Dynacrypt® gives its users the option to measure the Index of Coincidence (IC) for any file that will be encrypted using Dynacrypt®. To find out the IC of the file if encrypted using Dynacrypt® do the following:

1.   Select Open File for Analysis from the File Menu or select the Icon on the DynaTool Bar. A File Browser dialog box will appear as shown below:

2.   Select the file to analyze from the File Browser dialog box and select the OK button.

3.   Select Index of Coincidence from the Analysis Menu on the Menu bar or the IoC Icon on the DynaTool Bar.

4.   The Index of Coincidence Dialog Box will appear showing the Index of Coincidence if the file is encrypted.

The Index of Coincidence is a measure that represents the likelihood of two letters in a cipher text document being the same. It is not a measure of the flatness of the cipher text profile but a good indication of whether the entire cipher text approximates a random distribution of symbols.

The Index of Coincidence ranges from .00390625 for a perfectly random distribution to .0667 for a mono-alphabetic or non-random distribution.

The Index of Coincidence is defined by

where f(i) is the frequency of occurrence of a cipher text symbol in the file and N is the total number of symbols in the cipher text file. To find the frequency of occurrence of a cipher text symbol, simply count the number of times a particular ASCII symbol appears in a file.