INFORMATION SECURITY MANAGEMENT

PROTECTION MECHANISMS - CRYPTOGRAPHY

Cryptography

• Encryption– The process of converting an original

message into a form that cannot be understood by unauthorized individuals

• Cryptology– The science of encryption– Composed of two disciplines:

– cryptography – cryptanalysis

Cryptography (cont’d.)

• Algorithm• Key• Keyspace

Encipher

Cryptosystem

Decipher

Common Ciphers

Most commonly used algorithms include:

Substitution

Transposition Plaintext: 0010…Key: 1 > 3, 2 > 4, 3 > 2, 4 > 1, …

Example: FROM -> MOFR

Common Ciphers

• XOR • ‘0’ XOR’ed with ‘0’ results in a ‘0’. (0 0 = 0)• ‘0’ XOR’ed with ‘1’ results in a ‘1’. (0 1 = 1)• ‘1’ XOR’ed with ‘0’ results in a ‘1’. (1 0 = 1)• ‘1’ XOR’ed with ‘1’ results in a ‘0’. (1 1 = 0)• If the two values are the same, you get “0”; if not, you get “1”• Process is reversible; if you XOR the ciphertext with the key

stream, you get the plaintext

01010111 01101001 01101011 01101001

11110011 11110011 11110011 11110011

= 10100100 10011010 10011000 10011010

10100100 10011010 10011000 10011010

11110011 11110011 11110011 11110011

= 01010111 01101001 01101011 01101001

Common Ciphers

• Book or running key cipher– Uses text in a book as the algorithm to decrypt

a message

– The key relies on two components: Knowing which book to use A list of codes representing the page number, line

number, and word number of the plaintext word

Symmetric Encryption

– Known as private key encryption

– Same key used to encrypt/decrypt the message

Symmetric Encryption Cryptosystem

• Data Encryption Standard (DES) – Based on the Data Encryption Algorithm which

uses a 64-bit block size and a 56-bit key– Cracked in 1997– Triple DES (3DES) improved version

• Advanced Encryption Standard (AES)– Based on the Rinjndael Block Cipher

Variable block length and a key length of either 128, 192, or 256 bits

Asymmetric encryption

Uses two different, but related keys Either key used to encrypt/decrypt message However, if Key A is used to encrypt the message,

then only Key B can decrypt it; conversely, if Key B is used to encrypt a message, then only Key A can decrypt it

Most valuable when one of the keys is private and the other is public

Figure 10-12 Public key encryption

Source: Course Technology/Cengage Learning

Asymmetric encryption

Digital Signatures

– Asymmetric process is reversed The fact that the message was sent by the organization that

owns the private key cannot be refuted This nonrepudiation is the foundation of digital signatures

• Based on:• Digital certificate• A certificate authority (CA)

Public key infrastructure (PKI)

• The entire set of hardware, software, and cryptosystems necessary to implement public key encryption

• PKI systems are based on public key cryptosystems and include digital certificates and certificate authorities

Encryption Operations (cont’d.)

• PKI provides the following services– Authentication– Integrity– Confidentiality– Authorization– Nonrepudiation

Using Cryptographic Controls

• Modern cryptosystems can generate unbreakable ciphertext

• Cryptographic controls used for:– e-mail and its attachments– e-commerce transactions– remote access through VPN connections

Email Cryptographic Controls

• Secure Multipurpose Internet Mail Extensions (S/MIME)

• Privacy Enhanced Mail (PEM)

Email Cryptographic Controls

• Pretty Good Privacy (PGP)

– Uses the IDEA Cipher A 128-bit symmetric key block encryption

algorithm with 64-bit blocks for message encoding

– Like PEM, it uses RSA for symmetric key exchange and to support digital signatures

Securing the Web

• IP Security (IPSec)– The primary and dominant cryptographic

authentication and encryption product of the IETF’s IP Protocol Security Working Group

– Combines several different cryptosystems: Diffie-Hellman key exchange Public key cryptography Bulk encryption algorithms Digital certificates

Securing the Web

• IPSec works in two modes of operation:– Transport

Only the IP data is encrypted, not the IP headers themselves

Allows intermediate nodes to read the source and destination addresses

– Tunnel The entire IP packet is encrypted and inserted as

the payload in another IP packet

– Often used to support a virtual private network

Securing the Web

• Secure Electronic Transactions (SET)– Encrypts credit card transfers with DES for

encryption and RSA for key exchange

• Secure Sockets Layer (SSL)– Uses RSA for key transfer

On IDEA, DES, or 3DES for encrypted symmetric key-based data transfer

HTTPS

Securing the Web - SSL

Securing the Web

• Secure Shell (SSH)– Provides security for remote access connections over

public networks by using tunneling, authentication services between a client and a server

– Used to secure replacement tools for terminal emulation, remote management, and file transfer applications

Hacking Cryptography

Known plaintext attack Ciphertext-only attack Replay attack

Managing Cryptographic Controls

• Don’t lose your keys• Know who you are communicating with• It may be illegal to use a specific encryption

technique when communicating to some nations• Every cryptosystem has weaknesses• Give access only to those with a business need• When placing trust into a certificate authority, ask

“Who watches the watchers?”

Managing Cryptographic Controls (cont’d.)• There is no security in obscurity• Security protocols and the cryptosystems

they use are installed and configured by humans– They are only as good as their installers

• Make sure that your organization’s use of cryptography is based on well-constructed policy and supported with sound management procedures