Secure Audit Logs with Verifiable Excerpts

Log files are the primary source of information when the past operation of a computing system needs to be determined. Keeping correct and accurate log files is important for after-the-fact forensics, as well as for system administration, maintenance, and auditing. Therefore, a line of research has emerged on how to cryptographically protect the integrity of log files even against intruders who gain control of the logging machine. We contribute to this line of research by devising a scheme where one can verify integrity not only of the log file as a whole, but also of excerpts. This is helpful in various scenarios, including cloud provider auditing.