MODERN CRYPTOGRAPHY

User Authentication and Data Integrity
using Symmetric Cryptography
Can only take place between two parties who are prepared to cooperate
with each other
Typical authentication scheme:
A and B share a secret key K which (they believe) is known
only to them
A sends a ‘challenge’ to B. If the response is the challenge
encrypted with key K then A believes the response is from B
Data Integrity:
If A sends a message to B with a cryptographic checksum using
K then B uses K to check the checksum and, if it is correct, knows
the message is unaltered and came from A
Note: A and B need to protect against replays etc
IMA 2009 31