Using AES encryption in .NET - CryptographicException saying the padding is invalid and cannot be removed
- by Jake Petroules
I wrote some AES encryption code in C# and I am having trouble getting it to encrypt and decrypt properly. If I enter "test" as the passphrase and "This data must be kept secret from everyone!" I receive the following exception:
System.Security.Cryptography.CryptographicException: Padding is invalid and cannot be removed.
at System.Security.Cryptography.RijndaelManagedTransform.DecryptData(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount, Byte[]& outputBuffer, Int32 outputOffset, PaddingMode paddingMode, Boolean fLast)
at System.Security.Cryptography.RijndaelManagedTransform.TransformFinalBlock(Byte[] inputBuffer, Int32 inputOffset, Int32 inputCount)
at System.Security.Cryptography.CryptoStream.FlushFinalBlock()
at System.Security.Cryptography.CryptoStream.Dispose(Boolean disposing)
at System.IO.Stream.Close()
at System.IO.Stream.Dispose()
...
And if I enter something less than 16 characters I get no output.
I believe I need some special handling in the encryption since AES is a block cipher, but I'm not sure exactly what that is, and I wasn't able to find any examples on the web showing how. Here is my code:
using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
public static class DatabaseCrypto
{
public static EncryptedData Encrypt(string password, string data)
{
return DatabaseCrypto.Transform(true, password, data, null, null) as EncryptedData;
}
public static string Decrypt(string password, EncryptedData data)
{
return DatabaseCrypto.Transform(false, password, data.DataString, data.SaltString, data.MACString) as string;
}
private static object Transform(bool encrypt, string password, string data, string saltString, string macString)
{
using (AesManaged aes = new AesManaged())
{
aes.Mode = CipherMode.CBC;
aes.Padding = PaddingMode.PKCS7;
int key_len = aes.KeySize / 8;
int iv_len = aes.BlockSize / 8;
const int salt_size = 8;
const int iterations = 8192;
byte[] salt = encrypt ? new Rfc2898DeriveBytes(string.Empty, salt_size).Salt : Convert.FromBase64String(saltString);
byte[] bc_key = new Rfc2898DeriveBytes("BLK" + password, salt, iterations).GetBytes(key_len);
byte[] iv = new Rfc2898DeriveBytes("IV" + password, salt, iterations).GetBytes(iv_len);
byte[] mac_key = new Rfc2898DeriveBytes("MAC" + password, salt, iterations).GetBytes(16);
aes.Key = bc_key;
aes.IV = iv;
byte[] rawData = encrypt ? Encoding.UTF8.GetBytes(data) : Convert.FromBase64String(data);
using (ICryptoTransform transform = encrypt ? aes.CreateEncryptor() : aes.CreateDecryptor())
using (MemoryStream memoryStream = encrypt ? new MemoryStream() : new MemoryStream(rawData))
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, transform, encrypt ? CryptoStreamMode.Write : CryptoStreamMode.Read))
{
if (encrypt)
{
cryptoStream.Write(rawData, 0, rawData.Length);
return new EncryptedData(salt, mac_key, memoryStream.ToArray());
}
else
{
byte[] originalData = new byte[rawData.Length];
int count = cryptoStream.Read(originalData, 0, originalData.Length);
return Encoding.UTF8.GetString(originalData, 0, count);
}
}
}
}
}
public class EncryptedData
{
public EncryptedData()
{
}
public EncryptedData(byte[] salt, byte[] mac, byte[] data)
{
this.Salt = salt;
this.MAC = mac;
this.Data = data;
}
public EncryptedData(string salt, string mac, string data)
{
this.SaltString = salt;
this.MACString = mac;
this.DataString = data;
}
public byte[] Salt
{
get;
set;
}
public string SaltString
{
get { return Convert.ToBase64String(this.Salt); }
set { this.Salt = Convert.FromBase64String(value); }
}
public byte[] MAC
{
get;
set;
}
public string MACString
{
get { return Convert.ToBase64String(this.MAC); }
set { this.MAC = Convert.FromBase64String(value); }
}
public byte[] Data
{
get;
set;
}
public string DataString
{
get { return Convert.ToBase64String(this.Data); }
set { this.Data = Convert.FromBase64String(value); }
}
}
static void ReadTest()
{
Console.WriteLine("Enter password: ");
string password = Console.ReadLine();
using (StreamReader reader = new StreamReader("aes.cs.txt"))
{
EncryptedData enc = new EncryptedData();
enc.SaltString = reader.ReadLine();
enc.MACString = reader.ReadLine();
enc.DataString = reader.ReadLine();
Console.WriteLine("The decrypted data was: " + DatabaseCrypto.Decrypt(password, enc));
}
}
static void WriteTest()
{
Console.WriteLine("Enter data: ");
string data = Console.ReadLine();
Console.WriteLine("Enter password: ");
string password = Console.ReadLine();
EncryptedData enc = DatabaseCrypto.Encrypt(password, data);
using (StreamWriter stream = new StreamWriter("aes.cs.txt"))
{
stream.WriteLine(enc.SaltString);
stream.WriteLine(enc.MACString);
stream.WriteLine(enc.DataString);
Console.WriteLine("The encrypted data was: " + enc.DataString);
}
}
