All Android devices support SHA-256. The NoSuchAlgorithmException indicates that a requested algorithm could not be found and is necessary because the method takes a String argument for the algorithm name. If you passed in “foo-256”, the method’s only recourse is to throw a NoSuchAlgorithmException because, for reasons beyond my understanding, there’s no algorithm called “foo-256”. … Read more
Create a newMessageDigest instance each time you need one. All of the instances returned from getInstance() are distinct. They need to be, as they maintain separate digests (and if that’s not enough for you, here’s a link to the source). ThreadLocal can provide a performance benefit when used with a threadpool, to maintain expensive-to-construct objects. … Read more
A message digest algorithm takes a single input — a message — and produces a “message digest” (aka hash) which allows you to verify the integrity of the message: Any change to the message will (ideally) result in a different hash being generated. An attacker that can replace the message and digest is fully capable … Read more