fast encryption for a large unicode text file

Question

I have a large unicode text file (35 MB) containing words separated by punctuation marks. I need to somehow hide the content of the file (at least from the majority of people who are not specialised in cracking).

The best way until now seemed like encryption. I know almost nothing about encryption. I tried to use the solution to a similar question "Simple 2 way encryption for C#" but it takes a long time to execute the encryption.

What is the fastest way (algorithm) that works out of the box (i.e. it is contained in the .Net lib)? A short example on how to use it would be nice :) I don't care how strong the encryption is, if you open the encrypted file with a text editor and don't see the words then it's perfect. The important part is speed.

If you don't need to access the file with a program, why not just use a passworded .zip file or something? — Marc B, Mar 11 '11 at 21:49
I've tried AES encryption as discribed here [Simple 2 way encryption for C#](http://stackoverflow.com/questions/165808/simple-2-way-encryption-for-c) but it's very slow. It didn't finish in more then 15 minuts on a core 2 duo (2.5 GHz) with 3GB RAM — ghet, Mar 11 '11 at 22:00
If you want to just "hide" the raw data, you could use a simple XOR obfuscation. Wouldn't stand up to any serious cryptological attack, but would hide things. — Marc B, Mar 11 '11 at 22:08
The biggest issue with security is not how secure it is, it is who gets the blame and is liable for the damages when it gets compromised. You do *not* want to be anywhere near that chain of blame. Do not implement your own encryption scheme, especially a weak one like tileryj suggests. Put the file on a secured file server with strong passwords in a server room with a lock. — Hans Passant, Mar 11 '11 at 22:11
15 minutes for AES on a 35MB file? TrueCrypt shows modern CPUs doing over 100MB/sec for AES and over 1500MB/sec for new AES-NI instruction set. 35MB should take somewhere between 25ms and 350ms, assuming not HD limited, not 15 minutes. — Bengie, Mar 11 '11 at 22:21
@Hans Passant Thanks for youre advice , but this isn't such an importan file , it doesen't contain passwords and such stuf , it only has some word paterns. — ghet, Mar 11 '11 at 23:32

score 3 · Answer 1 · edited May 23 '17 at 11:44

3

AES is pretty fast still, here's some help implementing it : Using AES encryption in C#

Anything other than industry standard Encryption is asking for problems sooner or later.

edited May 23 '17 at 11:44

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answered Mar 11 '11 at 21:50

DaveShaw

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score 0 · Answer 2 · answered Mar 11 '11 at 21:52

0

What have you tried so far? Are standard encryptions like AES and blowfish too slow?

You can always do something simple like xor-ing the contents against some pass-code repeated to the same length as the file.

answered Mar 11 '11 at 21:52

tilleryj

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I've tried AES encryption as discribed here [Simple 2 way encryption for C#](http://stackoverflow.com/questions/165808/simple-2-way-encryption-for-c) but it's very slow. It didn't finish in more then 15 minuts on a core 2 duo (2.5 GHz) with 3GB RAM – ghet Mar 11 '11 at 21:58
I guess I would try the xor method then. Does it make sense the way I described it? – tilleryj Mar 11 '11 at 22:03
yes xor does it for me. It encripts the 32MB in 1 - 2 seconds. Thanks!! – ghet Mar 11 '11 at 22:58

score -1 · Answer 3 · answered Mar 11 '11 at 23:13

As tilleryj said

xor-ing the contents against some pass-code repeated to the same length as the file is simple and fast

but it is les safe then other encription types. I wrote a simple class that helps you encript a string using another string as a password usig the xor method. hope some else can use it.

`using System;
using System.Text;

namespace MyEncriptionNameSpace
{
    class XorStringEncripter
    {
        private string __passWord;
        public XorStringEncripter(string password)
        {
            if (password.Length == 0)
            {
                throw new Exception("invalide password");
            }
            __passWord = password;
        }
        public string encript(string stringToEncript)
        {
            return __encript(stringToEncript);
        }

    public string decript(string encripTedString)
    {
        return __encript(encripTedString);
    }

    public string __encript(string stringToEncript)
    {
        var encriptedStringBuilder = new StringBuilder(stringToEncript.Length);
        int positionInPassword = 0;

        for (int i = 0; i < stringToEncript.Length; i++)
        {
            __corectPositionInPassWord(ref positionInPassword);
            encriptedStringBuilder.Append((char)((int)stringToEncript[i] ^ (int)__passWord[positionInPassword]));
            ++positionInPassword;
        }
        return encriptedStringBuilder.ToString();
    }

    private void __corectPositionInPassWord(ref int positionInPassword)
    {
        if (positionInPassword == __passWord.Length)
        {
            positionInPassword = 0;
        }
    }
}

}`

actualy encript and decript do the same thing , I provided bouth to avoid confusion on using the same function for bouth encription and decrition. This is because if you have a nuber A and you xor it with B and you obtain C then if you xor C and B you get A.
A xor B = C ---> C xor B = A

fast encryption for a large unicode text file

3 Answers3