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/she 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. Now the recipient is able to read the original pre-ciphered message.
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 from Public-key Cryptography (this article's topic) and from Private-key Cryptography (the previous article's topic).
Entering GnuPG...
tags: #public_key #publickey #cryptography #key #privacy
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