008 Key Distribution with examples and some
- 1. Key Management and Distribution Presented by Sir Najam
- 2. What is key management? ļ Key management is the set of techniques and procedures supporting the establishment and maintenance of keying relationships between authorized parties. ļ A keying relationship is the state wherein communicating entities share common data(keying material) to facilitate cryptography techniques. This data may include public or secret keys, initialization values, and additional non-secret parameters.
- 3. ļ Key management encompasses techniques and procedures supporting: 1. initialization of systems users within a domain; 2. generation, distribution, and installation of keying material; 3. controlling the use of keying material; 4. update, revocation, and destruction of keying material; and 5. storage, backup/recovery, and archival of keying material.
- 4. Objectives The objective of key management is to maintain keying relationships and keying material in a manner that counters relevant threats In practice an additional objective is conformance to a relevant security policy
- 5. Threats 1. compromise of confidentiality of secret keys 2. compromise of authenticity of secret or public keys. 3. unauthorized use of public or secret keys
- 6. Security Policy Security policy explicitly or implicitly defines the threats a system is intended to address Security policy may affect the stringency of cryptographic requirements, depending on the susceptibility of the environment in questions to various types of attack.
- 7. Key management techniques ļ Public-key techniques Primary advantages offered by public-key techniques for applications related to key management include: 1. simplified key management 2. on-line trusted server not required 3. enhanced functionality
- 8. Key management techniques ļ Key management a) Symmetric-key encryption encryptio n decryptio n plaintext plaintext symmetric key generator secret key secret key ciphertex t
- 9. Key management techniques b) public-key encryption encryption decryption asymmetric key pair generation plaintext ciphertext plaintext public key private key secure channel (private and authentication) secure channel (authentication only) unsecured channel (no protection)
- 10. Key management techniques ļ Techniques for distributing confidential keys Key layering and symmetric-key certificates Key layering: 1. master keys ā keys at the highest level in the hierarchy 2. key-encrypting keys ā symmetric keys or encryption public keys used for key transport or storage of other keys 3. data keys ā used to provide cryptographic operations on user data
- 11. Key management techniques symmetric-key certificates: Symmetric-key certificates provide a means for a KTC(Key Translation Center) to avoid the requirement of either maintaining a secure database of user secrets (or duplicating such a database for multiple servers), or retrieving such keys from a database upon translation requests.
- 12. Key management life cycle 1. user registration 2. user initialization 3. key generation 4. key installation 5. key registration 6. normal use 7. key backup 8. key update 9. archival 10. key de-registration and destruction 11. key recovery 12. key revocation
- 13. Key Distribution ļ given parties A and B have various key distribution alternatives: 1. A can select key and physically deliver to B 2. third party can select & deliver key to A & B 3. if A & B have communicated previously can use previous key to encrypt a new key 4. if A & B have secure communications with a third party C, C can relay key between A & B
- 16. Key Distribution Issues ļ hierarchies of KDCās required for large networks, but must trust each other ļ session key lifetimes should be limited for greater security ļ use of automatic key distribution on behalf of users, but must trust system ļ use of decentralized key distribution ļ controlling key usage
- 17. Simple Secret Key Distribution ļ Merkle proposed this very simple scheme ļ allows secure communications ļ no keys before/after exist
- 18. Secret Key Distribution with Confidentiality and Authentication
- 19. Distribution of Public Keys ļ can be considered as using one of: ļ public announcement ļ publicly available directory ļ public-key authority ļ public-key certificates
- 20. Public Announcement ļ users distribute public keys to recipients or broadcast to community at large ļ eg. append PGP keys to email messages or post to news groups or email list ļ major weakness is forgery ļ anyone can create a key claiming to be someone else and broadcast it ļ until forgery is discovered can masquerade as claimed user
- 21. Publicly Available Directory ļ can obtain greater security by registering keys with a public directory ļ directory must be trusted with properties: ļ contains {name,public-key} entries ļ participants register securely with directory ļ participants can replace key at any time ļ directory is periodically published ļ directory can be accessed electronically ļ still vulnerable to tampering or forgery
- 22. Public-Key Authority ļ improve security by tightening control over distribution of keys from directory ļ has properties of directory ļ and requires users to know public key for the directory ļ then users interact with directory to obtain any desired public key securely ļ does require real-time access to directory when keys are needed ļ may be vulnerable to tampering
- 24. Public-Key Certificates ļcertificates allow key exchange without real-time access to public-key authority ļa certificate binds identity to public key ļ¬usually with other info such as period of validity, rights of use etc ļwith all contents signed by a trusted Public-Key or Certificate Authority (CA) ļcan be verified by anyone who knows the public- key authorities public-key