But you’re giving enemies the possibility of communicating without being able to tamper with that communication. To what extent is it harmful when you see this type of “encryption” (someone rightfully stated SHA-256 is not an encryption algorithm), you know it’s the NSA?
I’ve read every answer above, and I still think someone should not completely exclude the possibility that they made it public because they have it solved. I think the answer to this question must be something THEY benefit from, contrary to what some suggested above that they’re doing this for being good benevolent people.
Compromising SHA256 doesn’t have sufficient impact on Bitcoin. A few ways for which it can impact Bitcoin is by:
SHA256 computation speedup - Yielding nothing significant other than increasing the difficulty a little.
Finding second preimage - Your resultant hash has to be valid with the valid block header hash, which is also quite difficult.
Collision - Somewhat similar to the difficulty above.
Generating hash collisions of Bitcoin Core files - Probably not the target in mind for NSA.
Cryptographers and mathematicians have reviewed SHA and the other algorithms released as standard by NIST for years which has concluded that they’re secure enough. The US government uses it, and practically every company that guards their state secrets uses it. It doesn’t take much to figure out any weaknesses when the entirety of the algorithm is public and available.
I understand how people might think of it as that way, but SHA family is pretty much a well known and audited algorithm. It would be far more suspicious if NSA or the government releases a closed-source and obfuscated exe and tells us to use it to replace the existing standards.