Created
January 29, 2018 09:05
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Android Decryptor (Helper class)
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class Decryptor(private val storage: SharedPreferences) { | |
private val ANDROID_KEY_STORE = "AndroidKeyStore" | |
private val TRANSFORMATION = "AES/GCM/NoPadding" | |
private var keyStore: KeyStore? = null | |
init { | |
initKeyStore() | |
} | |
@Throws(Exception::class) | |
private fun initKeyStore() { | |
keyStore = KeyStore.getInstance(ANDROID_KEY_STORE) | |
keyStore!!.load(null) | |
} | |
@Throws(Exception::class) | |
fun decryptDataWithAES(alias: String): String { | |
var alias = alias | |
alias = alias + "_AES" | |
val base64InitVector = storage.getString(alias + "_initVector", null) | |
val base64Encryption = storage.getString(alias + "_encryption", null) | |
if (TextUtils.isEmpty(base64InitVector) || TextUtils.isEmpty(base64Encryption)) | |
throw NullPointerException("Not found initialization vector or encryption data for specified alias") | |
val encryptionIv = Base64.decode(base64InitVector, Base64.NO_WRAP) | |
val encryptedData = Base64.decode(base64Encryption, Base64.NO_WRAP) | |
Log.d("AndroidKeyStore", "encrypted data: " + Arrays.toString(encryptedData) + " encrypted iv: " | |
+ Arrays.toString(encryptionIv)) | |
val cipher = Cipher.getInstance(TRANSFORMATION) | |
val spec = GCMParameterSpec(128, encryptionIv) | |
cipher.init(Cipher.DECRYPT_MODE, getSecretKey(alias), spec) | |
return String(cipher.doFinal(encryptedData), StandardCharsets.UTF_8) | |
} | |
fun decryptDataWithRSA(alias: String): String { | |
var alias = alias | |
alias = alias + "_RSA" | |
val base64PublicKey = storage.getString(alias + "_publicKey", null) | |
val base64Encryption = storage.getString(alias + "_encryption", null) | |
val keyBytes = Base64.decode(base64PublicKey, Base64.NO_WRAP) | |
val encryption = Base64.decode(base64Encryption, Base64.NO_WRAP) | |
val spec = X509EncodedKeySpec(keyBytes) | |
var decodedBytes = ByteArray(0) | |
try { | |
val keyFactory = KeyFactory.getInstance(KeyProperties.KEY_ALGORITHM_RSA) | |
val key = keyFactory.generatePublic(spec) | |
val cipher = Cipher.getInstance(KeyProperties.KEY_ALGORITHM_RSA) | |
cipher.init(Cipher.DECRYPT_MODE, key) | |
decodedBytes = cipher.doFinal(encryption) | |
} catch (e: Exception) { | |
e.printStackTrace() | |
} | |
return String(decodedBytes, StandardCharsets.UTF_8) | |
} | |
@Throws(Exception::class) | |
private fun getSecretKey(alias: String): SecretKey { | |
return (keyStore!!.getEntry(alias, null) as KeyStore.SecretKeyEntry).getSecretKey() | |
} | |
} |
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