# Simplified concept of a digital currency

karthik · updated · flag

Just like the physical currency we dealt with in the previous lesson, we can make up a digital file and call it a currency and use it to trade as well. Let’s look at an example.

## Coin¶

Let’s say you are an artist and you sell paintings once in a while to your friends Pam and Diego. Pam’s cool too! She makes her own tooth paste and she sells it to you for a small price. And Diego is a geek and he fixes all your computers and gets paid for it too.

But you three find it a bit of hassle to run to the ATM or use the card every time you got to pay. So you all decide to create a digital currency to easily pay each other without any intermediary bank or payment processor. You create a text file and call it buddycoin and set a value for it based on the real currency.

## Ledger¶

Now when you need to pay Pam, say 30 buddycoins, instead of sending the buddycoin file 30 times, you record the transaction as Jane sent Pam 30 buddycoins on Jan 1, 2020, in a paper or better in a neat tabulation like the one below. We’ll call this the ledger.

Sender Receiver No. of buddycoins Date
Jane Pam 30 Jan 1, 2020
Jane Diego 40 Feb 5, 2020
Pam Jane 20 Feb 8, 2020

## Trust¶

As a token of trust, you keep this ledger open and always accessible to all three of you.

But now Diego brings his colleague Sid into this system. He makes delicious sandwiches, but still, you can’t trust an outsider with this public ledger. What if he adds a false transaction that states Pam paid him 200 buddycoins? So as a method to authorise each transaction, you all come up to an agreement to append your signature per transaction.

Sender Receiver No. of buddycoins Date Signature
Jane Pam 30 Jan 1, 2020 𝓙𝓪𝓷𝓮
Jane Diego 40 Feb 5, 2020 𝓙𝓪𝓷𝓮
Pam Jane 20 Feb 8, 2020 𝓟𝓪𝓶
Diego Sid 50 Feb 15, 2020 𝓓𝓲𝓮𝓰𝓸

But … signatures can be forged way easily. So to solve this, you move the tabulation to a spreadsheet on a computer. And instead of signing with your name or initials, you use a sign with a secret word every time you send buddycoins to someone. And this is not just any random secret word, but a word that’s taken from a book of words that is unique to you.

The ledger would now look like this.

Sender Receiver No. of buddycoins Date Signature
Jane Pam 30 Jan 1, 2020 bunnyhopstwice
Jane Diego 40 Feb 5, 2020 coldweather
Pam Jane 20 Feb 8, 2020 schrutefarms
Diego Sid 50 Feb 15, 2020 ihatewater

So now, If someone would want to fake a transaction, they will have to set a secret word in a way that it must exist in the actual sender’s book of words when checked later. This way, even though the ledger is public, your buddycoin is forge proof. And also, by maintaining local copies of the ledger you can compare it for validation when needed.

And that’s what a digital currency is. Proceed to the next lesson to learn about real cryptocurrencies.