Cryptography of the Internet - Part 0
=====================================


This article is a continuation, of "Part Base", to understand
the evolution of cryptography.  Do read the previous, "Part
Base", article.

The Private-key Cryptography is, still today, the strongest
type of Cryptography.  But, it has a slightly non-technical
problem; which is, the correspondents have to exchange a
*secret* (for example, a private number) in a *secure* way.
Preferably in-person.  They have to do this first and foremost,
before starting the private correspondence.  Sometimes this is
not possible, or not convenient.

Public-key Cryptography aims at solving this *private*/*secret*
exchange, by (somewhat) eliminating it from the procedures.
Yes, it is possible, and it works!

With Public-key Cryptography, the correspondents each have
a keypair.  And each keypair is composed by one public key and
one private key.  With the private key, a correspondent does
some type of cryptography operation, and with the public key
a correspondent does the opposite type of the private's key
cryptography operation.

Today, the type of operations (that a key can do), and its
opposites type of operations (that the other key can do) are
the following:

 _______________________________________
|            A Keypair                  |
._______________________________________.
|  Private key   |  Public key          |
|----------------+----------------------|
| Decrypting     | Encrypting           |
| Signing        | Verifying            |
| Authenticating | Validating Auth.     |
| Signing Key    | Verifying a Key Sig. |
+---------------------------------------+

Important note, and it may be confusing to the reader: a
keypair's *private* key and *Private*-key Cryptography are
different things.  When we are talking about a keypair's private
key, we are already talking about Public-key Cryptography.
We are talking about one of the keys that is part of a keypair
in Public-key Cryptography.  And, Private-key Cryptography is
a cryptography type different from Public-key Cryptography.
Private-key Cryptography is the type of cryptography that I
talk about in my previous article (the "Part Base" article).
The "private" naming somewhat overlap, though.

So...  with Public-key Cryptography one has a keypair, and one
puts his/hers keypair's public key in a publicly reachable place,
such as in a Webpage.  And one keeps his/her keypair's private
key for himself/herself.

When a correspondent wants to initiate a private communication
with a recipient, this correspondent only has to get the public
key of the recipient of the communication.  Once this sender
has the (publicly available) public key of the recipient, he/her
can already have a private communication with this recipient.

The public key of the recipient will be used to encrypt the
message to this recipient.  This recipient will then use his/hers
own private key do transform the encrypted (private) message,
into the original text of the message sent by the sender.

Take a moment to re-read all the text so far.

As it happens, Public-key Cryptography, on its own, is not
particularly efficient at generating encrypted messages.  So,
today, what most people call "Public-key Cryptography", is
actually a Hybrid-type of Cryptography that takes the best of
Public-key Cryptography (this article's topic) and of Private-key
Cryptography (the previous article's topic).

Entering GnuPG...


tags: #public_key #publickey #cryptography #key #privacy

---
keyboardan

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