Blockchain Basics & Cryptography

Blockchain Design Features

• Blockchain is a timestamped append-only log. There is no editing or deletion. We can only add to an existing blockchain.
• It is secured via cryptography
  • Hash functions for tamper resistance and integrity
  • Digital signatures for consent

Cryptographic Hash Function

• Convert any input into a unique fixed length output/a hash
• Deterministic: the same input always lead to the same output/hash
• Can be efficiently computed
• Preimage resistant: it’s infeasible to reverse engineer (not mathematically impossible)
• Collision resistant: it’s infeasible that two inputs will generae the same hash
• Avalenche effect: Changing the input slightly will completely change the has
• Puzzle friendliness: knowing the part of the input will not help much in finding the rest of the input

Block Header

Blockheader is a 80-bytes (160-bit) data containing six fields.

Bitcoin Blockheader of Block at Height 645,536

Bitcoin Blockheader Data Fields

Source: https://medium.com/fcats-blockchain-incubator/understanding-the-bitcoin-blockchain-header-a2b0db06b515

Merkle Tree

A tree structure in which each leaf node is a hash of a block of data, and each non-leaf node is a hash of its children. Source: https://en.wikipedia.org/wiki/Merkle_tree

Asymmetric Cryptography & Digital Signatures

• A pair of public key and private key are generated from random numbers using one-way functions so it is imfeasible to deduce the private key from the public key
• The sender encrypts the message using the receiver’s public key and one-way functions so it is not feasible to infer the original message
• The receiver can then decrypt the message using his private key