license-key

A simple licensing library in Golang, that generates license files
containing arbitrary data.

Note that this implementation is quite basic and that in no way it could
prevent someone to hack your software. The goal of this project is only
to provide a convenient way for software publishers to generate license keys
and distribute them without too much hassle for the user.

How does it works?

1. Generate a private key (and keep it secure).
2. Transform the data you want to provide (end date, user email...) to a byte array (using json or gob for example).
3. The library takes the data and create a cryptographically signed hash that is appended to the data.
4. Convert the result to a Base 64 string and send it to the end user.
5. when the user starts your program verify the signature using a public key.

lkgen

A command line helper lkgen is also provided to generate private keys and create licenses.
Install it with the following command :

go install github.com/hyperboloide/lk/lkgen

See the usage bellow on how to use it (or enter lkgen --help-long):

usage: lkgen [<flags>] <command> [<args> ...]

A command-line utility to generate private keys and licenses.

Flags:
  --help  Show context-sensitive help (also try --help-long and --help-man).

Commands:
  help [<command>...]
    Show help.


  gen [<flags>]
    Generates a base32 encoded private key.

    -c, --curve=p384     Elliptic curve to use.
    -o, --output=OUTPUT  Output file (if not defined then stdout).

  pub [<flags>] <key>
    Get the public key.

    -o, --output=OUTPUT  Output file (if not defined then stdout).

  sign [<flags>] <key>
    Creates a license.

    -i, --input=INPUT    Input data file (if not defined then stdin).
    -o, --output=OUTPUT  Output file (if not defined then stdout).

Examples

Generating a new license:

Below is an example of code that generates a license from a private key and a struct containing the end date and a user email that is marshalled to json.

// a base32 encoded private key generated by `lkgen gen` note that you might
// prefer reading it from a file, and that it should stay secret!
const privateKeyBase32 = "FD7YCAYBAEFXA22DN5XHIYLJNZSXEAP7QIAACAQBANIHKYQBBIAACAKEAH7YIAAAAAFP7AYFAEBP7BQAAAAP7GP7QIAWCBCRKQVWKPT7UJDNP4LB5TXEQMO7EYEGDCE42KVBDNEGRIYIIJFBIWIVB6T6ZTKLSYSGK54DZ5VX6M5SJHBYZU2JXUFXJI25L2JJKJW4RL7UL2XBDT4GKYZ5IS6IWBCN7CWTMVBCBHJMH3RHZ5BVGVAY66MQAEYQEPSS2ANTYZIWXWSGIUJW3MDOO335JK3D4N3IV4L5UTAQMLS5YC7QASCAAUOHTZ5ZCCCYIBNCWBELBMAA===="

// Here we use a struct that is marshalled to json, but ultimatly all you need is a []byte.
doc := struct {
	Email string    `json:"email"`
	End   time.Time `json:"end"`
}{
	"test@example.com",
	time.Now().Add(time.Hour * 24 * 365), // 1 year
}

// marshall the document to []bytes (this is the data that our license will contain).
docBytes, err := json.Marshal(doc)
if err != nil {
	log.Fatal(err)
}

// Unmarshal the private key
privateKey, err := lk.PrivateKeyFromB32String(privateKeyBase32)
if err != nil {
	log.Fatal(err)
}

// generate your license with the private key and the document
license, err := lk.NewLicense(privateKey, docBytes)
if err != nil {
	log.Fatal(err)

}
// the b32 representation of our license, this is what you give to your customer.
licenseB32, err := license.ToB32String()
if err != nil {
	log.Fatal(err)
}
fmt.Println(licenseB32)

Validating a license:

Before your execute your program you want to check the user license, here is how with key generated from the previous example:

// A previously generated license b32 encoded. In real life you should read it from a file...
const licenseB32 = "FT7YOAYBAEDUY2LDMVXHGZIB76EAAAIDAECEIYLUMEAQUAABAFJAD74EAAAQCUYB76CAAAAABL7YGBIBAL7YMAAAAD73H74IAFEHWITFNVQWS3BCHIRHIZLTORAGK6DBNVYGYZJOMNXW2IRMEJSW4ZBCHIRDEMBRHAWTCMBNGI3FIMJSHIYTSORTGMXDOMBZG43TIMJYHAVTAMR2GAYCE7IBGEBAPXB37ROJCUOYBVG4LAL3MSNKJKPGIKNT564PYK5X542NH62V7TAUEYHGLEOPZHRBAPH7M4SC55OHAEYQEXMKGG3JPO6BSHTDF3T5H6T42VUD7YAJ3TY5AP5MDE5QW4ZYWMSAPEK24HZOUXQ3LJ5YY34XYPVXBUAA===="

// the public key b32 encoded from the private key using: lkgen pub my_private_key_file`.
// It should be hardcoded somewhere in your app.
const publicKeyBase32 = "ARIVIK3FHZ72ERWX6FQ6Z3SIGHPSMCDBRCONFKQRWSDIUMEEESQULEKQ7J7MZVFZMJDFO6B46237GOZETQ4M2NE32C3UUNOV5EUVE3OIV72F5LQRZ6DFMM6UJPELARG7RLJWKQRATUWD5YT46Q2TKQMPPGIA===="

// Unmarshal the public key.
publicKey, err := lk.PublicKeyFromB32String(publicKeyBase32)
if err != nil {
	log.Fatal(err)
}

// Unmarshal the customer license.
license, err := lk.LicenseFromB32String(licenseB32)
if err != nil {
	log.Fatal(err)
}

// validate the license signature.
if ok, err := license.Verify(publicKey); err != nil {
	log.Fatal(err)
} else if !ok {
	log.Fatal("Invalid license signature")
}

result := struct {
	Email string    `json:"email"`
	End   time.Time `json:"end"`
}{}

// unmarshal the document.
if err := json.Unmarshal(license.Data, &result); err != nil {
	log.Fatal(err)
}

// Now you just have to check that the end date is after time.Now() then you can continue!
if result.End.Before(time.Now()) {
	log.Fatal("License expired on: %s", result.End.Format("2006-01-02"))
} else {
	fmt.Printf(`Licensed to %s until %s`, result.Email, result.End.Format("2006-01-02"))
}

A Complete example

Bellow is a sample function that generate a key pair, signs a license and verify it.

// create a new Private key:
privateKey, err := lk.NewPrivateKey()
if err != nil {
	log.Fatal(err)

}

// create a license document:
doc := MyLicence{
	"test@example.com",
	time.Now().Add(time.Hour * 24 * 365), // 1 year
}

// marshall the document to json bytes:
docBytes, err := json.Marshal(doc)
if err != nil {
	log.Fatal(err)

}

// generate your license with the private key and the document:
license, err := lk.NewLicense(privateKey, docBytes)
if err != nil {
	log.Fatal(err)

}

// encode the new license to b64, this is what you give to your customer.
str64, err := license.ToB64String()
if err != nil {
	log.Fatal(err)

}
fmt.Println(str64)

// get the public key. The public key should be hardcoded in your app to check licences.
// Do not distribute the private key!
publicKey := privateKey.GetPublicKey()

// validate the license:
if ok, err := license.Verify(publicKey); err != nil {
	log.Fatal(err)
} else if !ok {
	log.Fatal("Invalid license signature")
}

// unmarshal the document and check the end date:
res := MyLicence{}
if err := json.Unmarshal(license.Data, &res); err != nil {
	log.Fatal(err)
} else if res.End.Before(time.Now()) {
	log.Fatal("License expired on: %s", res.End.String())
} else {
	fmt.Printf(`Licensed to %s until %s \n`, res.Email, res.End.Format("2006-01-02"))
}