How can I iterate through all possible values of a byte array of size n?
For my question n = 16, but a general answer would be appreciated.
So I have a byte array:
byte[] key;
My problem is that I want to iterate over all possible values of each element in this array in combination. I know this will take a long time and I am not going to actually fill this loop, just to create a loop that at least tries to do it.
For example:
First iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
}
Second iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
}
Third iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
}
Final iteration:
//Math.Pow(2,128) is the max no. of iterations right?
byte[] key;
for(int i = 0; i < Math.Pow(2,128); i++)
{
key = new byte[16] {255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255};
}
Obviously I just coded the array above. I need a way to get it right. Again, I know there are many different combinations. All I need is a way to start repeating all possible values. How do I do this in my loop?
those. that I have to replace the body of my loop to iterate over all possible values of a 16 byte array.
What I have tried:
In the body of the loop, I've tried the following:
key = new byte[16] { (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i, (byte)i };
Obviously wrong, will only test a small subset of the possible values. Just try i = 0, ..., 255 and start over when i = 256 -> (bytes) i = 0.
I suspect I need some more nesting. Perhaps up to 16 nested loops, which seems crazy and probably wrong? I can't seem to fix this problem, any help would be greatly appreciated!
Purpose: The purpose of this question is to demonstrate how practical ineffective brute-force cryptanalysis is. The rest of my program is working, I just got stuck in this loop.
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If you don’t understand: 16 bytes is the Guid size or the size of the standard cryptographic key size. There are so many combinations that you cannot even list a fraction. Maybe you can list the last 8 bytes if you parallelize 1000 machines and wait a year.
You can do this easily by running a for loop from 0 to ulong.MaxValue
. I present this as an answer because this very simple idea allows you to start enumerating and, in fact, never get to the point where you are done.
for (ulong i = 0; i < ulong.MaxValue; i++) {
var bytes = new [] {
0, 0, 0, 0, 0, 0, 0, 0
, (byte)(i >> (7 * 8))
, (byte)(i >> (6 * 8))
, (byte)(i >> (5 * 8))
//...
, (byte)(i >> (0 * 8)) };
}
Or just use 16 nested loops. I don't think this is crazy because it is so simple that it is clearly correct.
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this is sample code without exception handling and kind of inefficiency to simulate a counter like the one you mentioned
public static void NextIteration(byte[] input)
{
if (input.All(x => x == 255))
throw new InvalidOperationException("there is no iteration left");
var converted = input.Select(x => (int) x).ToArray();
converted[0]++;
for (var i = 0; i < converted.Length; i++)
{
if (converted[i] == 256)
{
converted[i] = 0;
converted[i + 1]++;
}
}
for (var i = 0; i < input.Length; i++)
{
input[i] = (byte) converted[i];
}
}
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