Network SecurityNetwork Security

by Georgi TodorovDowling College

Oakdale, NY, 11769http://mcs.dowling.edu/POCS/

by Georgi TodorovDowling College

Oakdale, NY, 11769http://mcs.dowling.edu/POCS/

POCS Seminar Series 2006POCS Seminar Series 2006

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Outline

The Network Security Problem

Cryptography

Modern Cryptography

Symmetric-Key Algorithms

Cryptanalysis

Public-Key Algorightms

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Outline

Digital Signatures

IPSec

Firewalls

VPN

Wireless security

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Outline

Kerberos

PGP

SSL

Practical: GnuPG

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The Network Security Problem

Computer Networks (before) - university researchers, corporate employees.

Computer Networks (now) - millions use it for banking, shopping, tax returns etc.

The Network Security Problem

Security is concerned with preventing unauthorized access or use of information or resources.

Reasons for security problems: for fun, for revenge, for theft

NOTE!!!

The biggest problems in security are caused by incompetent employees, bad security procedures, and inside attacks rather than decoding encrypted messages stolen from tapped phone lines.

Cryptography“Cryptography or cryptology is a field of mathematics and computer science concerned with information security and related issues, particularly encryption and authentication.” - Wikipedia [1]

The term comes from Greek and it means “secret writing”, hence cryptology -> “the study of secret writing”

Cryptanalysis is the study of codebreaking

Modern CryptographyModern cryptography includes the following main areas of study:

Symmetric-key cryptography

Public-key cryptography

Cryptanalysis

Cryptographic primitives

Cryptographic protocols

Symmetric-key algorithm

“Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related cryptographic keys for both decryption and encryption.” - Wikipedia [2]

Two types:

Stream ciphers - one bit at a time

Block ciphers - number of bits(64) as a single unit

Symmetric-key algorithm

Hundreds or thousands of times faster

Encryption functions are reversible

Same input produces same output

DES, AES

Symmetric-key algorithm - DES (Data Encryption Standard)Developed by IBM and adopted by the U.S. Government in january 1977

Encoding:

Text is divided into 64 bits

First stage: Permutation of the text

16 rounds of processing: key(last32bits); XOR(first32bits,key(last32bits));Flip pair

Last stage: inverse permutation

Problems: too short -> 3DES (2 keys)

Symmetric-key algorithm - AES (Advanced Encryption Standard)Developed by two Belgian cryptographers, Joan Daemen and Vincent Rijmen

Operates on a 4x4 array of bytes (or more for more than 128 bit key size). Each round of AES excluding the last one consist of four steps:

AddRoundKey, SubBytes, ShiftRows, MixColumns

For more info:http://en.wikipedia.org/wiki/Advanced_Encryption_Standard

CryptanalysisDifferential cryptanalysis -> technique for attacking any block cipher, stream ciphers and cryptographic hash functions. How differences in an input can affect the resultant difference at the output.

DES can be successfully broken with an effort on the order of 2^47 chosen plaintexts.

Linear cryptanalysis -> works by XORing certain bits in the plaintext and ciphertext together.

It can break DES in only 2^43 known plaintexts

Electrical power consumtion (3 volts for 1 and 0 for 0)-> very powerful

Timing analysis - if, else -> different timing

Public-Key Algorithms

Based on the computational complexity of number theory

Encryption (public) key is different from the decryption(private) key. One cannot be forged by the other but one is inverse of the other.

Diffie-Hellman key exchange protocol -> the first to show that public-key cryptography was possible

Public-Key Algorithms - RSA

(Rivest, Shamir, Adleman)

MIT 1978

It has survived ALL ATTEMPTS to break it.

One big disadvantage -> quite slow (at least 1024 bit keys)

Widely used today

Public-Key Algorithms - RSA

(Rivest, Shamir, Adleman)

Summary:

Choose to large prime numbers p and q such that p != q, randomly and independently from each other

compute n = p*q

compute the totient Ф(n) = (p-1)(q-1)

Choose an integer e such that 1 < e < Ф(n), which is comprime to Ф(n)

Compute d such that de = 1 mod Ф(n).

Public-Key Algorithms - RSA

(Rivest, Shamir, Adleman)Summary:

Public key consists of n and ePrivate key consists of n and d

Example:p = 61 — first prime number (to be kept secret or deleted securely)q = 53 — second prime number (to be kept secret or deleted securely)n = pq = 3233 — modulus (to be made public)e = 17 — public exponent (to be made public)d = 2753 — private exponent (to be kept secret)The public key is (e, n). The private key is d. The encryption function is:encrypt(m) = m^e mod n = m^17 mod 3233where m is the plaintext. The decryption function is:decrypt(c) = c^d mod n = c^2753 mod 3233where c is the ciphertext.To encrypt the plaintext value 123, we calculateencrypt(123) = 123^17 mod 3233 = 855To decrypt the ciphertext value 855, we calculatedecrypt(855) = 855^2753 mod 3233 = 123

Public-Key Algorithms - RSA

(Rivest, Shamir, Adleman)

Security:

The RSA problem -> taking eth roots module a composite n: m^e=c mod n where (e,n) is the public key, and c is the ciphertext.

Factoring Large numbers -> As of 2005 the largest number factored b general-purpose methods was 663 bits long, using state-of-the-art distributed methods. No polunomail-time method is known so far!

Digital Signatures

Symmetric-Key signatures - > requires central authority that knows everything and whom everyone trusts

Public-Key signatures -> eliminates the requirement of aa central authority

Message DigestOne-way hash function

Simpler than signature

Properties:

Given P, it is easy to compute MD(P)

Given MD(P), it is effectively impossible to find P

Given P no one can find P’ such that MD(P’)=MD(P)

A change to the input of even 1 bit produces a very different output

MD5 and SHA-1

IPSec

“IPsec (IP security) is a standard for securing Internet Protocol (IP) communications by encrypting and/or authenticating all IP packets. IPsec provides security at the network layer.” - Wikipedia [3]

Two modes: Tunnel mode: port-to-port communications securityTransparent mode: end-to-end security

Dominant use in VPNs

Mandatory part in IPv6

Firewalls

Description by Andy Tanenbaum: “Firewalls are just a modern adaptation of that old medieval security standby: digging a deep moat around your castle. This design forced everyone entering or leaving the castle to passover a single drawbridge, where they could be inspected by the I/O police.” [4]

Network layer firewalls do not allow packets to pass through unless they match the rules. These rules are defined by the administrator, or build-in ones are used

Application layer firewalls may stop all packets coming from or to an application (browser, ftp, mail)

Proxies may act as firewall

NAT -> Network Address Translation -> multiple hosts behind a single IP

VPN - Virtual Private Network

A overlay network on top of a public network with the properties of a private network.

Based on virtual circuits

Used to connect remote sites of a company

Secure VPN protocols include:

IPsec

SSL (OpenVPN, tun/tap)

PPTP(M$)

Wireless Security

WEP (Wired Equivalent Privacy) - Stream cipher based on the RC4 algorithm

64bit WEP uses 40 bit key plus 24bit initialization vector forming RC4 traffic key.

After US Gov. restrictions were lifted, 128bit web with 104bit key size was introduced

Average break time 3 min

WPA and WPA2 (Wi-Fi Protected Access)128-bit key and 48-bit IV plus Temporal Key Integrity Protocol

Personal -> pre-shared key

Enterprise -> 802.11X authentication

Requires strong password for Personal

Kerberos

Authentication protocol which allows individuals communicating over an insecure network to prove their identity to one another in a secure manner

Builds on symmetric-key cryptography and requires trusted third party

Uses: OpenSSH, NFS, PAM, SOKS, Apache, Devicot IMAP3 and POP3 server and others

Kerberos

Outline:Client and three servers(Authentication server, ticket-granting server and required service server)

client sends name to AS

AS sends session key and ticket to client encrypted with client’s secret key(ask for pwd and rm from system)

Client decrypts session and ticket and sends to TGS, encrypted with TGS’ secret key asking for ticket with SS

TGS returns two versions of the session key for client and SS, one encrypted with Client’s secret key and the other encrypted with SS’ secret key.

Now Client and SS can talk

If Client wants to talk to another SS, he sends a new ticket request directly to TGS

PGP - Pretty Good Privacy

PGP provides cryptographic privacy, compression and authentication

Uses both public-key and symmetric-key cryptography

Outline:PGP generates MD5 of the message and encrypts the result with sender’s private RSA key

Encrypted hash and message are concatenated and compressed.

An IDEA message key is generated and used to encrypt the compressed with IDEA in cipher feedback mode

Also the key is encrypted with the recipient's public key.

Both are concatenated and converted to base64 and sent.

The recipient reverses base64, decrypts the IDEA with his private key, deripts the archive, extracts, and decrypts the hash using senders public key, than generates a new hash and compares both.

PGP - Pretty Good Privacy

Supported RSA lengths:

1. Casual(384 bits): can be broken easily today.

2. Commercial(512 bits): breakable by three-letter organizations

3. Military ( 1024 bits): Not breakable by anyone on earth

4. Alien (2048 bits): Not breakable by anyone on other planets, either

Many public key servers are available

SSL - Secure Sockets Layer/Transport Layer

Security (TLS)SSL exchanges records; each record can be optionally compressed, encrypted and packed with message authentication code. It also contains content_type field that specifies which upper layer protocol is being used.

Phases:

Peer negotiation for algorithm support

Public key encryption-based key exchange and certificate-based authentication

Symmetric cipher-based traffic encryption

Supported protocols:

RSA, Diffie-Hellman, DSA, Fortezza, RC2, RC4, IDEA, DES, 3DES, AES, MD5, SHA

SSL runs on layers beneath application protocols (HTML,SMTP,NNTP) and above the TCP transport protocol, which forms part of the TCP/IP protocol suite.

It can add security to any protocol that uses reliable connections.

GnuPG

GnuPG - Complete implementation of the OpenPGP Internet standard

'GnuPG' currently supports ElGamal (signature and encrytion), DSA, AES, 3DES. Blowfish, Twofish, CASTS, MD5, SHA-1, RIPE-MD-160 and TIGER, and has language support for sixteen different languages.

http://eudoragpg.sourceforge.net/ver2.0/en/download/index.html -> Eudora plugin

http://www.sente.ch/software/GPGMail/English.lproj/GPGMail.html -> Apple Mail

http://enigmail.mozdev.org/download.html -> Mozilla, General Windows GnuPG

References

[1] http://en.wikipedia.org/wiki/Cryptography

[2] http://en.wikipedia.org/wiki/Symmetric_key_algorithm

[3] http://en.wikipedia.org/wiki/IPsec

[4] Andrew Tanenbaum, “Computer Networks 4th Edition”, CH8,