Schneier on Security

Clive Robinson • August 14, 2021 12:22 AM

@ Thumbo,

Flimsy quantum cryptography in the field

Quantum Cryptography[1], contrary to it’s name, is not “cryptography” in terms of encryption/decryption, but more correctly “Quantum Key Distribution”.

That is, the actual “encryption algorithm” used is the normal “One Time Pad” with all it’s limitations.

Which means that the authentication it offers, at it’s widest scope, only covers the Shannon Channel between the OTP encryption and decryption mixer functions (XOR / ADD etc).

All legislation for Government Snooping so far has been above that Shannon Channel at the plaintext level. Thus they get access to the unauthenticated section between the “user and the security end point”.

The implication being that they can do anything the “user” can. Thus inject false / fake messages would fall in that range of activities.

To prevent such injection of false / fake messages your authentication layer would have to be above it. If using a Crypto Algorithm this means you would have to move the “security end point” closer to the user than the attacker can get.

Whilst as I’ve described in the past how you can do this with a paper and pencil cipher such as the OTP, Government legislation is determined to stop you using any kind of third party technology by making it illegal to manufacture and sell unless it has a “The Government wins” back-door not just inserted but connected up to a communications network the Government have control over.

Thus your options are limited to,

1, Buy and use illegal equipment.
2, Design and make illegal equipment.
3, Use a system not legislated against.

Whilst you can show mathmatically that the Government objective can always be defeated as Option 3 will always be open to you. It in no way guarantees you anything over a single bit of secure channel with any given message[2]. So the downside of any such system is a very limited secure channel bandwidth compared to the plaintext message size.

I could trot out the mathmatics to show that in all such systems the likely hood of an attacker getting a message authenticated by “luck” is low but possible. And further the likelihood is related to the number of bits in the secure channel and their individual probability functions. But you can find that in standard refrences.

[1] See BB84 and later.

[2] If you think about it the minimum secure channel / covert message you can send is message(TXed|NotTXed) at some pre aranged point in time. Thus you could arange some system where by messages sent on some agreed number of seconds increment are to be taken as valid whilst all other times are regarded as invalid. So this lack of bandwidth of a bit/message whilst limiting is not preventing.

Clive Robinson • August 15, 2021 2:40 AM

@ Thumbo, ALL,

Not thinking about all the issues of corruptible chips, software, devices before you get to that point to send a fake message.

Sadly that’s exactly where the Government through the advice of the SigInt agencies with their half century or more of experience have decided is the best place to attack with legislative and regulatory control…

First though “History is important”, these days not everyone remembers the “Morris Worm”[1] or more importantly the father of it’s creator Bob Morris[2] who was a Senior NSA Scientist. Who in an invited talk in 1995[3] gave two points many should realy learn and take to heart in all areas of life where there is a duty of confidentiality.

In fact Robert Morris himself emphasized that the attendees should write down these points,

1, Never underestimate the attention, risk, money and time that an opponent will put into reading traffic.

2, Rule 1 of cryptanalysis – Always check for plaintext.

Both readily apply to the war on cryptography and now war on authentication by current Goverments rapidly heading down the authoritarian or Police State route…

As you now see the total communications path between two parties always has three parts. The two insecure “plaintext” parts required for the “user interface” at either end. Thus past the security end points, and the middle –hopefully– secure part between of the communications channel between the two security end points.

Whilst in most cases not impossible to attack, the secure part of the communications channel if correctly implemented is well beyond current resources so remains secure for some time to come. Which just leaves what occures on the plaintext side of the security end points at the user interface for effective technical attacks.

Thus from an authoritarian Government view point the only sensible area to gain control of and maintain it, is either or both of the insecure user interfaces before/after the security end points that mark the secure part of the communications path.

With the use of modern technology by most communicating parties an authoritarian Government needs only to dictate what happens in those two insecure “plaintext” user interface areas to get everything they want to surveill nearly the entire population by “collect it all”.

It’s a point I keep making about those “Security Apps” on Smart Devices and mobile phones which are “insecure by design” because of the environment the users chose to use them in. People need to look beyond the “neat tech” to “the whole system” (which unfortunately can be complex).

Look at it this way, it matters not a jot how secure the secure part of the communications path between the security endpoints is, if an attacker can simply “end run” the security end points via the OS or other Apps a user has on their device.

And trust me when I say every Smart device/phone is riddled with such security vulnerabilities by accident or design (See comment in talks[3] about designing with a “Walker inside” it’s even more true today than it was back then). But why trust my word? Instead look at the number of “Walled Garden” supposadly checked and verified apps both Google and Apple have had to pull from their “app stores” because they had malware stealing peoples private information… The real question being “how much more is there they have missed?”…

Hopefully my above will convince rather more than just you that people need to think of “whole systems” of communications rather than “parts of systems”. Because as our host @Bruce used to point out “it’s the weakest link in the chain” where things fail.

Is there a solution to the security end point being in the wrong place?

Yes, and I’ve mentioned it before and I usually use the example of a “pencil and paper” / “Hand Cipher” One Time Pad(OTP). That way what goes into the “user interface” of the Smart decice/phone is already securely authenticated, encrypted, or both, and beyond any “collect it all” technical attacks as it has moved the securiry end points off of the technology. But… as always there is a downside, it does require the users to practice good operational security, something few can do even if their lives and liberty realy do depend on it[4].

[1] Robert T. Morris Worm from 1988 https://en.m.wikipedia.org/wiki/Morris_worm

[2] Robert H. Morris, NSA scientist and cryprographer, https://en.m.wikipedia.org/wiki/Robert_Morris_(cryptographer)

He has also had attributed to him the quote,

“The three golden rules to ensure computer security are: do not own a computer; do not power it on; and do not use it.”

Which kind of makes the point behind secure paper and pencil hand ciphers for authentication and encryption.

[3] The invited Robert H. Morris talk was at Crypto 95, where there was also a talk by Adi Shamir. Both have some serious and almost timeless points to consider, that are just as valid today as they were a quater century or more ago, which you can read at,

http://www.ieee-security.org/Cipher/ConfReports/conf-rep-Crypto95.html

[4] You would think that “master criminals” as portrayed by the authorities that are again portrayed as the “king pins” of “Serious Organised Crime”(SOC) would have high operational security as they face potentially “life in jail” or worse. Well as seen by the recent faux-security phones and the way they used them that they had not a jot of “Operational Security” practice amoungst the lot of them. Who are thus now fighting via very expensive lawyers to have the evidence collected from the faux-security phones not be allowable to be used in court… So the moral is effectively four fold,

1, Humans are lazy.
2, Humans are easily conned.
3, Humans are not to be trusted.
4, Most humans don’t learn from history.

Makes you wonder how we have survived as long as we have 😉