Chapter 1. General
Since we are going to talk about cryptology, we will first explain in general a few things that have to do with the subject.
Cryptology consists of two Greek words, namely “krypto” and “logos” or “logie”. “Krypto” means “to cover or hide” and “logos” means “word” and logie means “science”. So cryptology means the science of hiding or hiding the word. This can be done in the following 2 ways:
-Steganography: hiding a message. In the next chapter we will give 2 examples of steganography.
-Substitution: encoding a message by replacing a letter with a pre-agreed letter.
In our paper we will only deal with substitution. Stenography has nothing to do with mathematics.
The science of cryptology can be divided into two main subjects: cryptography and cryptanalysis. Cryptography (encryption) is the design and use of secret scripts, and cryptanalysis (decryption) is the analysis and breaking of secret scripts. Both are done with the help of keys, you have a text and with the help of an agreed key (a means of translation) you convert it into an encrypted text (and with the help of this key or another key you can convert this encrypted text back to the original text). The key can involve multiplication, addition, shifting, etc. of letters. The different ways are discussed later in the paper. Incidentally, in further discussion of the concept of cryptology, we will mainly focus on encryption. Since decryption comes from this and is therefore not really important to us.
The word cryptography also comes from the Greek language and is derived from the words ‘krypto’ and ‘graphe’. ‘Graphe’ means “the writing, the writing” and as has been said before, ‘Krypto’ means ‘to hide, to cover”. So cryptography means hiding the writing.
There are many forms of encryption, for example Diffie-Hellman, RSA and Vigenère. For the time being, we can divide these into two main groups, namely asymmetric and symmetric encryption.
The difference between asymmetric and symmetric encryption is that symmetric encryption uses only one key for both encryption and decryption, and asymmetric encryption uses two keys. One to encode, it’s public. And one to decode, this one is secret. The advantage of asymmetric encryption is that it is very difficult to crack. However, symmetric encryption is much faster and easier. Two examples of asymmetric encryption are Diffie-Hellman and RSA, and Vigenère is an example of symmetric encryption. Incidentally, it must be said that nowadays the Hybrid encryption system is also used; this is a mixture of asymmetric and symmetric encryption. To ensure speed, symmetric encryption is used to encrypt the data. And to ensure security, asymmetric encryption is used to decrypt the symmetric keys.
Whichever cryptosystem you use, it must always meet three requirements:
1. Absolute confidentiality. If you have a secure cryptosytem, someone who intercepts the message should have no idea about the message.
2. Signature Property. The recipient of the encrypted message must be absolutely sure that the message he receives actually comes from the sender. This should be so clear that it could even convince a judge.
3. Integrity. The recipient of the encrypted message must be able to be sure that the content of the message has not been tampered with.
The above three requirements must guarantee a good cryptosystem, a fourth requirement that has not so much to do with the system but more to do with dealing with the system is the Need to Know principle, with a cryptosystem you have to make sure that as few people as possible know about your key, then it is much easier to keep a system secret.
Some secret scripts have succeeded better than the others. Many old cryptosystems are easier to decipher by means of modern techniques, for that time they were perfect systems since the technique of decryption was not yet that advanced. Unfortunately, even now, modern deciphering techniques are not always able to decipher ancient secret scripts, a famous example being the secret runes on the Swedish stone Rök. These have not been decoded to this day.