No it isn’t. It should be obvious that I meant: if one knows the latter, then one knows the former, completely regardless of the relative strength or entropy of the strings involved.
For website logins and all kinds of online services, I allow 1Password to generate passwords that are very long and comprised of all sorts of kinds of characters. These are quite impossible to memorise, and unless and until quantum computers become used practically, these passwords have so much entropy that they’re virtually immune to cracking.
For the 1Password master key (which I have to memorise) I use an extremely long and complex string that I never write down, type or store anywhere else, and which I have memorised by my own mnemonic method. I’ve used it for so long now that my brain has developed a motor program (‘muscle memory’) for it, so that I find my hands can type it faster than my brain can recall it in other ways. I’ll call this my “complex” password.
This is fine for 1Password, as the frequency with which I need to use it is low enough to justify the “long” time (a good few seconds) taken to type it. A similar “complex” password which I also memorise using my mnemonic is also good for the DT3 sync store, since I hardly ever have to enter that.
But the frequency of needing to enter a login password for my Mac is much, much higher; thus I have been using a string that has much less entropy: in other words, a less secure password. Call this my “simpler” password.
I had ‘faith’ in my simpler password to stop the casual physical snooper.
However now I see that the complex password is practically (if not actually) as secure as the simpler password in the keychain.
@rmschne: yes, of course I am thinking of physical access to my Mac.
I see that the only way to better secure the sync store is to use another complex ‘meatware’ password for my Mac login. This may be even more necessary now that access to one’s Apple ID on the web is often by way of the computer account login password.
*Password, encryption key, same difference, Most of the time we’re just talking about a string that has as much entropy as is practical for the frequency that one is required to use it. I could make the sync store string even longer and keep it in 1Password, but even then it would still be “reliant” on the Mac login password string. But really there’s little point in quibbling about labels.