chapter6

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"X: 0 1 1 0 1 1 0 0 Y: 1 0 1 0 0 1 1 1 __________________________ X ∧ Y:

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" "One-time pads

use a different substitution alphabet for each letter of the plaintext message. C = (P + K) mod 26

" Symmetric key cryptosystems

use a shared secret key available to all users of the cryptosystem.

"Transposition ciphers

use an encryption algorithm to rearrange the letters of a plaintext message, forming the ciphertext message.decryption algorithm simply reverses the encryption transformation to retrieve the original message. Shuffle chars

"Asymmetric cryptosystems

use individual combinations of public and private keys for each user of the system

" Substitution ciphers

use the encryption algorithm to replace each character or bit of the plaintext message with a different character. example: caesar cipher

" "columnar transposition

uses keyword. example: A T T A C K E R 1 7 8 2 3 5 4 6

" OR operation (represented by the __ symbol)

v

"Codes ,

which are cryptographic systems of symbols that represent words or phrases, are sometimes secret, but they are not necessarily meant to provide confi dentiality. xample, a spy might transmit the sentence "The eagle has landed"

" possible way to decrypt the Enigma message

with contemporary technology was to use a similar machine with the same rotor settings used by the transmitting device.

" AND operation (represented by the __ symbol)

∧

" NOT operation (represented by the __ symbol)

∼ or !

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"X: 0 1 1 0 1 1 0 0 Y: 1 0 1 0 0 1 1 1 __________________________ X ∨ Y:

1 1 1 0 1 1 1 1

"X: 0 1 1 0 1 1 0 0 Y: 1 0 1 0 0 1 1 1 ___________________________ X XOR Y:

11001011

" Modern cryptographic systems use at least a ___ key to protect data against prying eyes

128-bit

" "8 mod 6 = 6 mod 8 = 10 mod 3 = 10 mod 2 = 32 mod 8 =

2 6 1 0 0

" "period analysis

Although polyalphabetic substitution protects against direct frequency analysis, it is vulnerable to a second-order form of frequency analysis called p eriod analysis , which is an examination of frequency based on the repeated use of the key.

__ vulnerable to a type of attack known as frequency analysis.

Ceasar Cipher

" Asymmetric key encryption can provide___ CIA

Confidentiality, integrity, authentication, and nonrepudiation

"one-time pads rules

Each one-time pad must be used only once.(VENONA) The key must be at least as long as the message to be encrypted. integrity- The one-time pad must be randomly generated. integrity- The one-time pad must be physically protected against disclosure.

"German military-industrial complex adapted a commercial code machine nicknamed __for government use.

Enigma

"CAST' when it is encrypted using the Caesar cipher:

FDVW

" "defi nes the hardware and software requirements for cryptographic modules that the federal government uses.

Federal Information Processing Standard (FIPS)

" Japanese used a similar Enigma machine, known as

Japanese Purple Machine

"Symmetric key cryptography has several weaknesses:

Key distribution is a major problem. Symmetric key cryptography does not implement nonrepudiation The algorithm is not scalable. Keys must be regenerated often.

" ROT12 cipher would turn an A into an

M

" "total number of keys required to completely connect n parties using symmetric cryptography is given by the following formula:

Number of Keys = n*(n-1)/2

" __ are also known as Vernam ciphers

One-time pads

C = (P + 3) mod 26 is caesar cipher encryption function. what will be decryption function

P = (C - 3) mod 26

"___ do not provide this guarantee of nonrepudiation

Secret key, or symmetric key, cryptosystems (such as simple substitution ciphers)

__can also be called secret key cryptography and private key cryptography.

Symmetric key cryptography

" "Two main types of cryptosystems enforce confi dentiality.

Symmetric key cryptosystems Asymmetric cryptosystems

" Caesar Cipher

To encrypt a message, you simply shift each letter of the alphabet three places to the right. For example, A would become D , and B would become E .

"top-secret effort known by the code name __ to attack the Enigma codes

Ultra

"major strengths of asymmetric key cryptography

Users can be removed far more easily from asymmetric systems. The addition of new users requires the generation of only one public-private key pair. Key regeneration is required only when a user's private key is compromised. Asymmetric key encryption can provide integrity, authentication, and nonrepudiation Key distribution is a simple process. No preexisting communication link needs to exist

Caesar Cipher - XYZ represents?

X becomes A , Y becomes B , and Z becomes C .

" running key cipher (also known as

a book cipher

one-time pad is example of

a stream cipher

" "transposition ciphers are examples of __ ciphers

block

" Usually the time and effort required to perform a complete ___ attack against an encryption system is what the work function represents

brute-force

possible way of attack on one way hash

bruteforce algorithm

" Codes vs Ciphers

codes work on words and phrases whereas ciphers work on individual characters and bits.

"Security practitioners use cryptographic systems to meet four fundamental goals:

confidentiality, integrity, authentication, and nonrepudiation.

primarily employed to perform bulk encryption and provides only for the security service of ___ CIA ?

confidentiality.

substitution introduces __ and the transposition introduces ___

confusion & diffusion

Cryptographic algorithms rely on two basic operations to obscure plaintext messages—

confusion and diffusion.

The art of creating and implementing secret codes and ciphers is known as

cryptography

"Together, cryptography and cryptanalysis are commonly referred to as

cryptology

" "Specifi c implementations of a code or cipher in hardware and software are known as

cryptosystems

" Message integrity is enforced through the use of encrypted message digests, known as

digital signatures created upon transmission of a message

Asymmetric key algorithms

each user has two keys: a public key, which is shared with all users, and a private key, which is kept secret and known only to the user.

"Cryptography ensures __ CIA

ensure confi dentiality, integrity, authentication, and nonrepudiation.

initialization vector (IV)

examples of a nonce.a random bit string that is the same length as the block size and is XORed with the message.

" The major strength of symmetric key cryptography

great speed at which it can operate. Symmetric key encryption is very fast, often 1,000 to 10,000 times faster than asymmetric algorithms.

"Asymmetric key algorithms encryption decryption

if the public key encrypts a message, then only the corresponding private key can decrypt it, and vice versa.

_ are used to create unique ciphertext every time the same message is encrypted using the same key.

initialization vector (IV)

" one-way function

is a mathematical operation that easily produces output values for each possible combination of inputs but makes it impossible to retrieve the input values

nonce

is a random number that acts as a placeholder variable in mathematical functions. nonce must be a unique number each time it is used.

Kerchoff principle

is that a cryptographic system should be secure even if everything about the system, except the key, is public knowledge

"no. of participants = 10. How many keys required for symmetric and Asymmertric

Asymmetric = 20 Symmetric = 10*(10-1)/2 = 45

" "__ provide a key revocation mechanism that allows a key to be canceled, effectively removing a user from the system.

Asymmetric cryptosystems

" "___ provide a key revocation mechanism that allows a key to be canceled, effectively removing a user from the system.

Asymmetric cryptosystems

___ cryptography is scaleable

Asymmetric cryptosystems

" ___ algorithms also provide support for digital signature technology.

Asymmetric key

___ also known as public key algorithms

Asymmetric key algorithms

"Caesar cipher also became known as the __ cipher.

ROT3 (or Rotate 3)

major weakness of public key cryptography is __

its slow speed of operation

Caesar cipher, Vigenère cipher, and one-time pad sound very similar. They are! The only difference is the ___

key length.Caesar shift cipher uses a key of length one, the Vigenère cipher uses a longer key (usually a word or sentence), and the onetime pad "uses a key that is as long as the message itself."

is the range of values that are valid for use as a key for a specifi c algorithm

key space - defined in bit size

" All cryptographic algorithms rely on __to maintain their security.

keys

" "Enigma

machine used a series of three to six rotors to implement an extremely complicated substitution cipher.

" "work function or work factor

measure the strength of a cryptography system by measuring the effort in terms of cost and/or time

" total number of keys required to completely connect n parties using Asymmetric cryptography is given by the following formula:

n*2

Diffusion

occurs when a change in the plain text results in multiple changes spread throughout the ciphertext.

Confusion

occurs when the relationship between the plain text and the key is so complicated that an attacker can't merely continue altering the plain text and analyzing the resulting ciphertext to determine the key.

"Block ciphers

operate on "chunks," or blocks, of a message and apply the encryption algorithm to an entire message block at the same time

" Stream ciphers

operate on one character or bit of a message (or data stream) at a time

"Vigenère cipher

polyalphabetic substitution cipher system is the Vigenère cipher. The Vigenère cipher uses a single encryption/decryption chart. ROWS : Plain text letter: Columns: Key letter Cell: Cipher letter

Cryptography provides added levels of security to data during

processing, storage, and communications.

Integrity can be enforced by both __ key cryptosystems.

public and secret

" "Nonrepudiation is offered only by

public key, or asymmetric, cryptosystems,

Symmetric key algorithms

rely on a "shared secret" encryption key that is distributed to all members who participate in the communications. This key is used by all parties to both encrypt and decrypt messages, so the sender and the receiver both possess a copy of the shared key.

XOR function

returns a true value when only one of the input valuesis true

the study of methods to defeat codes and ciphers

ryptanalysis

" Ceasar Cipher decrypt the message

simply shift each letter three places to the left.

"This separation of duties and two-person control contained in a single solution is called ___

split knowledge. best example of split knowledge is seen in the concept of key escrow

Caesar cipher is an example of a r

stream cipher

"three types of algorithms

symmetric encryption algorithms, asymmetric encryption algorithms, and hashing algorithms