selfupdate

Overview ¶

Package selfupdate provides functionality to implement secure, self-updating Go programs (or other single-file targets).

For complete updating solutions please see Equinox (https://equinox.io) and go-tuf (https://github.com/flynn/go-tuf).

Basic Example ¶

This example shows how to update a program remotely from a URL.

import (
	"fmt"
	"net/http"

	"github.com/fynelabs/selfupdate"
)

func doUpdate(url string) error {
	// request the new file
	resp, err := http.Get(url)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	err := update.Apply(resp.Body, update.Options{})
	if err != nil {
		if rerr := update.RollbackError(err); rerr != nil {
			fmt.Println("Failed to rollback from bad update: %v", rerr)
		}
	}
	return err
}

Binary Patching ¶

Go binaries can often be large. It can be advantageous to only ship a binary patch to a client instead of the complete program text of a new version.

This example shows how to update a program with a bsdiff binary patch. Other patch formats may be applied by implementing the Patcher interface.

import (
	"encoding/hex"
	"io"

	"github.com/fynelabs/selfupdate"
)

func updateWithPatch(patch io.Reader) error {
	err := update.Apply(patch, update.Options{
		Patcher: update.NewBSDiffPatcher()
	})
	if err != nil {
		// error handling
	}
	return err
}

Checksum Verification ¶

Updating executable code on a computer can be a dangerous operation unless you take the appropriate steps to guarantee the authenticity of the new code. While checksum verification is important, it should always be combined with signature verification (next section) to guarantee that the code came from a trusted party.

selfupdate validates SHA256 checksums by default, but this is pluggable via the Hash property on the Options struct.

This example shows how to guarantee that the newly-updated binary is verified to have an appropriate checksum (that was otherwise retrived via a secure channel) specified as a hex string.

import (
	"crypto"
	_ "crypto/sha256"
	"encoding/hex"
	"io"

	"github.com/fynelabs/selfupdate"
)

func updateWithChecksum(binary io.Reader, hexChecksum string) error {
	checksum, err := hex.DecodeString(hexChecksum)
	if err != nil {
		return err
	}
	err = update.Apply(binary, update.Options{
		Hash: crypto.SHA256, 	// this is the default, you don't need to specify it
		Checksum: checksum,
	})
	if err != nil {
		// error handling
	}
	return err
}

Cryptographic Signature Verification ¶

Cryptographic verification of new code from an update is an extremely important way to guarantee the security and integrity of your updates.

Verification is performed by validating the signature of a hash of the new file. This means nothing changes if you apply your update with a patch.

This example shows how to add signature verification to your updates. To make all of this work an application distributor must first create a public/private key pair and embed the public key into their application. When they issue a new release, the issuer must sign the new executable file with the private key and distribute the signature along with the update.

import (
	"crypto"
	_ "crypto/sha256"
	"encoding/hex"
	"io"

	"github.com/fynelabs/selfupdate"
)

var publicKey = []byte(`
-----BEGIN PUBLIC KEY-----
MFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEtrVmBxQvheRArXjg2vG1xIprWGuCyESx
MMY8pjmjepSy2kuz+nl9aFLqmr+rDNdYvEBqQaZrYMc6k29gjvoQnQ==
-----END PUBLIC KEY-----
`)

func verifiedUpdate(binary io.Reader, hexChecksum, hexSignature string) {
	checksum, err := hex.DecodeString(hexChecksum)
	if err != nil {
		return err
	}
	signature, err := hex.DecodeString(hexSignature)
	if err != nil {
		return err
	}
	opts := update.Options{
		Checksum: checksum,
		Signature: signature,
		Hash: crypto.SHA256, 	                 // this is the default, you don't need to specify it
		Verifier: update.NewECDSAVerifier(),   // this is the default, you don't need to specify it
	}
	err = opts.SetPublicKeyPEM(publicKey)
	if err != nil {
		return err
	}
	err = update.Apply(binary, opts)
	if err != nil {
		// error handling
	}
	return err
}

Building Single-File Go Binaries ¶

In order to update a Go application with self-update, you must distributed it as a single executable. This is often easy, but some applications require static assets (like HTML and CSS asset files or TLS certificates). In order to update applications like these, you'll want to make sure to embed those asset files into the distributed binary with a tool like go-bindata (my favorite): https://github.com/jteeuwen/go-bindata

Non-Goals ¶

Mechanisms and protocols for determining whether an update should be applied and, if so, which one are out of scope for this package. Please consult go-tuf (https://github.com/flynn/go-tuf) or Equinox (https://equinox.io) for more complete solutions.

selfupdate only works for self-updating applications that are distributed as a single binary, i.e. applications that do not have additional assets or dependency files. Updating application that are distributed as mutliple on-disk files is out of scope, although this may change in future versions of this library.