Cryptography Primer
By Jonathan Roach
Hello and welcome to
my primer article on cryptography!
cryp-tog-ra-phy (krip-taw-graph-e)
The process or skill of communicating in or deciphering
secret writings or ciphers.
Introduction
Prying eyes,
espionage, fraud, and theft of personal information.
These are a few of
the reasons for concealing, masking, shadowing
or encrypting
information in order to minimize the chance of that
information being
revealed to potentially dangerous or mischievous
individuals/organizations.
Okay, okay... maybe
it's not that big of a deal, maybe you just want
to feel covert when
you send email to your friends or something.
The method used to
achieve the above is referred to as "Cryptography",
and this article is
aimed at giving you a basic look into the world of
data encryption and
providing you with Visual Basic source code to get
you started on your
way.
What does Cryptography do?
Cryptography
conceals or hides data in order to make it un-readable to
the average person,
it is used to secure documents and data by mixing
or scrambling the
original data into mumbo jumbo basically.
Take this generic
example of encryption, lets say you want to send an
email to your
friend, and you don't want anyone else to see the true
message you are
going to send, because... it's top secret of course.
Your original
message would look something like this:
"Hey Frank... I got that new
encryption handbook."
You would then
perform an encryption routine on the message before
sending your email
and the result would look something like this:
"Ì’ˆ/žŸ¨“ˆáÝ ??|“œ»ˆ³ßÝ??©§† ˆ³ß?|“œ?©§†"
You get the idea,
the original text is all scrambled and basically not of any
use to anyone, or so
it appears...
So now you send your
encrypted mail off to Frank, if Frank is unaware of
encryption then he
will probably mail you back and say something along
the lines of
"What the heck is this stuff you sent me?".
However, because you
sent it off to your good buddy Frank and he is
using the same
encryption/decryption software that you are, and he is
aware of the
code/key needed to reverse your scrambled message all
is well and he can
view your message, while any others who may have
intercepted it along
the way could not, or at least had a heck of a time
in doing so...
So there you have
it, Cryptography scrambles/transforms data.
Cryptography Overview
Cryptography
requires an encryption algorithm and a key; in it's basic form
that is.
Due to the nature of
this article I will not go into great detail on the many
methods of
encryption and key methods in use today but I will provide
you with the base
foundation for encryption/decryption.
An encryption
algorithm is simply the engine or code that handles all of
the processes that
transform the original text (plaintext) into encoded text
(ciphertext).
This engine simply
performs mathematical and/or logical operations on the
plaintext to
transform it into the ciphertext and vice versa.
The key as it's name
implies is just that, it is the key (code) that allows the
algorithm to
encrypt/decrypt data.
Common Cryptography Algorithms
There are many
different algorithms for encrypting/decrypting data in use
around the world
today, some of them are very complex and others are
more simplistic,
however they all serve the same purpose.
Below is a short
listing on some of the different cryptography algorithms;
DES - United States
Data Encryption Standard
3DES - The above,
encoded 3 times
RSA - Rivest, Shamir
and Adleman
GOST - Developed by
scientists of the former Soviet Union
IDEA - A component
of PGP (Pretty Good Privacy)
There are many more,
but the above should be a starting point for you
to seek out more
info on the net.
The One-Time Pad
The one-time pad is
one of the simplest encryption algorithms, it involves
a key being used
which is the same length as the plaintext and then using
simple math on the
plaintext via the key, the math could be multiplication
or exclusive-or
(XOR) for example;
Dim plainText As
String
Dim cipherKey As
String
Dim Counter As
Integer
Dim Char As String
Dim keyChar As
String
Dim cipherText As
String
Private Sub Crypt()
plainText =
"CovertText"
cipherKey =
"password42"
MsgBox “Before: “
& plainText
'Encrypt it
For Counter = 1 To
Len(plainText)
Char = Asc(Mid(plainText, Counter, 1))
keyChar = Asc(Mid(cipherKey, Counter, 1))
cipherText = cipherText & Chr(Char Xor
keyChar)
Next Counter
MsgBox “After: “
& cipherText
plainText =
""
'Decrypt it
For Counter = 1 To
Len(cipherText)
Char = Asc(Mid(cipherText, Counter, 1))
keyChar = Asc(Mid(cipherKey, Counter, 1))
plainText = plainText & Chr(Char Xor
keyChar)
Next Counter
MsgBox “Back to
original: “ & plainText
cipherText =
""
End Sub
Just copy the above
code and paste it into a new project, then add a
command button and
in its click event put a call to the Crypt() sub.
As follows,
Private Sub
Command1_Click()
Crypt
End Sub
Run the project and
click the button to see it in action.
There is a problem
with the above encryption algorithm though, first
off if you want to
encrypt something that is large in size the key size
would also be very
large.
For example if you
wanted to encrypt a string that is 50 characters in
length then your key
would also have to be 50 characters in length,
kind of a pain for
our good friend Frank to have to enter a 50 character
decoding key for a
simple message.
This problem can be
overcome with our next topic, which deals with
the key length
problem by using a repeating key.
Repeating Key Algorithm - Viginere
Cipher
This type of
encryption algorithm deals with a key that repeats during
the
encryption/decryption process, for example the algorithm above
uses a character by
character algorithm, it performs math operations
on each character in
the plaintext and key until the length of the key
and plaintext is
reached - because the key and plaintext are the same
length.
However with a
repeating key, our key can be any length we choose
as when the end of
the key is reached in our algorithm we simple start
again at the begin
of the key until our plaintext encryption is completed.
Take this generic
example, if our plaintext is "I have top secret codes"
and our key is
"Pass"; obviously the key is shorter than our plaintext.
Thus we are in our
loop to encrypt our plaintext and this is how it looks:
plaintext char = I key
char = P
plaintext char = Space key char = a
plaintext char = h key char = s
plaintext char = a key char = s
plaintext char = v key char = P
plaintext char = e key char = a
plaintext char = Space key char = s
You get the idea?
The key just repeats until the length of the plaintext
is reached. This
method is much more practical and flexible for key names
anyway.
Below is a sample
algorithm that uses a repeating key.
Private Sub Crypt()
cipherKey =
"pw201"
plainText =
"Top-Secret Message from Roach"
cipherText =
""
KeyIndex = 1
MsgBox "Before:
" & plainText, 0, "Before Encryption"
For Counter = 1 To
Len(plainText)
Char = Asc(Mid(plainText, Counter, 1))
keyChar = Asc(Mid(cipherKey, KeyIndex, 1))
cipherText = cipherText & Chr(Char Xor
keyChar)
KeyIndex = KeyIndex + 1
If KeyIndex > Len(cipherKey) Then
KeyIndex = 1
Next Counter
MsgBox "After
Encryption: " & cipherText, 0, "Original:" & plainText
End Sub
Once again you can
paste this into a new project and call the Crypt()
sub from a buttons
click event to try it out. To reverse the encryption
just run the
encrypted text back through the counter loop in place of
the plaintext.
Thank you for
sticking with me through this brief article on the subject,
I hope that you
gained a little knowledge about encryption from this.
Note: I do not claim
that you shall become an encryption expert or
that any of the
methods described in this article are bomb proof,
crack proof, water
proof... whatever, I merely wanted to share the
basic knowledge of
the subject.
Regards,
Jonathan Roach
(12(12 Vote))