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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 lvh »

CiPHPerCoder wrote: post #29
lvh wrote: post #11

Hi! I'm the author. Happy to answer questions.

Hi lvh, Do you intend to complete this book at some indeterminate point in the future? Is there anything that any of us can do to help make it happen?

I'm not sure what "complete" would entail :) For example: would a description of Noise be in scope? I think so but I'm not sure. People come up with new cool stuff that's useful to median developers on the regular (say, NMR) that feels like it ought to be added/updated. So I think it's forever a WIP and that's OK since I'm not really printing the book?

Re: Crypto 101 – Introductory course on cryptography

#32

Post by pbsd »

blattimwind wrote: post #23
throwawaymath wrote: post #14

Earlier quoted context omitted.

It actually makes a lot of sense for practical purposes. This probably looks strange to you because most introductory cryptography texts strictly segregate stream and block ciphers. The standard pedagogical style bifurcates modern symmetric encryption into one of these two categories and talks about things like synchronization, on-the-fly encryption, speed, error correction, etc. between the two. In point of fact, th…

> Many (most?) stream ciphers actually use blocks internally. I don't think there have been any new designs for a good while that didn't. RC4 is, I think, the last actual stream cipher that saw widespread use (apart from designed-as-broken telco crypto). The same observation can be made for classified crypto, where they used to use bit-stream ciphers like Walburn or Saville (efficient, relatively low gate count hardw…

Most of the eSTREAM finalists (http://www.ecrypt.eu.org/stream/index.html) are not block-based. I think only Salsa20 matches that description.

More generally, I think the distinction between a "block-based stream cipher" and a block cipher (or permutation) mode is the degree to which you abstract away the block cipher. Personally I wouldn't put them together. Counter mode completely abstracts away the cipher, assuming it is an idealized pseudorandom function; sponge-based modes also abstract away the permutation as ideal in most cases; stream ciphers usually do not do this, and use weaker (but still sometimes block-based) primitives to generate output. There are, for example, sponge modes that use very few rounds past the initialization, which makes them more streamy than spongy. So their cryptanalysis is often different.

Re: Crypto 101 – Introductory course on cryptography

#33

Post by lvh »

pbsd wrote: post #32
blattimwind wrote: post #23

Earlier quoted context omitted.

> Many (most?) stream ciphers actually use blocks internally. I don't think there have been any new designs for a good while that didn't. RC4 is, I think, the last actual stream cipher that saw widespread use (apart from designed-as-broken telco crypto). The same observation can be made for classified crypto, where they used to use bit-stream ciphers like Walburn or Saville (efficient, relatively low gate count hardw…

Most of the eSTREAM finalists ( http://www.ecrypt.eu.org/stream/index.html ) are not block-based. I think only Salsa20 matches that description. More generally, I think the distinction between a "block-based stream cipher" and a block cipher (or permutation) mode is the degree to which you abstract away the block cipher. Personally I wouldn't put them together. Counter mode completely abstracts away the cipher, assum…

> More generally, I think the distinction between a "block-based stream cipher" and a block cipher (or permutation) mode is the degree to which you abstract away the block cipher.

Just to make sure I understand you correctly, for example:

- CTR: definitely a stream cipher, and a synchronous one at that

- CBC: maybe a little like a stream cipher (you're e.g. exposed to the block width, and also less like most stream ciphers because asynchronous)

- AEZ: extremely not (because you're exposed to round counts)

That makes perfect sense to me, since that's where I felt the analogy started getting tenuous :)

Re: Crypto 101 – Introductory course on cryptography

#34

Post by [deleted] »

lvh wrote: post #33
pbsd wrote: post #32

Earlier quoted context omitted.

Most of the eSTREAM finalists ( http://www.ecrypt.eu.org/stream/index.html ) are not block-based. I think only Salsa20 matches that description. More generally, I think the distinction between a "block-based stream cipher" and a block cipher (or permutation) mode is the degree to which you abstract away the block cipher. Personally I wouldn't put them together. Counter mode completely abstracts away the cipher, assum…

> More generally, I think the distinction between a "block-based stream cipher" and a block cipher (or permutation) mode is the degree to which you abstract away the block cipher. Just to make sure I understand you correctly, for example: - CTR: definitely a stream cipher, and a synchronous one at that - CBC: maybe a little like a stream cipher (you're e.g. exposed to the block width, and also less like most stream c…

[deleted]

Re: Crypto 101 – Introductory course on cryptography

#36

Post by weinzierl »

leroy_masochist wrote: post #7

+1 for the fact that the "get book" button on linked site just downloads the pdf .

Thanks, for the comment. I wouldn't have bothered with this otherwise. Normally a "Download our PDF|Whitepaper|Whatever" is a 100% sure way to make me close a site immediately nowadays - and this is what I did. Just stumbled upon your comment because the tab was still open and it was the first comment.

VirusTotal seems to be cool with the file too, so that's how it should be.

https://www.virustotal.com/#/file/fe42077288cfaa6d1d1b83c088...

Re: Crypto 101 – Introductory course on cryptography

#37

Post by lvh »

weinzierl wrote: post #36
leroy_masochist wrote: post #7

+1 for the fact that the "get book" button on linked site just downloads the pdf .

Thanks, for the comment. I wouldn't have bothered with this otherwise. Normally a "Download our PDF|Whitepaper|Whatever" is a 100% sure way to make me close a site immediately nowadays - and this is what I did. Just stumbled upon your comment because the tab was still open and it was the first comment. VirusTotal seems to be cool with the file too, so that's how it should be. https://www.virustotal.com/#/file/fe42077…

You can get the org mode plaintext source here: https://github.com/crypto101/book.

It doesn't read as well as the PDF because there's a ton of illustrations and _something_ has to render them.

Re: Crypto 101 – Introductory course on cryptography

#39

Post by komali2 »

blattimwind wrote: post #24
komali2 wrote: post #18

Oh interesting. I recently got "Applied Cryptography" in one of the nostarchpress sales. I expected it to be turbo technical and way outside my league but popped it open on a whim one day. So far it's incredibly accessible, does anyone have thoughts on that versus this course? Worth taking the course after I finish Applied cryptography?

Incidentally, Applied Cryptography is often critiqued for making crypto seemingly easy and incredibly accessible, which led to some people implementing very nice fails. For practical purposes the later Cryptography Engineering book is probably a better choice.

That's an interesting point. However, I am not interested in implementing/engineering cryptography (ever), just having a decent idea of what's going on. Is this still a failure of the book I should watch out for?

Re: Crypto 101 – Introductory course on cryptography

#40

Post by komali2 »

lvh wrote: post #20
komali2 wrote: post #18

Oh interesting. I recently got "Applied Cryptography" in one of the nostarchpress sales. I expected it to be turbo technical and way outside my league but popped it open on a whim one day. So far it's incredibly accessible, does anyone have thoughts on that versus this course? Worth taking the course after I finish Applied cryptography?

Do you mean "Serious Cryptography"? Applied Cryptography isn't a No Starch Press book.

No, I do mean Applied Cryptography. I may have picked it up in a humble bundle sale in hindsight.
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