New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here

Operating Systems

by: Mireya Heidenreich

Operating Systems CS 5523

Mireya Heidenreich
GPA 3.55


Almost Ready


These notes were just uploaded, and will be ready to view shortly.

Purchase these notes here, or revisit this page.

Either way, we'll remind you when they're ready :)

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

Class Notes
25 ?




Popular in Course

Popular in ComputerScienence

This 8 page Class Notes was uploaded by Mireya Heidenreich on Thursday October 29, 2015. The Class Notes belongs to CS 5523 at University of Texas at San Antonio taught by Staff in Fall. Since its upload, it has received 7 views. For similar materials see /class/231395/cs-5523-university-of-texas-at-san-antonio in ComputerScienence at University of Texas at San Antonio.

Similar to CS 5523 at UTSA

Popular in ComputerScienence


Reviews for Operating Systems


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 10/29/15
CS 5523 Lecture 19 Security Case Studies I Questions on laboratory 3 l Introduce laboratory 4 I Review scenarios I NeedhamSchroeder I Bn39ef summary of common algon39thms I Kerberos Simplified overview of secret key encryption Encrypted message EK M MK Decrypted message DK EK M DK MK M ltis hard to get M from MK without knowing K Scenario 1 Secret communication with shared secret key Alice and Bob share a secretkey KAB Alice wants to send a secret message M to Bob 1 Alice uses KAB and an agreed encryption function EKAB M to encrypt and send message M to Bob 2 Bob reads the encrypted messages using the corresponding decryption function DKAB M How can Bob and Alice safely get the shared key KAB How can Bob know that M wasn t a replay Scenario 2 Authenticated communication with a server Alice wants to access Bob s les on a local le server Sara is a trusted authentication server that holds passwords and current secret keys 1 Alice sends a message to Sara asking for a ticket to access Bob 2 Sara sends Alice a response encrypted with KA that is a ticket encrypted with KB and a new secret key KAB for communication ticketKB KAB KA 3 Alice decrypts response with KA 4 Alice sends ticket herD and request R to Bob ticketKB Alice R 5 Bob decrypts ticket using KB the ticket was KAB Alice KB This is the simpli ed scenario for Kerberos KAB is the session key Simplified overview of public key encryption Keys come in pairs K1 and K2 Keep one public and one private If you encrypt with K1 you can decrypt with K2 and vice versa DK2 EK1 M M and DK1 EK2 M M Scenario 3 Authenticated communication with public keys Bob has generated a publicprivate key pair There is a trusted authority that gives out key certi cates Alice accesses a key distribution center to obtain a public key certi cate with Bob s public key Alice extracts Bob s public key KBM Alice creates a new secret key KAB and encrypts KAB known string with KBM Alice sends unique keyname KAB known stringKBW to Bob A N Am Bob decrypts KAB known stringKBM using KB 5 Bob and Alice now communicate with KAB This is the scenario for the widely used hybrid cryptographic protocol prv Scenario 4 Digital signatures with a secure digest function Alice wants to sign document M so that any recipient can verify it came from Alice This assumes thatAice has a pn39vatepublic key pair A digest is like a checksum Alice computes a xedlength digest DigestM Alice encrypts DigestM with her private key certi cate with Bob s public key and makes M DigestMKAWa vailable Bob reads M DigestMKapJ extracts M and computes DigestM Bob applies K AM to DigestMKWv to obtain DigestM and compares the value with his computed value Ms Aw Figure 74 Alice s bank account certificate 1 Certi cate type Account number 2 Name Alice 3 Account 6262626 4 Certifying authority Bob s Bank 5 Signature Digest eld2 eld 3K 5an Mum39s om Ex lenthDulmme ma mm mama ysm comm new Edn 3 AddxsunWeslAyPnblnha 2mm Figure 75 Publickey certificate for Bob s Bank 1 Certi cate type Public key 2 Name Bob s Bank 3 Public key KBpub 4 Certifying authority Fred 7 The Bankers Federation 5 Signature DigesIO ield2 eld 3KF w Mum39s om Ex lenmsDulmnn ma mug Dism bntad ysm Cmepts AndDeslgn Edn 3 AddisonWeslAYPubl luE 2mm Figure 713 X509 Certificate format subject Distinguished Name Public Key Issuer Distinguished Name Signature Period of validity Not Before Date Not A er Date Administrative information Version Serial Number Fxtenrlerl Information Mum39s om Ex lenmsDulmnn ma mug Dism bntad ysm Cmepts AndDeslgn Edn 3 AddisonWeslAYPubl luE 2mm Some popular encryption schemes I TEA tiny encryption algorithm Wheeler and Needham 1994 uses 32 rounds with combinations of XOR text shifts I DES Data Encryption Standard National Bureau of Standards 1977 obsolete because of short keys successfully cracked by brute force attacks in 1997 and a machine was built in 1998 that could crack keys in 3 days Replaced by AES Advanced Encryption Standard NIST 1999 I RSA Rivest Shamir and Ademan public key encryption based on factoring products of large primes widely used RSA s patent just expired Some popular encryption schemes continued I 3DES tripleDES ANSI 1985 apply DES 3 times with two keys very slow I lDEA International Data Encryption Algorithm Lai and Massey 1990 based on group algebra with 8 rounds ofXOR I MD5 used for data digests Rivest 1992 four rounds applying 4 nonlinear functions to each of 16 32bit segments I SHA NIST 1995 based on Rivest s MD4 algorithm to produce a 160 bit digest Figure 714 Performance of encryption and secure digest algorithms Key sizehash size bits Extrapolated PRB optimized kbytess kbytesec TEA 128 700 DES 56 350 7746 TripleDES 112 120 2842 IDEA 128 700 4469 RSA 512 7 RSA 2048 1 MDS 128 1740 62425 SHA 160 750 25162 ummgamm campaign 33125335333 sum emmmsgn m 3 Figure 715 The Needham Schroeder secretkey authentication protocol Header Message Notes 1 AgtS A B N A requests S to supply a key for communication A with B 2 SgtA N B K S returns a message encrypted in A s secret key A K 15 containing a newly generated key K A 5 and a AB K5KA ticket encrypted in B s secret key The nonce N A demonstrates that the message was sent in response to the preceding one A believes that S sent the message because only S knows A s secret key 3 AgtB Kw AKB A sends the ticket to B 4 BgtA NBKAB B decrypts the ticket and uses the new key KAB to encrypt another nonce N 5 5 AgtB N5 UK A demonstrates to B that it was the sender ofthe previous message by returning an agreed 39 o N Mum39s om Ex lenmsDolmnn ma mug Dishian ysm Contains mama Edn 3 mismwtsiaymmm 2mm Kerberos I Follows Needham and Schroeder very closely I Uses time values as nonces I When userlogs in the login program sends user s name to the kerberos authentication server I If useris known server replies with a session key and a nonce encrypted in the user s password and a ticket for TGS I Afterlogin program authenticates the information it can erase the user s password from memory Figure 716 System architecture of Kerberos Kerberos Key Distribution Centre Step A 1 Request for TGS 39 server ticket 4 Server ticket quot Step C 5 Service request Request encrypted with session key ely encrypted with session ke nmmvs Gm Ex lenmsDulrmn ma mug stha nntad ysm Contains AridDeslgn Edn 3 AddxsunWeslAyPublnhm 2mm Login session setup 39 Server session setup DoOperation a Client Server 0 s


Buy Material

Are you sure you want to buy this material for

25 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."

Allison Fischer University of Alabama

"I signed up to be an Elite Notetaker with 2 of my sorority sisters this semester. We just posted our notes weekly and were each making over $600 per month. I LOVE StudySoup!"

Bentley McCaw University of Florida

"I was shooting for a perfect 4.0 GPA this semester. Having StudySoup as a study aid was critical to helping me achieve my goal...and I nailed it!"

Parker Thompson 500 Startups

"It's a great way for students to improve their educational experience and it seemed like a product that everybody wants, so all the people participating are winning."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.