SQL bigint hash to match c# int64 hash [duplicate]

Question

This question already has an answer here:

• SQL Server varbinary bigint with BitConverter.ToInt64 values are different 1 answer

I am trying to create a universal hashing alogrithim that hashes a string as a 64 bit int.

I am able to hash the strings correctly: sql:

select  
    convert
    (
        varchar(64),
        HASHBYTES
        (
            'SHA1',
            'google.com'
        ),
        2
    )

returns BAEA954B95731C68AE6E45BD1E252EB4560CDC45

C#

    System.Security.Cryptography.SHA1 c = System.Security.Cryptography.SHA1.Create();
    System.Text.StringBuilder sb = new StringBuilder();
    byte[] b = c.ComputeHash(Encoding.UTF8.GetBytes("google.com"));
    for (int i = 0; i < b.Length;i++ )
    {
        byte by = b[i];
        sb.Append(by.ToString("x2").ToUpper());
    }

    return sb.ToString();

retruns BAEA954B95731C68AE6E45BD1E252EB4560CDC45

However when I convert to a bigint/long the values do not match: sql:

select  
    convert
    (
        bigint,
        HASHBYTES
        (
            'SHA1',
            'google.com'
        )
    )

returns 2172193747348806725

c#:

    System.Security.Cryptography.SHA1 c = System.Security.Cryptography.SHA1.Create();
    byte[] b = c.ComputeHash(Encoding.UTF8.GetBytes("google.com"));
    return BitConverter.ToInt64(b, 0);

returns 7501998164347841210

Any ideas on how to get these numbers to match?

Answer 1

Your SQL bigint takes the last 8 bytes while the c# implementation takes the first 8 bytes (and reverses them because its running on little endian).

Take the proper Range of the array in C# and reverse it. Then you should be fine.

Did some coding:

System.Security.Cryptography.SHA1 c = System.Security.Cryptography.SHA1.Create();
byte[] b = c.ComputeHash(Encoding.UTF8.GetBytes("google.com"));
long value = BitConverter.ToInt64(b, 12);
value = IPAddress.HostToNetworkOrder(value);

Debug.WriteLine(value);
// writes 2172193747348806725