You can verify the integrity of downloaded files against checksums
provided in SHA256SUMS
or SHA512SUMS
files on Debian mirrors. You can find them in the same places as the installation images
itself.
Visit the following locations:
To compute the checksum of a downloaded installation file, use
sha256sum filename.iso
respective
sha512sum filename.iso
and then compare the shown checksum against the corresponding one in the
SHA256SUMS
respective SHA512SUMS
file.
The Debian CD FAQ has
more useful information
on this topic (such as the script check_debian_iso
, to semi-automate
above procedure), as well as instructions, how to verify the integrity of the above checksum
files themselves.