Digital signature with Java

Digital signatures are often used to verify software and software makers to ensure that the software code is not in any way.

Tarnish.

Alternatively, using digital signatures to ensure software "cleaning" and "authentic", that is, software

From its manufacturer or publisher until the end user has not been tampered with others during this time.

This article gives a simple review of the relevant concepts of digital signatures, given Java to create and use

Digital signature specific method.

First, digital signature and its function

Digital Signing Algorithm (DSA) is one of the "Public Key Cardiode Algorithm", so let us

"Private Key / Public Keys" begins to make a simple review.

1. Private key encryption and limitations

Private Key Encryption System encrypts and decrypts using unique keys (ie, private keys). This key

The sender and the recipient must be shared. That is, if the armor is to be encrypted by it, the one needs to use a key.

Encrypt information; after the acceptance of the message, you must use the same key to decrypt information.

This method obviously has a very serious disadvantage. For example, the received parties must have the same key, this

Seeking must have a safe protocol to ensure the reliability of key transfer; second, there is an urgent encryption message

When you want to send, you may not complete the transfer due to no keys of the recipient; third, if you want to send the news to a lot

Different groups need to correspond to each group, maintain many different keys.

In order to overcome the weaknesses of the private key encryption system, people introduced the public key encryption system.

2. Public key encryption

Public key encryption does not require a sender and recipient of a message to know the other party's key, you can access

This encryption information.

The public key encryption system uses a key pair (public key and private key) to encrypt and decrypt information.

Its encryption is also very simple: information encrypted with public key can only be unwave with the private key corresponding to it;

Information with private key encrypted, anyone who has a per capita with the corresponding public key can be unbearable. Therefore, private

There is always a personal storage without having to pass it, and the public key can be authorized to use others without destroying security.

There will always be one-to-one relationship between sex, public key and private key. Specifically,

First, if the information is encrypted with the public key of the recipient, only those who should receive this message

Can decrypt it (ie, only people who have a private key corresponding to the public key can be decrypted). E.g,

The armor is to send an encrypted email from B, and the armor must be encrypted with the public key of B.

Second, if the information is encrypted by the sender's private key, any of the officials of the sender

The recipient can decrypt information to determine that the information is indeed from the sender, and information

The content has not been disrupted by any unintentional or malicious destruction.

The second point described above is the meaning of digital signature.

3. Digital signature features

A digital signature is a fixed length binary digital stream, which is attached to the signed data.

It can be used with any type of digital data, except for the most ordinary code software. Can also be used in passwords,

Email and electronic documentation. The main functions of digital signatures are: preventing the original document from being contaminated or changed;

Prevent don't use your heart to use others name to spread fraudulent news; and who is the certificate of document author

According to, wait.

Second, create and use digital signatures with Java

In addition to the features mentioned above, there is a more realistic meaning of digital signatures with Java. The most common is:

Applying digital signatures can break through some of the browser's security in security. For example, your browser is general

Will reject the online Java program read and write the files of your local hard drive or get your local information (such as your user)

Name, etc.), even if you confirm that the Java program is "reliable" (in fact you can't fully confirm

A program is really "reliable"). If you have to run the Java program, you must close your browsing

Safety inspection function of the unit, but this is tantamount to set the local system as "no fire in the city." Use a digital sign

The name can be perfectly solved this problem: When the browser "feel" is used to you, after the signature Java applet,

It automatically searches for the matching digital signature and checks, if successful, the browser determines the Java applet.

It is "trust", so I am released. In this way, it is guaranteed that security, but also allows the true "trusted" Java program to have many privileges (see the Java program).

In JDK1.1, the work related to digital signatures is done by the tool program javakey.

Javakey is a command line tool provided by Sun to generate a number of archive files (JAR files).

Word signature and manage the key database.

Below we will take a specific example to see the steps to create and use digital signatures,

The concept and explanation will be given in the example.

1. Creation of Java Programs and Digital Signatures (Steps to Encrypted or Signed)

The following Java applet is very simple, its main function is: get the current login of Win95 / 98 system

The user's name string, then writes it to the Test.txt file of the current directory of the local hard drive.

Import java.awt. *;

Import java.io. *;

Import java.lang. *;

Import java.applet. *;

Public class myapp extends applet {

DataOutputStream out_file;

Public void paint (graphics g) {

Try {

String YourName = System.getProperty ("User.Name");

OUT_FILE = New DataOutputStream (New FileoutputStream ("Test.txt"));

OUT_FILE.WRITECHARS ("Your name:" YourName "/ N");

OUT_FILE.CLOSE ();

g.drawstring ("Your Name Has Been Written to File ", 20, 20);

}

Catch (IOException E) {

g.drawstring ("File I / O Error", 12, 12);

}

Catch (securityException se) {

g.drawstring ("You CAN Not Write to Disk or Get User Name.", 12, 12);

}

}

}

// end of myapp.java

After compiling myapp.java into myapp.class, send it to your browser with myApp.html below.

(The command is appletViewer myApp.html).