Lecture 4: Stream Ciphers and Linear Feedback Shift Registers by Christof Paar

[lixiao]

Dear Professor Paar,

Thank you very much for sharing your lectures on YouTube! I am learning more from you than from my professor and my tutor. Our lecturer at the University of Melbourne can't even speak proper English, let alone teaching Cryptography. I solute you, and wish you the best!

You're awesome!

[introductiontocryptography]

There are different assumptions about Oscar's capabilities. The 4 major ones are: It is always true that he knows ciphertext and does not know the key. Often it is also assumed that he knows part of the plaintext, e.g., a file header. Another assumption that is often made is that he can choose the ciphers or even the plaintext. A good crypto system should be secure against all these attacks.

Re timing: This is application specific. In classical communication security settings where Oscar is listening-in on the channel, e.g., the Internet or an air link, he also has the timing information. Also in embedded systems such as a smart card, he can observe the timing behaviour in a very detailed fashion. --- Hope this helps, christof

[Yuri-btwl]

*Topics*

Recap & Lecture program 0:20
Introduction to LFSR 3:00
General LFSR 34:20
Attack against single LFSR 1:13:37

[DeckSeven]

Another great lecture on stream ciphers! What I find great here is that Christof Paar proves that PRNGs alone are useless for encryption unless being used as a layer in a cryptographic system, as he suggests at the end of this lecture. Although I would forget PRNGs altogether and directly focus on TRNGs and CSRNGs.

[thesickbeat]

In a computer engineering course in NL our homework is to read your book. I'm happy I found out that you've provided lectures. Really helps a ton!

[manorujas]

You are an amazing teacher . Thank you so much !

[xyz]

I was very confused about the 'P' part, but then ex1 came and it all started to make sense. Thank you sir this was very beautiful.

[raar]

Thank you professor Paar for your useful video lectures.

[Sara-mgeo]

I stopped going to my class and studying your amazing lectures, thank you Sir

[potkettle]

Fantastic. Just subscribed and bought the book.
My own understanding towards OTP ciphers, was via Vigenère, which I thought you would touch on. I understand RC4 to basically be a key-stretched version of Vigenère part way towards an OTP.
Looking forward to the rest of the series.

[MaxB_]

1:05:47 - I did not completely understand why the polynomial was x^4 + x + 1. In my eyes it would have been x^4 + x^3 + 1

[slavkochepasov]

1:29:04 "the but" is known as LFSR shrinking-generator. See A5/1 cipher for example as referenced by the professor.

[prithviprakash]

This may seem a little off topic, but towards the end of the lecture when you talk about breaking the Stream Cipher using LSFRs, given the vast number of implementations of different cryptographic algorithms, how would Oscar know that he is dealing a Stream, and not a block, or an Asymmetric Cipher?
Great lectures, btw, really enjoying them and learning a lot.
Thank you, Professor Christof Paar!

[نعمانمنذرمحمودالجميلي]

from IRAQ, thank you for this amazing explanation . big love <3

[shojin]

I'm confused is when you say 2 to the m -1, you wrote it as 2 times m -1. Did you mean it as 2 to the power of m -1 or 2 times m -1 ?

1:17:20
1:27:41
52:20

[Nuram]

wenn ich gewusst hätte dass es in der bochumer university so geile profs gibt wär ich dahin gegangen :D klasse und sehr verständlich erklärt! Hat mich als Software-Engineer sehr weitergebracht ;)

[KatieSwordvideos]

боже, благослови ютуб! Это именно то что мне было нужно!

[prajganesh]

Does the cellphone and cell tower share the same seed? How are they able to decrypt?

[gildasgaetan]

Thanks you professor. I started course to LFSR and now i like working at home. My project research is in area of cryptography and i have many lacks to this area. Nevertheless, your courses are a good tools to starts implementing my works

[smrititiwari]

most important equation of the day since 1911 :P