# All you need to know about Cryptography

Cryptography is a fundamental tool in the fight against cybercrime.

What is encryption, and what does it mean? The etymology helps to understand: Kryptós (hidden) and graphía (writing) are the two Greek words that make up the term cryptography. The latter is nothing but a system designed to make a message unreadable for those who do not have the solution to decode it. Which cryptography system is used in computer science? Here’s all you need you to know about cryptography. Read on!

The meaning of cryptography

Today communication - of any kind - has acquired an increasingly central role in the life of each of us; in the internet age, billions of information (even sensitive) is circulating on the network. That's why it has become even more necessary to develop sophisticated systems capable of guaranteeing a high level of privacy of some of these data.

Therefore, computer coding, as we know it today, is a continually evolving subject. And precisely because of its continuous evolution, experts never advise against relying on the latest cryptographic algorithm released: paradoxically. It is guaranteed by systems that are already known and publicly tested (a feature that obviously cannot be guaranteed in the case of newer algorithms).

What is a cryptographic system, and how does it work?

Cryptography can be defined as a system that through the use of a mathematical algorithm, acts on a sequence of characters, transforming it. This transformation is based on the value of a secret key, i.e., the parameter of the encryption/decryption algorithm. Precisely the secrecy of this key represents the security key of every cryptographic system.

Two types of encryption

Based on the kind of key used, this computer cryptography system can be divided into two types: symmetric and asymmetric encryption. When a single key is present, we can say it as symmetric key or secret key cryptography (the sender's and recipient's keys are the same). When instead there are two distinct encryption keys, we can say it as asymmetric or public-key cryptography (the encryption key is public, while the decryption key is private).

Symmetric cryptography: some examples

The symmetric cryptography, therefore, foresees the use of a single key both to hide the message and to unlock it and is relatively fast and simple to implement compared to other types of encryption (such as the asymmetric one).

The most common algorithm used today in symmetric key cryptography is called Advanced Encryption Standard (AES). The two Belgian cryptographers, Joan Daemen and Vincent Rijmen developed the Advanced Encryption Standard at the request of the National Institute of Standards and Technology in the late 90s. It became a public standard at the end of 2001.

AES is based on various operations performed on 16-byte data blocks, repeated several times, called rounds, and consists of three 128-bit block ciphers (precisely divided into 4 × 4 8-bit sub-blocks).

In 2003 the US National Security Agency approved the 128-bit AES to protect all government information classified as secret and AES at 192 and 256 bits for so-called top-secret documents. The main disadvantage of symmetric key cryptography is it involved must exchange the key This need to distribute and manage a large number of keys in a secure manner, for most cryptographic services implies the need to make use of other types of encryption algorithms.

Asymmetric cryptographic algorithms

Asymmetric algorithms use two interdependent keys, one to encrypt the data, and the other to decode them i.e. one private and one public. If one key is used for the encryption operation, the other must be used for decryption and vice versa. The private key is known only by the owner; it must be kept secret and must not be shared with anyone else, while all correspondents share the public one.

Being aware of the public key does not allow us to trace the private key in any way. RSA is much slower than symmetric encryption, data is generally encrypted with a symmetric algorithm, and then the relatively short symmetric key is encrypted using RSA. It allows you to securely send other parties the key needed to decode the data, along with symmetrically encrypted data.

Data encryption, hash algorithm, and verification of message integrity

The cryptographic hash function transforms a certain amount of data, such as a file or a message of variable length, in a short fixed string (called hash value or message digest. This data encryption system is mainly used to verify the integrity of a message or to check that the data in question has not changed.

In fact, any accidental or intentional changes to the data will change the value of the hash. A good hash is unidirectional and must, therefore, be extremely difficult to invert (thus not allowing going back to the original value). MD5 and SHA-1 have long been the most widely used hash algorithms, but are now considered weak and are replaced by SHA-2 (which includes SHA-224, SHA-256, SHA-384 or SHA-512).

They are algorithmically similar to SHA-1, and so, according to experts, a new hash standard, SHA-3, will be selected in the coming years.

Lattice-based and quantum cryptography

The encryption on lattices based (latex-based) uses two-dimensional algebraic constructs known, precisely as "lattices," resistant to quantum computation schemes.

The lattice-based primitives have already been inserted correctly in cryptographic protocols such as TLS and Internet Key Exchange, and potentially, all the most widespread security protocols can be made secure by replacing algorithms vulnerable to those of this nature.

Lattice-based encryption is also the basis for another encryption technology called Fully Homomorphic Encryption or FHE. It can allow you to perform file calculations without having to decrypt them by operating two encrypted data we obtain an encrypted result. It once deciphered, is equal to the effect that would be obtained by performing the same process on the two unencrypted data.

The quantum cryptography is based on an approach that uses properties of quantum mechanics when the key is exchanged so that it cannot be intercepted without the sender and receiver noticing. In fact, we talk about the quantum distribution of keys, which is a transmission that can boast a condition of secrecy that is perfect from a mathematical point of view.

Author: Vicki Lezama

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