C#

my_str += (char)(letters[c] ^ keys[cc]);

char[] chars = new char[Data.Length];
for (int c = 0; c < Data.Length; c++) {
	chars[c] = (char)(((int)Data[c]) ^ keys[cc++ % i]);
}
string my_str = new string(chars);

my_str += (char)(letters[c] ^ keys[cc]);

my_str += String.fromCharCode((src.charCodeAt(c) ^ keys[cc]));

OhFBBxQWEBFLGgsEHgoVRBwSEAYCCw==

OhhBBh4eCRNPEQkMBQQVVRgaHggBBQ==

Convert.ToBase64String(Encoding.ASCII.GetBytes(my_str))

*/
private static var base64chars:String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

/**
* Encodes a base64 string.
*/
public static function encode(src:String):String {
    var i:Number = 0;
    var output:String = new String("");
    var chr1:Number, chr2:Number, chr3:Number;
    var enc1:Number, enc2:Number, enc3:Number, enc4:Number;
    while (i < src.length) {
        chr1 = src.charCodeAt(i++);
        chr2 = src.charCodeAt(i++);
        chr3 = src.charCodeAt(i++);
        enc1 = chr1 >> 2;
        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
        enc4 = chr3 & 63;
        if(isNaN(chr2)) enc3 = enc4 = 64;
        else if(isNaN(chr3)) enc4 = 64;
        output += base64chars.charAt(enc1)+base64chars.charAt(enc2);
        output += base64chars.charAt(enc3)+base64chars.charAt(enc4)
    }
    return output;
}

tim_gunning wrote:

in c# i used
Convert.ToBase64String(Encoding.ASCII.GetBytes(my_str))

Guffa wrote:

To create a 100 character string, you will have created 10 kB of strings. To create a 1000 character string, you will have created 1 MB of strings.