Introduction to Applied Cryptography, Lecture notes of Cryptography and System Security

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Introduction of Applied Cryptography

Chun-Jen (James) Chung

Arizona State University

Outline

 Security and cryptography concepts

 Classical Encryption Techniques

Security objectives (contd)

A lice (^) B ob

Internet

An example

UGETGV Secret?

by Caesar with k=

C onfidentiality (^) Encryption

by DES, 3DES, AES, etc

E

Confidentiality : the protection of transmitted data from passive attacks (release of message contents and traffic analysis)

Insecure Channel

The “secret” can be viewed by a 3rd party

The data has not been viewed by a 3rd party

UGETGV

SECRET

Shift 2

secret (^) How? UGETGV

Shift by 1?

TFDSFU

by 2?

UGETGV

Caesar cipher

key = 2

We will revisit this later

Substitution

(Transposition)

Security objectives (contd)

A lice (^) B ob

Internet

Wire transfer $ to B

E

Wire transfer $ to E

The data has not been modified in transit

I ntegrity Crytographic Hash func.

Inputs (e.g., msgs)

One way hash

Fixed-size output

Use HMAC(Hashed message authentication code), such as HMAC-MD5, HMAC-SHA

I ntegrity: the assurance that data received are exactly as sent by an authorized entity (i.e., contain no modification, insertion, deletion, or replay)

Security objectives (contd)

Alice (^) Bob

Internet

E

For any information system to serve its purpose, the information must be available when it is needed

Distributed Denial of Service (DDoS) attacks

Source: http://memeburn.com

A vailability

Security objectives : summary

Alice (^) Bob

Internet

The data can not been viewed by a 3rd party

The data has not been modified in transit

The data must be available when it is needed

C onfidentiality

I ntegrity

A vailability

Authentication

Encryption

Hash func.

Encryption Message Authentication code (MAC)

Hash func.

Non-repudiation

Cryptography

Security objectives (contd)

Alice in South Island

Bob in North island

Internet

E

The claimed sender is the true sender (^) A uthentication Encryption

Message Authentication code (MAC)

Hash func.

A uthentication : the assurance that the communicating entity is the one that it claims to be.

Security objectives (contd)

2. Service or product

1. Order

3. calculation

4. Demand payment

5. “I did not purchase”

N on repudiation Provides protections against^ denial^ by one of the

entities involved in a communication of having

participated in all or part of the communication

Security objectives summary

 Confidentiality

• Prevent/detect/deter improper disclosure of information

 Integrity

• Prevent/detect/deter improper modification of information
• Authentication=Origin Integrity (or with Data Integrity)

 Availability

• Prevent/detect/deter improper denial of access to services

provided by the system

 These objectives have different specific

interpretations in different contexts

Introduction to Cryptography

Classical Encryption

CryptologyCryptology

Cryptography Cryptanalysis

Shared-key Cryptography

Public-key Cryptography Protocols^

TCP/IP protocol -> SSL, IPsec, etc RFID authentication protocol

Computationally secure vs. information-theoretically secure

Arizona State University

Cryptography (ciphers only)Cryptology

Cryptography Cryptanalysis

Shared-key Cryptography

Public-key Cryptography Protocols

Source: Prof. Baktier’s lecture at WPI

Classification of encryption algorithmsEncryption algorithms

Private key Public key

Block Stream

Feistel SPN etc random (^) randomPseudo

Later…

e.g., DES, Triple-DES SEED, Blowfish

e.g., AES

Symmetric key Asymmetric key

64 bits, 128 bits, etc

1 bit (or 1 byte)

conventional, secret-key, single key

Encryption Decryption

Plaintext ciphertext Plaintext

Key Key

Encryption Decryption

Plaintext ciphertext Plaintext

Encryption Key Decryption Key

• Block ciphers take a number of bits and encrypt them as a single unit, padding the plaintext so that it is a multiple of the block size.
• Stream ciphers encrypt the digits (typically bytes) of a message one at a time.