Bitcoin Hash: Everything to Know

By  Beluga Research October 24, 2023

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  • A Bitcoin hash is a cryptographic function that takes input data of any size and produces an output string of a fixed size, or hash, to store data on the blockchain.
  • Hashes store information, such as the parties and amounts involved in the purchase, sale and trade of Bitcoin tokens
  • Bitcoin adds blocks after it successfully verifies the hashes
  • Bitcoin hash's advantages include data integrity and the securing of digital signatures, while its disadvantages include computational intensity and potential vulnerability


A Bitcoin hash is a cryptographic function that takes input data of any size and produces an output string of a fixed size, or hash, to store data on the blockchain. Bitcoin's hashes are always 64 digits.

The information in a hash can range from the digital signatures for a transaction to limited information about the entities behind mining operations and the rewards provided to them for this work. After the network reaches its target hash, it closes the block. It reaches consensus when the network validates transactions and information about blocks.

A Brief History

Hash functions have been around since the 1950s. Their practical applications in cryptography emerged in the early 2000s. Bitcoin was introduced in January 2009. Cryptocurrency platforms came to use hash functions to store information from this point forward.

Solving the hash for a Bitcoin block requires an enormous amount of computation. This explains why new bitcoins are mined over significant periods of time. A network's hash rate is the volume of computational power that is provided to the network through mining.

Bitcoin Hash: Everything to Know

A Bitcoin hash serves multiple purposes to ensure that the Bitcoin platform is secure and reliable. A hash function is a mathematical algorithm that takes an input, or message, and produces a fixed-size string of characters. This is also called an output, hash value or digest. Even a slight change in the input generates a completely different output.

Bitcoin uses Secure Hash Algorithm 256-bit, aka SHA-256, as its hash function. This means that the algorithm generates a 256-bit hash value. The total hash value is represented by a string of 64 hexadecimal (16 per set) characters that offer numerous possible hash values.

Mining is a primary application of Bitcoin hash. Miners compete to solve a complex mathematical puzzle by repeatedly hashing block contents until meeting the proof-of-work (PoW) condition. The process verifies transactions and secures the network against attacks.

Hash functions in Bitcoin are also used to create digital signatures, which authenticate transactions. A user signs a transaction with their private key. The resulting digital signature is hashed. The hash value is included in the transaction data. It can be verified with the sender's public key.

Getting Started

Hash functions are deterministic, meaning that they always generate the same output for the same input. They generate unique hashes for different inputs. Hash functions serve as building blocks for various operations in the Bitcoin network. A primary application is creating digital signatures for Bitcoin transactions.

Unique Aspects

  • Computational irreversibility. It is nearly impossible to reverse-engineer, or determine, the original input from the hash output. This ensures data integrity and prevents tampering.
  • Collision resistance. It is highly improbable for two different inputs to produce the same hash output. Bitcoin requires collisions to be extremely rare to maintain network security. Easy collisions would open the door to potential attacks like double-spending, defined as spending the same tokens twice, or forging transactions.
  • Use of hash functions in the mining process. This adds new transactions to the blockchain. Miners repeatedly hash different inputs until they find a hash that meets specific criteria. This computationally intensive process secures the network against attacks.


  • Data Integrity - Bitcoin hash functions maintain the integrity of blockchain data. Each block has a unique hash. Any changes to the data produce a different hash. This makes it nearly impossible for malicious actors to tamper with the blockchain undetected.
  • Immutability - Bitcoin's immutability relies on hash functions. When a block is added to the blockchain, its hash is stored in the next block. This links the two blocks. Modifying a block requires recalculating its hash and all subsequent hashes. This is what makes the blockchain resistant to retroactive changes.
  • Secure Digital Signatures - Bitcoin uses digital signatures to verify transaction authenticity. Hash functions generate these signatures. Hashing a transaction and encrypting it with the sender's private key creates a unique digital signature. Anyone can verify the digital signature using the sender's public key. The verification ensures the transaction's integrity and origin.
  • Efficient Verification - Hash functions make transaction verification efficient. Instead of comparing entire blocks or transactions, Bitcoin nodes compare only hash values. This reduces computational resources needed for validation. It enables faster and more scalable transactions.
  • Merkle Trees - Bitcoin employs Merkle trees, a type of data structure, to store and verify large sets of transactions. Hash functions generate unique hashes for each transaction. It combines them until a single root hash is obtained. This root hash represents the entire set, which allows efficient verification.


  • Computational Intensity - Bitcoin's hashing algorithms require substantial computational power and energy consumption. The SHA-256 algorithm used by Bitcoin demands significant resources. The use of energy has a negative impact on the environment. It also limits participation in mining to entities with resources.
  • Centralization of Mining Power - The computational intensity has led to centralization in Bitcoin mining. Large mining pools and entities with substantial computing power have an advantage over individual miners. This raises the concern that the network is seeing more centralization.
  • Limited Scalability - Bitcoin's hash function affects scalability. As transactions increase, so does the blockchain size. Each new block requires new hash computations. Larger blocks require more storage and processing capacity. Bitcoin is exploring alternative scaling solutions.
  • Quantum Vulnerability - Hash functions like SHA-256 may be vulnerable to attacks by quantum computers. Quantum advancements could break the mathematical problems securing Bitcoin's hash functions. Developing quantum-resistant hash functions is crucial for long-term security.
  • Hash Collision Probability - Collisions may occur where different inputs produce the same output hash. This could be highly unlikely for well-designed hash functions like SHA-256. Yet the potential introduces a small degree of uncertainty and potential for unexpected behavior.