Cryptography 101

ARPA Official
4 min readNov 20, 2023


Cryptography is the study and practice of sending secret messages. It has been practiced for thousands of years. Its students have applied their craft to every aspect of human existence. If a message between top generals, a group of business associates, or two lovers is encoded or hidden, it has benefited from advances in cryptography.

Evidence for the use of cryptography goes back to at least 1900 BCE in ancient Egypt. An ancient Indian political document written by the philosopher Chanakya stresses the usefulness of secret messages. A famous cipher, the Caesar cipher, is named for its most prominent user.

Of course, there are big differences between how cryptography works now and how it worked back then. Classical cryptography tends to rely on substitution ciphers- systems that replace one letter with another one. It is easy to understand why this is; people before modern computing had to be able to write and solve coded messages by themselves. It also means that the codes are fairly easy to crack.

For example, let’s take a look at the Caesar cipher. It works by taking the alphabet and pairing it with a cipher alphabet that is three letters shifted. A is paired with X, B with Y, C with Z, D with A, and so on. When using the cipher to send a message, the word “lemon” becomes “ibjlk.” While this looks like gibberish, it can be solved fairly easily, given enough time and enough text. In English, there are only 25 letter shifts to use. A determined attacker could check them all until they crack the code. If somebody gets their hands on the key- the name for the information used to encode or decode the message- they can skip to just reading it.

While more complicated substitutions exist, the Vigenère cipher is a particularly famous one; they tend to be weak to the same attacks. With enough time, a person without a computer can figure out and crack the encoding system.

Modern cryptography, which started around 1970, allows for much more complicated encryption and decryption techniques. Some contemporary cryptography models, like public key encryption, became possible with technological advances. In the case of public key encryption, this is because technology allows for the public key, which is used to encrypt messages, to be shared far and wide while allowing the private key, which decrypts them, to remain securely in the hands of the person or persons authorized to read the messages. Until the 1970s, such a system was impossible.

To explain, imagine that you and a friend are exchanging messages with the Caesar cipher. You have to both have the same key to write and decode messages. If your friend suddenly decided to start shifting four letters backward, you would be unable to read anything they wrote. If either of you or a hypothetical third friend in the group, wanted to make a change to the code, you’d have to share the new code with all of them.

Modern computing systems allow for an encryption key to be shared widely while a second decryption key is kept private. In systems with the infrastructure for public key cryptography, anyone can send anyone else a message, but only the intended receiver can read it.

Other, more complicated systems are also now possible due to computing technology. Many of them still come down to the same basic function as classical ciphers- they take a message, encode it into ciphertext, and allow the intended recipient to decode it back into plain text.

Today, cryptography has many applications. Many people are familiar with its uses in blockchain technology. The tools described above allow for many operations, including End-to-End Encryption, Zero Knowledge Proofs, public key encryption, and hash functions, among others. These operations are much more advanced than just swapping out letters or using invisible ink but rely on similar principles to achieve similar ends. They take information and conceal it in a way that keeps it safe from prying eyes while allowing authorized parties to read it.

Cryptography is an ancient practice that allows for information to be shared with selected people. Modern technology has made it accessible to more people than ever before and increased its effectiveness.

About ARPA

ARPA Network (ARPA) is a decentralized secure computation network built to improve the fairness, security, and privacy of blockchains. ARPA threshold BLS signature network serves as the infrastructure of verifiable Random Number Generator (RNG), secure wallet, cross-chain bridge, and decentralized custody across multiple blockchains.

ARPA was previously known as ARPA Chain, a privacy-preserving Multi-party Computation (MPC) network founded in 2018. ARPA Mainnet has completed over 224,000 computation tasks in the past years. Our experience in MPC and other cryptography laid the foundation for our innovative threshold BLS signature schemes (TSS-BLS) system design and led us to today’s ARPA Network.

Randcast, a verifiable Random Number Generator (RNG), is the first application that leverages ARPA as infrastructure. Randcast offers a cryptographically generated random source with superior security and low cost compared to other solutions. Metaverse, game, lottery, NFT minting and whitelisting, key generation, and blockchain validator task distribution can benefit from Randcast’s tamper-proof randomness.

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