The software is downloaded through a temporary download link which is provided
in an email sent to the client after a successful purchase.

Software download file: TimesTables-3.0-Linux-x86-Install-Jre

Verify the file integrity, unchanged/undamaged status after download:
Download checksum archive file from: www.jfundi.com/downloads/times-tables-30-checksums

Unzip installation checksum file in the same directory as downloaded software file:
gunzip < TimesTables-3.0-Linux-x86-Install-Jre.tar.gz | tar xvf -

Checksum files uncompressed:
TimesTables-3.0-Linux-x86-Install-Jre.md5
TimesTables-3.0-Linux-x86-Install-Jre.sha1
TimesTables-3.0-Linux-x86-Install-Jre.sha224
TimesTables-3.0-Linux-x86-Install-Jre.sha256
TimesTables-3.0-Linux-x86-Install-Jre.sha384
TimesTables-3.0-Linux-x86-Install-Jre.sha512

Search for executable md5sum, sha1sum, etc. (command in terminal: whereis md5sum)
Type in Terminal: $/usr/bin/md5sum -c TimesTables-3.0-Linux-x86-Install-Jre.md5
$/usr/bin/shasum -c TimesTables-3.0-Linux-x86-Install-Jre.sha1
$/usr/bin/shasum -c -a 224 TimesTables-3.0-Linux-x86-Install-Jre.sha224
...
If all checksums verified OK, the download file is verified and OK, install it!