Practices in Security

1. Practices in Security Bruhadeshwar Bezawada

2. Key Management • Set of techniques and procedures supporting the establishment and maintenance of keying relationships between authorized parties • Initialization of system users within a domain • Generation, distribution, and installation of keying material • Controlling the use of keying material • Update, revocation and destruction of keying material • Storage, backup/recovery, and archival of keying material

3. Types Key Management • Automated Key Management • More than N^2 Keys • Stream cipher • Initialization vectors are used • Large amount of data needs to be encrypted in short amount of time • Long term session keys are used in multicast sessions • Frequent change in session key is expected • Manual key management • Environment has limited bandwidth or high RTT • Information has low value • Total volume of traffic is very low • Scale of each deployment is very limited

4. Cryptographic Primitives • Hash Functions • Symmetric key algorithms • Asymmetric key algorithms

5. Cryptographic primitives • Hash functions do not require keys, provide • data authentication and integrity services • compression of messages for digital signature and verification • derivation of keys in key establishment algorithms • generate deterministic random numbers

6. Cryptographic primitives • Symmetric key algorithms require the same key across all operations, provide • data confidentiality • authentication and integrity in the form of MACs • key establishment • generation of deterministic random numbers

7. Cryptographic primitives • Asymmetric key, public key algorithms, enable • digital signatures • establish cryptographic keying material • generate random numbers • Exercise : Enumerate all hash functions, all symmetric key ciphers and all public-key crypto systems available currently. Differentiate between commercially available and non-commercial algorithms

8. Types of keys • Private signature key (public-private keys) • Public signature verification keys • Symmetric authentication key • Private authentication key • Public authentication keys • Symmetric data encryption key

9. Types • Symmetric and asymmetric random number generation keys • Symmetric master key • Private key transport key • Public key transport key • Symmetric key agreement key (also, key wrapping key)

10. Types • Private ephemeral key agreement key • Public ephemeral key agreement key • Symmetric authorization keys • Private authorization key • Public authorization key

11. General Terms in Key Management • Key registration • Key revocation • Key transport • Key update • Key derivation • Key confirmation • Key establishment • Key agreement

12. Terms • Registration authority • Security domain • Self-signed certificate

13. Valuable Information in Addition to Cryptographic Keys • Domain parameters • Initialization vectors, shared secrets, RNG seeds, nonces, random numbers • Intermediate results • Key control information • Passwords • Audit information

14. Cryptoperiods • Time span during which a specific key is authorized for use by legitimate entities, or the keys for a given system will remain in effect. A good cryptoperiod • Limits amount of information protected by a given key from disclosure • Limits amount of exposure if a single key is compromised • Limits use of particular algorithm to its estimated effective lifetime • limits time available to penetrate physical, procedural, and logical access mechanisms that protect a key

15. Risk Factors to Consider for Cryptoperiods • Strength of cryptographic implementations • Operating environment, secure limited access, open office or public terminal • Volume of information or transactions • Security objective • Re-keying method • Number of nodes sharing the key/copies of the key • Threat to information

16. Other Factors Affecting Cryptoperiods • Communication vs Storage • E.g., keys used for online transactions are likely to have smaller cryptoperiods • Keys used for storage will have higher, as cost of re-encryption is high • Cost of Key Revocation and Replacement • Changing keys can be an expensive process • Encryption of large databases • Revocation of large number of keys • Expensive security measures are justified for such cases as the cryptoperiod can be made high

17. Factors Affecting Public Keys • Private keys may have longer cryptoperiods than public-keys when used for confidentiality • When used for challenge (dynamic) authentication both public and private keys can have the same cryptoperiod • When used for digital signatures public keys can have longer cryptoperiods than private keys as they will be necessary to verify certificates

18. Cryptoperiods for Different Keys • Private signature key (public-private keys) • 1-3years • Public signature verification keys • Symmetric authentication key • 2-3 years • Private authentication key • 1-2years • Public authentication keys • 1-2years • Symmetric data encryption key • 3years

19. Cryptoperiods for Different Keys • Symmetric and asymmetric random number generation keys • Depends on the RNG technique • Symmetric master key • 1 year • Private and Public key transport keys • Private 2years, public 1-2 years • Symmetric key agreement key (also, key wrapping key) • 1-2years

20. Cryptoperiods for Different Keys • Private and public ephemeral key agreement key • Time required to complete the key agreement protocol • Symmetric authorization keys • 2years • Private and Public authorization keys • 2years

21. Other Parameters • Domain parameters stay for the cryptoperiod • IV is associated with the information and stays as long as the information is held • Shared secrets are destroyed as soon as the necessary key derivations are complete • RNG seeds are destroyed immediately • Intermediate results are destroyed immediately

22. Algorithms, Key Sizes and Strengths

23. Factors to be Considered For Design of New System • Sensitivity of information and system lifetime • Algorithm selection • System design wrt performance and security • Pre-implementation evaluation • Testing • Training • System implementation and transition • Post-implementation evaluation