RSA Android -> PC incompatible

Question

I am using RSA to encrypt a secret and then sending it to another host. The code works perfectly when it's done on PC -> PC traffic, but throws the following Exception for Android -> PC traffic.

The javax.crypto.BadPaddingException: Blocktype mismatch: 0
sun.security.rsa.RSAPadding.unpadV15(RSAPadding.java:332)
sun.security.rsa.RSAPadding.unpad(RSAPadding.java:272)
com.sun.crypto.provider.RSACipher.doFinal(RSACipher.java:354)
com.sun.crypto.provider.RSACipher.engineDoFinal(RSACipher.java:380)
javax.crypto.Cipher.doFinal(Cipher.java:2121)

What must I do to resolve this issue?

public byte[] encrypt(byte[] plaintext){
    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.ENCRYPT_MODE, publicKey);
    return cipher.doFinal(plaintext);
}

public byte[] decrypt(byte[] ciphertext){
    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.DECRYPT_MODE, privateKey);
    return cipher.doFinal(ciphertext);
}

Please provide a [minimal, complete, and verifiable example](http://stackoverflow.com/help/mcve). — Deacon, May 15 '15 at 18:17
Check if this answer solves the problem: http://stackoverflow.com/a/7760365/233596 — Jim Flood, May 15 '15 at 23:26

score 0 · Answer 1 · answered Feb 21 '21 at 06:04

import android.util.Base64
import java.security.KeyFactory
import java.security.spec.PKCS8EncodedKeySpec
import java.security.spec.X509EncodedKeySpec
import javax.crypto.Cipher

class RSAUtils {

val ALGORITHM = "RSA"
val PUBLIC_KEY = "" // Enter Public key here
val PRIVATE_KEY = "" // Enter Private key here

fun encrypt(text: String): String? {
    return encryptRSA(text)?.let { byteArrayToString(it) }
}

fun decrypt(text: String): String {
    return decryptRSA(stringToByteArray(text))
}

private fun encryptRSA(text: String): ByteArray? {
    var cipherText: ByteArray? = null
    try {
        // generate publicKey instance
        val byteKey = stringToByteArray(PUBLIC_KEY)
        val X509publicKey = X509EncodedKeySpec(byteKey)
        val kf: KeyFactory = KeyFactory.getInstance(ALGORITHM)
        val publicKey =  kf.generatePublic(X509publicKey)
        // get an RSA cipher object and print the provider
        val cipher: Cipher = Cipher.getInstance(ALGORITHM)
        // encrypt the plain text using the public key
        cipher.init(Cipher.ENCRYPT_MODE, publicKey)
        cipherText = cipher.doFinal(text.toByteArray())
    } catch (e: Exception) {
        e.printStackTrace()
    }
    return cipherText
}

private fun decryptRSA(text: ByteArray): String {
    var dectyptedText: ByteArray? = null
    try {
        // generate privateKey instance
        val byteKey = stringToByteArray(PRIVATE_KEY)
        val keySpec = PKCS8EncodedKeySpec(byteKey)
        val kf: KeyFactory = KeyFactory.getInstance(ALGORITHM)
        val privateKey = kf.generatePrivate(keySpec)
        // get an RSA cipher object and print the provider
        val cipher = Cipher.getInstance(ALGORITHM)
        // decrypt the text using the private key
        cipher.init(Cipher.DECRYPT_MODE, privateKey)
        dectyptedText = cipher.doFinal(text)
    } catch (ex: java.lang.Exception) {
        ex.printStackTrace()
    }
    return String(dectyptedText!!)
}

private fun stringToByteArray(text: String): ByteArray {
    return Base64.decode(text, Base64.DEFAULT)
}

private fun byteArrayToString(byteArray: ByteArray): String {
    return Base64.encodeToString(byteArray, Base64.DEFAULT)
}
}

https://github.com/kushalgupta0565/RSAEncryption - working fine in android, you just need to pass your PUBLIC/PRIVATE keys

RSA Android -> PC incompatible

1 Answers1