Somerdata’s range of Audio Surveillance products come with built-in file integrity checking.

One of the issues often raised with audio recordings that may be required for evidential or auditing purposes is ‘How do I know that the file has not been altered?’.

This is an obvious problem with digital data. Most any multimedia file format can be manipulated if enough time and effort is spent in doing it. In fact it’s probably true to say the there is never a 100% foolproof method of proving that a recording hasn’t been altered.

So we are left with proving the likelihood that a recording has not been altered. And there are several methods of doing this some of which can be used in combination.

Firstly,  securing the original recording and handling it in a secure and auditable manner are key requirements. This often takes the form of multiple copies stored in secure locations, suitably marked and recorded. This should always be done with important and/or unrepeatable recordings.

Secondly, the recording process itself  should contribute security  by preventing unauthorised access to recording.

Thirdly, marking or creating a signature of the recording that is embedded within it can detect when alterations or corruptions have taken place.

The first process is down to you – quality handling procedures are a first priority and a must if recording integrity is to be proven.

The second and third processes are available using Somerdata’s Audio recording products.

Each recorder can be secured with a password. Data can only be retrieved using the set password. Attempts to circumvent this cause the recording to be erased.

Additionally, each recording is marked with information that is embedded in the output file.  Our Recorder Manager software is able to check the file produced for integrity and source information. So you an tell which recorder made the recording, that the data has not been changed from the original and vital statistics about the recording that are difficult to fake.

You can (and should!) take exact copies of the files but you can’t edit them without compromising the stored integrity information.

So, you may not be able to  stop files being altered, but you can tell when they have been!

Obviously we don’t publish the methods we used but if you need to know and we think you should, talk to us.

Simon Banks, January 2010