文档介绍：Key Management and Certificates
By the power vested in me I now declare this text
and this bit string ‘name’ and ‘key’. What RSA
has joined, let no man put asunder
— Bob Blakley
Key Management
Key management is the hardest part of cryptography
Two classes of keys
• Short-term session keys (sometimes called ephemeral keys)
– Generated automatically and invisibly
– Used for one message or session and discarded
• Long-term keys
– Generated explicitly by the user
Long-term keys are used for two purposes
• Authentication (including access control, integrity, and non-
repudiation)
• Confidentiality (encryption)
– Establish session keys
– Protect stored data
Key Management Problems
Key certification
Distributing keys
• Obtaining someone else’s public key
• Distributing your own public key
Establishing a shared key with another party
• Confidentiality: Is it really known only to the other party?
• Authentication: Is it really shared with the intended party?
Key storage
• Secure storage of keys
Revocation
• Revoking published keys
• Determining whether a published key is still valid
Key Lifetimes and promise
Authentication keys
• Public keys may have an extremely long lifetime (decades)
• Private keys/conventional keys have shorter lifetimes (a year or
two)
Confidentiality keys
• Should have as short a lifetime as possible
If the key promised
• Revoke the key
Effects promise
• Authentication: Signed documents are rendered invalid unless
timestamped
• Confidentiality: All data encrypted with it promised
Key Distribution
Alice retains the private key and sends the public key to
Bob
Mallet intercepts the key and substitutes his own key
Mallet can decrypt all traffic and generate fake signed
message
Key Distribution (ctd)
A certification authority (CA) solves this problem
CA signs Alice’s key to guarantee its authenticity to Bob
• Mallet can’t substitute his key since the CA won’t sign it
Cert