Java KeyPairGenerator

Jakob Jenkov
Last update: 2018-01-24

The Java KeyPairGenerator class ( is used to generate asymmetric encryption / decryption key pairs. An asymmetric key pair consists of two keys. The first key is typically used to encrypt data. The second key which is used to decrypt data encrypted with the first key.

Public Key, Private Key Type Key Pairs

The most commonly known type of asymmetric key pair is the public key, private key type of key pair. The private key is used to encrypt data, and the public key can be used to decrypt the data again. Actually, you could also encrypt data using the public key and decrypt it using the private key.

The private key is normally kept secret, and the public key can be made publicly available. Thus, if Jack encrypts some data with his private key, everyone in possession of Jack's public key can decrypt it.

Creating a KeyPairGenerator Instance

To use the Java KeyPairGenerator you must first create a KeyPairGenerator instance. Creating a KeyPairGenerator instance is done by calling the method getInstance() method. Here is an example of creating a Java KeyPairGenerator instance:

KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");

The getInstance() method takes the name of the encryption algorithm to generate the key pair for. In this example we use the name RSA.

Initializing the KeyPairGenerator

Depending on the algorithm the key pair is generated for, you may have to initialize the KeyPairGenerator instance. Initializing the KeyPairGenerator is done by calling its initialize() method. Here is an example of initializing a Java KeyPairGenerator instance:


This example initializes the KeyPairGenerator to generate keys of 2048 bits in size.

Generating a Key Pair

To generate a KeyPair with a KeyPairGenerator you call the generateKeyPair() method. Here is an example of generating a KeyPair with the KeyPairGenerator:

KeyPair keyPair = keyPairGenerator.generateKeyPair();

Jakob Jenkov

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