P2L7: Public Key Cryptography Flashcards
Symmetric encryption is also referred to as secret-key or single-key encryption.
True
The ciphertext-only attack is the easiest to defend against.
True
A brute-force approach involves trying every possible key until an intelligible translation of the ciphertext into plaintext is obtained.
True
AES uses a Feistel structure.
False
Each block of 64 plaintext bits is encoded independently using the same key? is a description of the CBC mode of operation.
False
Timing attacks are only applicable to RSA.
False
Using PKCS (public-key cryptography standard), when RSA encrypts the same message twice, different ciphertexts will be produced.
True
The Diffie-Hellman algorithm depends for its effectiveness on the difficulty of computing discrete logarithms.
True
A key exchange protocol is vulnerable to a man-in-the-middle attack if it does not authenticate the participants.
True
Just like RSA can be used for signature as well as encryption, Digital Signature Standard can also be used for encryption.
False
In general, public key based encryption is much slower than symmetric key based encryption.
True
________ is the original message or data that is fed into the encryption process as input.A. Plaintext B. Encryption algorithm C. Decryption algorithm D. Ciphertext
A
Which of the following would allow an attack that to know the (plaintext of) current message must be the same as one previously transmitted because their ciphtertexts are the same?A. CBC B. ECB C. CFB D. OFB
B
________ is a term that refers to the means of delivering a key to two parties that wish to exchange data without allowing others to see the key. A. Session key B. Subkey C. Key distribution technique D. Ciphertext key
C
Which of the following feature can only be provided by public-key cryptography?A. Confidentiality protection B. Integrity protection C. Non-repudiation D. None of the above
C
Cryptographic systems are generically classified by _______.A. the type of operations used for transforming plaintext to ciphertext B. the number of keys used C. the way in which the plaintext is processed D. all of the above
D
________ attacks have several approaches, all equivalent in effort to factoring the product of two primes.A. Mathematical B. Brute-force C. Chosen ciphertext D. Timing
A
________ are analogous to a burglar guessing a safe combination by observing how long it takes to turn the dial from number to number.A. Digital standards B. Mathematical attacks C. Ciphers D. Timing attacks
D
_________ was the first published public-key algorithm.A. NIST B. Diffie-Hellman C. RC4 D. RSA
B
The principal attraction of ________ compared to RSA is that it appears to offer equal security for a far smaller bit size, thereby reducing processing overhead.A. ECC B. MD5 C. Diffie-Hellman D. none of the above
A
To decrypt using DES, same algorithm is used, but with per-round keys used in the reversed order.
True
With Triple DES the effective key length can be 56, 112, and 168
True
Each round of DES contains both substitution and permutation operations.
True
The logics behind the S-boxes are well-known and verified
False
To decrypt using AES, just run the same algorithm in the same order of operations.
False
Each operation or stage in AES is reversible.
True
AES can support key length of 128, 192, 256
True
AES is much more efficient than Triple DES.
True
CBC is more secure than ECB.
True
We can have both confidentiality and integrity protection with CBC by using just one key.
False
RSA is a block cipher in which the plaintext and ciphertext are integers between 0 and n - 1 for some n.
True
If someone invents a very efficient method to factor large integers, then RSA becomes insecure.
True
What type of math are public key algorithms based on?
Modular arithmetic
What is the additive inverse of the below?
8 mod 10
12
because…
8 + 12 mod 10 = 0
What is the multiplicative inverse of the below?
3 mod 17
6
because…
3*6 mod 17 = 1
Does RSA support public or single key encryption?
Public
Does RSA support digital signatures?
Yes
What key-length is supported for RSA?
Any, but most use 128
Given that p = 3 and q = 11
What is step 1 in the RSA algorithm?
Compute n and totient(n).
n = pq
n = 311 = 33
totient(n) = (p-1)*(q-1) totient(n) = (3-1)*(11-1) totient(n) = 2*10 = 20
Given that p = 3 and q = 11 and the computed n, therefore, is 33 while the totient(n) is 20. And given that e = 7
What is step 2 in the RSA algorithm?
Calculate d.
We need to find the answer to the equation…
e * d mod totient(n) = 1
7 * d mod 20 = 1
3 = d
So public key is (7, 33) and private key is (3, 33)
Why is RSA secure and what would have to happen to make it not secure from a mathematical perspective?
It’s secure because it relies on factoring large numbers, which is computationally slow. If an algorithm is discovered that can efficiently compute the factors of large numbers then RSA encryption would no longer be secure
What are the special case plaintext that produce the same cipher texts that are regardless of the keys used?
1, -1 and 0
Given that prime q = 23 and primitive root a = 5, and Alice chose 6 as her secret key while Bob chose 15 as his secret key… what number does Alice show Bob and Bob show Alice?
- Alice To Bob –> 5^6 mod 23 = 8
* Bob To Alice –> 5^15 mod 23 = 19
What are the key points of the Diffie Hellman Key Exchange algorithm?
- The shared/secret key itself is never transmitted
- Uses discrete logarithms which are hard to crack ASSUMES q is a large prime (at least 300 digits long)
- ɑ^x mod q where alpha is the primitive root, x is the chosen secret key and q is the prime
What are the shortcoming of the Diffie Hellman algorithm?
- Expensive exponential operation, so DOS attacks are possible
- Only works for key exchange
- No authentication or digital signatures
What is the Bucket Brigade Attack and how is it overcome?
- type of Man-In the-Middle
- Intercepts message Alice sends out and redirects it back to herself, leading Alice to think she received a message from Bob. It does the same thing on Bob’s side.
- This can be overcome just by publishing the public key rather than sending it and risking redirected messages
What are two other public key algorithms besides Diffie Hellman and RSA?
DSS and ECC
