Quiz 1 Topics ECE6612 - Computer Network Security Spring 2013 These slides are in

Quiz 1 TopicsECE6612 - Computer Network Security

Spring 2015

These slides are in http://www.csc.gatech.edu/copeland/jac/6612/slides/

Click on “05 Quiz-1 topics.ppt”

Past Quizzes and Answers are in “Resources” on T-square/

You may bring one 8.5” by 11” reference sheet to the quiz. It must be handwritten by you. Both sides are available.

Otherwise, pencil or pen, and a simple calculator only (no stored text or wireless access).

Chapter 1 - IntroDefinitions and examples:

Security Attacks (Spoofing, Interception, Trojan Horse, Bot, Worm, IP & Port Scanning, Sniffing, Root Kit, Spam, Malware, ...)

Services (below, P & 4A’s) & Mechanisms (e.g., Encryption)Privacy (Secrecy)

Authentication (Identification & Nonrepudiation)Authorization (limit access based on

Authentication)Alteration Protection - IntegrityAvailability (avoid Denial of Service Attacks)

Combination of Authentication and Authorization:Access Control (good password, use of hashes)

RFC's (IETF “Request for Comments”)IEEE (802.x LANs), ISO (X.509 Cert), NIST (AES Encryption)

Defenses (Firewalls, Virus Detection, Honey Pots or Honey Nets, …)

1st of 3 Basic Rules: No Security without physical (access) security.2

Chapter 2 - Cryptography

Conventional (Secret-Key), cryptographer vs. cryptanalyst , plaintext, ciphertext, decrypt vs. decipher, number of possible keys (time for exhaustive search), characteristics of good encryption and random numbers.Feistel structure: DES, 3-DES, Blowfish (but not AES) Crypto-feedback: CBC, CFB, Streaming-mode Key distribution, use of a session key (why). Concept of Information Entropy (encryption, compression) Use of redundancy to recognize plaintext and break codes (Caesar codes, substitution codes, block codes). Self-synchronizing codes (pros and cons), link versus end-to-end encryption.Prove quality of encryption technique (Fundamental Tenet)?Hash algorithms: output same size, one-way, weak or strong collision resistance. How are they used, which are safe today: MD5, SHA-1, SHA-2 (SHA-256 or SHA-512), SHA-3.

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Chapter 3 - Public-Key and AuthenticationRole of trusted authority (CA) - who (is/are) the top level CA(s). How does your browser use them. Man-in-the-middle attack (when is it effective, how do you defeat it). MAC and MIC, one-way hashes (desired characteristics) RSA and Diffie-Hellman (basic operation), uses. How does modulo arithmetic simplify calculations, add to security? RSA security depends on the difficulty of factoring large prime numbers. Digital Signatures, certificates, CA, Web transactions. PKI (Public Key Infrastructure): What is needed besides distribution of Public-Private Keys? (Revocation database). Email Encryption and Signing: Use of session key per message and it’s encryption with each recipient’s Public Key.

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Chapter 4 - Authentication ApplicationsKerberos: How is user (person) authenticated, tickets, role of KDC, and Nonce (replay attack). How does it solve the key distribution problem for n*(n-1)/2 pairs of hosts.X.509 Authentication (certificates, steps of a Web buy) Review slides from Feb. 4, 2013 lecture – “07b-SSL_TLS 2013.pdf”Chain of authentication (CA hierarchy). Theory and PracticeCertificate Authority (who, where found)Digital Signature - how is it done, what does it do?SSH (SCP and SFTP): How do they securely replace Telnet and FTP? What’s needed to allow secure login without a password? What is an “SSH Tunnel”?How are passwords safely stored, and compared to typed-in password? What is a Dictionary Attack, and how is it foiled?How are keys safely stored on a computer, and accessed?

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Certificate Authority generates the“signature” that is added to raw

“Certificate”

MIC

Hash

Raw “Certificate” has user name, public key, expiration date, ...

RawCert.

SignedCert.

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Generate hash codeof Raw Certificate

Encrypt hash code with CA’s private key to form CA’s signature

Signed CertificateRecipient can verify signature using CA’s public key.

Email PrivacyEstablishing Keys

• Public Key Certification• Exchange Public Keys

Multiple Recipients • Encrypt message m with session key, S• Encrypt S with each recipient's key• Send: {S; Kbob}, {S; Kann}, ... , {m; S}

Authentication of Source (digital signatures)• Hash (MD5, SHA2) of message, encrypted with

signer's private key. Check by decrypting with signer's public key, and compare to new hash.

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From "PGP Freeware for MacOS, User's Guide" Version 6.5, Network Associates, Inc., www.pgp.com

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Digital Signature

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PGP Email Receiver

Public Key RingYour Private Key Ring

p.144-145 ed.3

Typed Passphrase

R64 Decode to binaryZIP Decompress

Receiver’sPrivate Key

Session Key

Sender’sPublic Key

Check Signature Message

H - HashDC - Symmetric DecryptionDP - Pub./Priv. Decryption

011001001011010101101010

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R64 Encode: Every 3 bytes split into 4 6-bit numbers

n = 0 to 63

printable characters a-z A-Z 0-9 + /

in a received message, “=“, “>”, CR, LF, ... are ignored

01011001 01001011 01010101 01101010

* for most 6-bit inputs, R64(n) just adds 64 (puts an “01” in front)

*

Simple Mail Transfer Protocol (SMTP, RFC 822)

SMTP Limitations - Can not transmit, or has a problem with:

• executable files, or other binary files (jpeg image).

• “national language” characters (non-ASCII)

• messages over a certain size

• ASCII to EBCDIC (or other character set) translation problems

• lines longer than a certain length (72 to 254 characters)

MIME Defined Five New Headers

• MIME-Version. Must be “1.0” -> RFC 2045, RFC 2046

• Content-Type. More types being added by developers (application/word)

• Content-Transfer-Encoding. How message has been encoded (radix-64)

• Content-ID. Unique identifying character string.

• Content Description. Needed when content is not readable text (e.g.,mpeg)

Canonical Form: Standard format for use between systems ( not a “native” format - GIF).11

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Investigating Email You ReceiveLook at “Raw” or “Source” Message to see:

Headers (from? -“Received:” headers (IP, time zone)HTML Links (where they will take you)

InvestigateSource (who sent it) -

Lowest "Received:” headerActive Links in

<a href= “http://{IP or URL}”>, {text} </a> Images (can compromise, or “Web Bug”) in

<img src=“{IP, URL or filename}” … > Programs to Use

nslookup (dig, host) - IP from URL, or URL from IPwhois - Register of domain (not URL)traceroute - path of packets through routers

Configure email reader to not download links automatically

TLS is Transport Layer Security (is not “IPsec Transport Level Security”)

TLS is used for email (SMTP/TLS or POP/TLS or IMAP/TLS)

SSL is used for secure Web access (HTTPS) (now uses TLS v.3)

Secure Shell, SSH, is Telnet + SSL + other features

Secure Copy, SCP, copies files using SSH (SFTP has FTP functions)

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The combinations are called:HTTPS SFTP ESMTP

SSH

SSL and TLS are above the TCP Socket, so it is part of the Application Layer (a “shim”)

Versions of SSL (v.1, v.2, v.3) and TLS (v1.0, v.1.1) should be replaced by TLS v.1.2

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Application Layer (HTTP)

Transport Layer(TCP,UDP)

Network Layer (IP)

E'net DataLink Layer

EthernetPhys. Layer

Network Layer

E'net DataLink Layer

E'net Phys.Layer

Network Layer

Web Server Browser

RouterBuffers Packets thatneed to be forwarded(based on IP address).

Application Layer (HTTP)

Transport Layer(TCP,UDP)

Network Layer (IP)

Token RingData-Link Layer

Token RingPhys. Layer

IP Address130.207.22.5

IP Address24.88.15.22

Port 80 Port 31337

Segment No. Segment No.

Token RingData Link Layer

Token RingPhys. Layer

Internet Architecture

IPsec - Security Associations

Transport, Host-Host

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Tunnel, Gateway-Gateway (Routers)

2: Application Layer 16

requesting hostjoe.poly.edu

root DNS server

local DNS serverdns.poly.edu

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4

5

6

authoritative DNS serverdns.urhcked.com

78

TLD DNS server

Fast Flux DNSURL in Phish -> One of Many bots

$ nslookup www.urhckd.com. answer 78.82.245.12

• Host at poly.edu wants IP address for www.urhckd.com

• Host sends a "recursion-requested" query request to dns.poly.edu.

• [Host is doing a non-recursive search]

• Local DNS server does a "recursive" search. This requires contacting several other DNS servers before the final answer is given to host.

Fast Flux - many IP’s of bot Phishing sites.

From “Computer Networking: A Top Down Approach Featuring the Internet”, by Jim Kurose & Keith Ross

$ nslookup www.urhckd.com. answer 53.119.24.124

Note: the dot after "com" below is necessary to avoid getting the same cached answer from dns.poly.edu.

DNS Hack #3

Local DNS NS-CNN.COM Hacker

TimeLookup www.cnn.com

<- Correct guess of one ID.

Probable no. of hits260*N/(256^2) =1 if N =252 Prob(hits>0)=0.63Total packets = 512

DNS Cache Poisoning - Birthday Attack

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<- Sending 260requests for same domain, cnn.com,and N Replieswith fake Auth. N.S. IP address.with random IDs

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

www.cnn.com is 66.66.66.66

dns.cnn.com is 64.236.90.21

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* Local DNS sends 260 queries with different IDs.

DOS Attack

Local DNS -> caches

www.cnn.com =66.66.66.66

DNS Hack #4

DNS Hack #0 – modify /etc/resolv.conf or Windows’ Registry,to change the IP of the Local DNS Server.

DNS Hack #1 – add a line to /etc/hosts or Windows’ Registry.

DNS Hack #2 – In URL link, hide the actual domain: e.g.,

http://www.usbank.com.customer.dhs5134.hk

DNS Hack #3 – Fast-Flux DNS: gives different IP every time.

DNS Hack #4 – Poison the Local DNS Server’s cache

(using a “Birthday” Attack)

Five DNS Hacks

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Summary - Problems and Solutions

64-bit Keys can be found by a Brute-Force AttackUse a 128-bit or larger key.

Code-book encrypting allows interchange and duplication of blocksUse Cipher-Block Chaining (Crypto-Feedback).

The same Plaintext encrypted with the same key = same CiphertextUse a random, non-repeating Initial Vector.

How do you know the Ciphertext was not altered?Include a Message Digest (Hash of Plaintext ).

How do you know the authenticity of the sender?Encrypt the Message Digest with the sender’s Private Key (3).

How do you manage encryption keys securely and efficiently?Key Management System (Kerberos) (4a)X.509 Certificates (SSL) – high level covered, and in talk on MondayPGP Email (5a) – only high level coveredPKI (Public Key Infrastructure) (3)

How do you authenticate passwords without storing them on the computer?Store crypto-hashes of the passwords (with “Salt”)

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The test will also cover these slide sets: 05a-PGP-Email.ppt (encrypt, sign, armor [base64])05c-Phishing Email.ppt (information in headers*)05e-Plain Text Email.ppt (how to view raw email)06a DNS.ppt (5 hacks)06-IP Networks.ppt (Routing Tables, IPsec: ESP, AH) Ethernet Addresses (how far do they go?), ARP07-SSL-SET (Dual Signature, separate information)

* Know uses of: nslookup, whois, traceroute, google.

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Homework ProblemsAnswers are posted in “Resources” on T-square

HW_1 Five basic Security Services, Mechanisms to provide those servicesSafer use of the Internet with email configuration, and HTTPS use.

HW-2 – Basic Principles, Brute Force Attack, Entropy

All encrypted messages can be deciphered by a brute-force attack. The time it takes (1) depends of the state-of-the-art in computers and special integrated circuits, and (2) the number of possible keys (= 2^entropy).

For a random binary number with N bits, the entropy = N.For a mixed password with different classes of symbols, the entropy is the sum of the entropy of the elements.

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HW-2 (cont.)If W is a word from a list of 40,000, then the entropy of a single word is: entropy(W) = log2( 40,000) = log10 (40,000)/log10(2) = 4.6 / 0.3 = 15.3If a password is WpW where p is one of 16 punctuation characters: entropy(WpW) = 15.3 + 4 + 15.3 = 34.6 bitsTo convert entropy to the number of possibilities M in decimal: M = 2^entropy = 2^34.6 = 2.6e10 possibilitiesA brute force attack would take M / [number of tries per hour] hours.To be very safe today, a password should have about 120 bits of entropy.

HW-3 – Use of Public/Private Keys, RSA, Diffie-Hellman, Kerberos, Secure Hashes.

Challenge: How HTTP passwords are encoded.22

Old quizzes are posted in “Resources” on T-square

Rules:i This quiz is closed book. One sheet of notes (8.5"x11") may be used

(both sides, your handwriting only). Pen or pencil, and a simple calculator are allowed.

ii Answer all questions and show all work to receive full credit.

iii Each regular sub-question counts 4 points (4 deducted from 100 for each missed question) unless otherwise noted.

iv Please do not ask the proctors any questions during the exam about exam questions. Part of the test is understanding the question, as written, without supplemental information. If you feel additional data is needed to solve the problem, make (and state) an assumption and then work the problem.

v. This is a time-limited test. All papers must be turned in 45 minutes after the start. If you find you are taking more than 10 minutes on a particular problem, move on and come back to that problem after finishing the others. The Georgia Honor Code applies (see last page). Answers should be 1 to 3 words, or a number (no essays, please), except for design questions (new in 2013).

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