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C# Aes Encryption IV and Key Size

I am quite new to AES Encryption and therefore have some question about IV and Key
The code I have written works, i can both encrypt and decrypt a String
Just for fun i tried to go on a Website https://www.devglan.com/online-tools/aes-encryption-decryption
And tried to see if the website can decrypt, if i give the same key and IV. but I ran into an error
The website said "Length of secret key should be 32 for 256 bits key size"
and "Length of initialization vector must be 16 with AES."
Is there anything I have done wrong?
static void Main(string[] args)
{
byte[] key = GenerateRandomByteArray(32);
Console.WriteLine($"Key: {Convert.ToBase64String(key)}");
byte[] encrypted = EncryptMessage("test message", key);
Console.WriteLine($"Encrypted : {Convert.ToBase64String(encrypted)}");
string decrypted = DecryptMessage(encrypted, key);
Console.WriteLine($"Decrypted: {decrypted}");
Console.ReadLine();
}
private static byte[] GenerateRandomByteArray(int size)
{
using (RandomNumberGenerator rng = RandomNumberGenerator.Create())
{
byte[] buffer = new byte[size];
rng.GetBytes(buffer);
return buffer;
}
}
public static byte[] EncryptMessage(string mess, byte[] secretkey)
{
byte[] encrypted;
using (Aes aes = Aes.Create())
{
aes.Key = secretkey;
//Generates a IV with 16 random bytes
aes.IV = GenerateRandomByteArray(16);
Console.WriteLine($"IV: {Convert.ToBase64String(aes.IV)}");
// Create an encryptor to perform the stream transform.
ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Writes the IV, so when we decrypt we can get the first 16 bytes where IV i located
msEncrypt.Write(aes.IV, 0, aes.IV.Length);
//Write all data to the stream.
swEncrypt.Write(mess);
}
encrypted = msEncrypt.ToArray();
}
}
}
// Return the encrypted bytes from the memory stream.
return encrypted;
}
public static string DecryptMessage(byte[] mess, byte[] key)
{
string plaintext = null;
// Create an Aes object
using (Aes aes = Aes.Create())
{
//Sets the AES key
aes.Key = key;
using (MemoryStream msDecrypt = new MemoryStream(mess))
{
//Reads the first 16 bytes from the message which is where the IV i stored
byte[] iv = new byte[aes.BlockSize / 8];
msDecrypt.Read(iv, 0, iv.Length);
//Sets the IV
aes.IV = iv;
// Create a decryptor to perform the stream transform.
ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
// Create the streams used for decryption.
//using (MemoryStream msDecrypt = new MemoryStream(mess))
//{
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
}
}
}
return plaintext;
}
Is i remember right GenerateRandomByteArray(32) is 256 bits for Key
And GenerateRandomByteArray(16) is 128 bits for IV
Output from Console:
Key: 3dmQoxqrAyoc5kMKQIQl8Hp4UVVCE8B64S19iNZOQRY=
IV: kO1nKUs08c/8mrlbHj3/xQ==
Encrypted : kO1nKUs08c/8mrlbHj3/xR43S5L3BJ5Ueg01xngw93I=
Decrypted: test message

IV of first 16 bytes gets remove from decrypted string? C#/Python3

I was wondering why the first 16 bytes of all my strings being encrypted, then when being decrypted are missing and how to fix this if it is possible. I am encrypting like so in c#
public static string EncryptString(string b_key, string plainText)
{
byte[] iv = new byte[16];
byte[] array;
using (Aes aes = Aes.Create())
{
aes.Key = Convert.FromBase64String(b_key);
aes.IV = iv;
ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
using (MemoryStream memoryStream = new MemoryStream())
{
using (CryptoStream cryptoStream = new CryptoStream((Stream)memoryStream, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter streamWriter = new StreamWriter((Stream)cryptoStream))
{
streamWriter.Write(plainText);
}
array = memoryStream.ToArray();
}
}
}
return Convert.ToBase64String(array);
}
and decrypting in python3 like so
enc = base64.b64decode(self.text)
iv = enc[:16]
cipher = AES.new(self.key, AES.MODE_CBC, iv)
plain_text = cipher.decrypt(enc[16:])
plain_text = self.dePKCS7_padding(plain_text)
return plain_text
Is readding the first 16 bytes possible? or must be used for encryption. I also want it to crypto safe but the first 16 bytes are kind of important is this possible? anyway to get around this in either c# or python3?

Based on the discussion in comments and inputs from #MichaelFehr and #user9014097, I came up with the following code.
In this code the IV of AES will have random value created when AES.Create() is called. And the same will be used in the outcome of the encrypted value.
The decryptString method will capture the iv value from the incoming encrypted string and assign it to AES while decrypting the string.
public static string EncryptString(string b_key, string plainText)
{
byte[] array;
using (Aes aes = Aes.Create())
{
aes.Key = Convert.FromBase64String(b_key);
ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
using (MemoryStream memoryStream = new MemoryStream())
{
// Adding aes.IV to the stream's start.
memoryStream.Write(aes.IV);
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter streamWriter = new StreamWriter(cryptoStream))
{
streamWriter.Write(plainText);
}
}
array = memoryStream.ToArray();
}
}
// The final encrypted outcome will be aes.IV+encryptedtext.
return Convert.ToBase64String(array);
}
public static string DecryptString(string key, string cipherText)
{
//input is iv+encrypted text, convert them to byte array.
byte[] buffer = Convert.FromBase64String(cipherText);
// byte array for iv
byte[] iv = new byte[16];
// byte array for rest of the cipher text.
byte[] cipherBuffer = new byte[buffer.Length - 16];
// copy first 16 bytes from the cipher text to iv.
Buffer.BlockCopy(buffer, 0, iv, 0, 16);
// copy rest of the cipher text to the cipher buffer to be decrypted.
Buffer.BlockCopy(buffer, 16, cipherBuffer, 0, buffer.Length - 16);
using (Aes aes = Aes.Create())
{
aes.Key = Convert.FromBase64String(key);
aes.IV = iv;
ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
using (MemoryStream memoryStream = new MemoryStream(cipherBuffer))
{
using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
{
using (StreamReader streamReader = new StreamReader(cryptoStream))
{
return streamReader.ReadToEnd();
}
}
}
}
}
I have following assumption in writing above code.
Length of IV is 16.
Python code (shared above) does not need split the input text based on some specific character. It takes first 16 bytes as IV value and rest of the bytes as cipher text.
I was able to encrypt and decrypt values successfully in C# using above methods.
I was not able to decrypt the value in python code as I have little to no idea on how to work with python.
You can test the outcome of above encryption in python to decrypt it. Let me know if it doesn't work as expected.
I hope this will help you solve your issue.

C# AES encryption behaving strangely

I am trying to encrypt a string in C# using this piece of code:
public static string AesEncrypt(string plainText, byte[] Key, byte[] IV)
{
// Create an Aes object with the specified key and IV
using Aes aesAlg = Aes.Create();
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create an encryptor to perform the stream transform
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for encryption
using MemoryStream msEncrypt = new MemoryStream();
using CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write);
using StreamWriter swEncrypt = new StreamWriter(csEncrypt);
// Write all data to the stream
swEncrypt.Write(plainText);
return Encoding.UTF8.GetString(msEncrypt.ToArray());
}
This is largely based on the sample found here: example.
However, the results are somewhat strange and unpredictable - one time I ran the code and got some string as a result, the other time the resulting string (and the msEncrypt stream) were empty, and one time the application even froze. I don't understand what the problem is.
Edit:
I just ran the code again, on this line:
aesAlg.Key = Key;
something strange happened, I got this error:
Here is how I actually call this method:
public static class Authentication
{
...
private static readonly AesEncryption aes = new AesEncryption();
public static string GenerateToken()
{
AuthenticationData data = new AuthenticationData()
{
// some data
};
string serialized = JsonConvert.SerializeObject(data);
return AesEncryption.AesEncrypt(serialized, aes.Key, aes.IV);
}
}

Maybe some problem with buffers and flushing the streams.
Try to using scope just swEncript before msEncript.ToArray()
public static string AesEncrypt(string plainText, byte[] Key, byte[] IV)
{
// Create an Aes object with the specified key and IV
using Aes aesAlg = Aes.Create();
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create an encryptor to perform the stream transform
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for encryption
using MemoryStream msEncrypt = new MemoryStream();
using CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write);
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt)) {
// Write all data to the stream
swEncrypt.Write(plainText);
}
return Encoding.UTF8.GetString(msEncrypt.ToArray());
}

There are two problems with this code.
The SteamWriter isn't closed before the stream is used. There's no call to StreamWriter.Flush either. StreamWriter uses a buffer internally and writes it out to the
stream when it's full.
The StreamWriter doesn't know it's writing to
a MemoryStream, all streams look the same to it. Given how small the
plaintext is in most examples, no flushing will occur before trying
to read the data from the memory stream.
UTF8 supports only a limited set of byte sequences. Good encryption algorithms though generate essentially random sequences. Some of them won't correspond to any valid UTF8 sequence. One of the most common way to encode binary data as text is to use Base64 encoding. That's what most encryption or hashing samples show.
The code should change to something like :
public static string AesEncrypt(string plainText, byte[] Key, byte[] IV)
{
// Create an Aes object with the specified key and IV
using Aes aesAlg = Aes.Create();
aesAlg.Key = Key;
aesAlg.IV = IV;
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
using MemoryStream msEncrypt = new MemoryStream();
using CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write);
using StreamWriter swEncrypt = new StreamWriter(csEncrypt);
swEncrypt.Write(plainText);
//CHANGES HERE
swEncrypt.Flush();
return Convert.ToBase64String(msEncrypt.ToArray());
}
The sample doesn't suffer from this problem because it uses explicit using blocks, so the writer is closed before the memory stream is used :
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
}
}
Neither Visual Studio nor Resharper would suggest using a using statement in this case, as the writer is clearly closed in the innermost block.
Don't mix using styles
You can mix using blocks and statements, eg :
using MemoryStream msEncrypt = new MemoryStream();
using CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write);
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
Given the confusion caused already though, you probably shouldn't. The code isn't that much cleaner and it already caused a problem. Someone else looking at the same code in the future may get confused as well and use a bad refactoring

Maybe the key and IV pass in each time you call the AesEncrypt method were different.
For me it's working fine with the example.
static void Main(string[] args)
{
Aes aesAlg = Aes.Create();
AesEncrypt("Hello World", aesAlg.Key, aesAlg.IV);
AesEncrypt("Hello World", aesAlg.Key, aesAlg.IV);
AesEncrypt("Hello World", aesAlg.Key, aesAlg.IV);
AesEncrypt("Hello World", aesAlg.Key, aesAlg.IV);
AesEncrypt("Hello World", aesAlg.Key, aesAlg.IV);
Console.ReadKey();
}
public static string AesEncrypt(string plainText, byte[] Key, byte[] IV)
{
// Create an Aes object with the specified key and IV
using (Aes aesAlg = Aes.Create())
{
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create an encryptor to perform the stream transform
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
// Create the streams used for encryption
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
swEncrypt.Write(plainText);
}
Console.WriteLine(BitConverter.ToString(msEncrypt.ToArray()));
return Encoding.UTF8.GetString(msEncrypt.ToArray());
}
}
}
}

Padding is invalid and cannot be removed aes [duplicate]

Please suggest me where i need to update/refactor the code to get rid of exception. I am getting exception while I try to decrypt the encrypted string using following code.
Following line is throwing exception
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
public string EncryptAuthenticationTokenAes(string plainText)
{
byte[] encrypted;
// Create an AesManaged object
// with the specified key and IV.
using (AesManaged aesAlg = new AesManaged())
{
// Create a decrytor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, aesAlg.IV);
aesAlg.Padding = PaddingMode.None;
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
}
}
}
// Return the encrypted bytes from the memory stream.
return Convert.ToBase64String(encrypted);
}
public string DecryptPasswordAes(string encryptedString)
{
//Convert cipher text back to byte array
byte[] cipherText = Convert.FromBase64String(encryptedString);
// Declare the string used to hold
// the decrypted text.
string plaintext = null;
// Create an AesManaged object
// with the specified key and IV.
using (AesManaged aesAlg = new AesManaged())
{
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
aesAlg.Padding = PaddingMode.None;
// Create the streams used for decryption.
using (MemoryStream msDecrypt = new MemoryStream(cipherText))
{
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read))
{
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
// Read the decrypted bytes from the decrypting stream
// and place them in a string.
plaintext = srDecrypt.ReadToEnd();
}
}
}
}
return plaintext;
}

Pretty standard bug when using CryptoStream, you forgot to force it to encrypt the last bytes of the stream. It keeps bytes in an internal buffer until enough of them arrive to emit a block. You must force the last few bytes out. Fix:
using (var msEncrypt = new MemoryStream())
using (var csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
using (var swEncrypt = new StreamWriter(csEncrypt)) {
swEncrypt.Write(plainText);
csEncrypt.FlushFinalBlock();
encrypted = msEncrypt.ToArray();
}
You got the exception when decrypting it because encrypted is missing the final padding. The real problem is caused by the using statement, you wouldn't have this problem if you waited obtaining the encrypted bytes until after the CryptoStream is closed. But that doesn't work well because the using statement on the StreamWriter also closes the CryptoStream and the MemoryStream. Explicitly using FlushFinalBlock() is the best workaround.

"Padding is invalid and cannot be removed" using AesManaged

I'm trying to get simple encryption/decryption working with AesManaged, but I keep getting an exception when trying to close the decryption stream. The string here gets encrypted and decrypted correctly, and then I get the CryptographicException "Padding was invalid and cannot be removed" after Console.WriteLine prints the correct string.
Any ideas?
MemoryStream ms = new MemoryStream();
byte[] rawPlaintext = Encoding.Unicode.GetBytes("This is annoying!");
using (Aes aes = new AesManaged())
{
aes.Padding = PaddingMode.PKCS7;
aes.Key = new byte[128/8];
aes.IV = new byte[128/8];
using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(),
CryptoStreamMode.Write))
{
cs.Write(rawPlaintext, 0, rawPlaintext.Length);
cs.FlushFinalBlock();
}
ms = new MemoryStream(ms.GetBuffer());
using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(),
CryptoStreamMode.Read))
{
byte[] rawData = new byte[rawPlaintext.Length];
int len = cs.Read(rawData, 0, rawPlaintext.Length);
string s = Encoding.Unicode.GetString(rawData);
Console.WriteLine(s);
}
}

The trick is to use MemoryStream.ToArray().
I also changed your code so that it uses the CryptoStream to Write, in both encrypting and decrypting. And you don't need to call CryptoStream.FlushFinalBlock() explicitly, because you have it in a using() statement, and that flush will happen on Dispose(). The following works for me.
byte[] rawPlaintext = System.Text.Encoding.Unicode.GetBytes("This is all clear now!");
using (Aes aes = new AesManaged())
{
aes.Padding = PaddingMode.PKCS7;
aes.KeySize = 128; // in bits
aes.Key = new byte[128/8]; // 16 bytes for 128 bit encryption
aes.IV = new byte[128/8]; // AES needs a 16-byte IV
// Should set Key and IV here. Good approach: derive them from
// a password via Cryptography.Rfc2898DeriveBytes
byte[] cipherText= null;
byte[] plainText= null;
using (MemoryStream ms = new MemoryStream())
{
using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write))
{
cs.Write(rawPlaintext, 0, rawPlaintext.Length);
}
cipherText= ms.ToArray();
}
using (MemoryStream ms = new MemoryStream())
{
using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
{
cs.Write(cipherText, 0, cipherText.Length);
}
plainText = ms.ToArray();
}
string s = System.Text.Encoding.Unicode.GetString(plainText);
Console.WriteLine(s);
}
Also, I guess you know you will want to explicitly set the Mode of the AesManaged instance, and use System.Security.Cryptography.Rfc2898DeriveBytes to derive the Key and IV from a password and salt.
see also:
- AesManaged

This exception can be caused by a mismatch of any one of a number of encryption parameters.
I used the Security.Cryptography.Debug interface to trace all parameters used in the encrypt/decrypt methods.
Finally I found out that my problem was that I set the KeySize property after setting the Key causing the class to regenerate a random key and not using the key that I was initially set up.

For whats its worth, I'll document what I faced. I was trying to read the encryptor memory stream before the CryptoStream was closed. I was naive and I wasted a day debugging it.
public static byte[] Encrypt(byte[] buffer, byte[] sessionKey, out byte[] iv)
{
byte[] encrypted;
iv = null;
using (AesCryptoServiceProvider aesAlg = new AesCryptoServiceProvider { Mode = CipherMode.CBC, Padding = PaddingMode.PKCS7 })
{
aesAlg.Key = sessionKey;
iv = aesAlg.IV;
ICryptoTransform encryptor = aesAlg.CreateEncryptor(sessionKey, iv);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
csEncrypt.Write(buffer, 0, buffer.Length);
//This was not closing the cryptostream and only worked if I called FlushFinalBlock()
//encrypted = msEncrypt.ToArray();
}
encrypted = msEncrypt.ToArray();
return encrypted;
}
}
}
Moving the encryptor memory stream read after the cypto stream was closed solved the problem. As Cheeso mentioned. You don't need to call the FlushFinalBlock() if you're using the using block.

byte[] rawData = new
byte[rawPlaintext.Length];
You need to read the length of the buffer, that probably includes the necessary padding (IIRC, been a few years).

Nobody answered, that actually MemoryStream.GetBuffer returns the allocated buffer, not the real data in this buffer. In this case it returns 256-byte buffer, while it contains only 32 bytes of encrypted data.

As others have mentioned, this error can occur if the key/iv is not correctly initialized for decryption. In my case I need to copy key and iv from some larger buffer. Here's what I did wrong:
Does not work: (Padding is invalid and cannot be removed)
aes.Key = new byte[keySize];
Buffer.BlockCopy(someBuffer, keyOffset, aes.Key, 0, keySize);
aes.IV = new byte[ivSize];
Buffer.BlockCopy(someBuffer, ivOffset, aes.IV, 0, ivSize);
Works:
var key = new byte[keySize];
Buffer.BlockCopy(someBuffer, keyOffset, key, 0, keySize);
aes.Key = key;
var iv = new byte[ivSize];
Buffer.BlockCopy(someBuffer, ivOffset, iv, 0, ivSize);
aes.IV = iv;
The OP did not make this mistake, but this might be helpful for others seeing the same error.