Crypto 101

https://www.crypto101.io/

by tptacek • 12 years ago

352 86 12 years ago

lvh16• 12 years ago

This is a preview release of Crypto 101, an introductory course on cryptography. It's a follow-up to a talk I gave last year at PyCon.

To paraphrase David Reid, abstinence-only crypto education isn't working. We need easily accessible crypto education for developers. This book, and, once they're done, the included exercises, hopes to help.

I will happily answer all your questions here, by e-mail (see profile) or on twitter (@lvh).

In case the website breaks down, here's the direct download URL: https://9d0df72831e4b345bb93-4b37fd03e6af34f2323bb971f72f0c0...

here's a magnet link: magnet:?xt=urn:btih:e4af18f490672c6f7982a03f427e099014013774&dn=Crypto 101March2014.pdf&tr=udp%3A%2F%2Ftracker.openbittorrent.com%3A8 0%2Fannounce&tr=udp%3A%2F%2Ftracker.publicbt.com%3A80&tr=udp%3 A%2F%2Ftracker.ccc.de%3A80&tr=udp%3A%2F%2Ftracker.istole.it%3A 80

bqe2• 12 years ago

Cool stuff, man.

Where do you think your book stands in relation to other books like Cryptography Engineering? Should people new to crypto read your book before or after CE, or instead of?

lvh16• 12 years ago

Thanks!

This is definitely in the same space as CE. When I just started writing this, tptacek wrote: http://sockpuppet.org/blog/2013/07/22/applied-practical-cryp...

... and that was a huge motivator and inspiration to me. So:

1. (Unlike Applied Cryptography) focus on things that you are actually likely to hit in the wild

2. (Unlike Cryptography Engineering) Written today, and hopefully perpetually updated; including things like ECC, all sorts of CBC attacks, et cetera.

3. (Unlike either) Free of charge, and freely redistributable :)

daturkel• 12 years ago

The book looks great. I don't have any experience in crypto really but will certainly be taking a look at the early chapters here for a foundation.

edit: ignore the below, just got to this explanation in the book!

The entire Crypto 101 project is publicly developed on Github under the crypto101 organization, including this book. https://github.com/crypto101/book

----

Excuse me if this info's on the website (I can't get to it right now, HN "hug of death" it appears), will you be open sourcing contribution to the book? I'm not saying it's necessary or that I even recommend it, just curious about your authorship model (and noticed the CC license at the beginning).

Also, did you make the book in LaTeX (or some TeX variant)? If so, will you be sharing the source? I always love looking at other people's TeX documents.

dfc2• 12 years ago

Latex source

Check the github link you posted, the book is right there. I also like looking at other people's tex files. The book was written with orgmode, so this could be a double treat, you get to see the tex as well as the orgmode used to generate the pdf.

UPDATE: The choice of non-free fonts is a peculiar choice. The math text looks a little strange in places. I am not sure if there is a package to fix up the math font for caslon, ie. one similar to the minion package. The euler fonts would work for a mathfont. Why not use something from texlive so that anyone can build a copy of the book that looks like the original and/or submit improvements? Everything looks nicer when you turn on microtype.

muaddirac• 12 years ago

Looks great (haven't read all of it yet).

Have you considered using something like Ipe to make diagrams for you?

lvh16• 12 years ago

Nope! I just started drawing some stuff and it stuck. I had never even heard of ipe. How's it compare to TikZ? (That seems like the closest thing I have played with.)

smnrchrds• 12 years ago

It would be nice if you collect email addresses so that you could inform interested individuals(that's me!) when the final version is released.

lvh16• 12 years ago

I'm actually trying to, but at the last minute I changed the magnet link to a HTTPS PDF link, which appears to open in a new window for most people :-/ Any help from people with frontend chops who could tell me how to fix that (apparently Content-Disposition isn't the answer?) would be much appreciated!

wiredfool• 12 years ago

Do you want patches/prs for copy editing? I've noticed 2 or 3 of them.

lvh16• 12 years ago

Absolutely! All the stuff is on Github, website and book (and source code for the exercises which I'm still hacking on): https://www.github.com/crypto101

Thanks in advance for your contributions!

hmottestad• 12 years ago

Had a look through and really enjoyed the picture examples, can even remember some of those examples from uni.

And I see you are using vectorisation of hand drawn diagrams (maybe you write on a whiteboard and then take a photo and vectorise it). If you have an ipad I would recommend GoodNotes and a good stylus (maybe the Adonit Jot Script).

lvh16• 12 years ago

Thank you for the kind words!

Due to a stupid oversight my iPad is stuck in storage somewhere a few countries over :( I really wish I could, but right now it's just me, white paper, a pen, a scanner and potrace. It's tedious, but workable :)

devindotcom3• 12 years ago

This looks helpful for people who are already very code-literate. But it seems like "101" should start with the absolute basics, stuff like classical cyphers, the history of cryptography, and definitions of basic terms. I realize that's not what the HN crowd really needs, but it would be a good place for hundreds of millions who are interested in learning what it really means for something to be secure, encrypted, hashed, etc. Anyone have a favorite resource to this end?

tptacek4• 12 years ago

I'm interested in what you think the value of studying classic ciphers is.

sillysaurus3• 12 years ago

FWIW, I got way more value out of the Matasano challenges than studying classic ciphers.

Do you think it'd be a not-terrible idea for newcomers to focus entirely on studying this? http://www.daemonology.net/blog/2009-06-11-cryptographic-rig...

draker• 12 years ago

For someone that is truly a beginner in cryptography it is helpful to understand at a very basic level how encryption/decryption works.

Using something simple as a Caesar cipher or ROT13 you can show how plaintext undergoes a transformation using an algorithm to create the cipher text and how that same algorithm is used to convert the cipher back to plaintext.

This simple idea provides the basis to discuss other cipher techniques (and their shortcomings); as well as provide an early example of symmetric-key algorithms.

devindotcom3• 12 years ago

Well I personally find clarity in the history of things — they provide context and a narrative for the topic in question. You don't start a class on warfare with Afghanistan, for instance, or even WWII. It's worth going back to the beginning, if only for a cursory look at how wars were fought, how innovations came about and when, and which of them is still influential.

Similarly, with crypto, I think it's about understanding how and why cryptography emerged, and learning about the arms race it developed into as people went from decoder-ring level encryption to the present state of the art. Knowing when and why key exchanges were first created, how they were broken back then, why one-time pads are still useful in some circumstances, and so on I think contributes to a larger understanding, something that exceeds a technical one - and I also believe that will lead to better implementation (though I don't have much to back that up).

Also, there are interesting stories in there. Learning why Enigma was unbreakable, and subsequently how it was broken and the attending circumstances, informed as they were by politics and strategic warfare, is a lesson not in cyphers, but in cryptography. I think that's important, though obviously that is not OP's goal! I just think it should the way one starts — at the beginning.

GhotiFish2• 12 years ago

They are easy to understand and provide a venue to use the cryoptographic terms that the students should learn to use.

Having to understand a complicated bit of cryptography while at the same time coming to terms with a big batch of nomenclature you haven't committed to memory is hard. Harder than I can handle anyway.

enraged_camel• 12 years ago

"Those who don't know history are doomed to repeat it."

lvh16• 12 years ago

Thanks! This is definitely targeted towards developers. There's certainly some sections that require you to be able to read some code, but I'd hope to eventually tone those down to a minimum. My personal popular science favorite for that is probably the Code Book by Simon Singh.

lhgaghl• 12 years ago

.io

not sure if legit

TrainedMonkey2• 12 years ago

Both coursera and udacity have amazing courses on crypto.

Udacity: https://www.udacity.com/course/cs387

Coursera crypto I: https://www.coursera.org/course/crypto

Coursera crypto II: https://www.coursera.org/course/crypto2

I took coursera crypto I myself. It was a lot of work, but I learned a ton.

agwa2• 12 years ago

Good luck trying to take Coursera's Crypto II: I've been signed up since August 2012, and every 3-6 months it has been delayed another 3-6 months. At this point I'm no longer expecting it to be offered.

Crypto I is not vaporware and is excellent.

dethstar• 12 years ago

Makes you wonder why aren't online classes kept, at least a year or something, in case the information is out of date (for technology)?

B-Con• 12 years ago

I have hopes for Crypto II. Based on Crypto I, Boneh likes to do a good job with the course and being who he is, he's probably just incredibly busy (the original Crypto I itself had two minor delays in the middle of the class), so it keeps getting postponed. I wouldn't be surprised to see it materialize eventually.

tbirdz• 12 years ago

It's really refreshing to have a site just give you the material without making you make an account, or sign up via email first.

skrowl• 12 years ago

Anyone else only get:

<html><head><title>Processing Failed</title></head><body><b>Processing Failed</b></body></html>

lvh16• 12 years ago

Yep. Too many open file descriptors. I'm trying to figure out how to fix that without taking the site down now.

EDIT: It should be hopefully slightly better right now...

Mithrandir• 12 years ago

Website: https://archive.is/fG4Fb

Book: https://9d0df72831e4b345bb93-4b37fd03e6af34f2323bb971f72f0c0...

kmtrowbr• 12 years ago

The "processing failed" banner is quite ironic considering our recent collective experiences with cryptography. Why the Mt.Gox failure and so many other hackings and exposures of supposedly-private data? "Processing Failed"

marshray2• 12 years ago

I don't read "Processing Failed" as an indication of hacking or a data breach.

Sounds to me more like an overloaded website falling back to a small static error page.

EGreg• 12 years ago

I already took Crypto 101. Where are the next ones? :)

mschuster912• 12 years ago

The "call to action" button "get the prerelease now" redirs me to https://www.crypto101.io/testfile ... obviously b0rken.

lvh16• 12 years ago

I have no idea why; the Docker container just started randomly serving a really old version (several hours ago) for no apparent reason, and then started serving the right thing. I seriously have no clue what happened.

I am very sorry. Have a direct PDF link: https://9d0df72831e4b345bb93-4b37fd03e6af34f2323bb971f72f0c0...

mschuster912• 12 years ago

...this is why one uses servers setup by hand on real, dedicated machines instead of five-level-virtualized piles of dung heap. Not unless the dung heap has refined over the course of a couple years.</rant>

Thanks for the link, it'll be a night lecture for me for some weeks, I can tell :)

richm442• 12 years ago

Just looking at the table of contents is a bit worrying. :-(

Why are block cipher modes like CBC and CTR, and issues like padding listed in the stream cipher section? Those aren't relevant to stream ciphers (though you can regard counter mode as turning a block cipher into a stream cipher).

Putting pbkdf2, scrypt bcrypt under key derivation functions but omitting them from the password storage section while technically accurate isn't really helping anyone.

Reading the text in enough detail to see if this is any good would take longer than I've spent, but the organisation of the material at least definitely needs some work.

lvh16• 12 years ago

Hi! Thanks for your comments. I feel that a more detailed reading would most likely address your concerns.

The book explicitly addresses why modes of operation (and their related bits, like padding) are in the stream cipher section. I've flip-flopped between putting them in one or the other a few times now, but I'm increasingly convinced that doing it this way (and having the book explicitly say that I'm doing it this way) makes the storyline, similar to the one I tried to keep in the talk, work better.

The password storage section talks about a lot of broken password stores, as a subsection of the chapter on hash functions. It explicitly refers to the key derivation function section at the end. This pattern comes back through the entire book: "we want to do X, and it may look like we can do X already with the tools P and Q we have already, but you actually still need R and S; here's why".

richm442• 12 years ago

Fair enough. I'll read it properly and then comment. :-)

ctlaltdefeat• 12 years ago

Who is the author? I can't find anything about him except for his real name and a self-description of "hacker". I'm confused why he thinks it's reasonable to create something so authoritative sounding as "crypto 101" without bothering to explain his credentials to do so.

grifpete• 12 years ago

Webpage not available - nice touch!

lvh16• 12 years ago

I am very sorry. Have a direct PDF link: https://9d0df72831e4b345bb93-4b37fd03e6af34f2323bb971f72f0c0...

lvh16• 12 years ago

I'm very sorry for the availability issues. All of my usual tricks for increasing the fd limit didn't work; then I realized this is because of two things:

1. I'm running inside a docker container 2. I'm using ubuntu instead of debian, and upstart conveniently ignores all the usual fd limits places like /etc/security/limits.conf.

TL;DR, be careful when experimenting with new fancy technology you don't understand.

I hope it's resolved now ;-)

albertoleal• 12 years ago

Host it on something like GitHub?

mnx• 12 years ago

So, is the kindle edition in the making, or not available anymore, or what is going on with it?

Mindless2112• 12 years ago

While there are also modes of operation (like OFB and CFB) that can produce self-synchronizing stream ciphers, these are far less common, and not discussed here.

Aw. :( Aren't there any noteworthy attacks against these modes?

pbsd• 12 years ago

While CFB can be considered a self-synchronizing stream cipher, OFB is a typical synchronous stream cipher. Being stream ciphers, these modes suffer from the usual bit-flipping attacks and nonce-reuse problems, same as CTR.

One problem specific to these feedback modes (and also to sponge functions) is the possibility of falling into a short cycle. A random permutation is expected to have log n cycles, with one big cycle taking around half of the values and a few shorter ones. Falling into a short cycle would imply quickly repeating the stream, which is catastrophic. The good news is that for a good block cipher the probability of this happening is overwhelmingly small, i.e., 1/2^(n-1) for block size n.

ams6110• 12 years ago

First time I hit the page, I got a https connection error, ssl_error_no_cypher_overlap

Tried it again and it's fine.

timv• 12 years ago

Likewise (running Firefox)

aaxx1503• 12 years ago

This seems like a great base. I'd love if there was a step-by-step guide to creating a cryptocurrency though. I'm trying to learn about it (without intending to release another onto the crap filled market) and there's not many guides. It seems like a well kept secret for now. Simply cloning one is giving me enough trouble, I can't generate the merkel root and move on from there. No documentation.

nullc• 12 years ago

Here. I'll start you on better class on cryptography than any video, pdf, or slide deck you're going to find.

Go to this repository, grab the code, and figure out how you can attack it: https://github.com/jackjack-jj/jeeq (of course, along the way go learn whatever you need to). There are several interesting weaknesses in this code, and yet it's not just a toy: it was briefly deployed in a widely used application.

(If you google for it, you might find some of my analysis on it, which would potentially spoil the learning experience, so I suggest you don't. Though if you finish with this one I can dig up some other weak cryptosystems.)

phazmatis• 12 years ago

Any crypto guide that doesn't include practical attacks against DES is a waste.

zxexz• 12 years ago

Then contribute to the guide.

capisce• 12 years ago

In Chrome pressing the "Get the pre-release now" button immediately opens the pdf in the same tab, which means it's not possible to subscribe for updates. I had to use Firefox instead for it to work as intended.

nyddle• 12 years ago

One can also learn crypto by doing with Matasano Crypto Challenges:

http://www.matasano.com/articles/crypto-challenges/

tehbrut• 12 years ago

Twice sent an email and did not receive any response

swah• 12 years ago

tptacek, are you involved with this?

angelbar2• 12 years ago

STOP !

angelbar2• 12 years ago

hahaha.... bad link sorry

Crypto 101

Related Stories