Android Development

Here am going to explain how we can generate RSA KeyPair (PrivateKey and PublicKey) from AndroidKeyStore also how we can get retrieve these keys from the AndroidkeyStore.

Here I am having an object file SecureStore.kt, where I am going to show you how we can generate RSA KeyPair (PrivateKey and PublicKey) also How we can read PrivateKey from the AndroidKeyStore.

Generate RSA KeyPair

fun generateDeviceKeyPair(): KeyPair {

val keyGen = KeyPairGenerator.getInstance("RSA", provider)

keyGen.initialize(

KeyGenParameterSpec.Builder(

DEVICE_KEYPAIR_ALIAS,

KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT

).setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)

.setKeySize(4096)

.build()

)

return keyGen.generateKeyPair()

}

The above function generateDeviceKeyPair() will generate a new RSA KeyPair from AndroidKeyStore with a KeySize 4096.

Getting PrivateKey from AndroidKeyStore

fun getDevicePrivateKey() : PrivateKey?{

if(androidKs.containsAlias(DEVICE_KEYPAIR_ALIAS))

return androidKs.getKey(DEVICE_KEYPAIR_ALIAS, null) as PrivateKey

return null

}

The above function getDevicePrivateKey() will return the PrivateKey of the RSA KeyPair which we created before

Final Code

package com.b-mates.utils

import android.security.keystore.KeyGenParameterSpec

import android.security.keystore.KeyProperties

import java.security.KeyPair

import java.security.KeyPairGenerator

import java.security.KeyStore

import java.security.PrivateKey

object SecureStore {

private const val provider = "AndroidKeyStore"

private const val DEVICE_KEYPAIR_ALIAS = "DEVICE_KEYPAIR_ALIAS"

val androidKs = KeyStore.getInstance(provider).apply { load(null) }