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Blockchain and more blockchain! That’s currently a common term, almost a fad in the corporate spheres. Everybody wants something with blockchain, even if they don’t know exactly what a “blockchain” is. Something about cryptocurrencies, right? Something like a new super-techy-thingamajig, right…?

Όχι ακριβώς, φίλε μου. Έτσι, μπορούμε να αρχίσουμε να δηλώνουμε τι ΔΕΝ είναι ένα blockchain και τι δεν είναι για:

* Blockchain isn’t a cryptocurrency.
* Blockchain isn’t an investment platform.
* Blockchain isn’t the bigger open-source platform.
* Το Blockchain ενδέχεται να μην είναι ένα κατανεμημένο σύστημα.
* Το Blockchain μπορεί να μην είναι αποκεντρωμένη Σύστημα.
* Blockchain isn’t magical.
* Blockchain can’t solve all your problems.
* Το Blockchain ενδέχεται να μην αυξάνει τα κέρδη σας με κανέναν τρόπο.

Ολα ΕΝΤΑΞΕΙ? Τότε, μπορούμε να ξεκινήσουμε να μάθω what a “blockchain” really is and what is its purpose in the universe.

A blockchain is…

Αυτό το πράγμα δεν είναι τίποτα περισσότερο από ένα λογιστικό καθολικό σε μια ψηφιακή κρυπτογραφημένη έκδοση. Sounds boring? Well, it’s kind of boring, to be honest. Where’s the magic in there? Why everybody is so excited? And why this thing has something to do με κρυπτονομίσματα; Ας εξηγήσουμε.

Πριν από δώδεκα χρόνια, το άτομο (ή ομάδα ανθρώπων) γνωστό ως Satoshi Nakamoto προσπαθούσε να λύσει το πρόβλημα των διπλών δαπανών στα ψηφιακά μετρητά με έναν αναξιόπιστο τρόπο. Εντάξει! Μπορούμε να επιβραδύνουμε λίγο. Η διπλή δαπάνη, βασικά, ξοδεύει τα ίδια ψηφιακά χρήματα περισσότερες από μία φορές (όπως θα έπρεπε). Ξέρετε, μπορείτε να αντιγράψετε και να επικολλήσετε σχεδόν τα πάντα στο Διαδίκτυο, γιατί όχι τα χρήματα;

To avoid this kind of behavior, we’ve trusted centralized institutions, like banks and governments. Once you send an electronic bank transfer, the bank’s system discounts that money from your account. If they weren’t there, probably the people would just spend the same money several times. And that it’s like a robbery.

Ετσι, Ο Satoshi σκεφτόταν σε ένα αυτόματο σύστημα να αντικαταστήσει αυτά τα κεντρικά ιδρύματα and make it possible to have digital cash without the double-spending problem at the same time. He/she/it grabbed then a kind of experimental cryptographic (encrypted) database created in the 70s and mixed it up with other techy-elements to create the first decentralized digital currency without a double-spending problem. And Bitcoin was born in 2009!

Εικόνα από τον Gerd Altmann / Pixabay

Αυτή η πειραματική κρυπτογραφική βάση δεδομένων είναι το περίφημο blockchain, παρόλο που κανείς δεν το γνώριζε τότε. Ούτε καν Satoshi: ήρθε το όνομα μετά το Bitcoin. Why not “crypto-database” or something like this, instead of “blockchain”? Well, it’s because the database is actually… a chain of blocks, as it sounds. Digital blocks.

Πώς λειτουργούν τα μπλοκ;

Every “block” is a little container of data (monetary transactions, in a cryptocurrency case), chained to all the others (pasts and futures) with something called “hashes”. These are the encrypted result from passing the data through a complex algorithm. Something like this (if we use the Αλγόριθμος SHA256):

*Initial data: You’ve transferred 1 BTC to Mike.
* Κατακερματισμένα δεδομένα: 710DAEB54021CCD83046E4FA16106E4DC10E5D617E4C28F61CE29C29CFAE823E

Every hash represents a unique identity for every transaction and every block (a group of transactions) in existence. All those identities mathematically merge later with each other, “chaining” themselves that way. So, if anybody tries to cheat, the hash of their transaction (the unique identity) will change; and if it changes, it’ll be unchained and become invalid automatically.

Εικόνα από την Christine Schmidt / Pixabay

For example, let’s remember our initial data (You’ve transferred 1 BTC to Mike). If we change even a little character in there, the hash will radically change as well:

*Initial data: You’ve transferred 2 BTC to Mike.
* Κατακερματισμένα δεδομένα: 005002AC29AE0D1944110DB27CC73E9090F013B15207D84F2086B8646DAF549E

The transaction isn’t valid anymore and you, poor mortal, can’t deceive the blockchain system. Even if the authorities aren’t supervising. But now, let’s simulate the “merging” between transactions. Let’s say those hashes are indeed both valid and represent the identities of two different blocks. Πώς συνδέονται μεταξύ τους; Φυσικά, ταυτίζονται. Ως αυτό:

* Αρχικά δεδομένα:
* Κατακερματισμένα δεδομένα: EDFE12B5DB008F6491BA671DBE6BA25BD89BD6445B5003E9B3789605DBD24AD8

And that’s it! If you want to change something and make it valid, you must first decipher and change every block in existence. Good luck with it.

A blockchain doesn’t work alone

Despite the math, that sophisticated ledger can’t work by itself. It needs the other elements Satoshi added to it: a distributed network of nodes (and people), the aforementioned algorithm to encrypt transactions and set the rules for the validators, the transactions to spend or “coins”, and private and public cryptographic keys. Let’s check quickly one by one.

Κατανεμημένο δίκτυο

Εικόνα από τον Gerd Altmann / Pixabay

It’s not the banks or governments, but someone should verify the transactions in some way. And, for decentralized systems (like most cryptocurrencies), that’d be a distributed network conformed by a lot of people all around the world and their computers and equipment (nodes). Especially the last ones.

Το πράγμα είναι, κάθε μέλος του δικτύου (γνωστό ως ανθρακωρύχος ή επικυρωτής) έχει ένα αντίγραφο ολόκληρου του blockchain στο υλικό τους, and their specialized software or mining equipment is in charge of verifying and keeping the record of every new transaction and mint new “coins”; following the mathematical rules set by the system’s algorithm. The result always should be the same for most validators, otherwise, the transaction or block will be invalid.

Ένας αλγόριθμος συναίνεσης

Image by Tomasz Mikołajczyk / Pixabay

We can define an algorithm as a set of steps and methods that are built —with math— to achieve a specific result or solve a problem. There’s a lot of algorithms out there, and not all of them work to build a blockchain. They should be very complex and strong, in order to maintain high security and force the rules among validators.

Ούτε κάθε σύστημα κρυπτογράφησης ή blockchain χρησιμοποιεί τον ίδιο αλγόριθμο. Bitcoin, για παράδειγμα, uses SHA256 (the one we used before), but Ethereum uses Ethash and Zcash uses Equihash. They’re different mathematical functions, but the purpose is the same: encrypt the data.  

Unspent transaction outputs (UTXOs)

Εικόνα από τον Matthias Wewering / Pixabay

We know the term sounds difficult, but these are the “digital coins” or transactions per se. They’re like fragments of property that work to exchange with other people. You can compare them with the bills or cents inside your physical wallet, as well.

Ιδιωτικά και δημόσια κρυπτογραφικά κλειδιά

Εικόνα από IntelFreePress / Flickr

Αυτά είναι μαθηματικά κλειδιά που λειτουργούν ως διευθύνσεις για την αποστολή και τη λήψη χρημάτων μέσα σε ένα blockchain. Το δημόσιο κλειδί είναι σαν αριθμός τραπεζικού λογαριασμού: you can share it freely to receive money. The private key, on the other side, works to “sign” the transactions and verify the real owner and their intention to send the funds. In other words, a private key is like a password, and both, the private and public key, form an “account” within the cryptocurrency or the blockchain.

“Blockchain” doesn’t mean “decentralized” always

As we said at first, a blockchain may not be distributed and may not be decentralized. It’s just a cryptographic ledger, after all, and the other elements that work with it can change according to the needs of their creators.

Satoshi Nakamoto was the first person to use it with Bitcoin, αλλά τον πηγαίο κώδικα for this kind of ledger is open to the public. It can be copied, pasted, modified, and even sold. So, a lot of people (and enterprises) all around the world have been trying this technology for their own uses, even beyond cryptocurrencies. The banks aren’t excluded: they like using blockchains to build new payment platforms. And, as you may imagine, these aren’t decentralized, but totally controlled by the institutional network.

Sometimes, blockchains don’t work with distributed networks, just with controlled internal networks. This kind of platform needs user permissions from the creators, so, they’re called “permissioned” or private blockchains. On the other side, cryptocurrencies and platforms like Bitcoin works with decentralized networks. That makes them “permissionless” or public.


Επαγγελματίας λογοτεχνίας στον κόσμο της κρυπτογράφησης από το 2016. Συγγραφέας, ερευνητής και bitcoiner. Εργασία για έναν καλύτερο κόσμο, με περισσότερη αποκέντρωση και καφέ.

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