Symmetric Key Cryptography Flashcards

1
Q

Electronic Code Book Mode (ECB)

A

Encrypts 64bit blocks of plain text using a set key. The same plain text repeated would result in the same cipher text. Not secure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Cipher block chaining mode (CBC)

A

XORs the plain text blocks with the preceding block of text. Uses initialization vector (IV). Issue is errors propagate because of the chaining process.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Cipher feedback mode (CFB)

A

Streaming version of CBC.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Output Feedback mode (OFB)

A

Same is CFB, but uses a seed value to XOR the plaintext rather than using the previous block of text. There is no chaining process so errors don’t propogate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Counter Mode (CTR)

A

Similar to OFB but doesn’t use a seed value for encryption process. It uses a counter value. Also doesn’t using chaining.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Galois/Counter Mode (GCM)

A

Similar to Counter Mode (CTR), but also includes data authenticity using authentication tags.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Counter with Cipher Block Chaining Message Authentication Code Mode (CCM)

A

Provides confidentiality and authenticity using a combination of CTR and CBC. Only used with 128 bit blocks. Used with a nonce that is changed each time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Nonce

A

Number used once. usually randomly generated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Data Encryption Standard (DES)

A

US created it in 1977 and is no longer secure. Basis for 3DES. 56bit key and 64bit block.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Triple DES (3DES)

A

168bit key. Not secure. No longer in use by gov’t agencies by end of 2023.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

International Data Encryption Algorithm (IDEA)

A

128 bit key. Used in PGP. Applied to 64bit blocks.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Blowfish

A

Variable key length up to 448 bit. Applied to 64bit blocks of data. Free for use.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Skipjack

A

80 bit key applied to 64bit blocks. Approved by US FIPS as the escrow encryption standard (EES). NIST and Dept of Treasury hold half of the key so they can decrypt the data if needed. Not used much because entities don’t trust escrow.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Rivest Cipher 4 (RC4)

A

Stream cipher with variable length key between 40 and 2048. Was used in WEP, WPA, SSL and TLS. No longer secure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

RC5

A

Variable block cipher (32, 64, 128). Variable key length 0 to 2040. A singled message was cracked in 4 years.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

RC6

A

Block cipher (128bit) using variable key (128, 192, 256). Was not selected for AES and not widely used.

17
Q

Advanced Encryption Standard (AES)

A

Based on the Rijndael block cipher. Required by FIPS 197 for encrypting sensitive, not classified, data. Supports three key lengths (128, 192, 256). Processes 128bit blocks.

18
Q

CAST-256

A

Not selected for use in AES

19
Q

Formula for calculating number of symmetric keys needed so all parties can communicate:

A

Number of symmetric keys needed =N(N-1)/2

Where N is the number of people needing to securely communicate.

20
Q

If 1 person loses their symmetric key among a group of people the formula for calculating how many keys need to be replaced where everyone was able to communicate with each other

A

Number of keys needing to be replaced= N-1

where N= original number of people with keys