Information Technology Reference
In-Depth Information
13.5 Authenticity Evidence
As noted above there are several types of evidence namely technical evidence and
non-technical evidence. We give some examples of each type next.
13.5.1 Technical Evidence
Each AS contain several possible technical points. An obvious one is that related to
Fixity, for example checksums or digests, used to check that the bit sequences are
unchanged. Of course each of these, regarded as a piece of information, will need it
own Representation Information, for example to define how the digest has been cal-
culated. The digest value will also have its own evidence of Authenticity since, as we
noted at the start of this Chapter, if we have doubts about that value then we will not
trust what any checks on digital object against the digest value will also be in doubt.
A related step could be someone verifying that a re-calculated digest confirms
the previous value, and recording that fact.
A related but different piece of evidence is needed if, for some reason, the
sequence has to be changed. This might arise if it is decided that the format in which
a document or dataset is held is no longer supportable. A new digest will have to be
calculated of course. But how do we know that the new document is an acceptable
replacement for the previous one? This is discussed in Sect.
13.6
.
13.5.2 Non-technical Evidence
Non-technical evidence is, for example, the reputation and trustability of the people
who recorded the evidence, or the reputation of the tools which are used, for example
to calculate the digests. This type of evidence is likely to be much more elusive
than the technical evidence, especially in an open world. In other words if we are
dealing with a limited community, for example state archives or within a scientific
discipline, personal reputations are likely to be well established, at least within a
limited timeframe. However we cannot make that assumption, as we must deal with
potentially a broader set of custodians, and a broader set of tools being used. Thus
the non-technical evidence is likely to be very difficult to collect and evaluate.
13.6 Significant Properties
Transformations are an important preservation technique but, as we have seen,
mean that the techniques such as digests cannot be used. The underlying question
is whether or not a particular transformed digital object can be said to have the
same level of authenticity as the object which underwent the transformation. As we
will see in this Section, what have been termed “significant properties” provide a
solution, although the concept has been used in the literature somewhat differently.
