| |
Part 1 - Cryptography School
Part 2 - Keys Public and Private
Part 3 - On Complexity and Cracking
Part 4 - Encrypting or Enciphering
Cryptography Part II
Keys, Public and Private
So if you have managed to get this far, you have some idea of what
a key is and a vague idea of how it is used. To recap, the key is
some kind of number or string of characters that is used to scramble
a message. How it does this exactly is not too important for our discussion,
but we will touch on it a bit in a while.
So what is this private key and public key stuff, anyway?
The Private Key
All cryptographic systems rely on at least two people having a copy
of the required key. If we make up a key to encipher messages, we
must also give the key to the person who needs to read the message.
This is how most encryption systems work. Only the people who need
to know are given the key. This makes it a Private Key System.
When a key is used to both encipher and decipher a message, it is
known as a two-way or symmetrical system. Most private key
systems are of this type, but they don't have to be.
Private key systems work very well among closed groups such as corporations,
governments, the military and individuals. But then, suppose we want
to buy some new CD's over the Internet. We need to send our credit
card info but not over an open connection where anyone can read it.
Of course, we don't want to do that, and we don't have a private key
with the CD company. What we need in this case is...
The Public Key
In a public key system, two different keys are used. One is used
to encipher the message and the other is used to decipher it. The
two are not the same, and knowing one will not allow you to figure
out the other. So the CD company publishes their public key, and
anybody, including us can use it to encipher our credit card info
and then send it to them, knowing it will be safe.
The CD company can decipher our message using their private key,
which only they know, and then send us our CD's.
This kind of system is known as an Asymmetrical or one-way system,
because each key only goes one direction.
All public key systems are asymmetrical. This is because if we gave
out a key that could both encipher and decipher, it would not be
very secure.
These two key systems are in widespread use today in many applications.
When you make a secure purchase over the internet, you are using
a system called SSL (Secure Socket Layer), but internally, this
system relies on a public key system called RSA. RSA is a public
key system that is used to make the secure connection and verify
the two parties. Internally, RSA relies on another, faster system
called RC4. This system is a private key system which uses a 128
bit (32 character) key.
More on Keys
We need to just mention a key system here called the One-Time Pad.
This was originally a pad of paper like a note pad containing pages
of scrambled letters and numbers. Each page was one key, and after
the key was used, the page was torn out and destroyed. The modern
equivalent is a Key Library. This also happens to be the only key
system that has never been broken, and it has been in use for around
100 years.
As we stated earlier, using the same key over and over can lead
to trouble. Patterns begin to show in the messages, and computers
are excellent at identifying these patterns.
The advantage of using a key only once is that you deny your enemies
time to crack your code because you have thrown the key away. This
forces the bad guys to crack every message or file on your computer
separately, starting from scratch, since each was encrypted with
a different key. It takes huge amounts of time and / or computing
power to crack even one message.
One problem with Public Key systems is that you cannot keep changing
the key every time you feel like it. Once you establish a key, you
are stuck with it. Although very secure, these keys are very large
and difficult to produce. This also makes them slow to encipher
and decipher. For these reasons, they are usually used to establish
secure connections using short messages.
This is how the Internet works. Once the Internet connection is
established using the Public Key system, it switches to a Private
Key system called RC4. RC4 is also the encryption system used by
Songs of the Universe.
In Private key systems the keys can be changed rapidly and encryption
/ decryption is usually many times faster than with public key systems.
Private keys are used when sending long and complicated messages.
Private keys are not better than public keys or vice versa. They
simply have different uses. As you have seen, public keys are used
when two companies or individuals who do not know each other must
do business together. Private keys are used when either the two
entities know each other, or after some mutual trust has been established,
as over a secure Internet connection. Private key systems are also
excellent for encrypting files on your computer network where several
people might be sharing the same computers.
Random Numbers and Pseudo-random Numbers as Keys
In order to produce complex keys, most computers use a function
called a 'Random Number Generator'. Actually, since the numbers
are not truly random, so they are more accurately referred to as
'Pseudo-Random Numbers'. Their advantage is that they are fast and
easy to produce. They also need a 'seed' number to get them started.
Unfortunately, if you can guess the seed, you can crack the code,
because the same seed will always produce the same series of numbers.
A better system is to use True Random Numbers, and the only sources
of these numbers are natural: Radio emissions from the stars, thermal
noise, radioactive decay and others. Songs of the Universe uses
these sources to produce numbers which are then used to make up
a Key Library, better known as the One-Time Pad.
Producing this 'random noise' sounds like a simple thing to do,
however it is not. Collecting the data for our key libraries can
be a slow process, especially for radioactive decay. Noise, or to
us songs, from the various stars and galaxies around the universe
is prone to interference from local sources - satellites, military
communications and microwave transmissions and so on. We must test
this data to assure that it contains no repeated or recognizable
patterns.
Although difficult to produce, key systems using True Random Numbers
and One-Time Pads are still the most secure systems ever devised.
OK, our next subject will be...
On Complexity and Cracking
Back to top...
|
|
