Please give a short and simple explanation for the following questions. (a) What
ID: 3815504 • Letter: P
Question
Please give a short and simple explanation for the following questions.
(a) What is the certificate?
(b) Please explain the meaning of CRL (certificate revocation list).
(c) Please describe the difference of distributing public key between PGP and S/MIME.
(d) Please describe the relation between Pass Phrase Pi and Private Key KRi.
(e) Please explain why the formidable operation in InvMixColumns is not so important in AES.
(f) Please explain why DES needs 16 rounds, but not 15 or 17?
(g) How do we choose the encryption key e in RSA?
(h) What is the man-in-the-middle attack?
(i) Please explain why DES needs a 32-bit swap after 16 rounds.
(j) What is the difference of passive attack and active attack?
PS: NOT IN CHINESE
Explanation / Answer
(a) Certificate is loaded into the browser to ensure that we are working on the correct website , It consists of the information about the owner , for example the e-mail address, name of the owner, Usage of the certificate, DN (Distinguished Name , CN (Common name) And the ID of the owner who certifies it.
(b) Certificate Revocation List is used in the web browsers which has the list of digital certificates and are revoked by using Certification Authority (CA) before their expiry date , It verifies whether the certificate is valid or not. It uses the TSL/SSL protocol and gives the identity of the cetificate owner.
(c) The S/MIME and PGP are used for securing mails .
The S/MIME consists of CMS and MIME , with the encoding rules and details . The CMS is Cryptographic Message Syntax which is in binary format and uses the X.509 certificates for public key distribution, It is widely used in corporations .
The Pretty Good Privacy is the implementation of the protocol OpenPGP , It uses public key cryptography and has its own encoding formats , It relies on Web of Trust and has an encoding layer called as ASCII Armor.
(d) The Pass Phrase is a string or phrase which is used to protect private key files , it encrypts the files and does not allows their unauthorized access by using secret key for encryption and decryption , The PassPhrase on the private key file can be changed by using OpenSSL by using the old pass-phrase and then by using the new pass-phrase.