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When you encrypt files with encryption key, you perform your interaction with
the program through "Enter encryption key" dialog
box. In this dialog box you can see the following information:
Current cipher – encryption
algorithm, which is currently used;
Current mode –
encryption mode, which is currently used;
Blocksize – the
size of block of the current algorithm (the length of initial vector is always equal to Blocksize);
Size of key –
shows minimal and maximal key length in bytes and step of the key (length of encryption key
must be a multiple of step value). The length of the key may vary from min. to the max.
number of bytes allowed by the current algorithm;
Key size in bytes –
spin control with which user can set desired length of the encryption key which will be
used for encryption. Key length will be automatically adjusted in accordance with
the step value.
For example, allowed lengths of the key for AES algorithm, which has step 8, include: 16,
24 and 32 bytes;
Hide key – check
box with which user can hide or show key editor window. It is recommended to always keep key
window hide unless key is being entered from keyboard;
Encryption key
editor window – when encryption or decryption with a key takes place,
the program uses as the encryption key the bytes shown in the "Encryption key" editor window. This window is divided into two parts: the hexadecimal part and
ASCII part. These two areas are intended to view the same data in different ways. When you
enter a key from keyboard or generate it, the bytes of the key are shown as
hexadecimal values on the left side and as ASCII characters on the right side
of the editor window.
This program for encryption and decryption with the user-provided encryption key uses
exactly the bytes that have been defined by user in this window without any further
transformation (compared to encryption with password, where user-provided
password is transformed in a rather complicated way into the encryption key).
You can
provide the encryption key from a file, input it from the keyboard or generate it.
Initial vector editor window – editor window for entering the initial vector. Initial vector
is the byte sequence, which is used in CBC, CFB and OFB encryption modes.
When user generates the encryption key, initial vector is always being
generated together with key. If user enters key from keyboard, he also must
always enter the initial vector. Though initial vector is not a secret
information, user can consider it as a part of encryption key, because for
decrypting data in modes mentioned above, user always must provide the initial
vector which was used for encryption. When user saves encryption key in a
file, initial vector automatically is saved in the same file.
Providing encryption key from a
file
In fact, you can use as an encryption key any
file whose size is more or equal to size of encryption key for the current
algorithm. For example, if the AES algorithm is used for encryption
and the length of the key was set equal to 32 bytes, then if you provide a file
as an encryption key, the first 32 bytes of the file will be shown in the "Encryption key"
editor window, the next 16 bytes will be shown in the "Initial vector"
editor window, and all the rest file contents are ignored. In general, this can be stated
in the following way: if "K" is the key length, then you must provide
a file whose size is not less than "K + Blocksize" bytes. If
the file size is less than K + Blocksize bytes, then the missing bytes in the encryption
key and initial vector are padded with zeros.
You have take into account that contents of the
absolute majority of files are not random and using such files as keys you may
seriously compromise the security of encryption. Also it is not recommended to use as encryption keys
files, which are located on your computer. Even if your hard disk contains
hundreds of thousands files, it's a matter of several minutes (or several tens minutes) to
test all of them as encryption keys. Also, it is not recommended to
use as encryption keys files, whose content can be modified.
It is important to remember
that if the length of the encryption key is less than the upper-range value, then it is
necessary before decryption to set the length of the key that has been used for
encryption. For example, if you encrypted the file with AES algorithm and 16 byte key, the
for decryption you must set length of key to 16 bytes. Otherwise key will be read
incorrectly. In order to avoid this and to provide a higher level of security encryption
with the key of maximum length is recommended.
Inputting encryption key from
the keyboard.
You can input encryption key and initial vector from the keyboard using both hexadecimal and ASCII areas
of "Encryption key" editor window for inputting.
When entering values in the hexadecimal area you can use
only hexadecimal digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. Each byte in a
hexadecimal area must be equal to the hexadecimal number from 00 to FF.
ASCII symbols representing hexadecimal values are shown to
the right of the hexadecimal area. For example, the hexadecimal value 41 is equal to the
letter "A" in the English alphabet. Some values do not have an ASCII equivalent,
i.e. there is no symbol that represents them on the screen. Such values are shown in the
ASCII area as dots. (But remember that "dot" itself has its own hexadecimal
value 2E and "space" has the hexadecimal value 20).
Generating encryption key
All the bytes of the key must be random and equiprobable
– this is one of the main requirements that encryption key has to meet. For example,
if the user uses in key only alpha-numeric values of bytes then these values are not
equiprobable with the other values of bytes, because the user uses only 26 lower-case
English letters, 26 upper-case English letters and 10 numeric values out of 256 possible
values for each byte in the key. In other words, only 62 values out of 256 possible values
are used in the key. Therefore, the number of possible keys decreases significantly and
the task of cryptanalysis of the ciphertext encrypted with such a key becomes easier.
With this program you can generate highly random encryption keys. 17
different random values such as current cursor position or current process ID
are retrieved from your computer during the key generating. The values are
hashed by the hash function SHA-1. Each subsequent value is added to the output
of the hash function and the result is hashed again. This cycle is repeated 1000
times. Some added values are changing even during the cycle, for example, the
number of milliseconds that elapsed since the Windows has started.
As a result, a highly random sequence of
bytes is created and the encryption key and initial vector are formed from this sequence.
Press the "Generate" button in
the "Enter encryption key" dialog box to generate new
encryption key and initial vector.
Note: We recommend that you always save
the encryption key immediately after generating. If the user generated the key and
encrypted a file with this key without saving the key, then it is impossible to restore
the key and to decrypt the file.
Read more about encryption keys:
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