RSA + AES Double Layer Encryption in Kotlin

Explanation:

1. User: Initiates the process by generating keys and providing data.
2. RSA Public/Private Keys: Represent the generation of RSA public and private keys.
3. AES Secret Key: Represents the AES key generation.
4. Data: Represents the data to be encrypted.
5. RSA Encryption/Decryption: Represents the RSA encryption and decryption processes.
6. AES Encryption/Decryption: Represents the AES encryption and decryption processes.

Steps:

• Encryption: Data is first encrypted using AES, and the AES-encrypted data is then encrypted with RSA.
• Decryption: The process is reversed: RSA-decrypted data is then decrypted using the AES key.

Here's an example of how you could implement RSA and AES double-layer encryption and decryption in Kotlin:

Dependencies:

First, make sure you have the required dependencies in your build.gradle file for encryption libraries:

dependencies {
    implementation 'org.bouncycastle:bcprov-jdk15on:1.70'
    implementation 'org.bouncycastle:bcpkix-jdk15on:1.70'
}

RSA + AES Double Layer Encryption/Decryption in Kotlin:

Step 1: Import required libraries

import java.security.KeyFactory
import java.security.KeyPair
import java.security.KeyPairGenerator
import java.security.PrivateKey
import java.security.PublicKey
import javax.crypto.Cipher
import javax.crypto.KeyGenerator
import javax.crypto.SecretKey
import javax.crypto.CipherInputStream
import javax.crypto.CipherOutputStream
import java.util.Base64

Step 2: RSA Encryption/Decryption functions

fun generateRSAKeys(): KeyPair {
    val keyPairGenerator = KeyPairGenerator.getInstance("RSA")
    keyPairGenerator.initialize(2048)
    return keyPairGenerator.generateKeyPair()
}

fun rsaEncrypt(publicKey: PublicKey, data: String): String {
    val cipher = Cipher.getInstance("RSA")
    cipher.init(Cipher.ENCRYPT_MODE, publicKey)
    val encryptedBytes = cipher.doFinal(data.toByteArray())
    return Base64.getEncoder().encodeToString(encryptedBytes)
}

fun rsaDecrypt(privateKey: PrivateKey, encryptedData: String): String {
    val cipher = Cipher.getInstance("RSA")
    cipher.init(Cipher.DECRYPT_MODE, privateKey)
    val decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedData))
    return String(decryptedBytes)
}

Step 3: AES Encryption/Decryption functions

fun generateAESKey(): SecretKey {
    val keyGenerator = KeyGenerator.getInstance("AES")
    keyGenerator.init(256) // 256-bit AES
    return keyGenerator.generateKey()
}

fun aesEncrypt(secretKey: SecretKey, data: String): String {
    val cipher = Cipher.getInstance("AES")
    cipher.init(Cipher.ENCRYPT_MODE, secretKey)
    val encryptedBytes = cipher.doFinal(data.toByteArray())
    return Base64.getEncoder().encodeToString(encryptedBytes)
}

fun aesDecrypt(secretKey: SecretKey, encryptedData: String): String {
    val cipher = Cipher.getInstance("AES")
    cipher.init(Cipher.DECRYPT_MODE, secretKey)
    val decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedData))
    return String(decryptedBytes)
}

Step 4: Combine RSA + AES for double-layer encryption

fun encryptDataWithDoubleLayer(data: String, publicKey: PublicKey, secretKey: SecretKey): String {
    // First layer: AES Encryption
    val aesEncryptedData = aesEncrypt(secretKey, data)

    // Second layer: RSA Encryption of the AES-encrypted data
    return rsaEncrypt(publicKey, aesEncryptedData)
}

fun decryptDataWithDoubleLayer(encryptedData: String, privateKey: PrivateKey, secretKey: SecretKey): String {
    // First layer: RSA Decryption
    val rsaDecryptedData = rsaDecrypt(privateKey, encryptedData)

    // Second layer: AES Decryption of the RSA-decrypted data
    return aesDecrypt(secretKey, rsaDecryptedData)
}

Step 5: Example usage

fun main() {
    // Generate RSA keys
    val keyPair = generateRSAKeys()
    val publicKey = keyPair.public
    val privateKey = keyPair.private

    // Generate AES key
    val secretKey = generateAESKey()

    // Data to be encrypted
    val data = "This is a secret message"

    // Encrypt data with double-layer encryption
    val encryptedData = encryptDataWithDoubleLayer(data, publicKey, secretKey)
    println("Encrypted Data: $encryptedData")

    // Decrypt the data
    val decryptedData = decryptDataWithDoubleLayer(encryptedData, privateKey, secretKey)
    println("Decrypted Data: $decryptedData")
}

Explanation:

1. RSA Key Pair Generation:

   • You generate a public and private key pair using RSA.

2. AES Key Generation:

   • An AES key is generated for symmetric encryption.

3. Double Layer Encryption:

   • First, the data is encrypted using AES.
   • Then, the AES-encrypted data is encrypted again using RSA.

4. Double Layer Decryption:

   • The RSA-encrypted data is first decrypted using the private RSA key.
   • The decrypted data is then decrypted using the AES key.

This example demonstrates how to use both RSA and AES for double-layer encryption in Kotlin!