Question

Briefly describe some desirable properties of a robust message digest algorithm. Outline two distinct examples of how a message digest algorithm may be employed to ensure the integrity of data.

Answer 1

Message Digest Algorithm

Message digest or a cryptographic hash function is a mathematical algorithm that maps the input data of arbitrary length into a fixed size string called message digest or hash value.

The most common message digest algorithm is MD5

Desirable properties of message digest algorithm are as follows

• Pre-Image resistance: This property implies that it should be computationally infeasible to reverse the hash function.
• Second Pre-image resistance: This means that for an input and its hash value it should be hard to find another input with same hash value or message digest.
• Collision Resistance: This property also called the collision-free hash function which means that no two different message will have the same hash value.

Integrity of data

• It refers to the validity of the transmitted message. message integrity is ensuring that the message is as it is sent and no alteration or modification is made on it.
• The common method is to use a hash function that produces a message digest that is difficult to reverse.

Outline two distinct examples of how a message digest algorithm may be employed to ensure the integrity of data

• Data integrity check(Checksum):
  • It generates a message digest of the transmitting message as a checksum and transmitted along with the message and at the receiver side the message is again given as input to the hash function and create a checksum and both the checksums are compared if they are same then it is sure that the message is not altered.
• Next method to ensure integrity is the use of Digital Signatures
  • A digital signature is a cryptographic value generated from data and a secret key by the user
  • The hash value of the message and the private key are input for the signature algorithm and generate a signature (Encryption)
  • The signature along with the message is sent to the receiver.
  • receiver create a hash value from the message itself and decrypt the signature using the verification algorithm. (Decryption)
  • if both hash values(Generated and decrypted) if both are same then both authenticity and integrity of the data is ensured.

The outline of the two examples are given in the figure below: