I'm sorry, but this entire discussion is missing the point. "Security by obscurity" refers to the practice of keeping the implementation details hidden, not just the key. The Enigma machine was a great example of this: despite being very good for its time (for years, the Allies only ever managed to decipher a handful of mostly useless messages without knowing its interior workings), once they came into possession of one, they managed to find the fatal flaw in its design within weeks and were able to decrypt all further communication with relative ease. Modern algorithms like AES, RSA, ECC, etc. don't have this issue β their designs have been openly published for decades, and yet no viable attack has been found that beats random guessing. OF COURSE they still involve the use of obscurity, if you will, because the protection offered by the algorithm is only as strong as the key is secret. But, unlike with the Enigma, the key is the only part that has to be kept a secret.