8 Appendix: Symmetric Key- Distribution 7 Acknowledgements 3.5 Passphrase Quality 4 Transferring Administrative Burdens 3.3 Certiicate Revocation Lists 3.4 Private-key Management 3.1 Authenticating the User 3.2 Authenticating the Ca Compliance Defects in Public-key Cryptography

A symmetric Key-Distribution Center is a trusted server that knows each user's password. The KDC issues temporary session-keys to users who know their passwords. Each user's initial session-key comes to him under his password's encryption. The KDC then uses this initial key to encrypt the user's subsequent session keys. 1. Account-Creation: The user proves his identity to the KDC's administrator not electronically. The administrator creates an initial password for the user, and tells the user to change it immediately. 2. Single-Sign-On At login, the user types his password, so as to decrypt his daily temporary session-key. The user applies this session-key in a similar protocol repeatedly through the day as he accesses services, gaining a new session-key for each different server. 3. Authenticating Others To communicate securely with other users and with networked services, the user applies various session-keys in a simple protocol. In each repetition of this authentication protocol , the KDC identiies the session-key's owners to each other. 4. Password-Change The KDC can require the user to change his password regularly, as a condition for access. When the user changes his password, the KDC can examine it, so as to enforce complexity criteria on the user's choice. The KDC stores the new password in the database, in a hashed form. 5. Account-Revocation Session-keys are timestamped to expire quickly, usually after 8 hours or even a few minutes. This discourages key-theft. If a user's password is compromised, then he must inform the CRL administrator, who manually replaces the user's password, and tells the user to change it immediately.. The KDC's trusted role gives it potential access to all of the system's traac. In return, the KDC takes responsibility for managing, validating, and renewing all of the system's keys. Thus, compared to a public-key system's security, all of the KDC's links are weakened somewhat, except for the weakest: the user's key-management link is greatly strengthened. management, smartcards just substitute the problem of physical security. Smartcards ooer no help for the problems of authenticated issuance and revocation. 6 Conclusion Compliance defects impede the sound management o f k eys and of user-accounts. These defects have arisen from the introduction of public-key cryptography into mass-market software As public-key security w as originally envisioned during the '70's and '80's, sophisticated users and sensible key-hygiene were taken for granted. For example, Privacy-Enhanced Mail's designers explicitly expected that the professionals who then used e-mail would …