Message Integrity : Hash Functions Flashcards
Explain how Hash Functions are used to provide message integrity without encryption…
Input data is fed into the hash function. This creates a digest. The digest is appended to the message and send to the recipients.
What is a potential issue with hashing without encryption?
Prone to a MIM attack, who could sit between recipients, copy the hash value, modify the message and re-append the has value to make it seem the message has integrity.
What happens is even 1 byte of the input message is changed?
The hash value is changed.
How does the recipient assess the integrity of the message?
The run the message through the hash function, and compare the hash values. If they’re different, the message has been modified.
Explain how message integrity with hash functions and encryption works…
The message is input into a hash function to create a digest. The digest is then encrypted via a key (usually recipients public key). the encrypted digest is appended to the message and send to the recipient.
What does encrypting the hash value achieve?
It should achieve integrity, since no subject should be able to access the hash value other than the intended recipient.
What are the 2 main properties of hash functions? Define each…
Pre-image resistant - Hash function is one way.
Second pre-image resistant - No 2 or more unique inputs of a hash function can map to the same value.
How do hash functions create a digest?
Input data is received and split into byte blocks. Each input block is mapped to a DES block in the hash function. The DES blocks start encrypting the input blocks in a linear way. Each DES block output acts as the input as the next DES block. This repeats until all input data blocks have been encrypted and a hash value is created.
