SHA-1 Hash Display

[Craig Maier]

The File SHA-1 Hash is displayed under the waveform statistics section under the Forensics Menu. Its is a cryptographic hash consisting of a 40 digit Hexadecimal number, which is essentially a fingerprint of the entire file. It is a good way to tell that one file is identical to another file. It can be useful in forensics to uniquely identify a file. That number is always calculated over the entire file regardless of the selected area.

[Marc Hildebrant]

So...I take it that any change to the original file would then change the value of the "SHA 1 Hash" ? I'm not familiar with the term.


Marc

[Craig Maier]

Marc,

I am not sure how sensitive it is. Would have to experiment more with it to see if it can be fooled..

Craig

[Craig Maier]

It seems to be very sensitive and selective. I just muted just one sample in a file (did not eliminate the sample - just made it zero in value) and the SHA1 value completely changed.

Craig

[Craig Maier]

Here is an example that you can experiment with. I created the following file using the Make Waves Signal Generator found under the Edit Menu:

1000 Hz
-10 dB
30 Seconds in Length
Stereo
44.1 kHz Sampling Rate
Sine Wave
16 Bit Resolution

The Waveform Statistics (found under the Forensics Menu) yield the following data:

Start Time = 00:00.0000
Stop Time = 00:30.0000
Selected Region = 00:30.0000sec
Sample rate = 44100Hz
Bit Depth = 16 Bits
SHA1 Hash of file= FA43B1048458C9940CCDD0FCEA1771A81FA1CC60
RMS = -13.0 dB
Rectified Avg = -13.9 dB
Max Pos Peak = -10.0 dB
Max Neg Peak = -10.0 dB
Crest Factor = 1.41
Max LF Level (<10Hz) = -65.2 dB
Avg LF Level (<10Hz) = -95.6 dB
Clipped samples = 0

Now, I went in and edited by muting one sample (not eliminating it, but just forcing it to become a value of 0). Here is the new Waveform Statistics for that change:

Start Time = 00:00.0000
Stop Time = 00:30.0000
Selected Region = 00:30.0000sec
Sample rate = 44100Hz
Bit Depth = 16 Bits
SHA1 Hash of file= 3CE09C5E7BDF0041209F2F4576CE6845B8DF28A8
RMS = -13.0 dB
Rectified Avg = -13.9 dB
Max Pos Peak = -10.0 dB
Max Neg Peak = -10.0 dB
Crest Factor = 1.41
Max LF Level (<10Hz) = -65.2 dB
Avg LF Level (<10Hz) = -95.3 dB
Clipped samples = 0


So, it seems to be very sensitive & selective. Give it a try.

Craig

ps - Your original Make Waves file should yield the same original SHA1 Hash value that I measured. However, you have a very small probability of muting the exact same sample as did I, so your second SHA1 will not likely be the same as mine.