On Thu, Jan 20, 2011 at 2:30 PM, <[email protected]> wrote: > On Thu, Jan 20, 2011 at 01:36:55PM +1100, Noon Silk wrote: >> Hah. I'm not sure how to take that; if you knew people wouldn't get >> the idea from your original message why wouldn't you clarify it up >> front? > > It's hard to know in what ways people will misunderstand you, > for the same reason it's hard to see bugs in code you wrote. > > But there's a funny thing about cryptographers: > > If you just state the formal problem, namely my last question(s), they > might give you an answer, but you probably won't get any answers > (possibly out of lack of a practical purpose), or you might get > answers that fail due to lack of context. > > But if you try and provide some context, often they'll try to provide > alternatives, rather than answering the question, often due to > misunderstanding the context or inadequacy of explanation. The > problem with this is that you then have to go back and re-clarify, > unless you rather tediously define all your terms, assumptions > and constraints a priori. The problem with that is it wastes > time on things that might not need explaining. > > But sometimes the process can be elucidating, not only in what they > don't understand from your explanation, which teaches you how to > explain when you want to be better understood, but also because they > sometimes present alternatives which might actually work. > > So this time I just tried my best to explain context, and now I'm > having to shore it up, but I have spare time on my hands. ;-) > >> > OTP won't work - simply XORing a printable character with a non-printable >> > won't guarantee a printable, for example, and symbols have to be printable. >> >> Well no, it won't, but it's surely obvious that you could make it such >> that it was in the printable range? > > That woudl make the obfuscated symbol larger than the non-obfuscated, > and that would require altering the structure of the container file, > which I can't do.
If you use the OTP to generate a number in the printable range, and swap on that basis, I fail to see how it will go to non-printable. I also fail to see how it alters the structure if it is a direct character-for-character replacement. > The constraint is not a maximum length, but that the function be > length-preserving. > >> > Furthermore, the symbols have to map to the same thing on subsequent >> > releases so crashes can be correlated across releases. >> >> This last point is just a function of your decoding process. You're >> implying that you want to match pre-decryption, not post-decryption. > > I'm saying if the symbol is "plaintext" and the obfuscated symbol is > "obfuscate", it has to be that way for every release, without sharing > a database of mappings between releases. This is so that crash > dumps across releases can be correlated. > >> I'd expect you'd want to match post-decryption, otherwise it would be >> trivial to correlate your "obfuscation" anyway, no? > > Obviously, the once you invert the obfuscation, then you should have > the original value. > > I'm not quite following you here, possibly you said "decryption" > instead of "obfuscation", in which case I must clarify that we do > actually want people to know where the symbols migrated across > releases. That is necessary for crash log analysis, though not > ideal from a security perspective. No, I said the right thing. I must admit I'm having a bit of trouble understanding exactly how you will be implementing this practically. I agree with you that the system I'm proposing is only good post-decryption. It's clearly more than obfuscating, but it satisfies your requirements, and gives a better level of security. But it's only practical if you have the development setup to allow it to be automated. If you don't have that, then I agree it's not practical and I leave to you come up with something else. > PS: Since you might be interested in OTPs, I run the OTP mailing list: > > http://lists.bitrot.info/mailman/listinfo/OTP > -- > Effing the ineffable since 1997. | http://www.subspacefield.org/~travis/ > My emails do not usually have attachments; it's a digital signature > that your mail program doesn't understand. > If you are a spammer, please email [email protected] to get blacklisted. -- Noon Silk http://dnoondt.wordpress.com/ (Noon Silk) | http://www.mirios.com.au:8081 > "Every morning when I wake up, I experience an exquisite joy — the joy of being this signature." _______________________________________________ cryptography mailing list [email protected] http://lists.randombit.net/mailman/listinfo/cryptography
