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how many bits generate aes.create() method in C#

I'm actually trying to make a secure file transfer program
and I would like to encrypt the sent file with the c# Aes.Create() method
but I wanted a AES-256 encryption and I'm not sure that the method does a 256 bits key
so I searched on Microsoft docs and many sketchy websites but I did find nothing.
So, how many bits generate Aes.Create()?
There is my code:
using System.Security.Cryptography;
namespace ConsoleApp1
{
internal class Program
{
public static void Main()
{
string original = File.ReadAllText(#"C:\SomePath");
// Create a new instance of the Aes
// class. This generates a new key and initialization
// vector (IV).
using (Aes myAes = Aes.Create())
{
// Encrypt the string to an array of bytes.
byte[] encrypted = EncryptStringToBytes_Aes(original, myAes.Key, myAes.IV);
// Decrypt the bytes to a string.
string roundtrip = DecryptStringFromBytes_Aes(encrypted, myAes.Key, myAes.IV);
//Display the original data and the decrypted data.
Console.WriteLine("Original: {0}", original);
Console.WriteLine("Encrypted: {0}", System.Text.Encoding.Default.GetString(encrypted));
Console.WriteLine("Round Trip: {0}", roundtrip);
}
}
static byte[] EncryptStringToBytes_Aes(string plainText, byte[] Key, byte[] IV)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("IV");
byte[] encrypted;
// 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);
}
encrypted = msEncrypt.ToArray();
}
}
}
// Return the encrypted bytes from the memory stream.
return encrypted;
}
static string DecryptStringFromBytes_Aes(byte[] cipherText, byte[] Key, byte[] IV)
{
// Check arguments.
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("IV");
// Declare the string used to hold
// the decrypted text.
string? plaintext = null;
// Create an Aes object
// with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create a decryptor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
// 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;
}
}
}
Yes, it's a modified version of Microsoft docs on Aes class: https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography.aes

AES is a block cipher. That means it encrypts a fixed-sized block of clear text bytes into a same-sized block of cipher text bytes (hence the term block cipher). AES uses 128-bit blocks, i.e. 16 bytes long. This is irrespective of key size.
To be able to encrypt data of an arbitrary length, block ciphers use different modes of operation. Depending on the mode, padding is applied, an initialization vector may be used, salt prepended, and dependencies between blocks are employed.
Hence, as a result, the total size of encrypted data may be slightly bigger than the original size of the unencrypted data. The difference accounts for (at least) the length of the initialization vector and/or salt and any padding to the nearest multiple of the cipher's block size.

padding is invalid and cannot be removed while decrypt AES

I am facing strange issue with AES encryption and getting error while decryption.
Error while decrypt:
padding is invalid and cannot be removed
Encrypt Method:
private static string Encrypt(string plainText, byte[] key)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (key == null || key.Length <= 0)
throw new ArgumentNullException("Key");
byte[] encrypted;
// Create an Aes object
// with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
Rfc2898DeriveBytes deriveBytes = new Rfc2898DeriveBytes("SharedPassword", key);
aesAlg.Key = deriveBytes.GetBytes(aesAlg.KeySize/8);
//aesAlg.IV = iv;
aesAlg.GenerateIV();
// Create a decrytor 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);
}
encrypted = msEncrypt.ToArray();
}
}
}
// Return the encrypted bytes from the memory stream.
return Convert.ToBase64String(encrypted);
}
Decrypt Method:
private static string Decrypt(string token, byte[] key)
{
byte[] cipherText = Convert.FromBase64String(token);
// Check arguments.
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (key == null || key.Length <= 0)
throw new ArgumentNullException("Key");
// Declare the string used to hold
// the decrypted text.
string plaintext = null;
// Create an Aes object
// with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
Rfc2898DeriveBytes deriveBytes = new Rfc2898DeriveBytes("SharedPassword", key);
aesAlg.Key = deriveBytes.GetBytes(aesAlg.KeySize / 8);
aesAlg.GenerateIV();
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
// 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(); // Error here
}
}
}
}
return plaintext;
}
I have tried many work around as mention below but none of them works.
AES decrypt fails with "Padding is invalid and cannot be removed"
C#: AES error: Padding is invalid and cannot be removed. Same key and everything, help
I don't get what is issue with code.

How to correctly and consistely get bytes from a string for AES encryption?

I am currently working on AES implementation in C#. The encryption method has two parameters: a string and a password. I am taking the supplied string and converting it to an array of bytes, so I can use it later for writing data to a stream with BinaryWriter.
The problem is that when I use Convert.FromBase64String(string) I get FormatException: Invalid length.and when I use Encoding.UTF8.GetBytes(string) my decryption method throws and invalid PKCS7.Padding exception.
I have been trying to solve this problem for the last couple of days. I have read near infinite questions in stackoverflow.com and other websites, but I still don't know what is the most reliable way to solve this problem.
Strings that will be used in this program are limited to sentences (ex. "Something to encrypt.") and numbers (ex. "12345").
Thank you in advance, here is the code I have at this point in time:
public class AESProvider {
public byte[] EncryptStringToBytes_Aes(string plainText, string Key)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
byte[] plainTextInBytes = Convert.FromBase64String(plainText);
byte[] encrypted;
//Create an Aes object
//with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
aesAlg.GenerateIV();
byte[] IV = aesAlg.IV;
//The Salt will be the first 8 bytes of the IV.
byte[] theSalt = new byte[8];
Array.Copy(IV,theSalt,8);
//A key for AES is generated by expanding the password using the following method.
Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(Key,theSalt);
byte[] aesKey = keyGen.GetBytes(16);
aesAlg.Key = aesKey;
// Create a decrytor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (BinaryWriter swEncrypt = new BinaryWriter(csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainTextInBytes);
}
encrypted = msEncrypt.ToArray();
}
}
// Prepend the IV to the ciphertext so it can be used in the decryption process.
using (MemoryStream ivPlusCipher = new MemoryStream())
{
using (BinaryWriter tBinaryWriter = new BinaryWriter(ivPlusCipher))
{
tBinaryWriter.Write(IV);
tBinaryWriter.Write(encrypted);
tBinaryWriter.Flush();
}
return ivPlusCipher.ToArray();
}
}
}
public byte[] DecryptStringFromBytes_Aes(byte[] cipherText, string Key)
{
// Check arguments.
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
// Declare the string used to hold
// the decrypted text.
byte[] decrypted;
// Create an Aes object
// with the specified key and IV.
// Create the streams used for decryption.
using (Aes aesAlg = Aes.Create())
{
aesAlg.Mode = CipherMode.CBC;
aesAlg.Padding = PaddingMode.PKCS7;
//Grab IV from ciphertext
byte[] IV = new byte[16];
Array.Copy(cipherText,0,IV,0,16);
//Use the IV for the Salt
byte[] theSalt = new byte[8];
Array.Copy(IV,theSalt,8);
Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(Key,theSalt);
byte[] aesKey = keyGen.GetBytes(16);
aesAlg.Key = aesKey;
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, IV);
using (MemoryStream msDecrypt = new MemoryStream())
{
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Write))
{
using (BinaryWriter srDecrypt = new BinaryWriter(csDecrypt))
{
//Decrypt the ciphertext
srDecrypt.Write(cipherText, IV.Length, (cipherText.Length - IV.Length));
}
decrypted = msDecrypt.ToArray();
return decrypted;
}
}
}
}
}

You need to convert between bytes and strings before and after encryption/decryption. This is not the same operation, and you should not use the same method.
When encrypting you start out with an arbitrary string. Convert this to a byte[] using Encoding.UTF8.GetBytes(). Encrypt it. The resulting byte[] can now be converted to a string using Convert.ToBase64String().
When decrypting you now start out with a Base64 encoded string. Decode this to a byte[] using Convert.FromBase64String(). Decrypt it. You now have the UTF-8 encoding of your original string, which you can decode using Encoding.UTF8.GetString().
Remember:
Encoding.UTF8 works to convert arbitrary strings to byte-arrays (but it can only convert byte-arrays that contain actual UTF8-encodings back).
Convert.[To/From]Base64String works to convert arbitrary byte-arrays to strings (but it can only convert strings that contain actual Base64-encodings back).

Looking at your lines
public byte[] EncryptStringToBytes_Aes(string plainText, string Key)
byte[] plainTextInBytes = Convert.FromBase64String(plainText);
Arbitrary plain text will not be a base 64 encoded string. Even if it is supposed to be base 64 encoded text, your error message indicates that the length is not divisible by 4
FormatException
The length of s, ignoring white-space characters, is not zero or a multiple of 4.
-or-
The format of s is invalid. s contains a non-base-64 character, more than two padding characters, or a > non-white space-character among the padding characters.
http://msdn.microsoft.com/en-us/library/system.convert.frombase64string(v=vs.110).aspx
If it is a base 64 encoded string, you need to pad it accorgingly
http://en.wikipedia.org/wiki/Base64

Convert.FromBase64String(string); is expected to receive a string generated by Convert.ToBase64String(byte[]); passing in a arbitrary string will not work.
The easiest solution is replace the BinaryWriter and BinaryReader with a StreamWriter and a StreamReader and not do any conversion at all.
public byte[] EncryptStringToBytes_Aes(string plainText, string Key)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
//Create an Aes object
//with the specified key and IV.
using (Aes aesAlg = Aes.Create())
{
aesAlg.GenerateIV();
byte[] IV = aesAlg.IV;
//The Salt will be the first 8 bytes of the IV.
byte[] theSalt = new byte[8];
Array.Copy(IV,theSalt,8);
//A key for AES is generated by expanding the password using the following method.
Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(Key,theSalt);
byte[] aesKey = keyGen.GetBytes(16);
aesAlg.Key = aesKey;
// Create a decrytor to perform the stream transform.
ICryptoTransform encryptor = aesAlg.CreateEncryptor(aesAlg.Key, IV);
// Create the streams used for encryption.
using (MemoryStream msEncrypt = new MemoryStream())
{
//You can write the IV here and not need to do it later.
msEncrypt.Write(IV, 0, IV.Length);
using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
{
using (StreamWriter swEncrypt = new StreamWriter (csEncrypt))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
}
//Move this outside of the using statement for CryptoStream so it is flushed and dipsoed.
return msEncrypt.ToArray();
}
}
}
Also, your decryption function is actually trying to encrypt the text a 2nd time, you need to pass the byte array in to the constructor of msDecrypt and put it in decryption mode.
public string DecryptStringFromBytes_Aes(byte[] cipherText, string Key)
{
// Check arguments.
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
// Create an Aes object
// with the specified key and IV.
// Create the streams used for decryption.
using (Aes aesAlg = Aes.Create())
{
aesAlg.Mode = CipherMode.CBC;
aesAlg.Padding = PaddingMode.PKCS7;
//Grab IV from ciphertext
byte[] IV = new byte[16];
Array.Copy(cipherText,0,IV,0,16);
//Use the IV for the Salt
byte[] theSalt = new byte[8];
Array.Copy(IV,theSalt,8);
Rfc2898DeriveBytes keyGen = new Rfc2898DeriveBytes(Key,theSalt);
byte[] aesKey = keyGen.GetBytes(16);
aesAlg.Key = aesKey;
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, IV);
//You can chain using statements like this to make the code easier to read.
using (MemoryStream msDecrypt = new MemoryStream(cipherText))
using (CryptoStream csDecrypt = new CryptoStream(msDecrypt, decryptor, CryptoStreamMode.Read)) //Notice this is Read mode not Write mode.
using (StreamReader srDecrypt = new StreamReader(csDecrypt))
{
//Decrypt the ciphertext
return srDecrypt.ReadToEnd();
}
}
}
There may be other errors with your code, but at least this gets you on the right track.

send encrypted message from C# to PHP

I'm trying to get two services to talk but I need to encrypt the message sent between them. It's early days so I'm hard coding the key, but here is what I have so far.
In c#
byte[] key = Convert.FromBase64String("QM3M8+Zbw5VYa70xtftksHHqM1UGmhOBjqOP82UtuAA=");
byte[] hexiv = Convert.FromBase64String("wRt00heBiu86mWSfuHmSag==");
using (RijndaelManaged myRijndael = new RijndaelManaged())
{
byte[] encrypted = EncryptStringToBytes(name, myRijndael.Key, myRijndael.IV);
string enc = Convert.ToBase64String(encrypted);
}
.....
static byte[] EncryptStringToBytes(string plainText, byte[] Key, byte[] IV)
{
// Check arguments.
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("Key");
byte[] encrypted;
// Create an RijndaelManaged object
// with the specified key and IV.
using (RijndaelManaged rijAlg = new RijndaelManaged())
{
rijAlg.Key = Key;
rijAlg.IV = IV;
// Create a decrytor to perform the stream transform.
ICryptoTransform encryptor = rijAlg.CreateEncryptor(rijAlg.Key, rijAlg.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);
}
encrypted = msEncrypt.ToArray();
}
}
}
This outputs my message as +CPJqIL6RhIHc5+u2Nvonw==
Then in PHP, I have the following:
$key = "Zbw5VYa70xtftksHHqM1UGmhOBjqOP82UtuAA=";
$hexiv = "wRt00heBiu86mWSfuHmSag==";
$string = base64_decode("+CPJqIL6RhIHc5+u2Nvonw==");
$cipher_alg = MCRYPT_RIJNDAEL_256;
$decrypted_string = mcrypt_decrypt($cipher_alg, $key, $string , MCRYPT_MODE_CBC, $hexiv);
echo $decrypted_string."<BR>";
But this is giving me Qˆ–⤻?/P¸Üu:·ey+–Uñ :,yL±­M
Hopefully the answer is fairly obvious but I can't see it.

You fell for the mcrypt trap.
MCRYPT_RIJNDAEL_256 isn't AES-256, it's the 256-bit block size variant of Rijndael. AES is always a 128-bit block size even with 256-bit keys.
Look into libsodium instead. There are bindings for .NET and PHP. If you upgrade to PHP 7.2 or higher, you should have it installed already.

How to Encrypt/Decrypt using AES in WinRT?

I am newbie in Cryptography.
Edited: It seems that I was wrong with using the right Encrypt/Decrypt algorithm so I change my question to:
How to convert these lines of codes to WinRT ?
The code is based on the code at http://msdn.microsoft.com/en-us/library/system.security.cryptography.aesmanaged.aspx
I need to do the same in WinRT:
Update:
There is a Cryptography and Certificate sample for WinRT (Windows 8.1) that solved my problem.
Please check: http://code.msdn.microsoft.com/windowsapps/Cryptography-and-3305467b
public static byte[] Encrypt(string plainText)
{
if (plainText == null || plainText.Length <= 0)
throw new ArgumentNullException("plainText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("Key");
byte[] encrypted;
using (AesManaged aesAlg = new AesManaged())
{
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create a decrytor to perform the stream transform.
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))
{
//Write all data to the stream.
swEncrypt.Write(plainText);
}
encrypted = msEncrypt.ToArray();
}
}
}
return encrypted;
}
And
public static string Decrypt(byte[] cipherText)
{
if (cipherText == null || cipherText.Length <= 0)
throw new ArgumentNullException("cipherText");
if (Key == null || Key.Length <= 0)
throw new ArgumentNullException("Key");
if (IV == null || IV.Length <= 0)
throw new ArgumentNullException("Key");
string plaintext = null;
using (AesManaged aesAlg = new AesManaged())
{
aesAlg.Key = Key;
aesAlg.IV = IV;
// Create a decrytor to perform the stream transform.
ICryptoTransform decryptor = aesAlg.CreateDecryptor(aesAlg.Key, aesAlg.IV);
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;
}

Yes it is possible, but you should use the same:
character encoding of the plaintext, such as UTF-8
mode of operation
padding algorithm
(optional) string encoding of the ciphertext, such as base64 encoding or the easier to debug hexadecimal encoding
And of course the correct cipher (AES instead of Rijndael),symmetric key size and value and IV. Make sure you check each of the IO to these functions separately. Do not rely on defaults, set each value explicitly.
Note that using ECB mode is insecure. Currently you are probably mixing CBC and ECB mode, which won't work. For secure communications you should use authenticated encryption or a MAC (using a second key).