ISRO2018-78

Question

Which one of the following algorithm is not used in asymmetric key cryptography?

1. RSA Algorithm
2. Gillie-Hellman Algorithm
3. Electronic Code Book Algorithm
4. None of the above

Comments

Electronic code book algorithm is not used in asymmetric key cryptography.Option C is correct.

Answer 1

Option C is correct. 
Please refer link : http://cryptowiki.net/index.php?title=Electronic_Code_Book_(ECB)
It is clearly mentioned that ECB is symmetric key encryption algorithm.
 

Comments

Deffie hellman Algoritham is also symmetric key. So why not B

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https://crypto.stackexchange.com/questions/6307/why-is-diffie-hellman-considered-in-the-context-of-public-key-cryptography

Answer 2

Ans C)

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Why not B) ?

The Diffie-Hellman key exchange is a public-key technology.Here is the basic function: 

1. Each party choses a private key $x$ or $y$
2. Each party calculates the corresponding public key $g^x$ or $g^y$.
3. Each party sends the public key $g^x$ or $g^y$  to the other party.
4. Each party uses the received public key together with its own private key to calculate the new shared secret    $(g^y)x=(g^x)y$.                                                                                                                                                                                                                                                                                                                                                                                                                         This might be what causes confusion: it is an asymmetric technology used to negotiate symmetric keys. But the same is valid for most other asymmetric technologies, like signature or encryption algorithms: At the core there is something asymmetric, but then we use a symmetric algorithm to do the bulk of the work. For example, with most asymmetric encryption algorithms we usually encrypt just a symmetric key for the actual message, with most signature algorithms we first hash a message, then asymmetrically sign the hash. The values $g^x$ or $g^y$ are named public keys, because they can be transmitted in plain, so anyone listening on the connection knows it. The values $x$ and $y$ never leave the choosers computer, so they stay private. $(x,g^x)$ and $(y,g^y)$ are the private-public key pairs here.                                  For more info: https://crypto.stackexchange.com/questions/6307/why-is-diffie-hellman-considered-in-the-context-of-public-key-cryptography                                    

Comments

DH uses two different numbers to derive the secret key. DH is asymmetric because each side has a different key to start with and they end up with the same secret key. I think it's a good way to envision that the symmetric keys they produce as the data.

DH is used to produce the symmetric key for a symmetric algorithm. DH in itself is not a data encryption algorithm necessarily but a way to agree on a secret key via a public network.

You'll the see the same thing with other asymmetric algorithms like SSL and TLS. They use asymmetric algorithms to create a symmetric key.

Answer 3

option b

• diffie hellman , AES,DES are example of symmetric key cryptography algorithm.
• RSA is a example of asymmetric key cryptography algorithm

Comments

In deffie hellman we send different keys but we use same key to compute the cipher text and so it doesn't come under symmetric key cryptography

Answer 4

Diffie-Hellman is an algorithm used to establish a shared secret(Key) between two parties. It is primarily used as a method of exchanging cryptography keys for use in symmetric encryption algorithms like AES,DES.

So, (B) Diffie Hellman Algorithm , is correct.