1. An index search : the tool used may be able to index all data, essentially
recording every word present, so that it can be searched. This type of search is
comprehensive as it does not generally care about the compression used, such
as in PDF’s or ZIP’s, where a real-time search would not be able to identify
all relevant keywords. Whilst this search is generally very slow to setup, once
completed all results are almost instantaneous (Windows performs a similar
action on your local computer).
2. A real-time search : a keyword can be created and run at any point in an
investigation—the search can take some time to complete. Typically a real-time
search is unable to search files that are compressed or in unusual formats, unless
they are first uncompressed.
Regular expressions (regexp) can be utilized to make a more specific keyword
search. Regexp is a way of defining a search pattern that utilizes wildcards and spe-
cial characters to offer more flexibility and power than a simple keyword search.
If
1234-1234 was provided as a serial number of a device, but it was not known
if it included a hyphen; if it could be replaced by another special character; or
if it existed at all then multiple search terms would need to be created (also see
Chapter 7).
Rather than attempt to write every possible search term a simple regexp search
could be created that covered this: for example
1234[.]?1234 .
The expression states that the characters in the brackets can be found zero or one
time (this is denoted with a
? ). Within the bracket is a . (dot), this is a regexp charac-
ter that denotes anything can be between the two numbers. It is good practice to test
a regexp before launching it on a case, as it is a more complex string than a simple
keyword search it can take more time to complete.
CORE EVIDENCE It is impossible to detail the core evidence available on the various operating and file
systems available within a single chapter; however there are several core evidential
areas that are typically applicable in a high-tech investigation:
•
File Slack : the way that files are stored on a device means that there is a
significant amount of storage space that is unused but is allocated to a file.
This is referred to as file slack and is simply the space between the end of a
file and the space it was allocated on a device. This slack space can contain