cross-posted from: https://fost.hu/post/226135
Let’s say, I create a bank with the caveat that all of my banking phone apps and webapps are FOSS (or if they depend on non-free components — banks probably do to communicate with each other —, then just OSS). Am I going to be behind the competition by doing this?
If the most secure crypto algorithms are the ones that are public, can we ensure the security of a bank’s apps by publicizing it?
Are they not doing this because they secretly collect a lot of data (on top of your payment history because of the centralized nature of card payments) through these apps?
EDIT: Clarifying question: Is there a technical reason they don’t publicize their code or is it just purely corporate greed and nothing else?
It would be unwise for a bank to publish its exact fraud detection and risk management policies, otherwise they could be easily circumvented. A lot of these policies will be embodied in their internal backend services.
Someone will now inevitably mention "security by obscurity". But Kerckhoff's Principle is specifically about cryptosystems which should derive their security solely from the strength of the keys. That way, confidentiality is still ensured even when details about the cryptosystem become known to adversaries.
But non-cryptographic aspects of security benefit from asymmetric knowledge, from grey areas, from increasing risk for adversaries.