Cs 3600 Mid-Term Study Week 7

Front 1

Keys

Back 1

Secret sequence of bits and instructions that governs the act of encryption and decryption.

Front 2

Breaking Ciphers

Back 2

Brute Force attack and Short Cut attack

Front 3

Brute Force Attack

Back 3

Decrypt the ciphertext with all keys
•If you can recognize the plaintext when it appears you’re done
•For most ciphers all keys, except the correct one, will decrypt a ciphertext to garbage

Front 4

Short Cut Attack

Back 4

Any attack that takes less effort than a brute force attack.
Usually uses "known plaintext" i.e. a part of the message that is already known.

Front 5

One-Time Cipher Pad

Back 5

This observation leads to key requirements for an unbreakable cipher
–The key is random
–The key is as long as the message
–The key is only used for one message
•If a cipher meets these requirements it is called a One-Time Pad

Front 6

Substitution transformations vice Permutation transformations

Back 6

Permutation is the rearranging or permuting (transposition) the bits of a message instead of changing, or substituting them. For example when writing a message backwards.

Front 7

Relationship between the length of binary keys and the Brute Force Attack

Back 7

The amount of keyspace determines how long the attack needs to run through every possible key.
A worst case Brute Force Attack that tries all combinations of all 3 DES keys takes 2^56*2^56*2^56= 2^168total iterations•

Front 8

DES

Back 8

Symmetric cipher. 56 bit

Front 9

3-Key Triple DES

Back 9

Triple DES is 168 bit.

Front 10

AES

Back 10

The Rijndael algorithm was selected to be the AES
•The Rijndael design addresses
–resistance to all known attacks
–speed and code compactness
–design simplicity
128-bit block lengths are approved for the AES

Front 11

Block cipher modes

Back 11

Divides a message into blocks of bits as plain text, placed into mathematical functions and outputs as cipher text.

ECB - Electronic Code Book (used for small amounts of data)
CBC - Cipher Block Chaining Mode (used for lots of data)
CTR - Counter mode - produces a stream.

Front 12

Electronic Code Book Mode

Back 12

each block of plaintext goes into a separate cipher block.

Front 13

Cipher Block Chaining Mode

Back 13

takes the output of the 1st encryption and XOR's it into the 2nd bloc.

Front 14

Conventional Cryptography

Back 14

General substitution cipher and shift cipher.

Front 15

Public key

Back 15

PKI and RSA

Front 16

Hash Functions

Back 16

Hashes are complicated checksums that produce long binary strings viewed in hex notation called hash values.

Front 17

Hash Function Properties

Back 17

Hash can be applied to any size message.
Produces a fixed size output.
Is easy to compute.
Given a message M1, it is not computationally feasible to find another message, M2, such that H(M2) = H(M1)
5.Given H(M) you cannot find M

Front 18

MAC

Back 18

Takes the last block of the cipher block chaining mode and uses that as a checksum

Front 19

Public Key Cryptography

Back 19

2 mathematically related keys. Data is encrypted with one key and decrypted with the other.

Front 20

RSA Short Cut Attack

Back 20

Use the factor of the modulus which is the same for the public and private keys

Front 21

Conventional cryptography

Back 21

Encrypt and decrypt with the same key.
Conventional ciphers are fast, between 1,000 and 10,000 times faster than public key ciphers
•Key distribution is the difficult part of conventional cryptography!!!

Front 22

Secret Key Cryptography

Back 22

Common name for Conventional cryptography

Front 23

Shared Key Cryptography

Back 23

Common name for Conventional cryptography.

Front 24

Private Key Cryptography

Back 24

Common name for Conventional cryptography.

Front 25

Single Key Cryptography

Back 25

Common name for Conventional cryptography.

Front 26

Symmetric cryptography

Back 26

Common name for Conventional cryptography.

Front 27

Secret Keys

Back 27

Sender and receiver use two instances of the same key for encryption and decryption.

Front 28

Public Key cryptography

Back 28

It was proposed to solve two problems
–Simplify the distribution of keys
–Enable the creation digital signatures
Public key cryptography is often called “asymmetric key”cryptography since it uses two different keys
•One of the 2 keys is called a public key and
•the other is called a private key
The 2 keys are mathematically related
•Data is encrypted with one key
•And decrypted with the other key
•That is it!!!

Front 29

Asymmetric key cryptography

Back 29

PKI - uses public and private keys

Front 30

DES (Data Encryption Standard)

Back 30

Symmetric block encryption.
54 bit key,
64 bits of which 8 bits for parity checking.

Front 31

AES (Advanced Encryption Standard)

Back 31

Rinjdael. 128(10 rounds) 192(12 rounds) 256(14 rounds).
AES uses 128

Front 32

One-Time Pad

Back 32

The key is random
The key is as long as the message
The key is only used for one message

Front 33

Electronic Code Book Mode

Back 33

64 bit.
Each block encrypted with the same key.
Fastest and easiest but patterns emerge when encrypting large amounts of data.

Front 34

Cipher Block Chaining Mode

Back 34

Does not reveal a pattern, because each block of texts, the key, and the value based on the previous block are processed in the algorithm and applied to the next block of text.

Used when lot's of data needs to be encrypted.

Front 35

2 key Triple DES

Back 35

112 bit key

Front 36

3 key triple DES

Back 36

Uses 48 rounds which makes it highly resistant to differential cryptanalysis.
Makes for a heavy performance hit.

Front 37

MD5

Back 37

Hash function. Message digest of 128 bits

Front 38

SHA

Back 38

Secure Hasing, NIST standard, up to 512 bits

Front 39

RSA

Back 39

Asymmetric cipher. Most popular public key algorithm.

Front 40

Hashing vs. MAC

Back 40

MAC uses a key, hashing does not.