Explain the MAC by using the general formula. Give an example of MAC algorithm.
Ø a MAC is a cryptographic checksum
MAC = CK(M)
l condenses a variable-length message M
l using a secret key K
l to a fixed-sized authenticator
Ø is a many-to-one function
l potentially many messages have same MAC
l but finding these needs to be very difficult
Describe the Arbitrated Digital Signature.
Ø involves use of arbiter A
l validates any signed message
l then dated and sent to recipient
Ø requires suitable level of trust in arbiter
Ø can be implemented with either private or public-key algorithms
Ø arbiter may or may not see message
X.509: Give description and definitions of the following: Certificate, and CA?
What is the algorithm of message receiving in PGP? Number below operations in the right order.
4… PGP retrieves the sender's public key from the public-key ring, using the Key ID field in the signature key component of the message as an index.
5… PGP recovers the transmitted message digest.
3… PGP then recovers the session key and decrypts the message.
6… PGP computes the message digest for the received message and compares it to the transmitted message digest to authenticate.
2… PGP prompts the user for the passphrase to recover the unencrypted private key.
1… PGP retrieves the receiver's private key from the private-key ring, using the Key ID field in the session key component of the message as an index.
7) What are the types of ‘modes’ that involve in IPSec? Describe these modes in few words.
Describe SSL Record Protocol involving in SSL.
SSL Record Protocol defines two services for SSL connections:
• Message Integrity: The Handshake Protocol also defines a shared secret key that is used to form a message authentication code (MAC), which is similar to HMAC
• Confidentiality: The Handshake Protocol defines a shared secret key that is used for conventional encryption of SSL payloads. The message is compressed before being concatenated with the MAC and encrypted, with a range of ciphers being supported as shown.