UNIVERSITY OF COLOMBO

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UNIVERSITY OF COLOMBO SCHOOL OF
COMPUTING
Security of Information Systems
DEGREE OF BACHELOR OF INFORMATION TECHNOLOGY
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Security Requirements
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Security Requirements
www.xyz.com
The Internet
You
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Security Requirements
www.xyz.com
The Internet
1. Authenticity
www.hacker.com
You
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Security Requirements
www.xyz.com
The Internet
1. Authenticity
2. Integrity
www.hacker.com
You
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Security Requirements
www.xyz.com
The Internet
1. Authenticity
2. Integrity
www.hacker.com
3. Confidentiality
You
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Security Requirements
www.xyz.com
The Internet
1. Authenticity
2. Integrity
www.hacker.com
3. Confidentiality
4. Availability
You
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Security Requirements
www.xyz.com
The Internet
1. Authenticity
2. Integrity
3. Confidentiality
4. Availability
5. Non-repudiation
You
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An Introduction to Cryptography
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Basic Concept
Cipher Algorithm
Cipher Text
Cipher Algorithm
Plain Text
Encrypted Data
Plain Text
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The Caesar Cipher
Plain Text A B C D E F G H I J K L M N O P Q
R S T U V W X Y Z
Cipher Text D E F G H I J K L M N O P Q R S T
U V W X Y Z A B C
Key
Ci E(Pi) Pi3
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Monoalphabetic Substitutions
Plain Text A B C D E F G H I J K L M N O P Q
R S T U V W X Y Z
Cipher Text K E Y G H I J K L M N O P Q R S T
U V W X Y Z A B C
Letter Frequency
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Polyalalphabetic Substitutions
Table for Odd Positions
Table for Even Positions
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The Perfect Substitution Cipher
One Time Pad

• Recipient need identical pad
• Pad position should be synchronized
• Plain text length Key length

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The Vernam Cipher
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Random Number Generation

• 1. Truly Random numbers
• Books
• CD

• 2. Pseudo Random numbers
• Linear congruential random number generation

Ri1 (a Rib) mod n
R1 (a R0b) mod n R2 (a R1b) mod n R3
(a R2b) mod n
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Message Authentication Code (MAC)
Message
MAC Algorithm
MAC
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Symmetric key Cryptograms
E n c r y p t i o n
Key
Someconfid entialtext essage)
in clear
D e c r y p t i o n
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The Data Encryption Standard-(DES)

• Background and History
• National Bureau of Standards (NBS),
• issued call for a public encryption algorithm in
  August 1974
• DES based on Lucifer from IBM
• DES is officially adapted as a U.S. federal
  standard on 23rd November 1976

Clear Text
K

• Overview of DES
• Plain text is encrypted as block of 64 bits
• Normal key length 56 bits

Cipher Text
Advance Encryption Standard-AES
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DES in Electronic Code Book Mode (ECB)
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DES in Cipher Block Chaining Mode (CBC)
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MAC based on CBC
Message
IV
K
K
K
K
MAC
64
64
64
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Triple DES (3DES)
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Asymmetric key Encryption Systems
E n c r y p t i o n
Public Key
Someconfid entialtext essage)
in clear
Private Key
D e c r y p t i o n
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Storage and Handling Public Keys
Keys Server
A
Public Keys
Private Key
Private Key
A
B
A
B
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Secure Sending of Data
A
B
Public Keys
Private Key
Private Key
A
B
Data
A
B
(Digital Envelope)
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Recovery of Data
A
B
Public Keys
Private Key
Private Key
A
Data
B
A
B
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Authenticity of Sender
A
B
(Digital Signature)
Public Keys
Private Key
B
Data
A
B
A
Private Key
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Verification of Signature
A
B
Public Keys
Private Key
A
Data
Private Key
B
A
B
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Authenticity of Sender and Receiver
A
B
Public Keys
Private Key
B
Data
B
A
Private Key
A
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Full Verification
B
(Senders/Receivers Authenticity, Message
Protection and Integrity )
Public Keys
Data
A
B
A
B
Private Key
Private Key
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Certificate Authority (CA)
Keys Server
Certificates
A
B
CA
MAC
A
B
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Digital Certificate
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Revest-Shamir-Adelman (RSA)
By Rivest, Shamir and Adelman in 1978
1. Find 2 large prime numbers p and q (100
digits512bits) 2. Calculate the product npq (n
is around 200 digits) 3. Select large integer e
relatively prime to (p-1)(q-1) Relatively prime
means e has no factors in common with
(p-1)(q-1). Easy way is select another prime that
is larger than both(p-1) and (q-1). 4. Select d
such that ed mod (p-1)(q-1)1
Two keys are d and e along with n
Encryption CPe mod n Decryption PCd mod n
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Applications

• S/MIME
• Secure/ Multipurpose Internet Mail
• SSL
• Secure Socket layer
• SET
• Secure Electronic Transaction
• Signed Applets

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SSL Protocol Layer

• SSL protocol runs on the TCP/IP and below the
  HTTP and IMAP

HTTP
LDAP
IMAP
Application Layer
Network Layer
Secure Sockets Layer
TCP/IP Layer
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SSL Handshake
1)Client sends SSL version number,Cipher
Settings,randomly generated data
CLIENT
SERVER
2)Server sends SSL version number,Cipher
Settings,randomly generated data
3)Client uses the info of STEP2 for SERVER
AUTHENTICATION if Failed TERMINATE if Successful
go to STEP 4
4)PreMaster Secret Generated for the session,
encrypts it with the Servers Public Key
5)If Server Requested for CLIENT
AUTHENTICATIONClient Sends Signed Data
Encrypted PreMaster Secret (This is Optional)
6)Server Authenticates Client, if failure
TERMINATE else decrypt PREMASTER SECRET to
generate MASTER SECRET
7)Both the Client and Server use the Master
Secret to Generate Session keys
8) and 9)Client and Server sends messages to
each other that Handshake is finished
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Further Information

• www.bit.lk
• Detailed Syllabus Topic Objectives
• Information ? Course Structure ?
• Semester 5
• Queries
• sisq_at_ucsc.cmb.ac.lk