winSHA1Sum

Built in C# and .NET, winSHA1Sum is an intuitive application you can use to calculate the SHA1 checksum of a file as well as to match it against another hash, in order to find out if the two associated files are identical or different.

Calculate and compare SHA1 hashes

It's wrapped in a user-friendly interface made from just one window that gives you an overview of all settings before starting a task.
You can resort to the traditional file browser to locate and open a file, in order to automatically compute its SHA1 hash and view it in this window.
This signature can be compared with another alphanumerical value typed on the spot or pasted from the Clipboard. Afterward, the tool brings up a small panel in the center of the screen to inform you whether the two checksums are different or the same.

No installation necessary, besides .NET Framework

The entire program is packed in a single and tiny executable file which can be conveniently copied anywhere on the disk or stored on a removable storage device, in order to easily run winSHA1Sum on any machine.
However, it requires you to have .NET Framework installed, since it was developed with the aid of this platform. On the other hand, it doesn't create files on the disk or add new entries to your system registry.

Evaluation and conclusion

It worked smoothly in our testing, without causing Windows to hang, crash or show error dialogs. We haven't come across any compatibility issues with newer Windows versions, considering that it hasn't been updated for a long time. SHA1 calculation and comparison jobs were executed instantly, during which the app remained light on system resources consumption.
Taking everything into account, winSHA1Sum proves to be a useful and speedy program for calculating and comparing SHA1 signatures to validate file integrity.