Donal Rafferty Donal Rafferty - 4 months ago 19
Java Question

Android Decryption Error

I am trying to encrypt and decrypt Strings in my Android application but I keep getting an InvalidKeyException error.

Here is my code:

//Generate Keys method

public void generateKeys() {
Calendar cal = Calendar.getInstance();
Date now = cal.getTime();
cal.add(Calendar.YEAR, 25);
Date end = cal.getTime();

KeyPairGenerator kpg = null;
try {
kpg = KeyPairGenerator.getInstance("RSA", "AndroidKeyStore");
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (NoSuchProviderException e) {
e.printStackTrace();
}
try {
kpg.initialize(new KeyPairGeneratorSpec.Builder(context)
.setAlias(KEY_ALIAS)
.setStartDate(now)
.setEndDate(end)
.setSerialNumber(BigInteger.valueOf(1))
.setSubject(new X500Principal("CN=" + KEY_ALIAS))
.build());
} catch (InvalidAlgorithmParameterException e) {
e.printStackTrace();
}

KeyPair kp = kpg.generateKeyPair();

KeyStore ks = null;
try {
ks = KeyStore.getInstance("AndroidKeyStore");
ks.load(null);
Enumeration<String> aliases = ks.aliases();
} catch (KeyStoreException e) {
e.printStackTrace();
} catch (CertificateException e) {
e.printStackTrace();
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}

KeyStore.Entry entry = null;
try {
entry = ks.getEntry(KEY_ALIAS, null);
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
} catch (UnrecoverableEntryException e) {
e.printStackTrace();
} catch (KeyStoreException e) {
e.printStackTrace();
}
if (!(entry instanceof KeyStore.PrivateKeyEntry)) {
Log.e(LOG_TAG, "Not an instance of PrivateKeyEntry.");
}
else{
privKey = ((KeyStore.PrivateKeyEntry) entry).getPrivateKey();
pubKey = ((KeyStore.PrivateKeyEntry) entry).getCertificate().getPublicKey();
}

}


//Encrypt Method

private String encryptString(String value){
byte[] encodedBytes = null;
try {
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
cipher.init(Cipher.ENCRYPT_MODE, pubKey);
encodedBytes = cipher.doFinal(value.getBytes());
} catch (Exception e) {
e.printStackTrace();
}

return Base64.encodeToString(encodedBytes, Base64.DEFAULT);
}


//Decrypt Method

private String decryptString(String value){
byte[] decodedBytes = null;
try {
Cipher c = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
c.init(Cipher.DECRYPT_MODE, privKey);
decodedBytes = c.doFinal(Base64.decode(value, Base64.DEFAULT));
} catch (Exception e) {
e.printStackTrace();
Log.e("Error", "Error = " + e);
return "SECURE_FAILURE";
}

return new String(decodedBytes);
}


//Test Code

generateKeys();
String encrypted = encryptString("Hello World");
Log.e("Encrypt", "encrypted = " + encrypted);
String decrypted = decryptString(encrypted);
Log.e("Decrypt", "decrypted = " + decrypted);


It looks like the encryption works OK as it prints out something like this:


encrypted =
SbA2iWWKQbDL7NTA9xvtjD/viYDdpx9fLRYTSZ8UQzdBy3QLqzkswBY21ErH7FPza3vZys4E4PZw
uxaGkRz0aC0FLqsYlbpcJernGm5+D5lRcBOaZmgkNY9pMf0YP75cBbcJdcmb1rDaH40nCRDnEoXv
rGESJRqT6p0NMzlZqdd9KO3tqfExwgservAWxPNtRDBbMgE4I/09418jM5Ock5eayfOuv/STwEy6
Ecd56UjFH63h+gP6ed2aMDhBVeExMxvdloY+VnsAxS5Dkoc2GdaljtjRuPK48HQASoJK8EwAMNpz


But when I try to decrypt I get the following error:


java.security.InvalidKeyException: Need RSA private or public key


I can't figure why I am getting this exception? Can anyone help?

Answer

Try using a different provider, like this:

Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidKeyStoreBCWorkaround");
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