I know it sounds trite but the first problem with secrets is "what is a secret?"...
It's one of those words that everybody knows what it means but then wave their arms with "you know secret" when you ask them to define it. If you look it up in various dictionaries you get two or three definitions in each... which does not help.About the simplest definition that's usefull is,
Something that is kept or meant to be kept unknown or unseen by others
Thus you have four key words,
Usually (but not always) the something can be abstracted to information directly or information about a physical object such as it's existance or location or other atributes. In which case Unseen becomes in effect the same as Unknown.
Which leaves us "others" which is one of the two subsets of all entities which is equal to "entities to which the information is unknown". Oddly perhaps the other subset "entities to which the information is known" can have zero members, and is infact the normal state for much information. This is because information is in effect transitory and is continously changing with time.
And that is missing from the above definition and is only aluded to by the word "kept". However as has been observed "information loves to be free" but that is actually the exception rather than the rule.
The reality as most historians will tell you is information gets lost in it's entirety or goes stale and in effect becomes decayed to the point where it is sufficiently out of context to be nolonger meaningful. This happens because information actually consists of two parts
2, Data Description or Meta data.
Neither is much use on their own. We see this with clay tablets that record transactions, because the recording only containss the data not the meta data as well we are left guessing as to the actual meaning of the data.
Because of this known problem we have archivists trying to reverse entropy and preserve documents in their original form even though much of them are in effect usless because they lack sufficient meta data.
However things are changing in this area because of the computer it is becoming possible to put data with only partial meta data into a database and draw inferences about the missing meta data. As this becomes known it is possible to further identify not just where data is missing but often it's value. That is it's become possible to re-create secrets...
This is one of the reasons the NSA want to record everything that moves on the internet over voice, video, fax and every other form of communication it's possible to record.
However there is a danger in that even a minor error in re-creating information, might easily generate secrets that never were.
That is potentialy such data could generate a faux secret, and use this as the basis for trying to pursue and potentialy convict people under conspiracy legislation...