bitwarden-android/src/Android/Services/KeyStoreBackedStorageService.cs

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using System.IO;
using Java.Security;
using Javax.Crypto;
using Android.OS;
using Bit.App.Abstractions;
using System;
using Android.Security;
using Javax.Security.Auth.X500;
using Java.Math;
using Android.Security.Keystore;
using Android.App;
using Plugin.Settings.Abstractions;
using System.Collections.Generic;
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using Java.Util;
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namespace Bit.Android.Services
{
public class KeyStoreBackedStorageService : ISecureStorageService
{
private const string AndroidKeyStore = "AndroidKeyStore";
private const string AndroidOpenSSL = "AndroidOpenSSL";
private const string KeyAlias = "bitwardenKey";
private const string SettingsFormat = "ksSecured:{0}";
private const string RsaMode = "RSA/ECB/PKCS1Padding";
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private const string AesKey = "ksSecured:aesKeyForService";
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private readonly ISettings _settings;
private readonly KeyStore _keyStore;
private readonly bool _oldAndroid = Build.VERSION.SdkInt < BuildVersionCodes.M;
private readonly ISecureStorageService _oldKeyStorageService;
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public KeyStoreBackedStorageService(ISettings settings)
{
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_oldKeyStorageService = new KeyStoreStorageService(new char[] { });
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_settings = settings;
_keyStore = KeyStore.GetInstance(AndroidKeyStore);
_keyStore.Load(null);
GenerateRsaKey();
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GenerateAesKey();
}
public bool Contains(string key)
{
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return _settings.Contains(string.Format(SettingsFormat, key)) || _oldKeyStorageService.Contains(key);
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}
public void Delete(string key)
{
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CleanupOldKeyStore(key);
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_settings.Remove(string.Format(SettingsFormat, key));
}
public byte[] Retrieve(string key)
{
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var formattedKey = string.Format(SettingsFormat, key);
if(!_settings.Contains(formattedKey))
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{
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return TryGetAndMigrateFromOldKeyStore(key);
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}
var cs = _settings.GetValueOrDefault<string>(formattedKey);
if(string.IsNullOrWhiteSpace(cs))
{
return null;
}
var aesKey = GetAesKey();
if(aesKey == null)
{
return null;
}
try
{
return App.Utilities.Crypto.AesCbcDecrypt(new App.Models.CipherString(cs), aesKey);
}
catch
{
Console.WriteLine("Failed to decrypt from secure storage.");
_settings.Remove(formattedKey);
return null;
}
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}
public void Store(string key, byte[] dataBytes)
{
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var formattedKey = string.Format(SettingsFormat, key);
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CleanupOldKeyStore(key);
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if(dataBytes == null)
{
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_settings.Remove(formattedKey);
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return;
}
var aesKey = GetAesKey();
if(aesKey == null)
{
return;
}
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try
{
var cipherString = App.Utilities.Crypto.AesCbcEncrypt(dataBytes, aesKey);
_settings.AddOrUpdateValue(formattedKey, cipherString.EncryptedString);
}
catch
{
Console.WriteLine("Failed to encrypt to secure storage.");
}
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}
private void GenerateRsaKey()
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{
if(_keyStore.ContainsAlias(KeyAlias))
{
return;
}
var start = Calendar.Instance;
var end = Calendar.Instance;
end.Add(CalendarField.Year, 30);
var subject = new X500Principal($"CN={KeyAlias}");
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if(_oldAndroid)
{
var gen = KeyPairGenerator.GetInstance(KeyProperties.KeyAlgorithmRsa, AndroidKeyStore);
var spec = new KeyPairGeneratorSpec.Builder(Application.Context)
.SetAlias(KeyAlias)
.SetSubject(subject)
.SetSerialNumber(BigInteger.Ten)
.SetStartDate(start.Time)
.SetEndDate(end.Time)
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.Build();
gen.Initialize(spec);
gen.GenerateKeyPair();
}
else
{
var gen = KeyGenerator.GetInstance(KeyProperties.KeyAlgorithmRsa, AndroidKeyStore);
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var spec = new KeyGenParameterSpec.Builder(KeyAlias, KeyStorePurpose.Decrypt | KeyStorePurpose.Encrypt)
.SetCertificateSubject(subject)
.SetCertificateSerialNumber(BigInteger.Ten)
.SetKeyValidityStart(start.Time)
.SetKeyValidityEnd(end.Time)
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.Build();
gen.Init(spec);
gen.GenerateKey();
}
}
private KeyStore.PrivateKeyEntry GetRsaKeyEntry()
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{
return _keyStore.GetEntry(KeyAlias, null) as KeyStore.PrivateKeyEntry;
}
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private void GenerateAesKey()
{
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if(_settings.Contains(AesKey))
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{
return;
}
var key = App.Utilities.Crypto.RandomBytes(512 / 8);
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var encKey = RsaEncrypt(key);
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_settings.AddOrUpdateValue(AesKey, Convert.ToBase64String(encKey));
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}
private App.Models.SymmetricCryptoKey GetAesKey()
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{
try
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{
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var encKey = _settings.GetValueOrDefault<string>(AesKey);
if(encKey == null)
{
return null;
}
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var encKeyBytes = Convert.FromBase64String(encKey);
var key = RsaDecrypt(encKeyBytes);
return new App.Models.SymmetricCryptoKey(key);
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}
catch
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{
Console.WriteLine("Cannot get AesKey.");
_keyStore.DeleteEntry(KeyAlias);
_settings.Remove(AesKey);
return null;
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}
}
private byte[] RsaEncrypt(byte[] input)
{
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var entry = GetRsaKeyEntry();
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var inputCipher = Cipher.GetInstance(RsaMode, AndroidOpenSSL);
inputCipher.Init(CipherMode.EncryptMode, entry.Certificate.PublicKey);
var outputStream = new MemoryStream();
var cipherStream = new CipherOutputStream(outputStream, inputCipher);
cipherStream.Write(input);
cipherStream.Close();
var vals = outputStream.ToArray();
outputStream.Close();
return vals;
}
private byte[] RsaDecrypt(byte[] encInput)
{
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var entry = GetRsaKeyEntry();
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var outputCipher = Cipher.GetInstance(RsaMode, AndroidOpenSSL);
outputCipher.Init(CipherMode.DecryptMode, entry.PrivateKey);
var inputStream = new MemoryStream(encInput);
var cipherStream = new CipherInputStream(inputStream, outputCipher);
var values = new List<byte>();
int nextByte;
while((nextByte = cipherStream.Read()) != -1)
{
values.Add((byte)nextByte);
}
inputStream.Close();
cipherStream.Close();
var bytes = new byte[values.Count];
for(var i = 0; i < bytes.Length; i++)
{
bytes[i] = values[i];
}
return bytes;
}
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private byte[] TryGetAndMigrateFromOldKeyStore(string key)
{
if(_oldKeyStorageService.Contains(key))
{
var value = _oldKeyStorageService.Retrieve(key);
Store(key, value);
_oldKeyStorageService.Delete(key);
return value;
}
return null;
}
private void CleanupOldKeyStore(string key)
{
if(_oldKeyStorageService.Contains(key))
{
_oldKeyStorageService.Delete(key);
}
}
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}
}