I need to export and import generated certificates with private keys to and from byte arrays, and I don't have any problems unless I use.NET framework 4.0 and 4.5. I'm generating self-signed. 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 generate RSA Public and Private Key Pairs using bouncy castle Crypto APIs The following sample code generates RSA public and private keys and save them in separate files. You can pass the file names as input parameters and the program generates keys with 1024-bit size. Similarly with producing many keys in Java. Therefore, converting from a Java-produced public key to a SSH-compatible public key is as simply as taking the last 65 bytes of that key (after Base64 decoding, where applicable), and concatenating these after the 39-byte header of a SSH key.

  • Java Cryptography Tutorial
  • Message Digest and MAC
  • Keys and Key Store
  • Generating Keys
  • Digital Signature
  • Cipher Text
  • Java Cryptography Resources
  • Selected Reading

You can decrypt the encrypted data using the Cipher class of the javax.crypto package. Follow the steps given below to decrypt given data using Java.

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.

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 the initialize() 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 public key

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

Step 5: Create a Cipher object

The getInstance() method of Cipher class accepts a String variable representing the required transformation and returns a Cipher object that implements the given transformation.

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

Step 6: Initialize the Cipher object

The init() method of the Cipher class accepts two parameters

  • An integer parameter representing the operation mode (encrypt/decrypt)
  • Key object representing the public key

Initialize the Cypher object using the init() method as shown below.

Step 7: Add data to the Cipher object

The update() method of the Cipher class accepts a byte array representing the data to be encrypted and updates the current object with the data given.

Update the initialized Cipher object by passing the data to the update() method in the form of byte array as shown below.

Step 8: Encrypt the data

The doFinal() method of the Cipher class completes the encryption operation. Therefore, finish the encryption using this method as shown below.

Step 9: Initialize the Cipher object for decryption

To decrypt the cypher encrypted in the previous steps you need to initialize it for decryption.

Therefore, initialize the cipher object by passing the parameters Cipher.DECRYPT_MODE and PrivateKey object as shown below.

Step 10: Decrypt the data

Finally, Decrypt the encrypted text using the doFinal() method as shown below.

Example

Following Java program accepts text from user, encrypts it using RSA algorithm and, prints the cipher of the given text, decrypts the cipher and prints the decrypted text again.

Output

The above program generates the following output −

  • Java Cryptography Tutorial
  • Message Digest and MAC
  • Keys and Key Store
  • Generating Keys
  • Digital Signature
  • Cipher Text
  • Java Cryptography Resources
  • Selected Reading

Cryptography is the art and science of making a cryptosystem that is capable of providing information security.

Cryptography deals with the actual securing of digital data. It refers to the design of mechanisms based on mathematical algorithms that provide fundamental information security services. You can think of cryptography as the establishment of a large toolkit containing different techniques in security applications.

What is Cryptanalysis?

The art and science of breaking the cipher text is known as cryptanalysis.

Cryptanalysis is the sister branch of cryptography and they both co-exist. The cryptographic process results in the cipher text for transmission or storage. It involves the study of cryptographic mechanism with the intention to break them. Cryptanalysis is also used during the design of the new cryptographic techniques to test their security strengths.

Cryptography Primitives

Cryptography primitives are nothing but the tools and techniques in Cryptography that can be selectively used to provide a set of desired security services −

  • Encryption
  • Hash functions
  • Message Authentication codes (MAC)
  • Digital Signatures

Cryptography in Java

The Java Cryptography Architecture (JCA) is a set of API’s to implement concepts of modern cryptography such as digital signatures, message digests, certificates, encryption, key generation and management, and secure random number generation etc.

Using JCA developers can build their applications integrating security in them.

To integrate security in your applications rather than depending on the complicated security algorithms you can easily call the respective API’s provided in JCA for required services.

Hash functions are extremely useful and appear in almost all information security applications.

A hash function is a mathematical function that converts a numerical input value into another compressed numerical value. The input to the hash function is of arbitrary length but output is always of fixed length.

Values returned by a hash function are called message digest or simply hash values. The following picture illustrated hash function.

Java provides a class named MessageDigest which belongs to the package java.security. This class supports algorithms such as SHA-1, SHA 256, MD5 algorithms to convert an arbitrary length message to a message digest.

To convert a given message to a message digest, follow the steps given below −

Step 1: Create a MessageDigest object

The MessageDigest class provides a method named getInstance(). This method accepts a String variable specifying the name of the algorithm to be used and returns a MessageDigest object implementing the specified algorithm.

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

Step 2: Pass data to the created MessageDigest object

After creating the message digest object, you need to pass the message/data to it. You can do so using the update() method of the MessageDigest class, this method accepts a byte array representing the message and adds/passes it to the above created MessageDigest object.

Step 3: Generate the message digest

You can generate the message digest using the digest() method od the MessageDigest class this method computes the hash function on the current object and returns the message digest in the form of byte array.

Generate the message digest using the digest method.

Example

Following is an example which reads data from a file and generate a message digest and prints it.

Output

The above program generates the following output −

MAC (Message Authentication Code) algorithm is a symmetric key cryptographic technique to provide message authentication. For establishing MAC process, the sender and receiver share a symmetric key K.

Essentially, a MAC is an encrypted checksum generated on the underlying message that is sent along with a message to ensure message authentication.

The process of using MAC for authentication is depicted in the following illustration −

Keypairgenerator Generatekeypair Always Generates Same Keys Lyrics

In Java the Mac class of the javax.crypto package provides the functionality of message authentication code. Follow the steps given below to create message authentication code using this class.

Step 1: Create a KeyGenerator object

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

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

Step 2: Create SecureRandom object

The SecureRandom class of the java.Security package provides a strong random number generator which is used to generate random numbers in Java. Instantiate this class as shown below.

Step 3: Initialize the KeyGenerator

The KeyGenerator class provides a method named init() this method accepts the SecureRandom object and initializes the current KeyGenerator.

Initialize the KeyGenerator object created in the previous step using this method.

Step 4: Generate key

Generate key using generateKey() method of the KeyGenerator class as shown below.

Step 5: Initialize the Mac object

The init() method of the Mac class accepts an Key object and initializes the current Mac object using the given key.

Step 6: Finish the mac operation

The doFinal() method of the Mac class is used to finish the Mac operation. Pass the required data in the form of byte array to this method and finsh the operation as shown below.

Example

The following example demonstrates the generation of Message Authentication Code (MAC) using JCA. Here, we take a simple message 'Hi how are you' and, generate a Mac for that message.

Output

The above program will generate the following output −

A cryptosystem is an implementation of cryptographic techniques and their accompanying infrastructure to provide information security services. A cryptosystem is also referred to as a cipher system.

The various components of a basic cryptosystem are Plaintext, Encryption Algorithm, Ciphertext, Decryption Algorithm, Encryption Key and, Decryption Key.

Where,

Generatekeypair

  • Encryption Key is a value that is known to the sender. The sender inputs the encryption key into the encryption algorithm along with the plaintext in order to compute the cipher text.

  • Decryption Key is a value that is known to the receiver. The decryption key is related to the encryption key, but is not always identical to it. The receiver inputs the decryption key into the decryption algorithm along with the cipher text in order to compute the plaintext.

Fundamentally there are two types of keys/cryptosystems based on the type of encryption-decryption algorithms.

Symmetric Key Encryption

The encryption process where same keys are used for encrypting and decrypting the information is known as Symmetric Key Encryption.

The study of symmetric cryptosystems is referred to as symmetric cryptography. Symmetric cryptosystems are also sometimes referred to as secret key cryptosystems.

Following are a few common examples of symmetric key encryption −

  • Digital Encryption Standard (DES)
  • Triple-DES (3DES)
  • IDEA
  • BLOWFISH

Asymmetric Key Encryption

The encryption process where different keys are used for encrypting and decrypting the information is known as Asymmetric Key Encryption. Though the keys are different, they are mathematically related and hence, retrieving the plaintext by decrypting cipher text is feasible.

The Keys and certificates used/generated are stored in a data base called as keystore. By default this database is stored in a file named .keystore.

You can access the contents of this database using the KeyStore class of the java.security package. This manages three different entries namely, PrivateKeyEntry, SecretKeyEntry, TrustedCertificateEntry.

  • PrivateKeyEntry
  • SecretKeyEntry
  • TrustedCertificateEntry

Storing a Key in keystore

In this section, we will learn how to store a key in a keystore. To store a key in the keystore, follow the steps given below.

Step 1: Create a KeyStore object

The getInstance() method of the KeyStore class of the java.security package accepts a string value representing the type of the keystore and returns a KeyStore object.

Create an object of the KeyStore class using the getInstance() method as shown below.

Step 2: Load the KeyStore object

The load() method of the KeyStore class accepts a FileInputStream object representing the keystore file and a String parameter specifying the password of the KeyStore.

In general, the KeyStore is stored in the file named cacerts, in the location C:/Program Files/Java/jre1.8.0_101/lib/security/ and its default password is changeit, load it using the load() method as shown below.

Step 3: Create the KeyStore.ProtectionParameter object

Instantiate the KeyStore.ProtectionParameter as shown below.

Step 4: Create a SecretKey object

Create the SecretKey (interface) object by instantiating its Sub class SecretKeySpec. While instantiating you need to pass password and algorithm as parameters to its constructor as shown below.

Step 5: Create a SecretKeyEntry object

Create an object of the SecretKeyEntry class by passing the SecretKey object created in the above step as shown below.

Step 6: Set an entry to the KeyStore

The setEntry() method of the KeyStore class accepts a String parameter representing the keystore entry alias, a SecretKeyEntry object, a ProtectionParameter object and, stores the entry under the given alias.

Set the entry to the keystore using the setEntry() method as shown below.

Example

The following example stores keys into the keystore existing in the “cacerts” file (windows 10 operating system).

Output

The above program generates the following output −

In this chapter, we will learn how to retrieve a key from the keystore using Java Cryptography.

To retrieve a key from the keystore, follow the steps given below.

Step 1: Create a KeyStore object

The getInstance() method of the KeyStore class of the java.security package accepts a string value representing the type of the keystore and returns a KeyStore object.

Create an object of the KeyStore class using this method as shown below.

Step 2: Load the KeyStore object

The load() method of the KeyStore class accepts a FileInputStream object representing the keystore file and a String parameter specifying the password of the KeyStore.

In general, the KeyStore is stored in the file named cacerts, in the location C:/Program Files/Java/jre1.8.0_101/lib/security/ and its default password is changeit, load it using the load() method as shown below.

Step 3: Create the KeyStore.ProtectionParameter object

Instantiate the KeyStore.ProtectionParameter as shown below.

Step 4: Create a SecretKey object

Create the SecretKey (interface) object by instantiating its Sub class SecretKeySpec. While instantiating you need to pass password and algorithm as parameters to its constructor as shown below.

Step 5: Create a SecretKeyEntry object

Create an object of the SecretKeyEntry class by passing the SecretKey object created in the above step as shown below.

Step 6: set an entry to the KeyStore

The setEntry() method of the KeyStore class accepts a String parameter representing the keystore entry alias, a SecretKeyEntry object, a ProtectionParameter object and, stores the entry under the given alias.

Set the entry to the keystore using the setEntry() method as shown below.

Step 7: Create the KeyStore.SecretKeyEntry object

The getEntry() method of the KeyStore class accepts an alias (String parameter) and, an object of the ProtectionParameter class as parameters and returns a KeyStoreEntry object then you can cast this it into KeyStore.SecretKeyEntry object.

Create an object of the KeyStore.SecretKeyEntry class by passing the alias for required key and the protection parameter object created in the previous steps, to the getEntry() method as shown below.

Step 8: Create the key object of the retrieved entry

The getSecretKey() method of the SecretKeyEntry class returns a SecretKey object. Using this method create a SecretKey object as shown below.

Example

Following example shows how to retrieve keys from a key store. Here, we store a key in a keystore, which is in the “cacerts” file (windows 10 operating system), retrieve it, and display some of the properties of it such as the algorithm used to generate the key and, the format of the retrieved key.

Output

The above program generates the following output −

Java provides KeyGenerator class this class is used to generate secret keys and objects of this class are reusable.

To generate keys using the KeyGenerator class follow the steps given below.

Step 1: Create a KeyGenerator object

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

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

Step 2: Create SecureRandom object

The SecureRandom class of the java.Security package provides a strong random number generator which is used to generate random numbers in Java. Instantiate this class as shown below.

Step 3: Initialize the KeyGenerator

The KeyGenerator class provides a method named init() this method accepts the SecureRandom object and initializes the current KeyGenerator.

Initialize the KeyGenerator object created in the previous step using the init() method.

Example

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

Output

The above program generates the following output −

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

The above program generates the following output −

Digital signatures allow us to verify the author, date and time of signatures, authenticate the message contents. It also includes authentication function for additional capabilities.

Advantages of digital signature

In this section, we will learn about the different reasons that call for the use of digital signature. There are several reasons to implement digital signatures to communications −

Authentication

Digital signatures help to authenticate the sources of messages. For example, if a bank’s branch office sends a message to central office, requesting for change in balance of an account. If the central office could not authenticate that message is sent from an authorized source, acting of such request could be a grave mistake.

Integrity

Once the message is signed, any change in the message would invalidate the signature.

Non-repudiation

By this property, any entity that has signed some information cannot at a later time deny having signed it.

Creating the digital signature

Let us now learn how to create a digital signature. You can create digital signature using Java following 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.

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 the initialize() method as shown below.

Step 3: Generate the KeyPairGenerator

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

Step 4: Get the private key from the pair

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

Get the private key using the getPrivate() method as shown below.

Step 5: Create a signature object

The getInstance() method of the Signature class accepts a string parameter representing required signature algorithm and returns the respective Signature object.

Create an object of the Signature class using the getInstance() method.

Step 6: Initialize the Signature object

The initSign() method of the Signature class accepts a PrivateKey object and initializes the current Signature object.

Initialize the Signature object created in the previous step using the initSign() method as shown below.

Step 7: Add data to the Signature object

The update() method of the Signature class accepts a byte array representing the data to be signed or verified and updates the current object with the data given.

Update the initialized Signature object by passing the data to be signed to the update() method in the form of byte array as shown below.

Step 8: Calculate the Signature

The sign() method of the Signature class returns the signature bytes of the updated data.

Calculate the Signature using the sign() method as shown below.

Example

Following Java program accepts a message from the user and generates a digital signature for the given message.

Output

The above program generates the following output −

You can create digital signature using Java and verify it following 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.

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

Step 2: Initialize the KeyPairGenerator object

The KeyPairGenerator class provides a method named initialize() method. 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 the initialize() method as shown below.

Step 3: Generate the KeyPairGenerator

You can generate the KeyPair using the generateKeyPair() method. Generate the keypair using this method as shown below.

Step 4: Get the private key from the pair

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

Get the private key using the getPrivate() method as shown below.

Step 5: Create a signature object

The getInstance() method of the Signature class accepts a string parameter representing required signature algorithm and returns the respective Signature object.

Create an object of the Signature class using the getInstance() method.

Step 6: Initialize the Signature object

The initSign() method of the Signature class accepts a PrivateKey object and initializes the current Signature object.

Initialize the Signature object created in the previous step using the initSign() method as shown below.

Step 7: Add data to the Signature object

The update() method of the Signature class accepts a byte array representing the data to be signed or verified and updates the current object with the data given.

Update the initialized Signature object by passing the data to be signed to the update() method in the form of byte array as shown below.

Step 8: Calculate the Signature

The sign() method of the Signature class returns the signature bytes of the updated data.

Calculate the Signature using the sign() method as shown below.

Step 9: Initialize the signature object for verification

To verify a Signature object you need to initialize it first using the initVerify() method it method accepts a PublicKey object.

Therefore, initialize the Signature object for verification using the initVerify() method as shown below.

Step 10: Update the data to be verified

Update the initialized (for verification) object with the data the data to be verified using the update method as shown below.

Step 11: Verify the Signature

The verify() method of the Signature class accepts another signature object and verifies it with the current one. If a match occurs, it returns true else it returns false.

Verify the signature using this method as shown below.

Example

Following Java program accepts a message from the user, generates a digital signature for the given message, and verifies it.

Output

The above program generates the following output −

You can encrypt given data using the Cipher class of the javax.crypto package. Follow the steps given below to encrypt given data using Java.

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.

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 the initialize() 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 public key

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

Get the public key using this method as shown below.

Step 5: Create a Cipher object

The getInstance() method of Cipher class accepts a String variable representing the required transformation and returns a Cipher object that implements the given transformation.

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

Step 6: Initialize the Cipher object

The init() method of the Cipher class accepts two parameters an integer parameter representing the operation mode (encrypt/decrypt) and, a Key object representing the public key.

Initialize the Cypher object using the init() method as shown below.

Step 7: Add data to the Cipher object

The update() method of the Cipher class accepts a byte array representing the data to be encrypted and updates the current object with the data given.

Update the initialized Cipher object by passing the data to the update() method in the form of byte array as shown below.

You keep the private key on your computer and provide the public key every time you launch an instance.To create key pairs, you can use a third-party tool such as OpenSSH on UNIX-style systems (including Linux, Solaris, BSD, and OS X) or PuTTY Key Generator on Windows. Oracle ilom ssh generate keys. If you're using a Linux distribution, you probably already have the ssh-keygen utility installed. If you already have an, you can use your existing pair and skip this step. Before You Begin. Proceed to.

Step 8: Encrypt the data

The doFinal() method of the Cipher class completes the encryption operation. Therefore, finish the encryption using this method as shown below.

Example

Following Java program accepts text from user, encrypts it using RSA algorithm and, prints the encrypted format of the given text.

Output

The above program generates the following output −

You can decrypt the encrypted data using the Cipher class of the javax.crypto package. Follow the steps given below to decrypt given data using Java.

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.

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

Step 2: Initialize the KeyPairGenerator object

Keypairgenerator Generatekeypair Always Generates Same Keys Video

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 the initialize() 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 public key

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

Step 5: Create a Cipher object

The getInstance() method of Cipher class accepts a String variable representing the required transformation and returns a Cipher object that implements the given transformation.

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

Step 6: Initialize the Cipher object

The init() method of the Cipher class accepts two parameters

  • An integer parameter representing the operation mode (encrypt/decrypt)
  • Key object representing the public key

Initialize the Cypher object using the init() method as shown below.

Step 7: Add data to the Cipher object

The update() method of the Cipher class accepts a byte array representing the data to be encrypted and updates the current object with the data given.

Update the initialized Cipher object by passing the data to the update() method in the form of byte array as shown below.

Step 8: Encrypt the data

The doFinal() method of the Cipher class completes the encryption operation. Therefore, finish the encryption using this method as shown below.

Step 9: Initialize the Cipher object for decryption

To decrypt the cypher encrypted in the previous steps you need to initialize it for decryption.

Therefore, initialize the cipher object by passing the parameters Cipher.DECRYPT_MODE and PrivateKey object as shown below.

Step 10: Decrypt the data

Finally, Decrypt the encrypted text using the doFinal() method as shown below.

Example

Following Java program accepts text from user, encrypts it using RSA algorithm and, prints the cipher of the given text, decrypts the cipher and prints the decrypted text again.

Output

The above program generates the following output −