Here's a simple way to check the MD5 checksum of a file in order to verify the origin of a file.
Open the Terminal app.
Type the following and hit Enter.
md5 /path/to/file
# MD5 (/path/to/file) = 64e7749cc4a60ec3d80707d0d69f5c1c
Note that you can also type md5 and then drag a file to the Terminal windows. Then hit Enter to run the command.