Can a Blockchain Be Hacked? (Early Stage Risk & Digital Signatures)
🤔 When a blockchain starts, initially there is only one node. Then someone else comes and makes a transaction and installs bitcoin core software too. Then there are 2 nodes. At that time, if one of the two modifies this ledger, does it count as hacked?
If one person sends 10 btc but the other changes it to 5, what does the sender do? Do they have to send another 5?
This is a very critical and important question regarding the initial phase of a blockchain. This question serves as the best foundation for understanding a 51% Attack and "Consensus."
Let's analyze this step by step:
The Early Stage Risk
When a blockchain first begins (for instance, when only Satoshi Nakamoto was present), its security is quite vulnerable. When only 2 Nodes exist, if one attempts fraud, establishing a "majority agreement" (Consensus) is difficult.
However, when designing the BITCOIN network, two solutions were provided for this:
- Proof of Work (Mining): To enter a transaction into the ledger, one cannot merely "write" it. To do so, computational power must be expended to solve a heavy mathematical problem. Even when only 2 Nodes are present, if the malicious actor cannot solve that math puzzle faster than the honest node working legitimately, the network will not accept their fraudulent transaction.
- The Genesis Period: In the early days of any blockchain, it is "nurtured" very cautiously. In BITCOIN, Satoshi Nakamoto initially operated several Nodes by himself, providing the necessary security (Hash power) to the network.
What if 10 BTC is changed to 5 BTC?
Let's imagine Node A (you) and Node B (the thief) exist. You send 10 BTC. The thief tries to alter that to 5 BTC. Here is where the blockchain's Cryptography (Hashing) begins to work:
- Digital Signature: When you send 10 BTC, that transaction is locked with your "Digital Signature" (Private Key). If the thief attempts to change it to 5 BTC, your signature will no longer correspond to that modified transaction.
- Validation: The thief sends that invalid transaction (5 BTC) to you. Your Node examines it: "The signature on this is invalid; this must be 10," and your Node rejects it.
- The Fork: Now the two Nodes hold two different ledgers. The ledger holding 10 with you, and the ledger holding 5 with the thief. The network always recognizes the "longest Chain that has performed the greatest amount of mathematical work." If the thief cannot single-handedly keep producing new blocks to extend their chain, everyone abandons their chain and unites around your valid Chain.
"Do you have to send another 5?" - NO!
Even though the thief changed it to 5, you do not have to send again. Why? Because your Node does not accept the change made by the thief. As other Nodes (joining in the future) audit the data from start to finish, they reject the thief's alteration because it violates the rules of Cryptography.
Put simply, the thief can alter only the ledger on their own computer. But they cannot force that onto the entire world.
"The Consensus War: How Crypto Prevents Cheating.
The security of a blockchain network depends on majority consensus. As the number of Nodes in the network increases, its security increases proportionally. If someone attempts to alter a transaction, Digital Signatures and Hashing technology identify that fraud instantaneously. For a malicious actor to control the network, they must seize more than 51% of the total computational power (Hash Power) present across the entire network. This is an undertaking practically so expensive and difficult that it is nearly impossible."
🤔 So does the thief not get the 10 btc? Or because they modified theirs to 5, do they now have 5 btc?
This is where the "Cryptography"—the mathematical security of a blockchain—functions most brilliantly. The short answer is: The thief receives all 10 BTC whether they want it or not; they cannot make it 5 BTC. Let's understand why this happens simply:
The Transaction is Already "Sealed"
When you send 10 BTC, that transaction contains information structured like this:
To : [Thief's Address]
Amount : 10 BTC
Signature: [Digital signature created with your Private Key]
All these data are bundled together and "Sealed." When the thief receives this message, they can write 5 instead of 10 in the ledger on their own Computer (Node).
Why Doesn't the Network Accept It?
The moment the thief erases 10 and types 5, your Digital Signature no longer matches that new number (5).
The rule of a blockchain network is this: If even a single dot or comma in a transaction is altered, the Signature that signed it becomes invalid. So even if the thief records 5 BTC in their ledger, the other Nodes (computers) across the network examine it and state: "The signature on this is wrong. This should be 10 BTC. The thief has falsified their ledger."
How Does the Thief Receive 10 BTC?
The decision that the thief receives 10 BTC is made not by the thief, but by the entire network. On every other Node across the world, it is recorded that 10 BTC moved from you to the thief. If the thief ever tries to send those BTC to someone else one day, they can send all 10 BTC. It doesn't matter if they say "I only have 5"; the network knows they possess 10.
What Happens to the Thief? (Isolation)
If the thief persists in broadcasting fraudulent data (Blocks) to the network claiming "No, I only received 5," what other Nodes do is ban/isolate the thief's Node from the network. The thief is then left stranded alone with their falsified ledger, separated from the "true Blockchain" recognized by the entire world.
"The Immutable Truth: Why You Can't Edit the Ledger.
Altering a data entry on a blockchain is not merely erasing a number and writing another. Every transaction is guarded by a Digital Signature, which is verified second by second by thousands of computers across the network. If someone attempts to modify their private ledger, their data will not align with the rest of the network's data, causing them to be automatically ostracized from the network. In this manner, truth is preserved through majority consensus."
🤔 Then, in a scenario with 2 nodes as mentioned earlier, can they not determine who is right? How do we know the correct person, and what is this digital signature?
If you wondered about this, your reasoning is exceptionally logical! When only 2 Nodes exist, because there is no majority, it is indeed impossible to decide purely by numbers who is right. That is precisely why an increase in the number of Nodes is essential for a blockchain to become secure. When only 2 Nodes exist, if someone commits fraud, it becomes a "your word against theirs" standoff.
However, the technical instrument that helps win this battle is the Digital Signature. Let's understand this simply:
What is this Digital Signature?
In the physical world, we put a signature at the end of a letter to verify "I wrote this myself." But anyone can forge that signature.
A Digital Signature is far more advanced—it is an unforgivable mathematical signature. It is formed by the combination of two components:
- Private Key: This is like the PIN of your ATM card. Only you know this. This is what you use to "sign" a transaction.
- Public Key: This is like your bank account number. Anyone can see this. Others use this to "verify" whether the signature you made is correct.
How Does a Digital Signature Work?
When you send 10 BTC, 3 steps take place:
- Hashing: All details of your transaction (From, To, Amount) are compiled together to create a "Fingerprint."
- Signing: Using your Private Key, you lock that Fingerprint. That is now what is called a "Digital Signature."
- Verification: When the recipient/network receives this message, they apply your Public Key to test whether that signature matches.
Why Can't the Thief Alter This?
Let's return to the 2-Node example. You sent 10 BTC and locked it with a Digital Signature. If the thief changes it to 5 BTC, that new data (5 BTC) will not match the Signature you generated. For the signature to match, the thief would need to possess your Private Key. Without it, the thief cannot generate a valid signature.
Even with only 2 Nodes present, the system mechanics dictate: 👇
No humans need to convene and decide here. The mathematics (Cryptography) embedded in the system proves who is telling the truth.
"Digital Signatures: The Mathematical Proof of Ownership.
In blockchain technology, trust is built not upon individuals, but upon mathematical certainties. Asymmetric Cryptography confirm the ownership of a transaction and the integrity of its contents. If someone attempts to tamper with a transaction, the digital signature associated with it breaks, and the network immediately rejects it. This is the primary factor guaranteeing security even in the absence of a central controller."
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