27. Symmetric Cryptography

symmetric

Is DES a symmetric or asymmetric encryption algorithm?

block

Is DES a block or stream cipher?

 64 bit blocks

What number bit block does DES encrypt?

56 bit key

What bit key does DES use?

True

True or False?

DES is now considered insecure.

symmetric

Triple DES is a symmetric or asymmetric encryption algorithm?

64-bit

Triple DES is a block cipher that works on what number bit blocks?

True

True or False?

When Triple DES is used with three keys, it has an effective key length of 112 bits, but weaknesses in the algorithm mean that it's no longer recommended for use.

Triple DES or 3DES

Three rounds of DES encryption produced much stronger security than existed with standard DES. This approach is known as what?

True

True or False?

Why Triple DES? Why not just use DES twice? The answer is that using the algorithm twice is subject to an attack known as the meet-in-the-middle attack that makes it no more secure than the standard DES algorithm.

symmetric

Is advanced encryption standard, or AES a symmetric or asymmetric encryption algorithm?

block

Is advanced encryption standard, or AES a block or stream cipher?

128 bit block

AES works on what bit blocks?

1. 128 bit key

2. 192 bit key

3. 256 bit key

AES allows what three different key lengths that are considered secure?

symmetric

Is Blowfish a symmetric or asymmetric encryption algorithm?

block

Is Blowfish a block or stream cipher?

Blowfish

What symmetric encryption algorithm allows you to use any key length you'd like as long as it falls in the range of 32 to 448 bits?

True

True or False?

Blowfish is no longer considered secure because there are known attacks against some weak encryption keys

symmetric

Is TwoFish a symmetric or asymmetric encryption algorithm?

128 bits

TwoFish works on blocks of how many bits?

1. 128 bits

2. 192 bits

3. 256 bits

TwoFish allows what three different key lengths?

True

True or False?

TwoFish is still considered secure for use today.

stream

Is RC4 a block or stream cipher?

symmetric

is RC4 a symmetric or asymmetric encryption algorithm?

between 40 and 2048 bits

RC4 allows a variable length key of what?

False, it is no longer considered secure for use on modern networks.

True or False?

RC4 is still considered secure for use on modern networks.

network communications

RC4 was widely used to encrypt what kinds of communications?

Electronic code book, or ECB mode

What cipher mode?

Simplest & least secure mode.

Processes 64bit blocks, encrypts block with the chosen key.

If same block encountered multiple times, same encrypted block is produced, making it easy to break.

Cipher block chaining, or CBC mode

What is the cipher mode?

Each block of unencrypted text is XORed with the block of ciphertext immediately preceding.

Decryption process simply decrypts ciphertext and reverses the XOR operation.

Cipher Feedback (CFB)

What is the cipher mode?

Is the streaming version of Cipher block chaining, or CBC mode.

Works on data in real time, using memory buffers of same block size.

When buffer is full, data is encrypted and transmitted.

Uses chaining, so errors propagate.

Output Feedback (OFB).

What is the cipher mode?

Operates similar to Cipher Feedback (CFB), but XORs the plain text with a seed value.

No chaining function, so errors do not propagate.

Counter (CTR)

What is the cipher mode?

Uses an incrementing counter instead of a seed.

Errors do not propagate.

Galois counter mode, or GCM

What is the cipher mode?

A variant of counter mode that adds authentication to the cipher process, supplementing the confidentiality capabilities of electronic code book, cipher block chaining, and traditional counter mode. 

counter mode

What is a functionality that allows a block cipher to act more like a stream cipher?

Steganography

What is the process of hiding information within another file so that it is not visible to the naked eye? It's the art of hiding information in plain sight, and it's a particularly valuable communication secrecy tool for those who do not want others to know that they are even communicating in the first place. 

What encryption mode feeds the previous encrypted block into the encryption of the next block?