Combiner. In many cases, certain cryptographic construction is believed to be se
ID: 3701000 • Letter: C
Question
Combiner. In many cases, certain cryptographic construction is believed to be secure, but later got broken. In order to build more robust systems. A combiner is one of such methods. Given two construc- tions (?1,?2) of a cryptographic primitive, a combiner will make calls to each construction and compile them into a third construction ?3. The third new construction will be secure as long as one of (?1,?2) is secure. Specifically, consider the following:
Given two constructions of symmetric encryption ?1 = (KeyGen1, Enc1, Dec1), ?2 = (KeyGen2, Enc2, Dec2), where the IND-CPA security of ?1 is based on Assumption-I, e.g, PRF, the IND-CPA security of ?2 is based on Assumption II, e.g., some mathematical assumption.
Construct a secure encryption scheme
?3 = (KeyGen3, Enc3, Dec3), which will be IND-CPA secure as long as one of Assumption-I or Assumption-II holds, and briefly explain why.
Explanation / Answer
As you know cryptography is the process to secure your data from unauthorised person or organization.
Symmetric encryption is the process where sender and receiver will have same key to encrypt the message and decrypt the ciper text. in this the major problem is to exchange the secret key. because both will have same key to encrypt or decrypt.
so, if we are encrpting with 1 key and decrypting it, then it is less secure as any one can try hit and trail to guess the key . to make it more complex to break the key and ciper .
we try to encrypt it twice with diffrent key so if anyone find any key it may confuse them that they got the actual msg but they will get the ciper text which is encrypted of different key.
so here 1 they will encrypt with key1 and then they will get the ciper text again they will encrypt that with other key2 and get the final ciper text to send receiver . receiver will again decrypt it with key2 first then with key to get the actual message send by sender.