Kotlin - RSA Encryption and Decryption example

The RSA algorithm (Rivest-Shamir-Adleman) is a cryptographic algorithm that is used for specific security services or purposes, which enables public-key encryption and is widely used to secure sensitive data, particularly when it is being sent over an insecure network such as the HTTP. A public key is shared publicly, while a private key is secret and must not be shared with anyone.
The following illustration highlights how asymmetric cryptography works:


Example 1: The Cipher Type: RSA/ECB/PKCS1Padding

import java.security.spec.PKCS8EncodedKeySpec
import javax.crypto.Cipher
import java.security.spec.X509EncodedKeySpec
import java.io.IOException
import java.security.*
import java.util.*

/*
* RSA Key Size: 1024
* Cipher Type: RSA/ECB/PKCS1Padding
*/
class RSAKotlinDemo1 {
var privateKey: PrivateKey
var publicKey: PublicKey

companion object {
// convert String publickey to Key object
@Throws(GeneralSecurityException::class, IOException::class)
fun loadPublicKey(stored: String): Key {
val data: ByteArray = Base64.getDecoder().
decode(stored.toByteArray())
val spec = X509EncodedKeySpec(data)
val fact = KeyFactory.getInstance("RSA")
return fact.generatePublic(spec)
}

// Encrypt using publickey
@Throws(Exception::class)
fun encryptMessage(plainText: String, publickey: String): String {
val cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding")
cipher.init(Cipher.ENCRYPT_MODE, loadPublicKey(publickey))
return Base64.getEncoder().encodeToString(cipher.doFinal

(plainText.toByteArray()))
}

// Decrypt using privatekey
@Throws(Exception::class)
fun decryptMessage(encryptedText: String?, privatekey: String):
String {
val cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding")
cipher.init(Cipher.DECRYPT_MODE, loadPrivateKey(privatekey))
return String(cipher.
doFinal(Base64.getDecoder().decode(encryptedText)))
}

// Convert String private key to privateKey object
@Throws(GeneralSecurityException::class)
fun loadPrivateKey(key64: String): PrivateKey {
val clear: ByteArray = Base64.getDecoder().
decode(key64.toByteArray())
val keySpec = PKCS8EncodedKeySpec(clear)
val fact = KeyFactory.getInstance("RSA")
val priv = fact.generatePrivate(keySpec)
Arrays.fill(clear, 0.toByte())
return priv
}

@Throws(Exception::class)
@JvmStatic
fun main(args: Array<String>) {
val secretText = "www.knowledgefactory.net"
val keyPairGenerator = RSAKotlinDemo1()
// Generate private and public key
val privateKey: String = Base64.getEncoder().

encodeToString(keyPairGenerator.privateKey.encoded)
val publicKey: String = Base64.getEncoder().

encodeToString(keyPairGenerator.publicKey.encoded)
println("Private Key: $privateKey")
println("Public Key: $publicKey")
// Encrypt secret text using public key
val encryptedValue = encryptMessage(secretText, publicKey)
println("Encrypted Value: $encryptedValue")
// Decrypt
val decryptedText = decryptMessage(encryptedValue, privateKey)
println("Decrypted output: $decryptedText")
}
}

init {
val keyGen = KeyPairGenerator.getInstance("RSA")
keyGen.initialize(1024)
val pair = keyGen.generateKeyPair()
privateKey = pair.private
publicKey = pair.public
}
}

Output:

Private  Key:

MIICdwIBADANBgkqhkiG9w0BAQEFAASCAmEwggJdAgEAAoGBANHdZHjuChS2Icoc+eUtPNLlhjZXgqPiy0o744sG/lBWdYyFamVcEBt28ExMxMtsznVrLQ9vz6V1eTNcwsuwjIfHePp4Vnedinc7U4CjqmhCY+tZab94iugJDLfh6Jbf7aDRcwuzbUK41VQwDWQcw5zcgIE0njfT3ULH/hqcSra9AgMBAAECgYBzu2CF49eBVnNJzzLr9Ed/kf2yiA3OLOqotGAmMiQaz6MhbA2heeSUEMIxgYBhIk60p/cAdUuQVjkRXw05YNINqwRuc4+/3pyNXXJ3EfyVLvjLePmdB2UFHvi+31WoXpbX1NNb8lf25G+5f58cgHsapjgWpGO9Bq2afPne1sZR4QJBAOpis/7Ytpbu68IiyukU8rNk4u+LtQXjyf3hX6NuccixSYurDTkmcPLOIJnXY9qmU2RFJjgP8bPHNo2QQyYRgVkCQQDlN8/MxNqSrZ8qSGLLJ37tCtECUnLn/tr6demUfJkLMxZI96cOi9v99DuTCISQdZDq1BS1hWNwwQ9ycuomdrAFAkApqyB6xwY28QTCv7K5GztGf0IE+h5VjLiFRQLeqCzcVABSLzermFTuJY0QLIWZAobCxbRUtSjwIBNnuWTmqKgJAkEAuvfAb0WvB+/JIYMz2oQX2yB0hhFcmvHeCmg9pBnR+DmulswzHwFj64zZP0C2aOMM1w8w6TOpfiJsCC3F4qPzRQJBAOQ6kJX8rEYAte9UI27IJ1o/JPGlatajCnHsJmzgHvkGhwqFVi9ip2DLBTAr2yRhWXnVp99tPlHTm3DY/yM/a7E=

Public Key:

MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDR3WR47goUtiHKHPnlLTzS5YY2V4Kj4stKO+OLBv5QVnWMhWplXBAbdvBMTMTLbM51ay0Pb8+ldXkzXMLLsIyHx3j6eFZ3nYp3O1OAo6poQmPrWWm/eIroCQy34eiW3+2g0XMLs21CuNVUMA1kHMOc3ICBNJ43091Cx/4anEq2vQIDAQAB

Encrypted Value:

uJ0oo4f3XbaiBUpiO49vVHKyelbdk8CIT1kOgEaiJ8XcwqM4OPZt7sHMKMWPjFE/84KQnphPdbog8uPe5DF33xNE8D5UgN+RfsUai0PQEVX07DdkiW8GnlKN0UOR8iNQoP9Dp2ir3V9pc4bKggDk7V7IxmoyP/dkbU/Jgi9OPRg=

Decrypted output: www.knowledgefactory.net 


Example 2: The Cipher Type: RSA/ECB/OAEPWithSHA-1AndMGF1Padding

import java.security.spec.PKCS8EncodedKeySpec
import javax.crypto.Cipher
import java.security.spec.X509EncodedKeySpec
import java.io.IOException
import java.security.*
import java.util.*

/*
* RSA Key Size: 2048
* Cipher Type: RSA/ECB/OAEPWithSHA-1AndMGF1Padding
*/
class RSAKotlinDemo2 {
var privateKey: PrivateKey
var publicKey: PublicKey

companion object {
// convert String publickey to Key object
@Throws(GeneralSecurityException::class, IOException::class)
fun loadPublicKey(stored: String): Key {
val data: ByteArray = Base64.getDecoder().
decode(stored.toByteArray())
val spec = X509EncodedKeySpec(data)
val fact = KeyFactory.getInstance("RSA")
return fact.generatePublic(spec)
}

// Encrypt using publickey
@Throws(Exception::class)
fun encryptMessage(plainText: String, publickey: String): String {
val cipher = Cipher.
getInstance("RSA/ECB/OAEPWithSHA-1AndMGF1Padding")
cipher.init(Cipher.ENCRYPT_MODE, loadPublicKey(publickey))
return Base64.getEncoder().encodeToString(cipher.doFinal

(plainText.toByteArray()))
}

// Decrypt using privatekey
@Throws(Exception::class)
fun decryptMessage(encryptedText: String?, privatekey: String):
String {
val cipher = Cipher.
getInstance("RSA/ECB/OAEPWithSHA-1AndMGF1Padding")
cipher.init(Cipher.DECRYPT_MODE, loadPrivateKey(privatekey))
return String(cipher.
doFinal(Base64.getDecoder().decode(encryptedText)))
}

// Convert String private key to privateKey object
@Throws(GeneralSecurityException::class)
fun loadPrivateKey(key64: String): PrivateKey {
val clear: ByteArray = Base64.getDecoder().
decode(key64.toByteArray())
val keySpec = PKCS8EncodedKeySpec(clear)
val fact = KeyFactory.getInstance("RSA")
val priv = fact.generatePrivate(keySpec)
Arrays.fill(clear, 0.toByte())
return priv
}

@Throws(Exception::class)
@JvmStatic
fun main(args: Array<String>) {
val secretText = "www.knowledgefactory.net"
val keyPairGenerator = RSAKotlinDemo2()
// Generate private and public key
val privateKey: String = Base64.getEncoder().

encodeToString(keyPairGenerator.privateKey.encoded)
val publicKey: String = Base64.getEncoder().

encodeToString(keyPairGenerator.publicKey.encoded)
println("Private Key: $privateKey")
println("Public Key: $publicKey")
// Encrypt secret text using public key
val encryptedValue = encryptMessage(secretText, publicKey)
println("Encrypted Value: $encryptedValue")
// Decrypt
val decryptedText = decryptMessage(encryptedValue, privateKey)
println("Decrypted output: $decryptedText")
}
}

init {
val keyGen = KeyPairGenerator.getInstance("RSA")
keyGen.initialize(2048)
val pair = keyGen.generateKeyPair()
privateKey = pair.private
publicKey = pair.public
}
}


Example 3: The Cipher Type: RSA/ECB/OAEPWithSHA-256AndMGF1Padding 

import java.security.spec.PKCS8EncodedKeySpec
import javax.crypto.Cipher
import java.security.spec.X509EncodedKeySpec
import java.io.IOException
import java.security.*
import java.util.*

/*
* RSA Key Size: 4096
* Cipher Type: RSA/ECB/OAEPWithSHA-256AndMGF1Padding
*/
class RSAKotlinDemo3 {
var privateKey: PrivateKey
var publicKey: PublicKey

companion object {
// convert String publickey to Key object
@Throws(GeneralSecurityException::class, IOException::class)
fun loadPublicKey(stored: String): Key {
val data: ByteArray = Base64.getDecoder().
decode(stored.toByteArray())
val spec = X509EncodedKeySpec(data)
val fact = KeyFactory.getInstance("RSA")
return fact.generatePublic(spec)
}

// Encrypt using publickey
@Throws(Exception::class)
fun encryptMessage(plainText: String, publickey: String): String {
val cipher = Cipher.
getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding")
cipher.init(Cipher.ENCRYPT_MODE, loadPublicKey(publickey))
return Base64.getEncoder().encodeToString(cipher.doFinal

(plainText.toByteArray()))
}

// Decrypt using privatekey
@Throws(Exception::class)
fun decryptMessage(encryptedText: String?, privatekey: String):
String {
val cipher = Cipher.
getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding")
cipher.init(Cipher.DECRYPT_MODE, loadPrivateKey(privatekey))
return String(cipher.
doFinal(Base64.getDecoder().decode(encryptedText)))
}

// Convert String private key to privateKey object
@Throws(GeneralSecurityException::class)
fun loadPrivateKey(key64: String): PrivateKey {
val clear: ByteArray = Base64.getDecoder().
decode(key64.toByteArray())
val keySpec = PKCS8EncodedKeySpec(clear)
val fact = KeyFactory.getInstance("RSA")
val priv = fact.generatePrivate(keySpec)
Arrays.fill(clear, 0.toByte())
return priv
}

@Throws(Exception::class)
@JvmStatic
fun main(args: Array<String>) {
val secretText = "www.knowledgefactory.net"
val keyPairGenerator = RSAKotlinDemo3()
// Generate private and public key
val privateKey: String = Base64.getEncoder().

encodeToString(keyPairGenerator.privateKey.encoded)
val publicKey: String = Base64.getEncoder().

encodeToString(keyPairGenerator.publicKey.encoded)
println("Private Key: $privateKey")
println("Public Key: $publicKey")
// Encrypt secret text using public key
val encryptedValue = encryptMessage(secretText, publicKey)
println("Encrypted Value: $encryptedValue")
// Decrypt
val decryptedText = decryptMessage(encryptedValue, privateKey)
println("Decrypted output: $decryptedText")
}
}

init {
val keyGen = KeyPairGenerator.getInstance("RSA")
keyGen.initialize(4096)
val pair = keyGen.generateKeyPair()
privateKey = pair.private
publicKey = pair.public
}
}

More Kotlin related topics,

Popular posts from this blog

Learn Java 8 streams with an example - print odd/even numbers from Array and List

Example 1: Java 8 program to print odd numbers from a List   import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; /*Java 8 Program to find Odd Numbers from a List*/ public class DriverClass { public static void main( String [] args) { List < Integer > numbers = Arrays. asList( 1 , 4 , 8 , 40 , 11 , 22 , 33 , 99 ); List < Integer > oddNumbers = numbers.stream(). filter(o -> o % 2 != 0 ). collect(Collectors.toList()); System.out.println(oddNumbers); } } 1. Initialize List using Arrays.asList() method. Java's built-in Arrays.asList() method converts an array into a list. This method takes an array as an argument and returns a List object. 2.  Java List interface provides stream() method which returns a sequential Stream with list of Integer as its source. 3. The Java stream filter() method allow
Read more

Java Stream API - How to convert List of objects to another List of objects using Java streams?

Image
In this section, we will show you how to convert a List of objects to another List of objects in Java using the Java streams map(). The ‘map’ method maps each element to its corresponding result. Java Stream API   The Java Stream API provides a functional programming approach over the object oriented capabilities of Java. It is used for processing collections of objects. The Stream in Java can be defined as a sequence of elements from a source List, Set or Array. Most of the stream operations return a Stream. This avails engender a chain of stream operations(stream pipe-lining). The streams withal support the aggregate or terminal operations on the elements. for example, finding the sum or maximum element or finding the average etc...Stream operations can either be executed sequentially or parallel. when performed parallelly, it is called a parallel stream.   Stream map() Method   The Java 8 Stream map() is an intermediate operation. It converts Stream<obj1> to Stream<obj2>
Read more

Registration and Login with Spring Boot + Spring Security + Thymeleaf

Image
In this section, we will learn how to create user registration and login using Spring boot, Spring security, Thymeleaf, JPA, and H2DB. The GitHub repository link is provided at the end of this tutorial. You can download the source code. Technologies used: Spring Boot 2.5.5  Spring Data JPA  Spring Security  Thymeleaf  Maven 3+  Java 17  H2 Database   User Interface User Registration Authentication Failed Authentication success Sign out Final Project Structure: Complete pom.xml: <? xml version ="1.0" encoding ="UTF-8" ?> < project xmlns ="http://maven.apache.org/POM/4.0.0" xmlns: xsi ="http://www.w3.org/2001/XMLSchema-instance" xsi :schemaLocation ="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" > < modelVersion >4.0.0</ modelVersion > < parent > < groupId >org.springframework.boot</ groupId > < artifactId >spring-boot-starter-pare
Read more

Java, Spring Boot Mini Project - Library Management System - Download

Image
Hello everyone, Hope you are doing well. Here, we provide a Library Management System mini-project for beginners, it's free for download. Maybe you can build more on top of this project and create your own product, that's all about you. The source code download link is provided at the end of this post. 1. Benefit of this project You could cover the following technologies and features by learning and debugging this mini project. Java 17 Java Stream Java Lamda Expressions Java Records Functional programming Object-oriented programming var Keyword in Java Generics in Java Java Switch Spring boot 2.6.4 Spring Security Thymeleaf template engine OpenCSV Spring Data JPA Server Side Pagination H2 Database  Bootstrap HTML CSS and more... 2. Objective Of Spring Boot On Library Management System The main objective of this project is to manage the details of the books, author, category, and publisher. Only Admin/Librarian will manage all these activities. Also, they can export the data in
Read more

ReactJS, Spring Boot JWT Authentication Example

Image
In this tutorial, we’ll create a user registration & login example using ReactJS, Spring Boot, Spring Security, and JWT authentication. You could download the source code from our Github repository, the download link is provided at the end of this tutorial. Technologies used Backend Technologies: Java 17 Spring Boot 2.7.0 Spring Security Spring Data JPA JWT H2 Database Frontend Technologies: React 17.0.1 Axios 0.27.2 Redux 4.0.5 Bootstrap 4.5.2 ReactJS - SpringBoot - JWT - Flow Backend Project Directory: Frontend Project Directory: Following is the screenshot of our application - User Registration: User Signin: Profile View: Access Resource: We will build two projects:  1. Backend:   spring-boot-security-jwt 2. Frontend: react-redux-jwt Project 1: spring-boot-security-jwt Pom.xml <?xml version = "1.0" encoding = "UTF-8" ?> <project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
Read more

Top 5 Java ORM tools - 2024

Image
  The term ORM refers to object-relational mapping, which uses objects to adapt programming languages to database systems while allowing them to function with SQL and object-oriented programming ideas. Any kind of database management system that can accomplish object mapping to the table in the virtual system is suitable for the implementation of ORM. Java has a wide variety of ORM tools, some of which are mentioned below: 1. Hibernate Hibernate is a lightweight, open-source, non-invasive Java ORM (Object-Relational Mapping) framework that allows developers to create objects that function independently of database software and create persistence logic in any Java or JavaEE application. It offers an abstraction layer, so developers don't have to bother about implementations; Hibernate handles these tasks internally, such as connecting to databases and creating queries to carry out CRUD operations, among other things. Persistence logic development is done with it. Persistence logic r
Read more

Java - Blowfish Encryption and decryption Example

Image
Blowfish is an encryption method developed by Bruce Schneier in 1993 as an alternative to the DES encryption method. It is significantly faster than DES and provides good encryption speed, although no effective cryptanalysis technique has been found to date. It is one of the first secure block ciphers that is not protected by any patents and is therefore freely available for anyone to use. This is a symmetric block cipher algorithm. Block size: 64 bits Key size: variable size from 32 to 448 bits number of subsections: 18 [P-array] number of rounds: 16 number of substitution blocks: 4 [each with 512 records of 32 bits each] develop  Example 1: Encryption and decryption using Blowfish import java.io.UnsupportedEncodingException; import java.nio.charset.Charset; import java.security.InvalidKeyException; import java.security.NoSuchAlgorithmException; import java.util.Base64; import javax.crypto.BadPaddingException; import javax.crypto.Cipher; import javax.crypto.IllegalBlockSizeExc
Read more

Spring boot video streaming example-HTML5

Image
Hello everyone, Today we will learn how to stream MP4 video using Spring Boot and Spring Web Flux.  The Source code download link is provided at the end of this post. New, Quarkus Practice User Interface   Project Structure: G radle(build.gradle) plugins { id 'org.springframework.boot' version '2.5.4' id 'io.spring.dependency-management' version '1.0.11.RELEASE' id 'java' } group = 'com.knf.demo' version = '0.0.1-SNAPSHOT' sourceCompatibility = '11' repositories { mavenCentral() } dependencies { implementation 'org.springframework.boot:spring-boot-starter-webflux' testImplementation 'org.springframework.boot:spring-boot-starter-test' testImplementation 'io.projectreactor:reactor-test' } test { useJUnitPlatform() } Service (VideoStreamingService.java) package  com.knf.demo.service ; import org.springframework.beans.factory.annotation. Autowired ; import org.springframework
Read more

Google Cloud Storage + Spring Boot - File Upload, Download, and Delete

Image
In this section, we will learn  how to  create a simple spring boot application to perform different file operations such as upload, download, list, and delete files from the Google Cloud Storage. 1.  A little bit of Background Google Cloud Storage Cloud Storage is a managed service for storing unstructured data. Store any amount of data and retrieve it as often as you like. More Info - click here! Spring Boot Spring Boot makes it easy to create stand-alone, production-grade Spring-based Applications that you can "just run".  More Info - click here! 2. Create a GCP Project First, Sign into the Google console at  https://console.cloud.google.com . You can create a new project by first selecting the project dropdown in the top left and selecting " New Project ". Next, specify your GCP  Project name  and  Project ID . Then  Click on the " CREATE " button. Copy " Project ID " and keep it for future purposes. 3. Create a Google Cloud Storage bucket Fr
Read more