C# – SQL 2005 MD5 Hash and C# MD5 Hash

cencryptionsqlsql-server-2005

I currently have a legacy database (SQL 2005) that generates hash strings for tokens. It does it like this…

DECLARE @RowID INT
DECLARE @hashString VARCHAR(128)

SET @RowID = 12345
SET @salt= 0xD2779428A5328AF9

SET @hashBinary = HASHBYTES(('MD5', @salt + CAST(@RowID AS VARBINARY(30)))
SET @hashString = sys.fn_varbintohexstr(@hashBinary)

If I execute this, I my hash string looks like this: "0x69a947fd71b853485007f0d0be0763a5"

Now, I need to replicate the same logic in C# so I can remove the database dependency for generating these hashes, and it has to be backward compatible.

I have implemented in C# like this:

byte[] saltBytes = BitConverter.GetBytes(0xD2779428A5328AF9);
byte[] pidBytes = BitConverter.GetBytes(12345);

byte[] bytesToHash = new byte[saltBytes.Length + pidBytes.Length];

for (int i = 0; i < saltBytes.Length; i++)
{
    bytesToHash[i] = saltBytes[i];
}

for (int i = 0; i < pidBytes.Length; i++)
{
    bytesToHash[saltBytes.Length + 1] = pidBytes[i];
}

MD5CryptoServiceProvider hasher = new MD5CryptoServiceProvider();
byte[] hashedBytes = hasher.ComputeHash(bytesToHash);

string hashString = BitConverter.ToString(hashedBytes).ToLower().Replace("-", "");

The problem is, my C# implementation generates this hash: "715f5d6341722115a1bfb2c82e4421bf"

They are obviously different.

So, is it possible to make the match consistently?

Best Answer

Looks to me like there's a bug in your second loop. Try changing the "+ 1" to "+ i"...

for (int i = 0; i < pidBytes.Length; i++)
{
    // the line below just overwrites the same position multiple times
    // bytesToHash[saltBytes.Length + 1] = pidBytes[i];
    bytesToHash[saltBytes.Length + i] = pidBytes[i];
}

In your example, you're just overwriting the same position in the array multiple times, instead of setting each item from that point forward.

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