edited by
8,459 views
27 votes
27 votes

Consider that $B$ wants to send a message $m$ that is digitally signed to $A$. Let the pair of private and public keys for $A$ and $B$ be denoted by ${K_{x}}^-$ and ${K_{x}}^+$ for $x=A, B$, respectively. Let $K_{x}(m)$ represent the operation of encrypting $m$ with a key $K_{x}$ and $H(m)$ represent the message digest. Which one of the following indicates the CORRECT way of sending the message $m$ along with the digital signature to $A$?

  1. $\left\{m, {K_{B}}^+(H(m))\right\}$
  2. $\left\{m, {K_{B}}^-(H(m))\right\}$
  3. $\left\{m, {K_{A}}^-(H(m))\right\}$
  4. $\left\{m, {K_{A}}^+(m)\right\}$
edited by

4 Answers

Best answer
45 votes
45 votes

B wants to send message $'m'$ to A.
Private keys are denoted by $K^{-}_{(x)}$ and public keys by $K^{+}_{(x)}$.
In digital signature, the private key of the sender is used to encrypt the message and its public key is used to decrypt.
So, $\{m, K^{-}_{(B)}(H(m))\}$ must be the correct way of sending the message.

The answer is option B.

edited by
5 votes
5 votes
While digitally signing a document, the sender uses his private key, ${K_b}^-$ to computer ${K_b}^-(m)$.

It is unusual that sender is using his private key (which is generally used for decrypting a message), but sender's goal is not to scramble the contents of the document, but rather to sign a document in a manner that is verifiable and nonforgeable.

One concern with signing data by encryption is that encryption and decryption are conceptually expensive. A more efficient approach is to introduce hash functions into digital signature. Using hash function, Sender signs the hash of the message rather than message itself, thus sender calculates ${K_b}^-(H(m))$.

So the answer is $\left \{ {m, {K_b}^-(H(m))} \right \}$
3 votes
3 votes
Option B is CORRECT bcoz Sender generates the digital signature using his own private key and verifies using sender's public key.
3 votes
3 votes

In digital signature -->

(1) Private key of sender is used to encrypt the message.

(2) Public Key of sender is used to decrypt the message

Answer:

Related questions

27 votes
27 votes
5 answers
1
Akash Kanase asked Feb 12, 2016
9,330 views
Anarkali digitally signs a message and sends it to Salim. Verification of the signature by Salim requires.Anarkali's public key.Salim's public key.Salim's private key.Ana...
39 votes
39 votes
12 answers
2