Entity Authentication

Key Concepts

Entity Authentication

• Alice and Bob share a key in advance

• Later, how can each side prove that they know the key? For example, if they want to prove they really are talking to each other

• A simple method is to use a challenge-response protocol

  • Alice sends a challenge that Bob can only answer if he knows the secret
  • Such a protocol is called a proof of knowledge protocol

• Unilateral: Alice wants Bob to prove he has the secret

• Mutual: Alice and Bob prove to each other they have the secret

Key Establishment

• How do Alice and Bob establish the secret key in the first place?
• Usually want to establish a session key, meaning a new key for each time you talk
  • key transport: one key chooses the key and needs to get it to the other party
  • key establishment: derive a shared key using information from both parties
• Generally want to authenticate the other party AND establish a session key all at once
• Key management is hard
  • establishing shared keys
  • securing them in transit and storage