3.1 Overview
When Cryptosystem ME6 is first run it appears (after activation) as follows:
You set the parameters for the encryption or decryption operation and then give the command to perform the operation by clicking on Do it!. A simple example of the use of the software will be given below.
You can specify which files in which subdirectories you wish to encrypt (or to decrypt) using wildcards, e.g. *.txt to encrypt all files with .txt suffix. You also specify whether you want (a) to overwrite the original files with their encrypted (or decrypted) versions or (b) to produce encrypted (or decrypted) files with different names.
You can request the program to operate on files not only in the specified input directory but also in all subdirectories lower than it. Thus it is possible to encrypt all files on a disk by requesting that files satisfying the file specification *.* be encrypted, beginning with the root directory and including all lower subdirectories in the operation.
After you have specified the conditions of the encryption or decryption operation you instruct ME6 to perform the operation, at which point the specifications are checked and any errors or exceptional conditions (such as insufficient space on the output file disk) are reported. If all seems in order then ME6 presents a complete description of the operation to be performed and asks you to confirm before proceeding. ME6 displays a progress report which provides a record of what files were encrypted or decrypted, and when. The report can be copied to the clipboard and thence into another program to save or to print.
3.2 Encrypting a file
This section and the following one provide a step-by-step explanation as to how to perform two simple operations, namely, encrypting and decrypting a single file using a key which you supply at the keyboard. A full explanation of the operation of the program is given in the following chapter.First you decide on the file you wish to encrypt and the name of the encrypted version. You select a file by first specifying the folder (a.k.a. subdirectory) which contains it by clicking on Input folder then you specify the file itself by clicking on Input file(s).
Suppose you've decided to encrypt the file test.doc in the C:\_temp folder. (If you don't have a \_temp folder on Drive C: then you may wish to create one for this exercise, and to copy a file into it and rename it test.doc.)
Click on 
and the usual file selection dialog box appears. Select test.doc.
After clicking on Open the main screen appears thus:
If you wanted the encrypted file to have the same name as the plaintext file (the input file) then you would simply click on the Output file(s) same? button to toggle the selection to Yes. In this example we encrypt to a file with a different name.
Clicking on Output file(s) brings up a window by means of which we can specify the output file to be test.enc:
| Clicking on Accept produces: | Now click on Encryption key to bring up the key menu: | |
 |  |
Click on Type key (with display) then enter (for example) "the quick brown fox":
Click on Yes to obtain:
Now click on Do it! and the confirmation window appears:
Click on Yes. The file is encrypted and the report window appears:
3.3 Decrypting a file
Decrypting a file is very similar to encrypting a file: Specify the operation as decryption, specify the input and output files as above, specify the encryption key and then do it.Here we will simply decrypt the file test.enc resulting from the encryption operation of the previous section (it is assumed that the software is in the state obtained from closing the report window at the end of the encryption operation above).
To decrypt test.enc click on Function to change the operation from encryption to decryption. Click on Single file, select test.enc and click on Open to obtain:
Now click on Output file(s), select Decrypt to a new file and enter test.dec:
The decryption key is the same as the encryption key and has already been specified in the encryption operaton, so click on Do it! to get the confirmation window:
Click on Yes. The file is decrypted and the report window appears:
This has been an example of encrypting and decrypting a single file. For multiple file encryption, operating on files in subdirectories, using a keyfile, etc., the appropriate section of Chapter 4 should be consulted.
3.4 Compatibility with antivirus software
When a file is encrypted the original plaintext file is purged, meaning that it is overwritten with random bytes before being deleted. If the Norton Antivirus Auto-Protect utility (or a similar antivirus utility) is active, and if the file extension of the plaintext file is .doc, .mdb, .xls or one of about twenty file extensions that are typically monitored by antivirus software then that software may suspend program execution and display a warning message, e.g., "ME6E20.EXE is attempting to write to the file DATA.DOC." Norton Antivirus then offers you the choice of stopping, continuing or excluding the action.If this happens then you have two options: (i) Each time the antivirus software displays a warning message tell it to continue. (ii) Disable your antiviral software for the duration of this run with Cryptosystem ME6. Either of these options will produce the same effects as if the antiviral software were not present, i.e., the plaintext file will be purged.
If you tell the antivirus software to exclude the action then the plaintext file will not be overwritten but it will still be deleted in the usual way. The ciphertext file will have been produced as usual, but the plaintext will still be present for forensic software to find.
When encrypting a file Cryptosystem ME6 checks to see if the file extension is one that Norton Antivirus normally monitors (these are the Auto-Protect default file extensions). If so then for each file, after the encryption has been performed, but before the plaintext file has been purged, ME6 will first ask:
If you answer Yes or Don't Know then a window such as the following appears:
The best thing to do is to disable the antivirus software while Cryptosystem ME6 is running (this can be done before the run or during the run). If you do not disable the antivirus software then clicking on OK will normally produce a warning message for each overwrite of the plaintext file.
The purge advice window does not appear when a plaintext file is being encrypted to a ciphertext file with a different name, because in this case the plaintext file is not deleted. The purge advice window also does not appear when an encrypted file with a .doc etc. extension is being decrypted, because the ciphertext file is simply deleted without being purged (there being no need to purge the ciphertext).
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