Rsa Key Pair Generator Java

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Contents

  • 3. Saving the Keys in Binary Format
  • Source Code

1. Introduction

Let us learn the basics of generating and using RSA keys in Java.

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  1. The following are Jave code examples for showing how to use initialize of the java.security.KeyPairGenerator class. You can vote up the examples you like. Your votes will be used in our system to get more good examples.
  2. The following are Jave code examples for showing how to use getInstance of the java.security.KeyPairGenerator class. You can vote up the examples you like. Your votes will be used in our system to get more good examples.
  3. With every doubling of the RSA key length, decryption is 6-7 times times slower.Hence, when there are large messages for RSA encryption, the performance degrades.In such scenarios, we first do an AES encryption of the messages and the key used for AES encryption is RSA encrypted and sent to the server.
  4. This chapter demonstrates how to generate an RSA based OpenPGP key pair with OpenPGP Library for Java. When we create an OpenPGP key pair, a few parameters must be passed. These include: Encryption key size in bytes (recommended between 1024 and 3072) User ID key algorithm (RSA or ELGAMAL) private key password list of preferred.
  5. The following are top voted examples for showing how to use java.security.KeyPairGenerator.These examples are extracted from open source projects. You can vote up the examples you like and your votes will be used in our system to generate more good examples.

Java provides classes for the generation of RSA public and private key pairs with the package java.security. You can use RSA keys pairs in public key cryptography.

Rsa Key Pair Generator Java

Public key cryptography uses a pair of keys for encryption. Distribute the public key to whoever needs it but safely secure the private key.

Public key cryptography can be used in two modes:

Encryption: Only the private key can decrypt the data encrypted with the public key.

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Authentication: Data encrypted with the private key can only be decrypted with the public key thus proving who the data came from.

2. Generating a Key Pair

First step in creating an RSA Key Pair is to create a KeyPairGeneratorfrom a factory method by specifying the algorithm (“RSA” in this instance):

Initialize the KeyPairGenerator with the key size. Use a key size of 1024 or 2048. Currently recommended key size for SSL certificates used in e-commerce is 2048 so that is what we use here.

From the KeyPair object, get the public key using getPublic() and the private key using getPrivate().

3. Saving the Keys in Binary Format

Save the keys to hard disk once they are obtained. This allows re-using the keys for encryption, decryption and authentication.

What is the format of the saved files? The key information is encoded in different formats for different types of keys. Here is how you can find what format the key was saved in. On my machine, the private key was saved in PKCS#8 format and the public key in X.509 format. We need this information below to load the keys.

3.1. Load Private Key from File

After saving the private key to a file (or a database), you might need to load it at a later time. You can do that using the following code. Note that you need to know what format the data was saved in: PKCS#8 in our case.

3.2 Load Public Key from File

Load the public key from a file as follows. The public key has been saved in X.509 format so we use the X509EncodedKeySpec class to convert it.

4. Use Base64 for Saving Keys as Text

Save the keys in text format by encoding the data in Base64. Java 8 provides a Base64 class which can be used for the purpose. Save the private key with a comment as follows:

And the public key too (with a comment):

5. Generating a Digital Signature

As mentioned above, one of the purposes of public key cryptography is digital signature i.e. you generate a digital signature from a file contents, sign it with your private key and send the signature along with the file. The recipient can then use your public key to verify that the signature matches the file contents.

Here is how you can do it. Use the signature algorithm “SHA256withRSA” which is guaranteed to be supported on all JVMs. Use the private key (either generated or load from file as shown above) to initialize the Signatureobject for signing. It is then updated with contents from the data file and the signature is generated and written to the output file. This output file contains the digital signature and must be sent to the recipient for verification.

6. Verifying the Digital Signature

The recipient uses the digital signature sent with a data file to verify that the data file has not been tampered with. It requires access to the sender’s public key and can be loaded from a file if necessary as presented above.

The code below updates the Signature object with data from the data file. It then loads the signature from file and uses Signature.verify() to check if the signature is valid.

And that in a nutshell is how you can use RSA public and private keys for digital signature and verification.

Source Code

Go here for the source code.

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Rsa Key Generation Java

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Java provides the KeyPairGenerator class. This class is used to generate pairs of public and private keys. To generate keys using the KeyPairGenerator class, follow the steps given below.

Step 1: Create a KeyPairGenerator object

The KeyPairGenerator class provides getInstance() method which accepts a String variable representing the required key-generating algorithm and returns a KeyPairGenerator object that generates keys.

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Create KeyPairGenerator object using the getInstance() method as shown below.

Step 2: Initialize the KeyPairGenerator object

The KeyPairGenerator class provides a method named initialize() this method is used to initialize the key pair generator. This method accepts an integer value representing the key size.

Initialize the KeyPairGenerator object created in the previous step using this method as shown below.

Step 3: Generate the KeyPairGenerator

You can generate the KeyPair using the generateKeyPair() method of the KeyPairGenerator class. Generate the key pair using this method as shown below.

Step 4: Get the private key/public key

You can get the private key from the generated KeyPair object using the getPrivate() method as shown below.

You can get the public key from the generated KeyPair object using the getPublic() method as shown below.

Example

Following example demonstrates the key generation of the secret key using the KeyPairGenerator class of the javax.crypto package.

Output

Generate Rsa Key Pair Online

The above program generates the following output −