Understanding Blockchain’s Core Technologies: Hashing, Public-Key Encryption, and Proof of Work

Blockchain's technical foundations include: SHA256 Hash Public‑key encryption Proof‑of‑work mechanism

(1) SHA256 Hash

The core hash algorithm used in blockchain is SHA256 . The output is a fixed‑length, one‑way hash that cannot be decrypted back to the original content. Even tiny differences in input produce vastly different results.

SHA256 provides collision resistance: distinct inputs x≠y will not produce the same hash H(x)=H(y). With 2^256 possible outputs, a collision would require about 2^256+1 attempts; at 10 000 hashes per second, this would take roughly 10^27 years, making collisions practically impossible.

(2) Public‑Key Encryption

This technique lets a user generate a public key (shareable) and a private key (kept secret). In a Bitcoin transfer from Chandler to Joey, the transaction includes three pieces of information:

Joey’s Bitcoin address (Joey’s public key)

Amount of Bitcoin transferred

Chandler’s Bitcoin address (Chandler’s public key)

All data and the digital signature (the hash of Chandler’s address and the amount, encrypted with his private key) are sent over the network for verification. Miners validate the transaction by:

Hashing the non‑encrypted data (amount and both public keys) to obtain Hash1 .

Decrypting the digital signature with Chandler’s public key to obtain Hash2 .

If Hash1 equals Hash2 , the transaction is valid.

(3) Proof‑of‑Work

In a decentralized ledger, anyone can add blocks, but trust is established through Proof‑of‑Work (PoW) . Miners solve computationally intensive puzzles to validate transactions and create new blocks.

Each block’s hash is derived from:

The previous block’s hash

The hash of the transaction data

A nonce

The resulting hash must start with a specified number of leading zeros.

For example, given the string "Hello, world!", miners append a nonce integer and compute SHA256 until the hash begins with "0000". On average, 4 251 attempts are needed to find such a nonce.

The first miner to discover the valid nonce wins the right to add the block to the blockchain, after which the network verifies and adopts the new block.

Conclusion

This brief overview introduces the essential blockchain technologies—SHA256 hashing, public‑key cryptography, and proof‑of‑work—providing a foundation for deeper exploration of blockchain applications.