Software updates and TUF
The TUF Advantage
TUF also uses text files with JSON-encoded data, so you can easily check the signatures manually and then check the file contents – because they are human readable. Because TUF does not rely on network encryption to protect the data or metadata in transit, you can deploy it over untrusted networks and even on untrusted servers. The worst thing an untrusted server can do is refuse to update the files, which the client software will detect. The untrusted server cannot, for example, include an updated timestamp file with older signed metadata, because the metadata will not be the listed version. The same goes for the actual files, which also means clients can run their own mirrors of the update server – even offline mirrors – assuming they have some way to move the files to them.
Projects Using TUF
Sadly, not a lot of people are using TUF. The good news is that several programming languages are now looking at using TUF to secure their plugin frameworks. Python's PyPI, for example, has PEP 458 , and some New York University students are working on adding TUF support to the RubyGems client .
Now you have an update system, and you're able to push a single file or an entire block of files to clients. What should you do about older versions with known security flaws? Because you control the timestamp file, you can change the metadata to make old files invalid, so even if someone keeps the old signed files around, the client won't use them. Whether or not you should do this is an open-ended question. For applications, it's probably not a bad idea, assuming the newer versions don't have bugs that prevent them from working. For programming language components, this may not be a safe choice because it could potentially break a large number of systems using your update system.
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