Cairo University
Institute of Statistical Studies and Research
Computer Science Dept.
Cs515 - Is517
Computer Security
Sheet1
1. InRSAForp=5,q=7.Ande=5getthepublickey
2. Encryptthefollowingmessageusingthepreviouskeys.
M1=17
M2=19
3. Assumethatn=15ande=3,en
LECTURE 8
KEY MANAGEMENT
Key Management: process of generating, storing,
agreeing upon and revoking keys
KEY MANAGEMENT WHAT IS IT?
Assuming that youve selected an appropriate,
well vetted symmetric encryption
technology, managing the keys that will be
us
Lecture 4
Data Encryption Standard (DES)
Dr. Nermin Hamza
1
From Classical Ciphers to Modern Ciphers
Classical Cipher Modern Cipher (Block
cipher)
Alphabetic letters Binary data
Easy to do
Large block size, large key space
DES=
Substitution + Transpos
Lecture 7
Authentication and Digital Signature
Dr. Nermin Hamza
Authentication Requirements
Attacks:
Traffic Analysis : traffic analysis occurs when
an eavesdroppers observes message traffic on
network. Not understand the actual message
content .
Message
Lecture 2 2013
Classical Encryption Techniques
Dr. Nermin Hamza
1
Introduction
Cryptography
Cryptography is the science of writing insecret code and is an ancient art .
The first documented use of cryptography in
writing dates back to circa 1900 B.C. b
Lecture 3
1
TRANSPOSITION CIPHERS
2
Transposition Ciphers
now consider classical transposition or
permutation ciphers
these hide the message by rearranging the
letter order
without altering the actual letters used
can recognise these since have the sam
Lecture 5
Asymmetric Cryptography
Private-Key Cryptography
Traditional private/secret/single key
cryptography uses one key
Shared by both sender and receiver
If this key is disclosed communications
are compromised
Also is symmetric, parties are equal
WHAT ABOUT THE KEY
1
Sub-key Generation
2
Permutation Choice
Note:
Only 56 bits
Are used
3
Each Iteration Uses a Different Sub-key
DES works on 64 bits of data at a time. Each
64 bits of data is iterated on from 1 to 16
times (16 is the DES standard).
F
Lecture 6
RSA Use in Encryption
to encrypt a message M the sender:
obtains public key of recipient PU=cfw_e,n
computes: C = Me mod n, where 0M<n
to decrypt the ciphertext C the owner:
uses their private key PR=cfw_d,n
computes: M = Cd mod n
note th