Method and system for recovering the validity of cryptographically signed digital data
According to the present invention, techniques, including a method and system, for restoring and/or validating data and/or associated signature log entries are provided. One embodiment of the present invention provides a method for validating a restored message, having an entry generated in a signature log for a message, where the entry includes cryptographic information associated with the message. Next, when said message is lost, the restored message is generated responsive to a request; and the restored message is validated using the signature log. In another embodiment a method for validating a selected log entry by using a signature log having a plurality of recorded log entries is provided. The method includes: computing a cryptographic value for the selected log entry; and determining if the cryptographic value is part of another recorded log entry.
1. A method for verifying a first log entry for a corresponding first message included in a first log comprising a plurality of log entries, wherein each log entry includes a hash value (H msg ) determined from a message corresponding to said each entry, wherein said each log entry further includes a hash value (H log ) determined from a previous log entry, wherein said each log entry further includes a signature value determined from the hash values H msg and H log , wherein one or more log entries among log entries P l to P k are checkpointed, the method comprising operating a computer to perform steps of:
receiving information for a log entry P j having a corresponding message M j ;
determining an index m, where l≧m≧k and m>j;
determining a hash value H by applying a hashing function on log entries P j to P m−1 ;
judging whether the hash value H is equal to a hash value associated with a subsequent log entry; and
outputting a result of the judging step.
2. The method of claim 1 wherein each of the one or more log entries among the log entries P l ,to P k that are checkpointed is publicly accessible.
3. The method of claim 2 wherein said each of the one or more log entries is publicly accessible over a mass media server.
4. The method of claim 1 wherein each checkpointed log entry is registered by an eligibility public establishment or a private notary.
5. The method of claim 1 wherein for each checkpointed log entry, data or a hash value of the data is included in a second log different from the first log, and the data includes a signature value associated with said each checkpointed log entry.
6. A method for verifying a log entry for a message included in a first log, wherein each log entry P i in the first log includes a hash value (H msg ) of a message corresponding to P i , a hash value (H log )of a previous log entry, and a signature value based H msg and H log , wherein one or more log entries among log entries P l to P k are checkpointed, the method comprising operating a computer to perform steps of:
receiving information for a first log entry P j having a corresponding message M j ;
receiving information for a second log entry P l having a corresponding message M l where l>j;
determining a hash value H by applying a hashing function on log entries P j to P l−1 ;
judging whether the hash value H is equal to a hash value associated with a subsequent log entry; and
outputting a result of the judging step.
7. The method of claim 6 further comprising checking whether the log entry P l is a checkpointed log entry.
8. The method of claim 6 wherein each of the one or more log entries among the log entries P l to P k that are checkpointed is publicly accessible.
9. The method of claim 8 wherein said each of the one or more log entries is publicly accessible over a mass media server.
10. The method of claim 6 wherein each checkpointed log entry is registered by an eligibility public establishment or a private notary.
11. The method of claim 6 wherein for each checkpointed log entry, data or a hash value of the data is included in a second log different from the first log, and the data includes a signature value associated with said each checkpointed log entry.