Why do these two file hashes have the same meaning when I use MemoryStream?

Question

I am writing a C # procedure that creates hashes from jpg files. If I pass an array of bytes to my SHA512 object, then I get the expected behavior, however, if I pass a memory stream, both files will always have a hash with the same value.

Example 1:

        SHA512 mySHA512 = SHA512.Create();

        Image img1 = Image.FromFile(@"d:\img1.jpg");
        Image img2 = Image.FromFile(@"d:\img2.jpg");
        MemoryStream ms1 = new MemoryStream();
        MemoryStream ms2 = new MemoryStream();

        img1.Save(ms1, ImageFormat.Jpeg);
        byte[] buf1 = ms1.GetBuffer();
        byte[] hash1 = mySHA512.ComputeHash(buf1);

        img2.Save(ms2, ImageFormat.Jpeg);
        byte[] buf2 = ms2.GetBuffer();
        byte[] hash2 = mySHA512.ComputeHash(buf2);

        if (Convert.ToBase64String(hash1) == Convert.ToBase64String(hash2))
            MessageBox.Show("Hashed the same");
        else
            MessageBox.Show("Different hashes");

This creates "different hashes." But one of the overloads of the ComputeHash method accepts a stream object, and I would rather use it. When I do this:

        SHA512 mySHA512 = SHA512.Create();

        Image img1 = Image.FromFile(@"d:\img1.jpg");
        Image img2 = Image.FromFile(@"d:\img2.jpg");
        MemoryStream ms1 = new MemoryStream();
        MemoryStream ms2 = new MemoryStream();

        img1.Save(ms1, ImageFormat.Jpeg);
        byte[] hash1 = mySHA512.ComputeHash(ms1);

        img2.Save(ms2, ImageFormat.Jpeg);
        byte[] hash2 = mySHA512.ComputeHash(ms2);

        if (Convert.ToBase64String(hash1) == Convert.ToBase64String(hash2))
            MessageBox.Show("Hashed the same");
        else
            MessageBox.Show("Different hashes");

This creates "Hashed the same."

What is going on here, am I missing?

Answer 1

MemoryStreams, .

ms1.Position = 0;
ms2.Position = 0;

Save.

: GetBuffer . ToArray, , . GetBuffer , ( ) , . GetBuffer, , , , , - .