How to do large file integrity check

Question

I need to do an integrity check for a single big file. I have read the SHA code for Android, but it will need one another file for the result digest. Is there another method using a single file?

I need a simple and quick method. Can I merge the two files into a single file?

The file is binary and the file name is fixed. I can get the file size using fstat. My problem is that I can only have one single file. Maybe I should use CRC, but it would be very slow because it is a large file.

My object is to ensure the file on the SD card is not corrupt. I write it on a PC and read it on an embedded platform. The file is around 200 MB.

Answer 1

You have to store the hash somehow, no way around it.

You can try writing it to the file itself (at the beginning or end) and skip it when performing the integrity check. This can work for things like XML files, but not for images or binaries. You can also put the hash in the filename, or just keep a database of all your hashes.

It really all depends on what your program does and how it's set up.