Bank transfers rely on account credentials and the bank’s approval. On the blockchain, no institution checks your identity for you—the network recognizes only one thing: a digital signature. Once you understand it, you’ll also understand why the private key is so important.

When sending out $BTC , the wallet signs the transaction with the private key, and nodes across the network use the public key to verify the signature. Current price: 75,034.01 (24h -1.01%).

A pair of keys:

Digital signatures use a pair of keys: the private key is used to generate the signature, and the public key is used to verify it. The private key is a randomly generated large number, and the public key is calculated from the private key using elliptic curve operations. Bitcoin and Ethereum both use the secp256k1 curve.

This operation is one-way: deriving a public key from a private key is easy, but working backward from a public key to a private key is computationally infeasible. So the public key and the address derived from it can be shared publicly, while the private key must be kept under your own control.

What a signature proves:

When you send a transaction, your wallet signs its contents with your private key, and nodes across the network verify the signature using your public key. If verification succeeds, it proves two things at once: the transaction really came from someone who controls the private key, and its contents haven’t been changed since it was signed. Change even a single byte in the amount or recipient address, and the original signature will no longer verify.

Keep in mind that a signature does not encrypt the transaction’s contents. The amount and address in an on-chain transaction remain visible to everyone. A signature answers “Who sent this, and has it been altered?”—not “Can others see it?”

Preventing a transaction from being used twice:

Every Ethereum transaction has an incrementing nonce, and each nonce can only be included in a block once. Transactions also include a chain ID (EIP-155), so a signed transaction cannot be replayed on another chain. Bitcoin, meanwhile, prevents the same coins from being spent twice by enforcing the rule that each unspent output can only be spent once.

Signatures aren’t just for transfers:

A signature request that pops up in your wallet isn’t necessarily for a transfer. It might be a token approval or an off-chain signed message. Some off-chain signatures, once signed, have the same effect as a direct approval, allowing the other party to use them to transfer your tokens.

So before signing, check the type of operation, the address you’re interacting with, and the amount. If you don’t understand it, don’t sign. Anyone who asks you to provide your private key or recovery phrase to “verify a signature” is running a scam.

My take:

On-chain, a signature is like your handwritten signature, and your private key is the only pen that can write it. If the pen is lost or stolen, no institution can help you revoke it. Take the time to understand the rules before you act, and don’t make decisions based on gut feelings.

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