C#: Base64 encoding

Question

Can anyone please let me know where I made a mistake in this code? This code is written in C#.NET. I need to write an algorithm for encoding a string using base64 format using C#.NET, and then decoded with base64_decode() using PHP. Please see the snippit below:

System.Security.Cryptography.RijndaelManaged rijndaelCipher = new System.Security.Cryptography.RijndaelManaged();
rijndaelCipher.Mode = System.Security.Cryptography.CipherMode.CBC;
rijndaelCipher.Padding = System.Security.Cryptography.PaddingMode.Zeros;
rijndaelCipher.KeySize = 256;
rijndaelCipher.BlockSize = 128;

byte[] pwdBytes = System.Text.Encoding.UTF8.GetBytes(_key);
byte[] keyBytes = new byte[16];

int len = pwdBytes.Length;
if (len > keyBytes.Length) len = keyBytes.Length;

System.Array.Copy(pwdBytes, keyBytes, len);

rijndaelCipher.Key = keyBytes;
rijndaelCipher.IV = keyBytes;

System.Security.Cryptography.ICryptoTransform transform = rijndaelCipher.CreateEncryptor();

byte[] plainText = Encoding.UTF8.GetBytes(unencryptedString);
byte[] cipherBytes = transform.TransformFinalBlock(plainText, 0, plainText.Length);

return Convert.ToBase64String(cipherBytes);

What problem are you having? Can't you base64 decode and the decrypt in php, or what? Are you getting any errors? — Klaus Byskov Pedersen, Nov 09 '11 at 14:28
Yes, am receiving some junk chars when am trying to decrypt it using base64_decode() function available in PHP. — Prabhu M, Nov 09 '11 at 15:12
The junk chars are probably the **encrypted** string. Why are you encrypting in the first place? See @Mike Duke Hall 's answer below. — Klaus Byskov Pedersen, Nov 09 '11 at 15:21
Please note that encode/decode and **encrypt/decrypt** are two very different things. — Klaus Byskov Pedersen, Nov 09 '11 at 15:22

score 6 · Accepted Answer · answered Nov 09 '11 at 14:31

6

I think your code sample is doing "encryption", and you want "encoding". For encoding a string with Based64 in C#, it should look like this:

 static public string EncodeTo64(string toEncode)
    {
        byte[] toEncodeAsBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(toEncode);
        string returnValue = System.Convert.ToBase64String(toEncodeAsBytes);
        return returnValue;
    }

And the PHP should look like this:

 <?php
  $str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
  echo base64_decode($str);
 ?>

answered Nov 09 '11 at 14:31

Duke Hall

582
4
12

2

Nice answer Duke. Strictly speaking you should access the GetBytes() method via 'System.Text.Encoding.ASCII.GetBytes(toEncode)' to avoid accessing to a static member of a type via a derived type. See [here](http://stackoverflow.com/questions/4945439/why-is-it-useful-to-access-static-members-through-inherited-types) for more info. – Dylan Hogg Oct 11 '12 at 00:18

score 0 · Answer 2 · edited May 23 '17 at 12:03

I need to write an algorithm for encoding a string using base64 format using C#.net

That's actually quite easy. You don't need all that cryptography stuff that your copy-and-pasted code is using. The following suffices:

byte[] bytes = Encoding.UTF8.GetBytes(inputString);  
string outputString = Convert.ToBase64String(bytes);

If you plan to send the data from C# to PHP via a HTTP GET request, don't forget to UrlEncode it. See this question for details:

C# to PHP base64 encode/decode

C#: Base64 encoding

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