我看到一小部分生产用户随机报告了这个与使用 Xamarin.Android 加密/解密字符串相关的异常，但不幸的是我无法重现它。
什么可能导致这种情况和/或我如何重现异常以便找出修复/解决方法？
[CryptographicException: Bad PKCS7 padding. Invalid length 147.]
Mono.Security.Cryptography.SymmetricTransform.ThrowBadPaddingException(PaddingMode padding, Int32 length, Int32 position):0
Mono.Security.Cryptography.SymmetricTransform.FinalDecrypt(System.Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount):0
Mono.Security.Cryptography.SymmetricTransform.TransformFinalBlock(System.Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount):0
System.Security.Cryptography.CryptoStream.FlushFinalBlock():0
com.abc.mobile.shared.Security+PasswordEncoder.DecryptWithByteArray(System.String strText, System.String strEncrypt):0
编辑:这是我用来加密/解密的代码
private string EncryptWithByteArray(string inPassword, string inByteArray)
{
byte[] tmpKey = new byte[20];
tmpKey = System.Text.Encoding.UTF8.GetBytes(inByteArray.Substring(0, 8));
DESCryptoServiceProvider des = new DESCryptoServiceProvider();
byte[] inputArray = System.Text.Encoding.UTF8.GetBytes(inPassword);
MemoryStream ms = new MemoryStream();
CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(tmpKey, mInitializationVector), CryptoStreamMode.Write);
cs.Write(inputArray, 0, inputArray.Length);
cs.FlushFinalBlock();
return Convert.ToBase64String(ms.ToArray());
}
private string DecryptWithByteArray (string strText, string strEncrypt)
{
try
{
byte[] tmpKey = new byte[20];
tmpKey = System.Text.Encoding.UTF8.GetBytes (strEncrypt.Substring (0, 8));
DESCryptoServiceProvider des = new DESCryptoServiceProvider ();
Byte[] inputByteArray = Convert.FromBase64String (strText);
MemoryStream ms = new MemoryStream ();
CryptoStream cs = new CryptoStream (ms, des.CreateDecryptor (tmpKey, mInitializationVector), CryptoStreamMode.Write);
cs.Write (inputByteArray, 0, inputByteArray.Length);
try {
cs.FlushFinalBlock();
} catch (Exception ex) {
throw(ex);
}
System.Text.Encoding encoding = System.Text.Encoding.UTF8;
return encoding.GetString(ms.ToArray());
}
catch (Exception ex)
{
throw ex;
}
}
编辑 2:
加密 key 始终是本地设备 ID。这是我得到这个的方法:
TelephonyManager telephonyMgr = Application.Context.GetSystemService(Context.TelephonyService) as TelephonyManager;
string deviceId = telephonyMgr.DeviceId == null ? "UNAVAILABLE" : telephonyMgr.DeviceId;
这是一个如何调用的例子:
string mByteArray = GetDeviceId();
string mEncryptedString = EncryptWithByteArray(stringToEncrypt, mByteArray);
string mDecryptedString = DecryptWithByteArray(mEncryptedString, mByteArray);
最佳答案
您没有提供有关您的用例的详细信息，但我想说这是因为您在加密和解密操作期间没有使用相同的密码设置。对称密码要求您在数据加密和解密期间使用完全相同的设置/参数。例如，对于 AES CBC，您需要在两个设备上使用完全相同的 key 、IV、密码模式和填充。最好在代码中明确设置这些设置:
System.Security.Cryptography.RijndaelManaged aes = new System.Security.Cryptography.RijndaelManaged();
aes.Key = new byte[] { ... };
aes.IV = new byte[] { ... };
aes.Mode = CipherMode.CBC;
aes.Padding = PaddingMode.PKCS7;
如果您确定您使用的是相同的设置，那么您还应该考虑一些数据在网络传输过程中被损坏或更改的情况。
在提供一些代码 fragment 后进行编辑:
你提供的解密方法对我根本不起作用，所以我把你所有的样本放在一起，并将它们变成代码，它做的事情和你的一样，但使用 IMO 更简洁的方法。例如这段代码使用了更健壮的“ key 派生”(请密码专家们见谅)，它也通过了基本的代码分析。
您应该能够轻松地使用公共(public)方法来执行您需要的操作:
string plainData = "This information should be encrypted";
string encryptedData = EncryptStringified(plainData);
string decryptedData = DecryptStringified(encryptedData);
if (plainData != decryptedData)
throw new Exception("Decryption failed");
实现和私有(private)方法如下:
/// <summary>
/// Encrypts string with the key derived from device ID
/// </summary>
/// <returns>Base64 encoded encrypted data</returns>
/// <param name="stringToEncrypt">String to encrypt</param>
public string EncryptStringified(string stringToEncrypt)
{
if (stringToEncrypt == null)
throw new ArgumentNullException("stringToEncrypt");
byte[] key = DeviceIdToDesKey();
byte[] plainData = Encoding.UTF8.GetBytes(stringToEncrypt);
byte[] encryptedData = Encrypt(key, plainData);
return Convert.ToBase64String(encryptedData);
}
/// <summary>
/// Decrypts Base64 encoded data with the key derived from device ID
/// </summary>
/// <returns>Decrypted string</returns>
/// <param name="b64DataToDecrypt">Base64 encoded data to decrypt</param>
public string DecryptStringified(string b64DataToDecrypt)
{
if (b64DataToDecrypt == null)
throw new ArgumentNullException("b64DataToDecrypt");
byte[] key = DeviceIdToDesKey();
byte[] encryptedData = Convert.FromBase64String(b64DataToDecrypt);
byte[] decryptedData = Decrypt(key, encryptedData);
return Encoding.UTF8.GetString(decryptedData);
}
private byte[] DeviceIdToDesKey()
{
TelephonyManager telephonyMgr = Application.Context.GetSystemService(Context.TelephonyService) as TelephonyManager;
string deviceId = telephonyMgr.DeviceId ?? "UNAVAILABLE";
// Compute hash of device ID so we are sure enough bytes have been gathered for the key
byte[] bytes = null;
using (SHA1 sha1 = SHA1.Create())
bytes = sha1.ComputeHash(Encoding.UTF8.GetBytes(deviceId));
// Get last 8 bytes from device ID hash as a key
byte[] desKey = new byte[8];
Array.Copy(bytes, bytes.Length - desKey.Length, desKey, 0, desKey.Length);
return desKey;
}
private byte[] Encrypt(byte[] key, byte[] plainData)
{
if (key == null)
throw new ArgumentNullException("key");
if (plainData == null)
throw new ArgumentNullException("plainData");
using (DESCryptoServiceProvider desProvider = new DESCryptoServiceProvider())
{
if (!desProvider.ValidKeySize(key.Length * 8))
throw new CryptographicException("Key with invalid size has been specified");
desProvider.Key = key;
// desProvider.IV should be automatically filled with random bytes when DESCryptoServiceProvider instance is created
desProvider.Mode = CipherMode.CBC;
desProvider.Padding = PaddingMode.PKCS7;
using (MemoryStream encryptedStream = new MemoryStream())
{
// Write IV at the beginning of memory stream
encryptedStream.Write(desProvider.IV, 0, desProvider.IV.Length);
// Perform encryption and append encrypted data to the memory stream
using (ICryptoTransform encryptor = desProvider.CreateEncryptor())
{
byte[] encryptedData = encryptor.TransformFinalBlock(plainData, 0, plainData.Length);
encryptedStream.Write(encryptedData, 0, encryptedData.Length);
}
return encryptedStream.ToArray();
}
}
}
private byte[] Decrypt(byte[] key, byte[] encryptedData)
{
if (key == null)
throw new ArgumentNullException("key");
if (encryptedData == null)
throw new ArgumentNullException("encryptedData");
using (DESCryptoServiceProvider desProvider = new DESCryptoServiceProvider())
{
if (!desProvider.ValidKeySize(key.Length * 8))
throw new CryptographicException("Key with invalid size has been specified");
desProvider.Key = key;
if (encryptedData.Length <= desProvider.IV.Length)
throw new CryptographicException("Too short encrypted data has been specified");
// Read IV from the beginning of encrypted data
// Note: New byte array needs to be created because data written to desprovider.IV are ignored
byte[] iv = new byte[desProvider.IV.Length];
Array.Copy(encryptedData, 0, iv, 0, iv.Length);
desProvider.IV = iv;
desProvider.Mode = CipherMode.CBC;
desProvider.Padding = PaddingMode.PKCS7;
// Remove IV from the beginning of encrypted data and perform decryption
using (ICryptoTransform decryptor = desProvider.CreateDecryptor())
return decryptor.TransformFinalBlock(encryptedData, desProvider.IV.Length, encryptedData.Length - desProvider.IV.Length);
}
}
真的很难说出您的代码到底出了什么问题，因为您的解密方法对我根本不起作用 - 很可能是因为它在写入模式下使用 CryptoStream 进行解密，这对我来说似乎有点奇怪。
代码到此为止。现在让我们开始加密，它真的很弱。它更像是一种混淆，可以保护数据不被意外地以纯文本形式显示(有些人对同一事物使用 BASE64 编码)。造成这种情况的主要原因是相对较旧的加密算法和易于预测的加密 key 。据我所知，在同一设备上运行的每个应用程序都可以在没有任何特权的情况下读取设备 ID。这意味着任何应用程序都可以解密您的数据。当然，您的 SQLite 数据库可能只能由您的应用程序访问，但如果您移除 SD 卡或对手机进行 Root，则情况不再如此。为了使这更好一点，您可以要求用户提供密码，然后使用它来派生唯一的加密 key ，但这是完全不同的问题。无论如何，我不太确定你试图通过这种加密实现什么 - 即使它被认为是弱的，它也可能完全满足你的需求。
希望这对您有所帮助。
关于android - 加密异常 : Bad PKCS7 padding，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28103676/