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Crypto 101 – Introductory course on cryptography

crypto101.io

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Re: Crypto 101 – Introductory course on cryptography

#31

Post by wolf550e »

gmluke wrote: post #26
stcredzero wrote: post #12

When I was taking Aikido, there was a day when the sensei was going through all of our techniques and showed how the uke (initiator of the attack, receiver of the technique) could turn things around on the tori . (receiver of the attack, initiator of the technique) It seemed like there were a half dozen ways each that a technique could go seriously wrong, and that many of them didn't require much skill, only determin…

This is slightly tangential since you specified a conspirator on the inside, but how easy is it to break a homegrown encryption algorithm if you don't have the source code? I assume there are tools (what are they?) that will break a simple caesar cipher if you have more than a sentence or so of plain text to work with. But if you strung together 2-3 broken algorithms and your attacker doesn't know which ones, is it s…

People who can break it won't spend the time breaking your homegrown crypto, so you won't get proof it's broken. But it's still broken. If lots of money or lives of political dissidents are at stake, it will be broken.

To have really capable people work on breaking your crypto for free, you have to be an insider. You become an insider by breaking other people's crypto. You can publish a break in an insider's crypto even if you are unknown. After you publish a few such papers, you become an insider and can publish your own crypto other people will spend their time trying to break.

People can learn the state of the art and develop an alternative to the common (NIST) choices which are no worse, but also no better. Some of those are blessed as "national pride ciphers" (GOST, Camellia, SEED, etc.).

Re: Crypto 101 – Introductory course on cryptography

#32

Post by clifanatic »

qwertyuiop924 wrote: post #22

Can any crypto people here on HN verify that this gets it right?

I'm the author of the book "Implementing SSL" (https://books.google.com/books?id=LfsC03f8oGsC&printsec=fron..., which covers a lot of the same ground as the link) and consider myself a crypto person - although I haven't had a chance to read every word and check through it with a fine tooth comb, based on what I've had a chance to review, it appears very accurate and very well laid out.

Re: Crypto 101 – Introductory course on cryptography

#33

Post by stcredzero »

gmluke wrote: post #26
stcredzero wrote: post #12

When I was taking Aikido, there was a day when the sensei was going through all of our techniques and showed how the uke (initiator of the attack, receiver of the technique) could turn things around on the tori . (receiver of the attack, initiator of the technique) It seemed like there were a half dozen ways each that a technique could go seriously wrong, and that many of them didn't require much skill, only determin…

This is slightly tangential since you specified a conspirator on the inside, but how easy is it to break a homegrown encryption algorithm if you don't have the source code? I assume there are tools (what are they?) that will break a simple caesar cipher if you have more than a sentence or so of plain text to work with. But if you strung together 2-3 broken algorithms and your attacker doesn't know which ones, is it s…

how easy is it to break a homegrown encryption algorithm if you don't have the source code?

A better question to ask is, how easy is it to break the protocols and the software using the protocols? We have secure ciphers. Those aren't where the problems in computer and network security lie.

Re: Crypto 101 – Introductory course on cryptography

#34

Post by stcredzero »

kaoD wrote: post #17
thfuran wrote: post #13

Earlier quoted context omitted.

What would be the purpose of such a class? If the point is to show that rolling your own security is bad, it seems like having an inside man would just help leave people convinced that they could have succeeded if only it weren't for that other guy.

Something tells me a conspirator wouldn't be required anyways. Your security is either sound or broken, i.e. probably broken unless you use proven implementations of proven cryptosystems with proven configurations. E.g. even if RSA is (currenly) safe, as well as its primitives and common configuration... rolling your own implementation will probably be subject to timing attacks.

Something tells me a conspirator wouldn't be required anyways.

The conspirator is there to teach about Defense in Depth. Systems that rely on just 1 "impenetrable" membrane tend to be brittle. Their failure is catastrophically sudden and complete, like glass breaking. Glass is way harder than steel, but steel structures are much more robust, because steel's ductility allows for partial failures and continued resistance/integrity.

Your security is either sound or broken

What about "Defense in depth?"

Re: Crypto 101 – Introductory course on cryptography

#35

Post by stcredzero »

reitanqild wrote: post #29
gmluke wrote: post #26

Earlier quoted context omitted.

This is slightly tangential since you specified a conspirator on the inside, but how easy is it to break a homegrown encryption algorithm if you don't have the source code? I assume there are tools (what are they?) that will break a simple caesar cipher if you have more than a sentence or so of plain text to work with. But if you strung together 2-3 broken algorithms and your attacker doesn't know which ones, is it s…

Also interested. Is there a general way to attack naive ciphers? I fall of at even a proper Vigenère cipher, although I guess I could hack together a terribly inefficient python script to test all options and then print them line by line and start visually scanning for patterns :-/

Vigenère ciphers based on xor: xor the ciphertext with itself at varying offsets. Stop when you detect likely plaintext in the result.

Re: Crypto 101 – Introductory course on cryptography

#36

Post by stcredzero »

wolf550e wrote: post #31
gmluke wrote: post #26

Earlier quoted context omitted.

This is slightly tangential since you specified a conspirator on the inside, but how easy is it to break a homegrown encryption algorithm if you don't have the source code? I assume there are tools (what are they?) that will break a simple caesar cipher if you have more than a sentence or so of plain text to work with. But if you strung together 2-3 broken algorithms and your attacker doesn't know which ones, is it s…

People who can break it won't spend the time breaking your homegrown crypto, so you won't get proof it's broken. But it's still broken. If lots of money or lives of political dissidents are at stake, it will be broken. To have really capable people work on breaking your crypto for free, you have to be an insider. You become an insider by breaking other people's crypto. You can publish a break in an insider's crypto e…

Ciphers aren't the place where security most often fails. The failures have to do with implementation. More commonly, they have to do with implementation of protocols and systems using the protocols.

Re: Crypto 101 – Introductory course on cryptography

#37

Post by stcredzero »

andrewflnr wrote: post #27
stcredzero wrote: post #12

When I was taking Aikido, there was a day when the sensei was going through all of our techniques and showed how the uke (initiator of the attack, receiver of the technique) could turn things around on the tori . (receiver of the attack, initiator of the technique) It seemed like there were a half dozen ways each that a technique could go seriously wrong, and that many of them didn't require much skill, only determin…

Aikido in particular seems to be very subtle, both in my experience and the opinion of an aikido black belt I've asked about it. If you restrict yourself to aikido techniques and your attacker has no such reservations, you have to be extremely good. I think it would be a mistake to give up on self-defense in general because of that. In any case, you have to go into it knowing it's not a guarantee, it just increases y…

Aikido in particular seems to be very subtle

Which aids in the analogy.

If you restrict yourself to aikido techniques and your attacker has no such reservations, you have to be extremely good.

Good for the analogy.

I think it would be a mistake to give up on self-defense in general because of that. In any case, you have to go into it knowing it's not a guarantee, it just increases your odds.

Good points for the analogy.

Re: Crypto 101 – Introductory course on cryptography

#38

Post by SkyMarshal »

andrewflnr wrote: post #27
stcredzero wrote: post #12

When I was taking Aikido, there was a day when the sensei was going through all of our techniques and showed how the uke (initiator of the attack, receiver of the technique) could turn things around on the tori . (receiver of the attack, initiator of the technique) It seemed like there were a half dozen ways each that a technique could go seriously wrong, and that many of them didn't require much skill, only determin…

Aikido in particular seems to be very subtle, both in my experience and the opinion of an aikido black belt I've asked about it. If you restrict yourself to aikido techniques and your attacker has no such reservations, you have to be extremely good. I think it would be a mistake to give up on self-defense in general because of that. In any case, you have to go into it knowing it's not a guarantee, it just increases y…

Yeah, I studied Aikido briefly in college and found it quite powerful when a petite 65yr old Japanese lady could inflict the most excruciating drop-to-your-knees pain I've ever felt with barely a touch. But it takes a decade or more of diligent practice to achieve that kind of skill, and I found Judo, BJJ, and Krav Maga quicker to become effective with.

Re: Crypto 101 – Introductory course on cryptography

#39

Post by CameronBanga »

Quick question, I had apparently Pinboarded this in March 2014. I see the PDF is still pre-release. Has anything changed with this, or is it kinda just coming up again because of recent political climate.

I'm fine either way, just curious if this has changed drastically from what I had looked at previously.

Re: Crypto 101 – Introductory course on cryptography

#40

Post by Cyph0n »

dom0 wrote: post #20
eponeponepon wrote: post #19

Earlier quoted context omitted.

There's a difficult rabbithole here - eventually you have to draw a line and decide to trust someone . Otherwise it's just layer after layer of paranoia until you implode in a puff of Philip Dick :)

Of course; my point is (and I assume that's also the point of other people who assert similar stances on the topic) that the average programmer or software engineer should leave these things to recognized cryptographers. This also highlights a peculiarity with cryptography, in that it is very hard to understand for laymen (assuming laymen are ppl with some CS or math education), so most arguments in discussions of la…

Look at DES or MD5. Were they not designed by cryptographers?

Or how about the whole Dual_EC_RBG backdoor fiasco? Yes, there was criticism right from the start, but it was adopted and used widely as far as I know. Heck, Dual_EC_RBG was only ousted in 2013:

"The ANSI X9F1 Tool Standards and Guidelines Group which discussed the backdoor also included three employees from the prominent security company RSA Security.[6] In 2004, RSA Security made an implementation of Dual_EC_DRBG which contained the NSA backdoor the default CSPRNG in their RSA BSAFE as a result of a secret $10 million deal with NSA. In 2013, after the New York Times reported that Dual_EC_DRBG contained a backdoor by the NSA, RSA Security said they had not been aware of any backdoor when they made the deal with NSA, and told their customers to switch CSPRNG."

Besides, I think it's a good learning exercise to try to implement cryptographic primitives based on existing implementations. My opinion is that such language would dissuade people from even trying to design one for fun.

Disclaimer: do not design your own crypto primitive for production use.

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