Difference between revisions of "Signing jar files with jarsigner"

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(Use of the Keytool Utility)
(Use of the Keytool Utility)
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  keytool -genkey -keystore refArchive/testkeystore -alias bob
 
  keytool -genkey -keystore refArchive/testkeystore -alias bob
 +
 +
* The default algorithm for Key Pairs is DSA. The -sigalg option can be set to generate other types of keys, such as DSA ones.
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* The Distinguished Name for Bob is:
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<code>CN=Bob, OU=testing, O=signer & Co., L=wonderland, ST=United Kingdom, C=UK</code>
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the password for accessing to the private key of Bob is:
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<code>bobspdw</code>
  
 
=== Visualize the content of the keystore ===
 
=== Visualize the content of the keystore ===
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  keytool -list -keystore refArchive/testkeystore   
 
  keytool -list -keystore refArchive/testkeystore   
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* which will show something like this if the keystore has just been created:
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<code>Keystore type: jks
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Keystore provider: SUN
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Your keystore contains 1 entry
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bob, Jan 28, 2007, keyEntry,
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Certificate fingerprint (MD5): 5C:B4:82:80:46:5D:C1:0B:48:DE:B6:50:F0:22:24:9D
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</code>
  
 
=== Extract of the public key certificate of Bob for dissemination ===
 
=== Extract of the public key certificate of Bob for dissemination ===

Revision as of 16:24, 7 March 2007

Most of the information in this note can be found in the `help' section of the jarsigner and keytool utilities:

jarsigner --help

keytool --help

Contents

Criteria for Signature Validity

The criteria of validity of a digital signature are the following:

  • No modification of the archive resources after the signature,
  • certificate not outdated (or not yet valid).

Moreover, the signer of the archive must be known, i.e. its public key certificate must be identified as trusted before the validation. Otherwise, any malicious third party can forge a similar certificate, potentially with the same signer name, and present a coherent signed archive.

Additional criteria of archive signature validity are defined in the context of the OSGi framework, that are specific to the deployment of components from third party repositories:

  • No resource removed from the archive after the signature,
  • No resource added from the archive after the signature,
  • The digital signature must immediately follow the Manifest file of the archive, to prevent caching malicious files.

This means that according to the security level you need, the Sun criteria of signature validity may not be sufficient.

Use of the JarSigner Tool

The Sun `Jarsigner' is a utility delivered along with Sun JDK. It has the ability to sign Java Archives (Jars), and to verify the validity their signature.

So as to test the jarsigner tool, you need to have a public/private key pair. The example are given with Bob's key pair.

  • The data used to conduce tests in this tutorial are found in the Media:jarsigner-test.zip file. Store it on you computer, and unzip the archive.

Following files are used:

  • the Keystore file, refArchive/testkeystore, contains the private and public key for Bob, and the public key for Alice
  • Bob's Public Key Certificate is stored in the file refArchive/bob.cert (it is also available directly from the keystore)
  • Alice's Public Key Certificate is stored in the file refArchive/alice.cert (it is also available directly from the keystore)
  • the archives fridgebundle-1.1.jar, fridgebundle-1.1.signed.jar, fridgebundle-1.1.unknownsigner.jar, bindex-manifestMainAttrsModified-1.0.jar, are various Jar Files, that are used for the test.


Sign a given jar archive

Sign the archive refArchive/fridgebundle-1.1.jar with bob's private key:

jarsigner -keystore refArchive/testkeystore -signedjar  
    refArchive/fridgebundle-1.1.signed.jar refArchive/fridgebundle-1.1.jar bob
 Enter Passphrase for keystore: password
 Enter key password for bob: bobspwd

Check that a signed jar is valid

Verify the signed archive refArchive/fridgebundle-1.1.signed.jar using the keystore refArchive/testkeystore:

jarsigner -verify -keystore refArchive/testkeystore refArchive/fridgebundle-1.1.signed.jar

Verify a signed jar with unknown signer

Verify the signed archive refArchive/fridgebundle-1.1.unknownsigner.jar using the keystore refArchive/testkeystore:

jarsigner -verify -keystore refArchive/testkeystore   
refArchive/fridgebundle-1.1.unknownsigner.jar

Some test with an invalid archive signature

Verify the signed archive refArchive/bindex-manifestMainAttrsModified-1.0.jar using the keystore refArchive/testkeystore:

jarsigner -verify refArchive/bindex-manifestMainAttrsModified-1.0.jar
jarsigner: java.lang.SecurityException: Invalid signature file digest 
    for Manifest main attributes


Remark: No warning is issued by the Sun Jarsigner if the signer of the archive is unknow to you. No matter who has signed the archive, this latter will be considered as valid !

Use of the Keytool Utility

The Sun keytool utility supports the management of DSA and RSA asymetric key pairs, as well as the management of public key certificates of third party actors.

Option:

  • use an existing keystore file

Example: the keystore file is named refArchive/testkeystore, and is accessible with the password password

If you specify a keystore that does not exist in the keytool options, it is automatically created and initialized with the given parameters (e.g. the password).

The default keystore in *nix systems is /home/user/.keystore. It is overridden by the -keystore option.

You can perform following tests so as to learn how to use the keytool:

Create a new DSA Key Pair for Bob

Generate a new DSA Key Pair for the user Bob, using the keystore refArchive/testkeystore:

keytool -genkey -keystore refArchive/testkeystore -alias bob
  • The default algorithm for Key Pairs is DSA. The -sigalg option can be set to generate other types of keys, such as DSA ones.
  • The Distinguished Name for Bob is:

CN=Bob, OU=testing, O=signer & Co., L=wonderland, ST=United Kingdom, C=UK the password for accessing to the private key of Bob is: bobspdw

Visualize the content of the keystore

Visualize the content of the keystore file refArchive/testkeystore:

keytool -list -keystore refArchive/testkeystore  
  • which will show something like this if the keystore has just been created:

Keystore type: jks Keystore provider: SUN Your keystore contains 1 entry bob, Jan 28, 2007, keyEntry, Certificate fingerprint (MD5): 5C:B4:82:80:46:5D:C1:0B:48:DE:B6:50:F0:22:24:9D

Extract of the public key certificate of Bob for dissemination

Store the Public Key Certificate for Bob in the file refArchive/bob2.cert, from the keystore file refArchive/testkeystore:

keytool -export -keystore refArchive/testkeystore -alias bob > refArchive/bob2.cert

Visualize a certificate

Visualize the content of the Public Key Certificate for Bob, contained in the file refArchive/bob.cert :

keytool -printcert -file refArchive/bob.cert 

Import a certificate

Import the Public Key Certificate of Alice refArchive/alice.cert in the keystore file refArchive/testkeystore:

keytool -import -keystore refArchive/testkeystore -file refArchive/alice.cert -alias alice  
password: password Trust this certificate? [no]: yes

Visualize again the content of the keystore

keytool -list -keystore refArchive/testkeystore

References

You can find further informations here: