What are good ways to learn cryptography

Darknet

The primary goal of cryptography is to protect communications between two or more people from other people. To this end, it provides the means to reduce the secrecy of communication to the secrecy of a few data, also known as keys. Many early trials are military and political and took place between states. In history, however, there have been repeated attempts to protect yourself from government access with the help of encryption. Today's cryptography offers ideal opportunities for this. It is therefore not surprising that in many struggles of minorities for their rights, anonymized and encrypted communication - for example in the Darknet - is an important instrument. [1] It is just as clear that, under the protection of the Darknet, business is being carried out or initiated that shy away from the public eye.

Basic Invention: The Key

The invention of the variable key marks the birth of cryptography. Since then we have differentiated between "algorithm" and "key". This also makes the role of the attacker clear for the first time. The easiest way to illustrate this is with the so-called Caesar disk. The mechanism on which it is based goes back to Gaius Julius Caesar and was further developed in the 15th century by the mathematician Leon Battista Alberti. Since the invention of the disc, it has been an integral part of cryptographic algorithms.

The Caesar disk consists of a small and a large circular disk, which are rotatably connected at their centers. The alphabet is written in a cyclical order on each disc. The alphabet on the outer disk is called the plain text alphabet, the one on the inner disk is called the ciphertext alphabet. Now sender and receiver first set a certain setting for their targets. This can be determined, for example, by specifying the letter on the inner disk that is next to the plain text letter A. For example, if they agree on the letter R, the discs are rotated so that where A is on the outside, R is on the inside. We'll talk briefly about the "R setting". The encryption is now carried out in such a way that a plain text letter is replaced by the ciphertext letter that is directly attached to it on the inner pane. So when encrypting you read from the outside in; accordingly, the decryption takes place by reading from the inside out.

Basically we can differentiate between two things: firstly, the machine, i.e. the general encryption method, which is also called the encryption algorithm; second, the bowl, in our case the special setting of the discs. This can be used to encrypt, i.e. convert plain text into ciphertext.

The original Caesar code is much more special. Caesar replaced every plaintext letter with the letter that comes three places after it in the alphabet. A becomes D, B becomes E and C becomes F. CAESAR becomes FDHVDU. Obviously, this procedure offers practically no security.

This also applies to all procedures that work with secret characters. The so-called Freemason Code is very well known: In this code, each letter is replaced by the lines that surround it (illustration 1). For example, instead of E, a square is drawn, instead of J a V-like symbol and instead of P an L-shaped symbol with a point.

Masonic code (& copy own illustration)


Secret signs offer no security whatsoever, but they are very popular - perhaps because it is believed that real secret signs "protect themselves". The security of all these procedures can collapse like a house of cards at any time. If an unauthorized person becomes aware of the allocation scheme, the system has lost all of its security in one fell swoop.

In the course of history it has been shown that it is almost impossible to keep algorithms, i.e. the basic procedures, secret. The basic principles of the procedures were repeatedly published or revealed, encryption machines were stolen or could be legally bought. For a long time, the inventors and developers feared that this would also make the process itself unsafe. The concern was as follows: Anyone who knows the process, especially whoever invented it, can break it. Many were intuitively aware that this should not be allowed, but it was not formulated until 1833 by the cryptologist Auguste Kerckhoffs: Becoming aware of the procedure must not endanger security. The key to security, however, is that the key is kept secret.

The key is the exclusive secret of the sender and recipient. This is how they protect themselves against the rest of the world. One can also say that the key is the strategic advantage that the recipient has over an attacker. The attacker may have large amounts of ciphertext, he knows the procedure, and he wants to get the plaintext. The question is whether he can do this without knowing the key. One can also turn the tables and measure the security of a procedure according to the chances of success of an attacker. If it is easy to get the plaintext without a key, then the process is insecure. It is safe when an attacker is confronted with a problem that he cannot solve.

The topmost requirement for the security of an encryption method is that an attacker has no chance of trying all the keys. This is not guaranteed with the Caesar disk with its 26 possible settings. With today's procedures, the key space should be at least 2128, better yet 2256 Elements. The latter number is greater than the number of atoms in the universe. In this respect, it is clear that no one, not even all computers on the Internet, can ever implement so many encryptions or decryptions.

Another aspect is important: With a shared key you can create space for secret communication not only for two, but for any number of people. If everyone in a group has the same key and the encryption cannot be broken, then this key acts like a wall protecting this group from the rest of the world.