Ryan Henry

Spring 2017 • Lecture 1

B504 /I538:Introduction toCryptography

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Administrivia

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Instructor• Instructor: Ryan Henry

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• Office hours: Fridays @ 10:30 — 11:30(or by appointment)

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http://homes.soic.indiana.edu/henry

henry@indiana.edu

LH 330E

- Alas, Ryan is stuck in Washington DC today ; - (

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Associate Instructor (AI)

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• Instructor: Swami Ramesh

• Office hours: Fridays @ 13:30 — 14:30(or by appointment)

swamivr@indiana.edu

LH 330A

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Required textbook

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Introduction to Modern Cryptography (2nd edition)

Jonathan Katz and Yehuda LindellChapman & Hall/CRC Cryptography and

Network Security SeriesNovember 2014

Katz’ website IU Bookstore CRC Press Amazon* * *

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Course website

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http://homes.soic.indiana.edu/henry/courses/b609/s17

The course website is the official source for:– assignments,– lecture slides,– important announcements,– supplemental material,– etc.

PLEASE CHECK THE COURSE WEBSITE FREQUENTLY!Also, Canvas: https://iu.instructure.com/courses/1600125

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Lectures

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Tuesdays and Thursdays

@ 13:00—14:15in Ballantine Hall (BH) 322

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Should I interrupt withquestions during lectures?

A: Only if you want answers(in other words: YES, PLEASE DO!)

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Grading and assessment

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8 assignments at 10% each

4 quizzes at 5% each

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Grading and assessment

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A+97% B+87% C+77% D+67%

A 93% B 83% C 73% D 63%

A- 90% B- 80% C- 70% D- 60%

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Homework

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• One assignment assigned every second Tuesday*

– Due before Tuesday lecture two weeks later

• Mostly written with some coding problems

– ASK FOR HELP EARLY!• We will stop providing help starting 10 days after assignment is distributed!

* with a few exceptions ― see the calendar

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Homework (sample timeline)

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Sun Mon Tue Wed Thu Fri Sat

Sun Mon Tue Wed Thu Fri Sat

week N:

week N+1:

Sun Mon Tue Wed Thu Fri Satweek N+2:

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Typesetting with

• Written portion of assignments must be typeset using

• We will give you the source for every assignment

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Q: By a show of hands, who here knows ?- If your hand is not up, good news: you get to learn !!

• SoIC has a site license for ShareLaTeX

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When do we starttalking aboutcartography?

A: Umm … Never!(this class is about cryptography!)

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Huh!? No maps??Well what in the @#%★‽! is

“cryptography”?

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What in the @#%★‽! isCryptography?And, more generally, what is this course all about?

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What is this class all about?• Short answer:The theoretical foundations of modern cryptography

• Cryptography ⊆ mathematics– No specific background is assumed, but

“mathematical maturity” will help– We will cover the necessary math as we go!

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What is this class all about?

15 https://xkcd.com/435/On the other hand, physicists like to say that physics is to math as sex is to masturbation

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What is this class all about?• Cartography, for starters• But also:

– particulars of deployed encryption schemes– specific “hard” problems– how to implement， use, or break specific

cryptographic software

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ADVICE: Don’t try to implement crypto yourself!

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I will make you write lots of proofs

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statement 1statement 2statement 3

⋮statement n

I don’t see whystatement 2

follows fromstatement 1NO MARKS FOR YOU!Peggy

(the prover)

Victor(the verifier)

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I will make you write lots of proofs

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Victor is very thorough yet very lazy- will catch every mistake you make…but- cannot be bothered to supply missing details

A perfectly valid complaint for Victor:

“I don’t understand!”(or even, “This is poorly written”) Victor

(the verifier)

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So it’s allmath and proofs?

(See ya—I’m dropping!)

NO!! WAIT!It’s not just any math andproofs…it’s super important，super cool math and proofs!

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“Core” crypto• Key establishment

• Secure communication

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m1

confidentiality/integrity

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More advanced crypto• Digital signatures

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More advanced crypto• Digital signatures• Anonymous communications

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More advanced crypto• Digital signatures• Anonymous communications• Oblivious computation

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More advanced crypto• Digital signatures• Anonymous communications• Oblivious computation

• Anonymous digital currencies

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Ƀ

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Cryptographic protocols• End-to-end verifiable elections

(as if anybody ever suspected an election was rigged!)

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Cryptographic protocols• End-to-end verifiable elections

(as if anybody ever suspected an election was rigged!)

• Secure multiparty computation

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f(x1，x2，x3，x4，x5)x1 x3 x5

x2 x4

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Crypto magic

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Zero-knowledge proofs

And a whole lot more…

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Modern cryptograpy == Science

• Three steps in modern crypto

1. propose a precise threat model2. propose a construction3. prove that breaking construction is “equivalent”

to solving an intractable problem (or impossible)

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That’s all for today, folks!

Thursday’s lecture: Discrete probability 101