CSCE 201 Introduction to Information Security Fall 2010 Data Protection

CSCE 201CSCE 201Introduction to Introduction to

Information Security Information Security Fall 2010Fall 2010

Data ProtectionData Protection

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Reading assignmentsReading assignments

Required for this class:– D. Cross, Data Protection and Recovery in Windows XP,

http://technet.microsoft.com/en-us/library/bb457020.aspx – M. Horowitz The Safest Way to Protect Sensitive

Computing Files, August 24, 2009, http://www.esecurityplanet.com/views/article.php/3835861/article.htm

– Wikipedia, Encryption, http://en.wikipedia.org/wiki/Encryption

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Sensitive Files

Must be protected from– Hackers– Other users

What to protect and at what level security policy

How to protect security policy

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Security Mechanism

Several alternatives Which one to choose?

– Level of assurance– User’s preferences (familiarity, ease of use,

recommendations, etc.)– User’s technical knowledge– Availability – Financial considerations– Etc.

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Data Protection via Operating System

Microsoft® Windows® XP provides many enhancements in the area of data protection – Encrypting File System (EFS) – Data Recovery Agents (DRA)

Best PracticesNote: EFS is only available on Windows

XP Professional; it is not supported on Windows XP Home Edition

What is Encryption?How secure it is?

Can you decrypt the followings?

HAY?OROWEU

How are you?

Hello

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Insecure communications

Sender

Snooper

Recipient

Insecure channel

Confidential

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Terminology

Plaintext (cleartext): a message in its original form

Ciphertext (cyphertext): an encrypted message Encryption: transformation of a message to hide

its meaning Cipher: cryptographic algorithm. A mathematical

function used for encryption (encryption algorithm) and decryption (decryption algorithm).

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Terminology

Decryption: recovering meaning from ciphertext

Cryptography: art and science of keeping messages secure

Cryptanalysis: art and science of breaking ciphertext

Cryptology: study of both cryptography and cryptanalysis

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Encryption and Decryption

Plaintext PlaintextEncryption Decryption

Ciphertext

Additional requirements:• Authentication

• Between communicating parties• Third-party authentication

• Non-repudiation• Integrity verification• Key distribution

• Secret key (secure distribution)• Public key (reliable distribution)


CryptanalysisCryptanalyst’s goal:

– Break message– Break key– Break algorithm

Secret Key Encryption(Symmetric key, Traditional)


Secret Key Cryptosystem

Encryption Decryption

Plaintext PlaintextCiphertext

K

Sender Recipient

C=E(K,M)M=D(K,C)

K needs secure channel


Basic Encryption Techniques

Substitution (confusion) Permutation (diffusion) Combinations and iterations of these


Simple Alphabetic Substitution

Assign a new symbol to each plain text symbol randomly or by key, e.g.,

C k, A h, B l

M=CAB

C =k h l

Advantages: large key space 26!

Disadvantages: trivially broken for known plaintext attack, repeated pattern, letter frequency distributions unchanged


Transposition Letters of the message are rearranged Break patterns, e.g., columnar transposition

Plaintext: this is a testt h i si s a t tiehssiatst!e s t !

Advantages: easy to implement Disadvantages:

Trivially broken for known plaintext attack Easily broken for cipher only attack


Symmetric Key Encryption Algorithms

Data Encryption Standard (DES)Advanced Encryption Standard (AES)


Public-Key EncryptionTwo keys – one is private one is publicSolves the key distribution problem (but

need reliable channel)Provides electronic signaturesSlower than secret-key encryption


Public-Key Encryption

Needed for security:– One of the keys must be kept secret– Impossible (at least impractical) to decipher

message if no other information is available– Knowledge of algorithm, one of the keys, and

samples of ciphertext must be insufficient to determine the other key


Confidentiality

ASender

BRecipient

Insecure channel

Plaintext PlaintextCiphertextEncryption Alg.

Decryption Alg.

B’s public key B’s private key

(need reliable channel)


Public Key Cryptosystem Concept conceived by Diffie and Hellman in 1976 Rivest, Shamir, and Adleman (RSA) describe a

public key system in 1978 Many proposals have been broken

e.g., Merkle-Hellman proposal broken by Shamir Serious candidates (public domain)

– RSA– El Gamal


Digital Signatures in RSA

AB

Insecure channel

Plaintext PlaintextSigned plaintext

Encryption Alg.

Decryption Alg.

A’s public keyA’s private key(need reliable channel)

Sign Verify


Signature and Encryption

D E D E

A B

Plaintext Plaintext

SignedPlaintext

SignedPlaintext

Encrypted Signed Plaintext

A’s private key

B’s public key

B’s private key

A’s public key


Hash Functions

Hash function h maps an input x of arbitrary length to a fixed length output h(x) (compression)

Accidental or intentional change to the data will change the hash value

Given h and x, h(x) is easy to compute (ease of computation)


Hash functions

Preimage resistant (one-way): if for all specified outputs, it is computationally infeasible to find any input that hashes to that output

Second-preimage resistent (weak collision resistant): if it is computationally infeasible to find any second input which has the same output as any specified input

Collision resistant (strong collision resistant): if it is computationally infeasible to find any two distinct inputs that has the same output


Attacks

First preimage attack: given a hash h, find a message m such that hash(m) = h

Second preimage attack: given a fixed message m1, find a different message m2 such that hash(m2) = hash(m1)

Attack complexity: 2n (considered too high for a typical output size of n=160 bits)

Practical attacks: Collision attack

Use of Encryption for Data Protection


Data Recovery

A process by which individual data elements such as files or folders are encrypted for more than one person or entity

Windows XP operating system: symmetrically encrypted data blocks

The symmetric key being protected by one or more public keys of a public/private key pair


Encrypting File System (EFS)

Provides file system-level encryption Enables files to be transparently encrypted on

NTFS file systems Protects confidential data from attackers with

physical access to the computer While the operating system is running: User

authentication and access control lists Attacker gains physical access to the computer:

need protection of harddrive


File system-level encryption

Individual files or directories are encrypted by the file system itself

Advantages:– Flexible file-based key management– Individual management of encrypted files – Access control can be enforced through the use of

public-key cryptography– Cryptographic keys are only held in memory while the

file that is decrypted by them is held open


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Documents

CSCE 201 Introduction to Information Security Fall 2010 Data Protection