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tuto
This is a short tutorial that shows you how to handle your keys (private and public) to create license using applications.
To handle coded licenses you need a key that encodes the license. To decode the license you need another key. The coding and decoding keys are not the same. This is a nice point in asymmetric cryptography and makes License3j available.
If both the coding and the decoding are using the same key then the license application would need the same key as the one that encoded the license. This way the key (the only key) would be available in the executing application and hackers very soon would extract the key no matter how hard you try to hide and bury it in the code. After that, they could be able to create new licenses. It is nonsense.
When you encode a license then you use a key that is known only to you. You keep it secret. The public pair of the keys that is needed to decode the license will go into the JAR file of the application.
Well, almost. To be more precise it is not the keys naked that
are handled, rather so-called key-ring files. These key-ring
files contain more keys. Some key-ring file contains only public
keys (pubring.pgp), while the other contains private keys
as well (secring.pgp).
To start work you need to generate keys and to store them in keyring files. For the purpose, we use GPG, an open source version of PGP, and the demo screens will come from Windows. It should be similar under Linux.
To start GPG you have to type gpg -h at the DOS
prompt and you will get the help screen:
E:\PROJECTS\research\licensor>gpg -h
gpg (GnuPG) 1.4.9 (Gpg4win 1.1.4)
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Home: C:/Documents and Settings/verhas/Application Data/gnupg
Supported algorithms:
Pubkey: RSA, RSA-E, RSA-S, ELG-E, DSA
Cipher: 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH
Hash: MD5, SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
Compression: Uncompressed, ZIP, ZLIB, BZIP2
Syntax: gpg [options] [files]
sign, check, encrypt or decrypt
default operation depends on the input data
Commands:
-s, --sign [file] make a signature
--clearsign [file] make a clear text signature
-b, --detach-sign make a detached signature
-e, --encrypt encrypt data
-c, --symmetric encryption only with symmetric cipher
-d, --decrypt decrypt data (default)
--verify verify a signature
--list-keys list keys
--list-sigs list keys and signatures
--check-sigs list and check key signatures
--fingerprint list keys and fingerprints
-K, --list-secret-keys list secret keys
--gen-key generate a new key pair
--delete-keys remove keys from the public keyring
--delete-secret-keys remove keys from the secret keyring
--sign-key sign a key
--lsign-key sign a key locally
--edit-key sign or edit a key
--gen-revoke generate a revocation certificate
--export export keys
--send-keys export keys to a key server
--recv-keys import keys from a key server
--search-keys search for keys on a key server
--refresh-keys update all keys from a keyserver
--import import/merge keys
--card-status print the card status
--card-edit change data on a card
--change-pin change a card's PIN
--update-trustdb update the trust database
--print-md algo [files] print message digests
Options:
-a, --armor create ascii armored output
-r, --recipient NAME encrypt for NAME
-u, --local-user use this user-id to sign or decrypt
-z N set compress level N (0 disables)
--textmode use canonical text mode
-o, --output use as output file
-v, --verbose verbose
-n, --dry-run do not make any changes
-i, --interactive prompt before overwriting
--openpgp use strict OpenPGP behavior
--pgp2 generate PGP 2.x compatible messages
(See the man page for a complete listing of all commands and options)
Examples:
-se -r Bob [file] sign and encrypt for user Bob
--clearsign [file] make a clear text signature
--detach-sign [file] make a detached signature
--list-keys [names] show keys
--fingerprint [names] show fingerprints
Please report bugs to <[email protected]>.
E:\PROJECTS\research\licensor>
To generate a key pair you have to issue the command
E:\PROJECTS\research\licensor>gpg --gen-key
gpg (GnuPG) 1.4.9; Copyright (C) 2008 Free Software Foundation, Inc.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Please select what kind of key you want:
(1) DSA and Elgamal (default)
(2) DSA (sign only)
(5) RSA (sign only)
Your selection? 5
You can choose any of the three algorithms. However, pay attention that the third (RSA) is identified by the number 5 and not 3!
RSA keys may be between 1024 and 4096 bits long.
What keysize do you want? (2048) 4096
You should choose a key size. Let it be 4096. It could be anything between 1024 and 4096, but I am paranoid.
Requested keysize is 4096 bits
Please specify how long the key should be valid.
0 = key does not expire
<n> = key expires in n days
<n>w = key expires in n weeks
<n>m = key expires in n months
<n>y = key expires in n years
Key is valid for? (0) 0
Key does not expire at all
Is this correct? (y/N) Y
I chose that the license key does not expire. In that case GPG asks if that is really what you wanted. (This time I was not paranoid.)
You need a user ID to identify your key; the software constructs the user ID
from the Real Name, Comment and Email Address in this form:
"Heinrich Heine (Der Dichter) <[email protected]>"
Real name: GrooWikiDemoKey
Email address:
Comment:
Then I selected an ID for the key. Because this name will be used to reference the encoding key, and because this key is technical and does not belong to a person I suggest that you specify a spaceless string as real name and leave the comment and the email address empty just pressing enter.
You selected this USER-ID:
"GrooWikiDemoKey"
Change (N)ame, (C)omment, (E)mail or (O)kay/(Q)uit? O
After you have done this you have to confirm your selection of the name for the key.
You need a Passphrase to protect your secret key.
This time STOP, and read first the following sentences. Now you have to specify a password that will be used when a license is encoded. Write it down on a piece of paper, or better use KeePass to store it. Or simply leave the passphrase empty, but in that case, store your secret keyring file in a secure place.
We need to generate a lot of random bytes. It is a good idea to perform
some other action (type on the keyboard, move the mouse, utilize the
disks) during the prime generation; this gives the random number
generator a better chance to gain enough entropy.
gpg: NOTE: you should run 'diskperf -y' to enable the disk statistics
gpg: NOTE: you should run 'diskperf -y' to enable the disk statistics
gpg: NOTE: you should run 'diskperf -y' to enable the disk statistics
gpg: NOTE: you should run 'diskperf -y' to enable the disk statistics
MQM could not display the text for error 536895891.
</pre>
Now go for a coffee. It will take a long time until you see:
<pre>
gpg: key 1D83E1B0 marked as ultimately trusted
public and secret key created and signed.
gpg: checking the trustdb
gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model
gpg: depth: 0 valid: 2 signed: 0 trust: 0-, 0q, 0n, 0m, 0f, 2u
pub 4096R/1D83E1B0 2009-07-05
Key fingerprint = A5AB 8CFD ED76 38AD 0347 47F1 9CBF F306 1D83 E1B0
uid GrooWikiDemoKey
Note that this key cannot be used for encryption. You may want to use
the command "--edit-key" to generate a subkey for this purpose.
The key rings are generated in the directory
C:\Documents and Settings\verhas\Application Data\gnupg
The name of the files are secring.pgp and
pubring.pgp.
Now that you have a public and a private key in two key ring files we go ahead and create encoded license file. To do that open your favorite text editor (mine one is vi) and create a license file:
edition=community
valid-until=2009.12.31
Save the content into a file named license-plain.txt
This time you have to start the command line processor included in the license3j JAR file. You also download a bat file from the GitHub repository that starts the program so you have to type:
E:\PROJECTS\research\licensor>license3j.bat encode --license-file=license-plain.
txt --keyring-file="c:\Documents and Settings\verhas\Application Data\gnupg\secr
ing.gpg" --key=GrooWikiDemoKey --password=******** --output=license.out
The ******** should, of course, be replaced with the
actual password of the secret key that you specified when
you created the key.
Now you can decode the license. This step will be done in your application program. Even though there is a 'decode' command in license3j program that decodes the license and displays the parameters that should otherwise be checked by the application. Now type
E:\PROJECTS\research\licensor>license3j.bat decode --license-file=license.out --
keyring-file="C:\Documents and Settings\verhas\Application Data\gnupg\pubring.gpg"
and you will get the result:
---LICENSE STRING PLAIN TEXT START
-- listing properties --
--=listing properties --
valid-until=2009.12.31
edition=community
--LICENSE STRING PLAIN TEXT END
Encoding license key id=7940001403357967922L
--KEY RING DIGEST START
byte [] digest = new byte[] {
(byte)0x34,
(byte)0xF6, (byte)0x86, (byte)0x9A, (byte)0xB7, (byte)0xC4, (byte)0x75, (byte)0xE4, (byte)0xB3,
(byte)0x48, (byte)0xF1, (byte)0x21, (byte)0xBA, (byte)0x75, (byte)0x08, (byte)0x1B, (byte)0x5E,
(byte)0x16, (byte)0x5D, (byte)0xB1, (byte)0x12, (byte)0x89, (byte)0x67, (byte)0x0E, (byte)0xB2,
(byte)0x3C, (byte)0x42, (byte)0x31, (byte)0xB2, (byte)0x2B, (byte)0xD7, (byte)0x24,
};
---KEY RING DIGEST END
E:\PROJECTS\research\licensor>
Using this command you can check that a license is decodable
but more importantly, you can get the ID of the key as returned
by the method getDecodeKeyId() and the digest of the
keyring that you are going to pack into your JAR file.
To see how to embed the license checking in your application visit the page sample license checking