C# Problem using blowfish NET: How to convert from Uint32[] to byte[]

Question

In C#,I'm using Blowfish.NET 2.1.3's BlowfishECB.cs file(can be found here)

In C++,It's unknown,but it is similiar.

In C++,the Initialize(blowfish) procedure is the following:

void cBlowFish::Initialize(BYTE key[], int keybytes)

In C#,the Initialize(blowfish) procedure is the same

public void Initialize(byte[] key, int ofs, int len) 

This is the problem:

This is how the key is initialized in C++

DWORD keyArray[2] = {0}; //declaration
...some code
blowfish.Initialize((LPBYTE)keyArray, 8);

As you see,the key is an array of two DWORDS,which is 8 bytes total.

In C# I declare it like that,but I get an error

BlowfishECB blowfish = new BlowfishECB();
UInt32[] keyarray = new UInt32[2];
..some code
blowfish.Initialize(keyarray, 0, 8);

The error is:

Argument '1': cannot convert from 'uint[]' to 'byte[]'

What am I doing wrong?

Thanks in advance!

Answer 1

You can use BitConverter to get the bytes from a UInt32.

---

To do this, you'll need to convert each element in a loop. I would do something like:

private byte[] ConvertFromUInt32Array(UInt32[] array)
{
    List<byte> results = new List<byte>();
    foreach(UInt32 value in array)
    {
        byte[] converted = BitConverter.GetBytes(value);
        results.AddRange(converted);
    }
    return results.ToArray();
}

To go back:

private UInt32[] ConvertFromByteArray(byte[] array)
{
    List<UInt32> results = new List<UInt32>();
    for(int i=0;i<array.Length;i += 4)
    {
        byte[] temp = new byte[4];
        for (int j=0;j<4;++j)
            temp[j] = array[i+j];
        results.Add(BitConverter.ToUInt32(temp);
    }
    return results.ToArray();
}

Answer 2

If you are using VS2008 or C# 3.5, try the following LINQ + BitConverter solution

var converted = 
  keyArray
    .Select(x => BitConverter.GetBytes(x))
    .SelectMany(x => x)
    .ToArray();

Breaking this down

• The Select converts every UInt32 into a byte[]. The result is an IEnumerable<byte[]>
• The SelectMany calls flattes the IEnumerable<byte[]> to IEnumerable<byte>
• ToArray() simply converts the enumerable into an array

EDIT Non LINQ solution that works just as well

List<byte> list = new List<byte>();
foreach ( UInt32 k in keyArray) {
  list.AddRange(BitConverter.GetBytes(k));
}
return list.ToArray();

Answer 3

If you need a faster way to convert your value types, you can use the hack I described in the following answer: What is the fastest way to convert a float[] to a byte[]?

This hack avoid memory allocations and iterations. It gives you a different view of your array in O(1).

Of course you should only use this if performance is an issue (avoid premature optimization).