- Cryptography and Security - Methods of Encryption and Decryption - What is an Algorithm? - Symmetric Algorithm - Asymmetric Algorithm - Hybrid Encryption - Hashing Algorithm - Securing the Algorithm or the Key - Hash Value and Rainbow Table - Digital Signature - PKI

1. Introduction to Cryptography and PKI
Presented By: Rabei Hassan

2. • Rabei Hassan
• CISSP-ISSAP, CCSP, CRISC, CISM, CISA, CEH, ECSA, CHFI, Security+
• MCTS, MCSE: Security, MCDBA, MCSA: Messaging
• More than 18 years working experience at various IT fields
• Infrastructure and Info Security Consultation and Training
• IT Management
• Web and Windows Application Development
• Systems and Database Administration
• https://au.linkedin.com/in/rabei-hassan-564b3214

3. Session Objectives
• Cryptography and Security
• Methods of Encryption and Decryption
• What is an Algorithm?
• Symmetric Algorithm
• Asymmetric Algorithm
• Hybrid Encryption
• Hashing Algorithm
• Securing the Algorithm or the Key
• Hash Value and Rainbow Table
• Digital Signature
• PKI

4. Cryptography and Security
Confidentiality
Integrity
Authenticity
Non-Repudiation

5. Methods of Encryption and Decryption
• Symmetric
• Use ONLY One Key for encryption and decryption
• Asymmetric
• Use Two Keys,
• One key will be used for encryption
• The other key will be used for decryption.
• Hashing
• One-Way encryption ..!

6. What is an Algorithm ?
• Instructions; the steps that we need to follow to do the operation.
• In general, it will has two types of instructions:
• Instructions for how to do the encryption
• Instruction for how to do the decryption
Symmetric
Algorithms
Encryption
Instructions
using Key X
Step 1 - ……..
Step 2 - ……..
Step 3 - ……..
Step 4 - ……..
Decryption
Instructions
using Key X
Step 1 - ……..
Step 2 - ……..
Step 3 - ……..
Step 4 - ……..
Asymmetric
Algorithms
Encryption
Instructions
using Key X
Step 1 - ……..
Step 2 - ……..
Step 3 - ……..
Step 4 - ……..
Decryption
Instructions
Using Key Y
Step 1 - ……..
Step 2 - ……..
Step 3 - ……..
Step 4 - ……..
Hashing
Algorithms
Instructions for
One-Way Encryption
No-KEY
Step 1 - ……..
Step 2 - ……..
Step 3 - ……..
Step 4 - ……..
Plain Text Cipher Text
Plain Text Hash Value

7. Symmetric Algorithms (1/3)
• Vigenere Cipher
• Plain Text : Welcome To Cryptography
• Key: RAMGuide
Encryption Instructions
1. Put the plain text in a raw.
2. Put the Key in a second line raw below the plain text raw.
3. If the key-size is smaller than the plain text size, then repeat it until it become the
same size as the plain text.
4. According to the table on the right section, the cipher text will be the inter section
between the character in the plain text raw and the character in the key raw.
Plain Text W E L C O M E T O C R Y P T O G R A P H Y
Key R A M G U I D E R A M G U I D E R A M G U
Cipher Text N E X I . . . . . . . . . . . . . . . . .
Decryption
Instructions

8. Binary Mathematics
X AND Y
X OR Y
X XOR Y
Both values need
to be true, so the
output will be
true.
One OR Two
values need to be
true so the final
value will be true.
One and Only One
value need to be
true so the final
value will be true.

9. Symmetric Algorithms (2/3)
• Vernam (One-Time Pad) Cipher
• Plain Text : Welcome
• Key: RAMGuid
Encryption Instructions
1. The key must be the same size as the plain text.
2. Put the Key in a second line raw below the plain text raw.
3. XOR between them on the bit level.
Plain Text
W
0101 0111
E
0100 0101
L
0100 1100
C
0100 0011
O
0100 1111
M
0100 1101
E
0100 0101
Key
R
0101 0010
A
0100 0001
M
0100 1101
G
0100 0111
U
0101 0101
I
0100 1001
D
0100 0100
Cipher Text 0000 0101 0000 0100 . . . . .
W 0 1 0 1 0 1 1 1
R 0 1 0 1 0 0 1 0
0 0 0 0 0 1 0 1
E 0 1 0 0 0 1 0 1
A 0 1 0 0 0 0 0 1
0 0 0 0 0 1 0 0
Decryption
Instructions

10. Symmetric Algorithms (3/3)
• DES …………………. [Key Size is …. 56-bit]
• 3DES ……………….. [Key Size could be …… 112-bit …… 168-bit]
• AES …………………. [Key Size could be ……. 128-bit ..… 192-bit …. 256-bit]

11. Asymmetric Algorithms
• Will use two keys:
• Public Key ……………………. [Any one can get a copy of it]
• Private Key ………………….. [Maintained by the owner]
• Public/Private key is for one entity/individual only.
Amr
Jana
1. Amr will send his Public Key to Jana 2. Jana will
encrypt the
message with
Amr Public Key3. Jana will send the secret message to Amr
4. Amr will
decrypt the
secret message
with his own
Private Key
Amr Public Key
Amr Private Key
Jana Private Key
Amr need to receive something securely from Jana
Amr Public Key

12. Asymmetric Algorithms
• Diffie-Hellman ………..[Key Exchange]
• EL Gamal …………………[Key Exchange – Encryption – Digital Signature]
• RSA ………………………….[Key Exchange – Encryption – Digital Signature]
• Elliptic Curve ………….. [Key Exchange – Encryption – Digital Signature]

13. Symmetric vs. Asymmetric Algorithms
Symmetric Asymmetric
Key Distribution X 
Performance Fast
Slow
1000 ~ 10,000 slower than Symmetric
Scalability X A
B
C
D
E
F
5 Keys
4 Keys
3 Keys
2 Keys
1 Key
Total number of Keys = 5 + 4 + 3 + 2 + 1 = 15
6 Entities (Individuals)
Symmetric
6 Entities (Individual) – each one will has two keys (Public/Private)
6 X 2 = 12
Asymmetric

14. Hybrid Encryption (Symmetric + Asymmetric)
HTTPS://www.Amazon.com
You want to Transfer your Credit-Card information securely
Amazon Public Key
Amazon Private Key
Amazon will send its Public Key
A session Symmetric
Key will be generated
locally on your own
machine
Credit Card
Information The Encrypted Credit-Card Information will be transferred to Amazon.com
Symmetric
Key The Session Symmetric Key will be transferred one time only during the whole session

15. Hash Algorithm (1/2)
• One-way encryption, that will generate a fixed length value.
ABC
Funny Hashing Algorithm 
1. Get the ASCII Code of each character
2. Multiply by the position
3. Get the Sum
1. A(65) B(66) C(67)
2. 65 X 1 66X2 67X3
3. 65 + 132 + 201
398

Securing
PasswordsIntegrity
[File Transfer]

16. Hash Algorithm (2/2)
• SHA1 ………………………… [160-bit]
• SHA2 ………………………… [256-bit / 512-bit]
• MD5 …………………………. [128-bit]

17. Securing the Algorithm or the Key ?
• Pros/Cos of securing the algorithm
• Pros/Cos of making the algorithms publicly accessible and securing
only the key
• The longer the key, the harder to be compromised.
Algorithm
Instructions
Know the exact algorithm
Know the exact key


4 Digits Key
[0110]
0000
0001
0010
0100
1000
.
.
.
.
2x = 24 = 16
128-bit Key = 2128 =
3.4028236692093846346337460743177e+38 
Brute-force
Attack
Key need to be
changed from
time to time

18. Hash Value and Rainbow Table
ABC

398Hashing
1. Generate “AAA”
2. Generate the Hash-Value for …… “AAA”
3. Compare the Hash-Value of ….. “AAA” …. with the stolen one
“BBB”
“BBB”
“BBB”
Value MD5 SHA1
AAA 3c01… 6f358…
BBB a2c9a… bb27f…
. . .
. . .
. . .
Demo: Generate and Crack Hash Value
Rainbow Table

19. Digital Signature
Amr
Jana
Jan Public Key
Amr Private Key
Amr Public Key
Jana Private Key
Amr want to send something securely to Jana
Modification to be detected / To be sure it is from Amr
1. Type a message “ABC”
2. Hash the message and get the hash value
3. Encrypt the hash value using the Amr Private Key
ABC
Hash
Value
ABC
Hash
Value
Hash
Value
Integrity
Authenticity
Non-Repudiation
Amr Public Key




20. Public Key Infrastructure – PKI
Public/Private
Public/Private
Public/Private
Public/Private
X.509
How can we transfer the Public Key / File Format

21. Public Key Infrastructure – PKI
Public/Private
Public/Private
Public/Private
Public/Private
Certificate Authority (CA)
Who Create/Generate this Certificate
Public Key
X.509
How can we transfer the Public Key / File Format
1. How can you trust this certificate ... ?
2. Does this site really belong to ... ?
Trust
A Trust B
B Trust C
Trust
Then A will Trust B 

22. Public Key Infrastructure – PKI
Public/Private
Public/Private
Public/Private
Public/Private
Certificate Authority (CA)
Who Create/Generate this Certificate
How can we transfer the Public Key / File Format
1. How can you trust this certificate ... ?
2. Does this site really belong to ... ?
Does this certificate really generated by a Trusted CA ?

23. Public Key Infrastructure – PKI
Public/Private
Certificate Authority (CA)
Public Key
Does this certificate really generated by a Trusted CA ?
Hash
Value
DS
Hash
Value
Public Key
Hash
Value
CA Public Key

Public Trusted CA Local Trusted CA
Demo: Where we can find Trusted CAs

24. Confidentiality
Integrity
Authenticity
Non-Repudiation
Public Key Infrastructure – PKI

25. Hybrid Encryption (Symmetric + Asymmetric)
HTTPS://www.Amazon.com
You want to Transfer your Credit-Card information securely
Amazon Public Key
Amazon Private Key
Amazon will send its Certificate (which contain its Public Key)
A session Symmetric
Key will be generated
locally on your own
machine
Credit Card
Information The Encrypted Credit-Card Information will be transferred to Amazon.com
Symmetric
Key The Session Symmetric Key will be transferred one time only during the whole session
Authenticity & Confidentiality

26. Digital Signature
Amr
Jana
Jan Public Key
Amr Private Key
Amr Public Key
Jana Private Key
Amr want to send something securely to Jana
Modification to be detected / To be sure it is from Amr
1. Type a message “ABC”
2. Hash the message and get the hash value
3. Encrypt the hash value using the Amr Private Key
ABC
Hash
Value
ABC
Hash
Value
Hash
Value
Integrity
Authenticity
Non-Repudiation
Amr Public Key




27. Public Key Infrastructure – PKI
Certificate Authority (CA)
Public Trusted CA Local Trusted CA
Number / Location
Administration
Servers/Computers
Users
Application/Services
Network Devices
Certificates
&
Backup
Confidentiality
Integrity
Authenticity
Non-Repudiation
Issue Policy and Methods
Distribution Policy and Methods

28. Session Objectives
• Cryptography and Security
• Methods of Encryption and Decryption
• What is an Algorithm?
• Symmetric Algorithm
• Asymmetric Algorithm
• Hybrid Encryption
• Hashing Algorithm
• Securing the Algorithm or the Key
• Hash Value and Rainbow Table
• Digital Signature
• PKI