I currently am learning Symmetric Cryptography in .NET. I wrote a demo as following:
private byte[] key = Encoding.ASCII.GetBytes("abcdefgh");
private byte[] IV = Encoding.ASCII.GetBytes("hgfedcba");
private byte[] encrypted;
public Form1()
{
InitializeComponent();
}
private void btnEncrypt_Click(object sender, EventArgs e)
{
this.textBox2.Text = this.Encrypt(this.textBox1.Text);
}
private void btnDecrypt_Click(object sender, EventArgs e)
{
this.textBox3.Text = this.Decrypt(this.textBox2.Text);
}
private string Encrypt(string plainText)
{
try
{
using (DESCryptoServiceProvider crypto = new DESCryptoServiceProvider())
{
crypto.Key = this.key;
crypto.IV = this.IV;
ICryptoTransform transform = crypto.CreateEncryptor(crypto.Key, crypto.IV);
using (MemoryStream stream = new MemoryStream())
{
using (CryptoStream cryptoStream = new CryptoStream(stream, transform, CryptoStreamMode.Write))
{
using (StreamWriter writer = new StreamWriter(cryptoStream))
{
writer.Write(plainText);
}
encrypted = stream.ToArray();
}
}
}
return Convert.ToBase64String(encrypted);
}
catch (Exception)
{
throw;
}
}
private string Decrypt(string cipherText)
{
try
{
string plainText = string.Empty;
using (DESCryptoServiceProvider crypto = new DESCryptoServiceProvider())
{
crypto.Key = this.key;
crypto.IV = this.IV;
ICryptoTransform transform = crypto.CreateDecryptor(crypto.Key, crypto.IV);
using (MemoryStream stream = new MemoryStream(Convert.FromBase64String(cipherText)))
{
using (CryptoStream cryptoStream = new CryptoStream(stream, transform, CryptoStreamMode.Read))
{
using (StreamReader reader = new StreamReader(cryptoStream))
{
plainText = reader.ReadToEnd();
}
}
}
}
return plainText;
}
catch (Exception)
{
throw;
}
}
Everything work as expected. But if I replace
return Convert.ToBase64String(encrypted);
And
using (MemoryStream stream = new MemoryStream(Convert.FromBase64String(cipherText)))
To
return Encoding.UTF8.GetString(encrypted);
And
using (MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(cipherText)))
I got an error at CryptoStream System.NotSupportedException
. After diagnostic the code, I found that Encoding.UTF8.GetBytes(cipherText)
have more bytes than encrypted
So what is the difference between using Convert.From/ToBase64String
and Encoding.UTF8.GetBytes/GetString)
?
The Convert. FromBase64String(String) method in C# converts the specified string, which encodes binary data as base-64 digits, to an equivalent 8-bit unsigned integer array.
ToBase64String(Byte[], Int32, Int32) Converts a subset of an array of 8-bit unsigned integers to its equivalent string representation that is encoded with base-64 digits. Parameters specify the subset as an offset in the input array, and the number of elements in the array to convert.
UTF-8 is a character encoding. It encodes Unicode codepoints (characters) into bytes.
Base64 is a binary-to-text encoding. It encodes bytes to text.
You need the latter in this case.
Encoding.UTF8.GetString
decodes a UTF-8-encoded byte array, which is lossy if there are invalid byte sequences (which is highly likely if you feed it random bytes like a ciphertext).
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