How a download user checks md5 after file download?

Question

We may notice many download sites provide md5 string. For example, when I download ABC.zip , along with an md5 string like: “ 2743a6a9fe6f873df1c7ed8ac91df5d7 *ABC.zip ”. I know the idea behind it, it's Digest algorithm to prevent file forge.

My question is how a user calculates md5 string for the ABC.zip , and compare it with value site provides? Any existing tool to generate md5 string?

Answer 1

It depends a bit on your operating system ofcourse. Under most Linux/Unix distributions you have an md5 or md5sum program available.

Example:

# md5sum eclipse-SDK-3.6RC3-linux-gtk.tar.gz
8eca528d2c0b33dae10ba8750b2e4b94  eclipse-SDK-3.6RC3-linux-gtk.tar.gz

It also has a check mode which does exactly what you're looking for:

# md5sum -c test.md5
eclipse-SDK-3.6RC3-linux-gtk.tar.gz: OK

(test.md5 has the output of the previous command)

Answer 2

On Linux systems, the program is usually named md5sum .

On BSD systems, the program is usually named md5 .

On Windows systems, aim users to http://en.wikipedia.org/wiki/Md5sum

Note that the md5sum and md5 utilities have a command-line option that can verify all the MD5 hashes listed in an MD5SUM file automatically:

sarnold@haig:~/bin$ md5sum * > /tmp/MD5SUM
sarnold@haig:~/bin$ md5sum -c /tmp/MD5SUM
aa-change: OK
aa-change.c: OK
briss: OK
mkvtom2ts: OK
muxer: OK
muxer_orig: OK

Answer 3

对于Windows，如果安装Cygwin，则md5sum可用。

Answer 4

Depends. Programming languages usually have a library to do this.

OS X has a command line utility 'md5'. Linux has something similar. For windows, no idea, but you can probably find something easily.