How to read and write encrypted files in Kotlin

How to read and write encrypted files in Kotlin.

Here's a step-by-step tutorial on how to read and write encrypted files in Kotlin.

Step 1: Import the necessary libraries

To work with encrypted files in Kotlin, you'll need to import the following libraries:

import java.io.*
import javax.crypto.*
import javax.crypto.spec.SecretKeySpec
import java.security.*
import java.util.Base64

Step 2: Generate a secret key

A secret key is required to encrypt and decrypt files. You can generate a secret key using the following function:

fun generateKey(): SecretKey {
    val keyGen = KeyGenerator.getInstance("AES")
    keyGen.init(128)
    return keyGen.generateKey()
}

Step 3: Encrypt a file

To encrypt a file, you need to read the file content and apply the encryption algorithm using the secret key. Here's an example of how to encrypt a file:

fun encryptFile(inputFilePath: String, outputFilePath: String, secretKey: SecretKey) {
    val cipher = Cipher.getInstance("AES")
    cipher.init(Cipher.ENCRYPT_MODE, secretKey)

    val inputFile = File(inputFilePath)
    val outputFile = File(outputFilePath)

    val inputStream = FileInputStream(inputFile)
    val outputStream = FileOutputStream(outputFile)

    val inputBytes = ByteArray(inputFile.length().toInt())
    inputStream.read(inputBytes)

    val outputBytes = cipher.doFinal(inputBytes)

    outputStream.write(outputBytes)

    inputStream.close()
    outputStream.close()
}

Step 4: Decrypt a file

To decrypt a file, you need to read the encrypted file content and apply the decryption algorithm using the secret key. Here's an example of how to decrypt a file:

fun decryptFile(inputFilePath: String, outputFilePath: String, secretKey: SecretKey) {
    val cipher = Cipher.getInstance("AES")
    cipher.init(Cipher.DECRYPT_MODE, secretKey)

    val inputFile = File(inputFilePath)
    val outputFile = File(outputFilePath)

    val inputStream = FileInputStream(inputFile)
    val outputStream = FileOutputStream(outputFile)

    val inputBytes = ByteArray(inputFile.length().toInt())
    inputStream.read(inputBytes)

    val outputBytes = cipher.doFinal(inputBytes)

    outputStream.write(outputBytes)

    inputStream.close()
    outputStream.close()
}

Step 5: Usage example

Here's an example of how to use the encryptFile and decryptFile functions:

fun main() {
    val inputFilePath = "input.txt"
    val outputFilePath = "output.txt"

    // Generate a secret key
    val secretKey = generateKey()

    // Encrypt the file
    encryptFile(inputFilePath, outputFilePath, secretKey)
    println("File encrypted successfully!")

    // Decrypt the file
    decryptFile(outputFilePath, "decrypted.txt", secretKey)
    println("File decrypted successfully!")
}

In this example, "input.txt" is the file you want to encrypt, and "output.txt" is the encrypted file. The decrypted file will be saved as "decrypted.txt".

That's it! You now have a step-by-step guide on how to read and write encrypted files in Kotlin. You can use these functions to secure your file contents.