Category: java Cryptography

Java Cryptography – Verifying Signature ”; Previous Next 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. //Creating KeyPair generator object KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(“DSA”); 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. //Initializing the KeyPairGenerator keyPairGen.initialize(2048); Step 3: Generate the KeyPairGenerator You can generate the KeyPair using the generateKeyPair() method. Generate the keypair using this method as shown below. //Generate the pair of keys KeyPair pair = keyPairGen.generateKeyPair(); 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. //Getting the private key from the key pair PrivateKey privKey = pair.getPrivate(); 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. //Creating a Signature object Signature sign = Signature.getInstance(“SHA256withDSA”); 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. //Initialize the signature sign.initSign(privKey); 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. byte[] bytes = “Hello how are you”.getBytes(); //Adding data to the signature sign.update(bytes); 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. //Calculating the signature byte[] signature = sign.sign(); 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. //Initializing the signature sign.initVerify(pair.getPublic()); 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. //Update the data to be verified sign.update(bytes); 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. //Verify the signature boolean bool = sign.verify(signature); Example Following Java program accepts a message from the user, generates a digital signature for the given message, and verifies it. Live Demo import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.PrivateKey; import java.security.Signature; import java.util.Scanner; public class SignatureVerification { public static void main(String args[]) throws Exception{ //Creating KeyPair generator object KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(“DSA”); //Initializing the key pair generator keyPairGen.initialize(2048); //Generate the pair of keys KeyPair pair = keyPairGen.generateKeyPair(); //Getting the privatekey from the key pair PrivateKey privKey = pair.getPrivate(); //Creating a Signature object Signature sign = Signature.getInstance(“SHA256withDSA”); //Initializing the signature sign.initSign(privKey); byte[] bytes = “Hello how are you”.getBytes(); //Adding data to the signature sign.update(bytes); //Calculating the signature byte[] signature = sign.sign(); //Initializing the signature sign.initVerify(pair.getPublic()); sign.update(bytes); //Verifying the signature boolean bool = sign.verify(signature); if(bool) { System.out.println(“Signature verified”); } else { System.out.println(“Signature failed”); } } } Output The above program generates the following output − Signature verified Print Page Previous Next Advertisements ”;

Java Cryptography – Encrypting Data ”; Previous Next 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. //Creating KeyPair generator object KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(“DSA”); 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. //Initializing the KeyPairGenerator keyPairGen.initialize(2048); 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. //Generate the pair of keys KeyPair pair = keyPairGen.generateKeyPair(); 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. //Getting the public key from the key pair PublicKey publicKey = pair.getPublic(); 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. //Creating a Cipher object Cipher cipher = Cipher.getInstance(“RSA/ECB/PKCS1Padding”); 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. //Initializing a Cipher object cipher.init(Cipher.ENCRYPT_MODE, publicKey); 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. //Adding data to the cipher byte[] input = “Welcome to Tutorialspoint”.getBytes(); cipher.update(input); 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. //Encrypting the data byte[] cipherText = cipher.doFinal(); Example Following Java program accepts text from user, encrypts it using RSA algorithm and, prints the encrypted format of the given text. Live Demo import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.Signature; import javax.crypto.BadPaddingException; import javax.crypto.Cipher; public class CipherSample { public static void main(String args[]) throws Exception{ //Creating a Signature object Signature sign = Signature.getInstance(“SHA256withRSA”); //Creating KeyPair generator object KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(“RSA”); //Initializing the key pair generator keyPairGen.initialize(2048); //Generating the pair of keys KeyPair pair = keyPairGen.generateKeyPair(); //Creating a Cipher object Cipher cipher = Cipher.getInstance(“RSA/ECB/PKCS1Padding”); //Initializing a Cipher object cipher.init(Cipher.ENCRYPT_MODE, pair.getPublic()); //Adding data to the cipher byte[] input = “Welcome to Tutorialspoint”.getBytes(); cipher.update(input); //encrypting the data byte[] cipherText = cipher.doFinal(); System.out.println(new String(cipherText, “UTF8″)); } } Output The above program generates the following output − Encrypted Text: ”???:]J_?]???;Xl??????*@??u???r??=T&???_?_??.??i?????(?$_f?zD??????ZGH??g??? g?E:_??bz^??f?~o???t?}??u=uzpUI????Z??l[?G?3??Y?UAEfKT?f?O??N_?d__?????a_?15%?^? ”p?_?$,9″{??^??y??_?t???,?W?PCW??~??[?$??????e????f?Y-Zi__??_??w?_?&QT??`?`~?[?K_??_??? Print Page Previous Next Advertisements ”;

Java Cryptography – KeyPairGenerator ”; Previous Next 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. Create KeyPairGenerator object using the getInstance() method as shown below. //Creating KeyPair generator object KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(“DSA”); 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. //Initializing the KeyPairGenerator keyPairGen.initialize(2048); 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. //Generate the pair of keys KeyPair pair = keyPairGen.generateKeyPair(); 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. //Getting the private key from the key pair PrivateKey privKey = pair.getPrivate(); You can get the public key from the generated KeyPair object using the getPublic() method as shown below. //Getting the public key from the key pair PublicKey publicKey = pair.getPublic(); Example Following example demonstrates the key generation of the secret key using the KeyPairGenerator class of the javax.crypto package. Live Demo import java.security.KeyPair; import java.security.KeyPairGenerator; import java.security.PrivateKey; import java.security.PublicKey; public class KeyPairGenertor { public static void main(String args[]) throws Exception{ //Creating KeyPair generator object KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(“DSA”); //Initializing the KeyPairGenerator keyPairGen.initialize(2048); //Generating the pair of keys KeyPair pair = keyPairGen.generateKeyPair(); //Getting the private key from the key pair PrivateKey privKey = pair.getPrivate(); //Getting the public key from the key pair PublicKey publicKey = pair.getPublic(); System.out.println(“Keys generated”); } } Output The above program generates the following output − Keys generated Print Page Previous Next Advertisements ”;