Cryptography: history and curiosities, the importance today

Keeping messages secret has never been an easy task, but humans have always tried to develop new methods to do so. Cryptography has been used since time immemorial to transmit information from one to another without potential interceptors having access to it. In this article we will talk about the history of cryptography, some of its most basic terms in order to understand how it works and the importance it has today in the most everyday activities we can imagine.

To understand what cryptography is, we first need to know where it came from or where it originated. Communicating secretly by concealing a message is known as steganography, derived from the words στεγανο(steganpos), meaning covert, and γραπτοζ (gráphos), meaning writing. An example of this can be found in ancient China where messages were written on fine silk which was then crushed into a small ball and covered with wax, which was then swallowed by the bearer of the message and the rest we all know how it turned out. This method has survived to the present day and is used by traffickers to carry illegal substances. With the advent of computers, messages were hidden in multimedia content, mixing bits of the original message between the bits of the file, but with the sophistication of technology, someone conscientious would be able to find out, so the study of cryptography began.

Cryptology comes from the Greek krypto and logos, which means the study of the hidden, the hidden, and within this we find two branches, cryptography and cryptanalysis. In this article we will focus on cryptography, which is the discipline responsible for hiding, concealing and making intelligible the message that we want to share between people, by means of a procedure known as encryption. In contrast, we have the other branch of cryptology, cryptanalysis, which is about breaking this encryption to recover the hidden information.

In the past, as we have mentioned, cryptography was mainly used to keep important messages hidden from third parties, especially in times of war, but nowadays it has other purposes:

❖ That the message is confidential, i.e. only authorised persons can access it.

❖ That the authenticity of both the recipient and the sender is guaranteed, i.e. to verify the identity of both.

That the message reaches the receiver in its entirety, i.e. that the message sent by A is the same as the message received by B.

Next, we will discuss some terms that will be very useful when it comes to better understanding how cryptography works.
To begin with, we need to know that there are two cryptographic methods depending on the type of key used:    

❖ Private key system or symmetric method, these are the methods that use a single key to both encrypt and decrypt the message.

Public key or asymmetric systems are methods in which the encryption and decryption processes are carried out with two keys, one public and one private, which are complementary.

There are two types of algorithms within symmetric encryption:

❖ Block cipher: consists of encrypting the original message by grouping it into blocks of a given size, for example 128 bits.

Stream cipher: the original message is encrypted bit by bit or byte by byte.

There are two methods of public key or asymmetric encryption:

❖ Encryption by substitution: this consists of substituting each letter of the alphabet in which the message we want to send is written and the elements of another alphabet, which may or may not be the same.

Encryption by transposition: this involves rearranging the letters of the clear text and placing them in a different position, so that the encrypted message contains the same characters as the original message, but in a different position.

These two encryption methods were used in classical cryptography, since nowadays, almost anyone, in a relatively short period of time, could obtain an original message that is encrypted by substitution or transposition.

As we have seen, cryptography has been used for thousands of years, and nowadays it is increasingly present in our daily lives, although most of the time we do not realise it. This happens for example when we shop online and pay with our bank card. For example, when we access our email, through the browser we can find a little padlock at the top of the domain bar, this means that we are browsing an encrypted page, but this does not mean that we are sending the information to the person we want, as someone could have come between us and the recipient and received the information. Cryptography is also present when we carry out actions with the Public Administration, through the electronic signature or the electronic ID. In the simple action of sending messages through the well-known WhatsApp app, we are making use of cryptography as communications are encrypted end-to-end, this type of encryption guarantees that only you and the person you are communicating with can read or listen to what you are sending and not even WhatsApp has access to this information.

As we can deduce, cryptography is also a very important tool in the field of cybersecurity. Nowadays, most jobs are industrialised and computerised in some way, which increases the risk of cyber-attacks, so the use of cryptography on communications or devices used in companies is an extra security measure that can always reduce attacks. For example, there are certificates for the authentication of devices through which we will be able to know who is behind each device connected to our network and thus be able to avoid threats.

In an almost computerised world, in which the main assets of companies and individuals are information, whether private, such as bank details or confidential information such as market strategies, we need cryptography together with cybersecurity so that communications and the transfer of information is as secure as possible and there are no intermediaries who try to access it or directly steal it.

Janira Pérez Sánchez, collaborator in the cybersecurity area of Sec2Crime