Computer and Network Security Risanuri Hidayat, Ir., M.Sc

Computer and Computer and Network SecurityNetwork Security

Risanuri Hidayat, Ir., M.Sc.Risanuri Hidayat, Ir., M.Sc.

Chapter 7Chapter 7Outline7.1 Introduction7.2 Ancient Ciphers to Modern Cryptosystems7.3 Secret-key Cryptography7.4 Public Key Cryptography7.5 Key Agreement Protocols7.6 Key Management7.7 Digital Signatures7.8 Public Key Infrastructure, Certificates and Certification Authoritities7.9 Cryptoanalysis7.10 Security Protocols

7.10.1 Secure Sockets Layer (SSL)7.10.2 Secure Electronic Transaction™ (SET™)

7.11 Security Attacks7.12 Network Security

7.12.1 Firewalls7.12.2 Kerberos7.12.3 Biometrics

7.13 Steganography

7.1 Introduction7.1 Introduction

Internet securityInternet security Consumers entering highly confidential informationConsumers entering highly confidential information Number of security attacks increasingNumber of security attacks increasing Four requirements of a secure transactionFour requirements of a secure transaction

Privacy Privacy – information not read by third party– information not read by third party

Integrity Integrity – information not compromised or altered– information not compromised or altered

Authentication Authentication – sender and receiver prove identities– sender and receiver prove identities

Non-repudiation Non-repudiation – legally prove message was sent and – legally prove message was sent and receivedreceived

AvailabilityAvailabilityComputer systems continually accessibleComputer systems continually accessible

7.2 Ancient Ciphers to Modern 7.2 Ancient Ciphers to Modern CryptosystemsCryptosystems

CryptographyCryptography Used to secure information, by encrypting itUsed to secure information, by encrypting it Transforms data by using a keyTransforms data by using a key

Key is a string of digits that acts as a password and makes the data Key is a string of digits that acts as a password and makes the data incomprehensible to those without itincomprehensible to those without it

Plaintext Plaintext – unencrypted data– unencrypted data Cipher-text – encrypted dataCipher-text – encrypted data Cipher of cryptosystem Cipher of cryptosystem – technique for encrypting messages– technique for encrypting messages

CiphersCiphers Substitution cipherSubstitution cipher

Every occurrence of a given letter is replaced by a different letterEvery occurrence of a given letter is replaced by a different letter

7.2 Ancient Ciphers to Modern 7.2 Ancient Ciphers to Modern CryptosystemsCryptosystems

Transposition cipherTransposition cipherShifts the ordering of lettersShifts the ordering of letters

Modern cryptosystemsModern cryptosystemsDigital, based on bits not the alphabetDigital, based on bits not the alphabet

Key length Key length – length of string used to encrypt and – length of string used to encrypt and decryptdecrypt

7.3 Secret-key Cryptography7.3 Secret-key Cryptography

Secret-key cryptographySecret-key cryptography Same key to encrypt and decrypt messageSame key to encrypt and decrypt message Sender sends message and key to receiverSender sends message and key to receiver

Problems with secret-key cryptographyProblems with secret-key cryptography Key must be transmitted to receiverKey must be transmitted to receiver Different key for every receiverDifferent key for every receiver Key distribution centers used to reduce these problemsKey distribution centers used to reduce these problems

Generates session key and sends it to sender and receiver Generates session key and sends it to sender and receiver encrypted with the unique keyencrypted with the unique key

Encryption algorithmsEncryption algorithms Dunn Encryption Standard (DES), Triple DES, Advanced Dunn Encryption Standard (DES), Triple DES, Advanced

Encryption Standard (AES)Encryption Standard (AES)


Encrypting and decrypting a message Encrypting and decrypting a message using a symmetric keyusing a symmetric key


Distributing a session key with a key Distributing a session key with a key distribution centerdistribution center

7.4 Public Key Cryptography7.4 Public Key Cryptography

Public key cryptographyPublic key cryptography Asymmetric Asymmetric – two inversely related keys– two inversely related keys

Private keyPrivate key

Public keyPublic key If public key encrypts only private can decrypt and vice If public key encrypts only private can decrypt and vice

versaversa Each party has both a public and a private keyEach party has both a public and a private key Either the public key or the private key can be used to Either the public key or the private key can be used to

encrypt a messageencrypt a message Encrypted with public key and private keyEncrypted with public key and private key

Proves identity while maintaining securityProves identity while maintaining security

RSA public key algorithm RSA public key algorithm www.rsasecurity.comwww.rsasecurity.com


Encrypting and decrypting a message Encrypting and decrypting a message using public-key cryptographyusing public-key cryptography


Authentication with a public-key algorithmAuthentication with a public-key algorithm

7.5 Key Agreement Protocols7.5 Key Agreement Protocols

Key agreement protocolKey agreement protocol Process by which parties can exchange keysProcess by which parties can exchange keys Use public-key cryptography to transmit Use public-key cryptography to transmit

symmetric keyssymmetric keys

Digital envelopeDigital envelope Encrypted message using symmetric keyEncrypted message using symmetric key Symmetric key encrypted with the public keySymmetric key encrypted with the public key Digital signatureDigital signature

7.5 Key Agreement Protocols7.5 Key Agreement Protocols

Creating a digital envelopeCreating a digital envelope

7.6 Key Management7.6 Key Management

Key managementKey management Handling and security of private keysHandling and security of private keys Key-generation is the process by which keys Key-generation is the process by which keys

are createdare createdMust be truly randomMust be truly random

7.7 Digital Signatures7.7 Digital Signatures

Digital signatureDigital signature Authenticates sender’s identityAuthenticates sender’s identity Run plaintext through hash functionRun plaintext through hash function

Gives message a mathematical value called hash valueGives message a mathematical value called hash value

Hash value also known as message digestHash value also known as message digest Collision occurs when multiple messages have same hash valueCollision occurs when multiple messages have same hash value Encrypt message digest with private-keyEncrypt message digest with private-key Send signature, encrypted message (with public-key) and hash Send signature, encrypted message (with public-key) and hash

functionfunction

TimestampingTimestamping Binds a time and date to message, solves non-repudiationBinds a time and date to message, solves non-repudiation Third party, timestamping agency, timestamps messagsThird party, timestamping agency, timestamps messags

7.8 Public Key Infrastructure, 7.8 Public Key Infrastructure, Certificates and Certification Certificates and Certification

AuthoritiesAuthoritiesPublic Key Infrastructure (PKI)Public Key Infrastructure (PKI) Integrates public key cryptography with digital Integrates public key cryptography with digital

certificates and certification authoritiescertificates and certification authorities Digital certificateDigital certificate

Digital document issued by certification authorityDigital document issued by certification authority

Includes name of subject, subject’s public key, serial Includes name of subject, subject’s public key, serial number, expiration date and signature of trusted third number, expiration date and signature of trusted third partyparty

Verisign (Verisign (www.verisign.comwww.verisign.com))Leading certificate authorityLeading certificate authority

Periodically changing key pairs helps securityPeriodically changing key pairs helps security

7.9 Cryptoanalysis7.9 Cryptoanalysis

CrpytoanalysisCrpytoanalysis Trying to decrypt ciphertext without Trying to decrypt ciphertext without

knowledge of the decryption keyknowledge of the decryption key Try to determine the key from ciphertextTry to determine the key from ciphertext

7.10 Security Protocols7.10 Security Protocols

Transaction security protocolsTransaction security protocols Secure Sockets Layer (SSL)Secure Sockets Layer (SSL) Secure Electronic TransactionSecure Electronic Transaction™™ (SET (SET™)™)

7.10.1 Secure Sockets layer 7.10.1 Secure Sockets layer (SSL)(SSL)

SSLSSL Uses public-key technology and digital Uses public-key technology and digital

certificates to authenticate the server in a certificates to authenticate the server in a transactiontransaction

Protects information as it travels over InternetProtects information as it travels over InternetDoes not protect once stored on receivers serverDoes not protect once stored on receivers server

Peripheral component interconnect (PCI) Peripheral component interconnect (PCI) cardscards

Installed on servers to secure data for an SSL Installed on servers to secure data for an SSL transactiontransaction

7.10.2 Secure Electronic7.10.2 Secure ElectronicTransaction™ (SET™)Transaction™ (SET™)

SET protocolSET protocol Designed to protect e-commerce paymentsDesigned to protect e-commerce payments Certifies customer, merchant and merchant’s bankCertifies customer, merchant and merchant’s bank RequirementsRequirements

Merchants must have a digital certificate and SET softwareMerchants must have a digital certificate and SET softwareCustomers must have a digital certificate and digital walletCustomers must have a digital certificate and digital wallet

Digital walletDigital walletStores credit card information and identificationStores credit card information and identification

Merchant never sees the customer’s personal informationMerchant never sees the customer’s personal informationSent straight to banksSent straight to banks

Microsoft AuthenticodeMicrosoft Authenticode Authenticates file downloadsAuthenticates file downloads Informs users of the download’s authorInforms users of the download’s author

7.11 Security Attacks7.11 Security Attacks

Types of security attacksTypes of security attacks Denial of service attacksDenial of service attacks

Use a network of computers to overload servers and cause them Use a network of computers to overload servers and cause them to crash or become unavailable to legitimate usersto crash or become unavailable to legitimate users

Flood servers with data packetsFlood servers with data packets

Alter routing tables which direct data from one computer to anotherAlter routing tables which direct data from one computer to another

Distributed denial of service attack comes from multiple computersDistributed denial of service attack comes from multiple computers VirusesViruses

Computer programs that corrupt or delete filesComputer programs that corrupt or delete files

Sent as attachments or embedded in other filesSent as attachments or embedded in other files WormWorm

Can spread itself over a network, doesn’t need to be sentCan spread itself over a network, doesn’t need to be sent


Types of virusesTypes of viruses Transient virusTransient virus

Attaches itself to specific programAttaches itself to specific program

Is run every time the program is runIs run every time the program is run Resident virusResident virus

Once loaded operates for duration of computer’s useOnce loaded operates for duration of computer’s use Logic bombLogic bomb

Triggers when a given condition is met, such as clock on computer Triggers when a given condition is met, such as clock on computer matching a specified timematching a specified time

Trojan horseTrojan horseMalicious program that hides within a friendly programMalicious program that hides within a friendly program

Web defacingWeb defacing Hackers illegally change the content of a Web siteHackers illegally change the content of a Web site


Anti-virus softwareAnti-virus software Reactive Reactive – – goes after already known virusesgoes after already known viruses www.mcafee.comwww.mcafee.com

VirusScan scans to search computer for virusesVirusScan scans to search computer for viruses

ActiveShield checks all downloadsActiveShield checks all downloads www.symantec.comwww.symantec.com

Another virus software distributorAnother virus software distributor

Computer Emergency Response Team (CERTComputer Emergency Response Team (CERT®®)) Responds to reports of viruses and denial of service attacksResponds to reports of viruses and denial of service attacks Provides CERT Security Improvement ModulesProvides CERT Security Improvement Modules www.cert.orgwww.cert.org

7.12 Network Security7.12 Network Security

Network securityNetwork security Allow authorized users accessAllow authorized users access Prevent unauthorized users from obtaining Prevent unauthorized users from obtaining

accessaccess Trade-off between security and performanceTrade-off between security and performance

7.12.1 Firewalls7.12.1 Firewalls

FirewallFirewall Protects local area network (LAN) from outside intrudersProtects local area network (LAN) from outside intruders Safey barrier for data flowing in and outSafey barrier for data flowing in and out Prohibit all data not allowed or permit all data not Prohibit all data not allowed or permit all data not

prohibitedprohibited

Types of firewallsTypes of firewalls Packet-filtering firewallsPacket-filtering firewalls

Rejects all data with local addresses from outsideRejects all data with local addresses from outside

Examine only source not contentExamine only source not content Application level firewallsApplication level firewalls

Attempt to scan dataAttempt to scan data

7.12.2 Kerberos7.12.2 Kerberos

KerberosKerberos Uses symmetric secret-key cryptography to Uses symmetric secret-key cryptography to

authenticate users in a networkauthenticate users in a network Authenticates who a client computer is and if Authenticates who a client computer is and if

he has the right’s to access specific parts of he has the right’s to access specific parts of the networkthe network

7.12.3 Biometrics7.12.3 Biometrics

BiometricsBiometrics Uses unique personal information to identifyUses unique personal information to identify

Examples are fingerprints, eyeball iris scans or Examples are fingerprints, eyeball iris scans or face scansface scans

7.13 Steganorgraphy7.13 Steganorgraphy

SteganographySteganography Practice of hiding information within other Practice of hiding information within other

informationinformation

Digital watermarksDigital watermarks Hidden within documents and can be shown Hidden within documents and can be shown

to prove ownershipto prove ownership


Example of a conventional watermarkExample of a conventional watermark

Courtesy of Blue Spike, Inc.


An example of steganography: Blue An example of steganography: Blue Spike’s Giovanni digital watermarking Spike’s Giovanni digital watermarking processprocess

Courtesy of Blue Spike, Inc.

Documents

Computer and Network Security Risanuri Hidayat, Ir., M.Sc