Encrypting a Single File Decrypting a Single File Anti-Malware Software Encrypting a Set of Files in a Folder Decrypting a Set of Files in a Folder

Use of a File Pattern Randomness report Use of a Keyfile The Setup

Encrypting a Single File

Before encrypting you must specify an encryption key. There are several ways to do this, but the easiest is to enter a key via the keyboard. For example:

A key should not consist only of normal words, because that would make it vulnerable to a dictionary attack (that is, an automated key search by trying all keys made up of words from a dictionary). Better to use an easily-remembered phrase such as "Now is the time for all good men" with some character inserted within each word, as above. Or one might simply use the first and last letters of each word, as in "nw is te te fr al gd mn", or eliminate the vowels, as in "nw s th tm fr ll gd mn" (but the key must consist of at least 16 characters).

The checksum changes with each keystroke. If you use a key regularly then you should memorize the associated checksum, so that if you make a mistake when typing the key you will notice that the checksum is not what is should be.

If you want to enter they key without it being displayed on-screen then 'Type key (without display)' allows you to do this, as in:

There are other ways of specifying a key, involving a keyfile; these are

When encrypting a single file 'in place', the confirmation window and the report window are very similar to the case of when the output file is different.

Decrypting a Single File

Anti-Malware Software

To be safe, however, it's best simply to disable any anti-malware software while running Cryptosystem ME6.

Encrypting a Set of Files in a Folder

When 'Files in a folder' is selected, the controls within the frame are activated (they are inactive when 'Single file' is selected). The operation can be modifed either (a) by specifying whether to include subfolders (if any) of the folder and (b) by specifying whether to include only files whose names match a given pattern (as explained below).

Here is an illustration of encrypting eight files in a folder \temp plus (since two of them are 'htm' files) two subfolders (holding images and other files associated with the two 'htm' files), for a total of 44 files, using the same key as above. Here is the initial setup. Note that 'Include all subfolders?' is set to 'Yes', and the textbox for a file pattern is empty (thus all files are included).

The current maximum number of files acts as a check on whether you are attempting to encrypt more files than you thought you were. In this case we simply set the maximum number to a larger number. Setting it to 50 and re-listing gives:

At the end of the operation the report window looks like this:

Decrypting a Set of Files in a Folder

As with encryption, it is highly recommended to list the files to be decrypted. In this case we obtain:

Note that all the randomness values are greater than 0.9, showing that the files are encrypted. Noting the randomness values of files to be decrypted protects against an accidental attempt to decrypt files which are not encrypted.

The confirmation window for decryption, and the report window, are very similar to those for encryption as shown above.

Use of a File Pattern

When decrypting, you have to be careful to specify the same file pattern to ensure that only the encrypted files will be decrypted. But if you forget, and attempt to decrypt all files, then listing the files before decryption will reveal that there are unencrypted files (those with low randomness value).

Randomness Report

A randomness value near zero means "very non-random" and a larger randomness value indicates a greater degree of randomness. Randomness values may range from close to zero up to nearly 1 (seldom above 0.975), with 0.9 and above indicating a high degree of randomness. Compressed files (such as 'zip' files often have a randomness value of about 0.8.

Randomness values are given in any listing of files to be encrypted or decrypted. A files must have at least 256 bytes in order to have a randomness measure. Files whose randomness is at least 0.9 are marked (in the listing) by an asterisk.

It is also possible in Cryptosystem ME6 to obtain a graphical display of randomness. This is done by taking each successive pair of bytes and treating them as an x-coordinate and a y-coordinate, and (with a black background) placing a white pixel at that point.

After selecting a single file for encryption, clicking on 'Randomness report' will give such a graphical display (such as below at left). If you then encrypt that file to a different output file, the randomness report will be like the image at right:

You can inspect the randomness of any file by specifying it as a single file then clicking on 'Randomness report'. In particular, if you are unsure as to whether a file you wish to encrypt is or is not already encrypted then specify it as the file to be encrypted and click on 'Randomness Report'. If the graphical display shows a randomness value > 0.9 (like the image at right) then the file is encrypted. Conversely, if you are unsure as to whether a file you wish to decrypt is in fact encrypted then specify it as the file to be decrypted and get a randomness report (a randomness value of < 0.8 means the file is not encrypted).

When you encrypt a single file 'in place', after the encryption the output file has the same location and name as the input file, and clicking on 'Randomness report' will show that the file is encrypted (the display will be the same as what you would get by encrypting the input file to a different output file).

Use of a Keyfile

The most secure key that you can use is a 64-byte random keyfile, since there are 256⁶⁴ such keys possible (more than 10¹⁵⁴). After clicking on 'Create random keyfile' the program asks for the location and name of the file to be created, then the byte values are obtained from your random mouse movements.

You can then inspect the bytes in the keyfile.

The Setup

Saving the setup, however, involves a security risk, since a setup file contains information about which file or folder was used in an operation. In the case of the setup-for-next-run file you are given the option, when quitting, of wiping (by overwriting) this file.