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Wireless Networking: Principles and Practice, Slides of Wireless Networking

Indian Institute of Technology Wireless Networking

Cryptography and Network Security, Cryptography Fundamentals, Cryptographic Privacy, Cryptographic Authentication, Cryptanalysis, Security Guarantees, Digital Encryption Standard, DES, Triple DES, RSA Public Key Crypto System, Taxonomy of Cipher, Key Management, Non Crypto Attacks, Advanced Computer Networks, Bhaskaran Raman, Computer Science Engineering, Kameswari Chebrolu, Electrical Engineering, Indian Institute of Technology, Kanpur, India.

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Jan-Apr 2007 CS698T: “Wireless Networks: Principles & Practice”, Bhaskaran Raman, Dept. of CSE, IIT Kanpur Topic 20

CS698T

Wireless Networks:

Principles and Practice

Topic 20

Introduction to Cryptography

Bhaskaran Raman,

Department of CSE, IIT Kanpur

http://www.cse.iitk.ac.in/users/braman/courses/wless-spring2007/

Partial preview of the text

Download Wireless Networking: Principles and Practice and more Slides Wireless Networking in PDF only on Docsity!

CS698T

Wireless Networks:

Principles and Practice

Topic 20

Introduction to Cryptography

Bhaskaran Raman,

Department of CSE, IIT Kanpur

http://www.cse.iitk.ac.in/users/braman/courses/wless-spring2007/

Cryptography and Network

Security

Reference: Whitfield Diffie and Martin E. Hellman,

“ Privacy and Authentication: An Introduction to

Cryptography”, i n Proc. IEEE, vol. 67, no.3, pp. 397 -

Cryptographic Privacy

Encrypt before sending, decrypt on receiving

– Terms: plain text and cipher text

Two components: key, and the algorithm

– Should algorithm be secret?

●

Yes, for military systems; no, for commercial systems

Key distribution must be secure

Sender Encryption

P

Decryption Receiver

C P

Eavesdropper

Network

C = S

(P) P = S

- K

(C)

Key: K

Cryptographic Authentication

The same system can also be used for

authentication

Sender Encryption

P

Decryption Receiver

P'

C'

Eavesdropper

Network

C = S

(P) P = S

- K

(C)

Key: K

Security Guarantees

Two possibilities:

– Unconditional

– Computational security

Unconditional security: an example

– One-time tape

Most systems have computational security

– How much security to have?

– Depends on cost-benefit analysis for attacker

Public-Key Systems

Shared-key ==> difficulties in key distribution

– C(n,2) = O(n^2) keys

Public key system

– Public component and a private component

– Two kinds:

●

Public key distribution: establish shared key first

●

Public key cryptography: use public/private keys in

encryption/decryption

– Public key cryptography can also be used for

digital signatures

Some Popular Systems

Private key systems:

– DES, 3DES

Public key systems:

– RSA: based on difficulty of factoring

– Galois-Field (GF) system: based on difficulty of

finding logarithm

– Based on knapsack problem

Digital Encryption Standard (DES)

64 bits + 64 bits 64 bits

Plain-text Key Cipher-text

P R1 R2 R16 P

Permutation, 16 rounds of identical operation, inverse permutation

L

R

L

R

F Ki

Each round uses

a different 48-bit

key K

(from K)

and a combiner

function F

Rivest, Shamir, Adleman (RSA)

Public-Key Crypto-System

Based on the fact that finding large (e.g. 100

digit) prime numbers is easy, but factoring

the product of two such numbers appears

computationally infeasible

Choose very large prime numbers P and Q

– N = P x Q

– N is public; P, Q are secret

Euler totient: Phi(N) = (P-1)(Q-1) = Number

of integers less than N & relatively prime to N

RSA (continued)

Next, choose E in [2, Phi(N)-1], E is public

A message is represented as a sequence

M1, M2, M3..., where each M in [0, N-1]

Encryption: C = M

mod N

Using the secret Phi(N), A can compute D

such that ED = 1 mod Phi(N)

ED = k x Phi(N) + 1

Then, for any X < N, X

k x Phi(N)+

Wireless Networking: Principles and Practice, Slides of Wireless Networking

Related documents

Partial preview of the text

Download Wireless Networking: Principles and Practice and more Slides Wireless Networking in PDF only on Docsity!

CS698T

Wireless Networks:

Principles and Practice

Topic 20

Introduction to Cryptography

Bhaskaran Raman,

Department of CSE, IIT Kanpur

http://www.cse.iitk.ac.in/users/braman/courses/wless-spring2007/

Cryptography and Network

Security

Reference: Whitfield Diffie and Martin E. Hellman,

“ Privacy and Authentication: An Introduction to

Cryptography”, i n Proc. IEEE, vol. 67, no.3, pp. 397 -

Cryptographic Privacy

Encrypt before sending, decrypt on receiving

– Terms: plain text and cipher text

Two components: key, and the algorithm

– Should algorithm be secret?

Yes, for military systems; no, for commercial systems

Key distribution must be secure

Sender Encryption

P

Decryption Receiver

C P

Eavesdropper

Network

C = S

(P) P = S

(C)

Key: K

Cryptographic Authentication

The same system can also be used for

authentication

Sender Encryption

P

Decryption Receiver

P'

C'

Eavesdropper

Network

C = S

(P) P = S

(C)

Key: K

Security Guarantees

Two possibilities:

– Unconditional

– Computational security

Unconditional security: an example

– One-time tape

Most systems have computational security

– How much security to have?

– Depends on cost-benefit analysis for attacker

Public-Key Systems

Shared-key ==> difficulties in key distribution

– C(n,2) = O(n^2) keys

Public key system

– Public component and a private component

– Two kinds:

Public key distribution: establish shared key first

Public key cryptography: use public/private keys in

encryption/decryption

– Public key cryptography can also be used for

digital signatures

Some Popular Systems

Private key systems:

– DES, 3DES

Public key systems:

– RSA: based on difficulty of factoring

– Galois-Field (GF) system: based on difficulty of

finding logarithm

– Based on knapsack problem

Digital Encryption Standard (DES)

64 bits + 64 bits 64 bits

Plain-text Key Cipher-text

P R1 R2 R16 P