I am trying to keep long-term logs of an app in such a way, that it could plausibly demonstrated to third parties/court that the application has processed certain data at a given time. The data can be represented in XML or text format. A simple gzipped log is not plausible, as I may have added or modified data afterwards, whereas an external logging service would be an overkill. Cost is an issue, we are not dealing with financial data or so, but rather some simple user generated content, where some malicious users tried to blame the operator in the past when things escalated and went to court.

My question:

1. Is there some kind of signing software for Linux that signs each element of a log in such a way, that it can be easily shown that no element can be added or modified afterwards? Plug-Ins into some free Splunk Alternatives would be fine too.

2. Ideally the software I am looking for should be under a GPL or similar license. I could probably achive something like this by using PGP/GPG sgning functions and including the previous elements signituares within the following element, but I would prefer to use some program where you do not have to argue about the validity of your own code.

Note to mods: I am not asking this question on Stackoverflow, because I am not looking for writing own code for reasons described above. I think this question rather fits into serverfault than superuser, as server-side logging software is discussed rather here than on superuser.