We present a solution for the problem of certificate revocation. This solution represents certificate revocation lists by authenticated dictionaries that support: (1) efficient verification whether a certificate is in the list or not and (2) efficient updates (adding/removing certificates from the list). The suggested solution gains in scalability, communication costs, robustness to parameter changes, and update rate. Comparisons to the following solutions (and variants) are included: "traditional" certificate revocation lists (CRLs), Micali's (see Tech. Memo MIT/LCS/TM-542b, 1996) certificate revocation system (CRS), and Kocher's (see Financial Cryptography-FC'98 Lecture Notes in Computer Science. Berlin: Springer-Verlag, 1998, vol.1465, p.172-7) certificate revocation trees (CRT). We also consider a scenario in which certificates are not revoked, but frequently issued for short-term periods. Based on the authenticated dictionary …