can also help against reverse-engineering in the long run,
as otherwise one can look at changes in how Go's standard library is obfuscated
to guess when the Go or garble versions were changed across a series of builds.
To always use a different seed for each build, use -seed=random
.
Note that extra care should be taken when using custom seeds:
if a -seed
value used in a build is lost, garble reverse
will not work.
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. This area is a work in progress; see #3.
-
Aside from
GOGARBLE
to select patterns of packages to obfuscate, there is no supported way to exclude obfuscating a selection of files or packages. More often than not, a user would want to do this to work around a bug; please file the bug instead. -
Go programs are initialized one package at a time, where imported packages are always initialized before their importers, and otherwise they are initialized in the lexical order of their import paths. Since garble obfuscates import paths, this lexical order may change arbitrarily.
-
Go plugins are not currently supported; see #87.
-
Garble requires
git
to patch the linker. That can be avoided once go-gitdiff supports non-strict patches. -
APIs like
runtime.GOROOT
andruntime/debug.ReadBuildInfo
will not work in obfuscated binaries. This can affect loading timezones, for example.
Contributing
We welcome new contributors. If you would like to contribute, see CONTRIBUTING.md as a starting point.