Ch11 Basic Cryptography

Chapter 11 Basic Cryptography Security+ Guide to Network Security Fundamentals, Third Edition

Objectives Define cryptography Describe hashing List the basic symmetric cryptographic algorithms Describe how asymmetric cryptography works List types of file and file system cryptography Explain how whole disk encryption works

What Is Cryptography? Cryptography - scrambles data The science of transforming information into an unintelligible form while it is being transmitted or stored so that unauthorized users cannot access it Steganography - hides data Hides the existence of the data What appears to be a harmless image can contain hidden data embedded within the image Can use image files, audio files, or even video files to contain hidden information

Caesar Cipher Used by Julius Caesar Caesar shifted each letter of his messages to his generals three places down in the alphabet So BURN THE BRIDGE becomes EXUQ WKH EUKFIG A  D B  E C  F D  G E  H F  I G  J H  K

Encryption and Decryption Encryption Changing the original text to a secret message using cryptography Decryption Change the secret message back to its original form

Cryptography and Security Cryptography can provide: Confidentiality of information Integrity of the information Availability of the data To users with the key Guarantee Authenticity of the sender Enforce Non-repudiation Sender cannot deny sending the message

Information Protection by Cryptography

Cryptographic Algorithms There are three categories of cryptographic algorithms: Hashing algorithms Symmetric encryption algorithms Asymmetric encryption algorithms

Hashing Algorithms Hashing is a one-way process Converting a hash back to the original data is difficult or impossible A hash is a unique “signature” for a set of data This signature, called a hash or digest , represents the contents Hashing is used only for integrity to ensure that: Information is in its original form No unauthorized person or malicious software has altered the data Common hash algorithms MD5, SHA-1

Hashing Algorithms (continued)

Hashing Algorithm Security A hashing algorithm is considered secure if: The ciphertext hash is a fixed size Two different sets of data cannot produce the same hash, which is known as a collision It should be impossible to produce a data set that has a desired or predefined hash The resulting hash ciphertext cannot be reversed to find the original data

Preventing a Man-in-the-Middle Attack with Hashing

Hashing Algorithms (continued) Hash values are often posted on Internet sites In order to verify the file integrity of files that can be downloaded

Hashing Algorithms Only Ensure Integrity

Message Digest (MD) Message Digest (MD) algorithm One common hash algorithm Three versions Message Digest 2 (MD2) Message Digest 4 (MD4) Message Digest 5 (MD5) Suffer from collisions Not secure See links Ch 11b, c, d

Secure Hash Algorithm (SHA) More secure than MD A family of hashes SHA-1 Patterned after MD4, but creates a hash that is 160 bits in length instead of 128 bits SHA-2 Comprised of four variations, known as SHA-224, SHA-256, SHA-384, and SHA-512 Considered to be a secure hash

SHA-3 is Being Chosen Now Link Ch 11d

Whirlpool A relatively recent cryptographic hash function Has received international recognition and adoption by standards organizations Creates a hash of 512 bits

Password Hashes Another use for hashes is in storing passwords When a password for an account is created, the password is hashed and stored The Microsoft NT family of Windows operating systems hashes passwords in two different forms LM (LAN Manager) hash NTLM (New Technology LAN Manager) hash Most Linux systems use password-hashing algorithms such as MD5 Apple Mac OS X uses SHA-1 hashes

Symmetric Cryptographic Algorithms

Symmetric Cryptographic Algorithms Symmetric cryptographic algorithms Use the same single key to encrypt and decrypt a message Also called private key cryptography Stream cipher Takes one character and replaces it with one character WEP (Wired Equivalent Protocol) is a stream cipher Substitution cipher The simplest type of stream cipher Simply substitutes one letter or character for another

XOR (eXclusive OR) With most symmetric ciphers, the final step is to combine the cipher stream with the plaintext to create the ciphertext The process is accomplished through the exclusive OR (XOR) binary logic operation One-time pad (OTP) Combines a truly random key with the plaintext

Block Cipher Manipulates an entire block of plaintext at one time Plaintext message is divided into separate blocks of 8 to 16 bytes And then each block is encrypted independently Stream cipher advantages and disadvantages Fast when the plaintext is short More prone to attack because the engine that generates the stream does not vary Block ciphers are more secure than stream ciphers

Information Protections by Symmetric Cryptography

DES and 3DES Data Encryption Standard (DES) Declared as a standard by the U.S Government DES is a block cipher and encrypts data in 64-bit blocks Uses 56-bit key, very insecure Has been broken many times Triple Data Encryption Standard (3DES) Uses three rounds of DES encryption Effective key length 112 bits Considered secure

Advanced Encryption Standard (AES) Approved by the NIST in late 2000 as a replacement for DES Official standard for U.S. Government Considered secure--has not been cracked

Animation of AES Algorithm Link Ch 11e

Other Algorithms Several other symmetric cryptographic algorithms are also used: Rivest Cipher (RC) family from RC1 to RC6 International Data Encryption Algorithm (IDEA) Blowfish Twofish

Asymmetric Cryptographic Algorithms

Asymmetric Cryptographic Algorithms Asymmetric cryptographic algorithms Also known as public key cryptography Uses two keys instead of one The public key is known to everyone and can be freely distributed The private key is known only to the recipient of the message Asymmetric cryptography can also be used to create a digital signature

Digital Signature A digital signature can: Verify the sender Prove the integrity of the message Prevent the sender from disowning the message ( non-repudiation ) A digital signature does not encrypt the message, it only signs it

Information Protections by Asymmetric Cryptography

RSA The most common asymmetric cryptography algorithm RSA makes the public and private keys by multiplying two large prime numbers p and q To compute their product ( n=pq ) It is very difficult to factor the number n to find p and q Finding the private key from the public key would require a factoring operation RSA is complex and slow, but secure 100 times slower than DES

Diffie-Hellman A key exchange algorithm, not an encryption algorithm Allows two users to share a secret key securely over a public network Once the key has been shared Then both parties can use it to encrypt and decrypt messages using symmetric cryptography

HTTPS Secure Web Pages typically use RSA, Diffie-Hellman, and a symmetric algorithm like RC4 RSA is used to send the private key for the symmetric encryption

Elliptic Curve Cryptography An elliptic curve is a function drawn on an X-Y axis as a gently curved line By adding the values of two points on the curve, you can arrive at a third point on the curve The public aspect of an elliptic curve cryptosystem is that users share an elliptic curve and one point on the curve Not common, but may one day replace RSA

Using Cryptography on Files and Disks

Encrypting Files: PGP and GPG Pretty Good Privacy (PGP) One of the most widely used asymmetric cryptography system for files and e-mail messages on Windows systems GNU Privacy Guard (GPG) A similar open-source program PGP and GPG use both asymmetric and symmetric cryptography

Encrypting Files: Encrypting File System (EFS) Part of Windows Uses the Windows NTFS file system Because EFS is tightly integrated with the file system, file encryption and decryption are transparent to the user EFS encrypts the data as it is written to disk On Macs, Filevault encrypts a user's home folder

Whole Disk Encryption Windows BitLocker A hardware-enabled data encryption feature Can encrypt the entire Windows volume Includes Windows system files as well as all user files Encrypts the entire system volume, including the Windows Registry and any temporary files that might hold confidential information TrueCrypt Open-source, free, and can encrypt folders or files

Trusted Platform Module (TPM) A chip on the motherboard of the computer that provides cryptographic services If the computer does not support hardware-based TPM then the encryption keys for securing the data on the hard drive can be stored by BitLocker on a USB flash drive

Cold Boot Attack Can defeat all currently available whole disk encryption techniques (link Ch 11i)

Ch11 Basic Cryptography

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Ch11 Basic Cryptography