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  • Intro
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  • BSV Academy
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      • Introduction
      • About BSV Blockchain
        • Introduction
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    • Hash Functions
      • What are Hash Functions?
        • The Differences Between Hashing and Encryption
        • The Three Important Properties of Hash Functions
        • The Hash Functions Found in BSV
      • Base58 and Base58Check
        • What is Base58 and Why Does Bitcoin use it?
        • What is Base58 and How Does BSV use it?
      • SHA256
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        • The BSV Unified Merkle Path (BUMP) Standard
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      • Merkle Trees and Simplified Payment Verification
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    • Digital Signatures
      • What are Digital Signatures
        • Background
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      • ECDSA Prerequisites
        • Disclaimer
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        • Introduction
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      • BSV and Digital Signatures
        • Introduction
        • BSV Transaction
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        • Summary
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    • BSV Theory
      • Abstract
        • Peer-to-Peer Cash
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        • Peer-to-Peer Network
        • Timechain and Proof-of-Work
        • CPU Power
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      • Introduction
        • Commerce on the Internet
        • Non Reversible Transactions
        • Privacy in Commerce
        • The Paradigm of Fraud Acceptance
        • What is Needed...
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        • Security and Honesty
      • Transactions
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        • Spending a Coin
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        • First Seen Rule
        • Broadcasting Transactions
        • Achieving Consensus
        • Proof of Acceptance
      • Timestamp Server
        • Timestamped Hashes
        • A Chain of Timestamped Hashes
      • Proof of Work
        • Hashcash
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        • Attacking the Longest Chain
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      • Network
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        • Breaking the Tie
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        • Spent Transactions
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        • Verification During Attack Situations
        • Maintaining an Attack
        • Invalid Block Relay System
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      • Combining and Splitting Value
        • Dynamically Sized Coins
        • Inputs and Outputs
        • A Typical Example
        • Fan Out
      • Privacy
        • Traditional Models
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        • Public Records
        • Stock Exchange Comparison
        • Key Re-Use
        • Privacy - Assessment 2
        • Linking Inputs
        • Linking the Owner
      • Calculations
        • Attacking the Chain
        • Things the Attacker Cannot Achieve
        • The Only Thing an Attacker Can Achieve
        • The Binomial Random Walk
        • The Gambler's Ruin
        • Exponential Odds
        • Waiting For Confirmation
        • Attack Via Proof of Work
        • Vanishing Probabilities
      • Conclusion
        • Conclusion Explained
    • Introduction to Bitcoin Script
      • Chapter 1: About Bitcoin Script
        • 01 - Introduction
        • 02 - FORTH: A Precursor to Bitcoin Script
        • 03 - From FORTH to Bitcoin Script
        • 04 - Bitcoin's Transaction Protocol
        • 05 - Transaction Breakdown
        • 06 - nLockTime
        • 07 - The Script Evaluator
      • Chapter 2: Basic Script Syntax
        • 01 - Introduction
        • 02 - Rules Around Data and Scripting Grammar
        • 03 - The Stacks
      • Chapter 3: The Opcodes
        • 01 - Introduction
        • 02 - Constant Value and PUSHDATA Opcodes
        • 03 - IF Loops
        • 04 - OP_NOP, OP_VERIFY and its Derivatives
        • 05 - OP_RETURN
        • 06 - Stack Operations
        • 07 - Data transformation
        • 08 - Stack Data Queries
        • 09 - Bitwise transformations and Arithmetic
        • 10 - Cryptographic Functions
        • 11 - Disabled and Removed Opcodes
      • Chapter 4: Simple Scripts
        • 01 - Introduction
        • 01 - Pay to Public Key (P2PK)
        • 02 - Pay to Hash Puzzle
        • 03 - Pay to Public Key Hash (P2PKH)
        • 04 - Pay to MultiSig (P2MS)
        • 05 - Pay to MultiSignature Hash (P2MSH)
        • 06 - R-Puzzles
      • Chapter 5: OP_PUSH_TX
        • 01 - Turing Machines
        • 02 - Elliptic Curve Signatures in Bitcoin
        • 03 - OP_PUSH_TX
        • 04 - Signing and Checking the Pre-Image
        • 05 - nVersion
        • 06 - hashPrevouts
        • 07 - hashSequence
        • 08 - Outpoint
        • 09 - scriptLen and scriptPubKey
        • 10 - value
        • 11 - nSequence
        • 12 - hashOutputs
        • 13 - nLocktime
        • 14 - SIGHASH flags
      • Chapter 6: Conclusion
        • Conclusion
    • BSV Infrastructure
      • The Instructions
        • The Whitepaper
        • Steps to Run the Network
        • Step 1
        • Step 2
        • Step 3
        • Step 4
        • Step 5
        • Step 6
      • Rules and their Enforcement
        • Introduction
        • Consensus Rules
        • Block Consensus Rules
        • Transaction Consensus Rules
        • Script Language Rules
        • Standard Local Policies
      • Transactions, Payment Channels and Mempools
      • Block Assembly
      • The Small World Network
        • The Decentralisation of Power
        • Incentive Driven Behaviour
        • Lightspeed Propagation of Transactions
        • Ensuring Rapid Receipt and Propagation of New Blocks
        • Hardware Developments to Meet User Demand
        • Novel Service Delivery Methods
        • MinerID
      • Conclusion
  • Research and Development
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    • Technical Standards
  • Support & Contribution
    • Join Our Discord
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  • Merkle-Damgård Hash Functions
  • MD4 and MD5
  • BSV's Hash Functions

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  1. BSV Academy
  2. Hash Functions
  3. What are Hash Functions?

The Hash Functions Found in BSV

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Last updated 4 months ago

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Merkle-Damgård Hash Functions

The fundamental issue with constructing a hash function is the fact that it must be able to take an input of arbitrary length and compress it into an output of a fixed length. If input is an arbitrary length, it's difficult to achieve second preimage resistance. Also, for a compression function to be collision resistant, it must take fixed length inputs that are longer than its output. One way to remedy this issue is to use a preprocessing step to pad the input to a fixed length rather than compress it directly. Once the input has been preprocessed, it can be compressed consistently.

In 1979, both Ralph Merkle and Ivan Damgård independently proved that so long as an appropriate padding scheme is used in the preprocessing step, and the compression function used is collision resistant (implying preiamge and second preimage resistance), it follows that the hash function itself is also collision resistant. The most popular hash functions in use today are based on this Merkle-Damgård method of construction.

Merkle-Damgård hash functions have three parts: input and preprocessing, compression, and final value construction and output. The preprocessing step pads the input message so its congruent to a fixed bitlength, e.g. 512 or 1024, and then appends the length of the input itself (this is called Merkle-Damgård strengthening). The compression step uses bitwise logical functions to compute and mutate the processed input in rounds using chaining variables to link each round. Finally, the chaining variables are concatenated and outputted most commonly in hexadecimal format.

MD4 and MD5

MD4 enjoyed short-lived success, but Rivest realized shortly after its release that it was likely to be insecure, so he designed MD5 shortly thereafter. Despite Hans Dobbertin's announcement of a collision found for MD5's compression function in 1996, MD5 enjoyed long-lived success. While cryptographers were recommending SHA-1 as a replacement to MD5 as early as 1996, MD5 continued to be used well into the early 2000s.

However, in 2004, Xiaoyun Wang, Dengguo Feng, Xuejia Lai, and Hongbo Yu developed an analytical collision attack that could reportedly be performed within an hour on an IBM p690 cluster. This marked the end for MD5 for use in key derviation and digital signatures. In 2008, CMU Software Engineering Institute announced MD5 was "cryptographically broken and unsuitable for further use".

Even so, the groundwork laid by MD4 and MD5 provided a practical framework for newer generations of hash functions to follow; including BSV's SHA-256 and RIPEMD-160 which both use 512 bit message blocks and 32 bit words.

BSV's Hash Functions

However, the following table displays the full range of hash functions commonly found in the greater BSV ecosystem; including SHA-512 and the HMACs of SHA-256 and SHA-512 which are often utilized by wallet implementations:

Hash Function
Output Length
Description
Example Application in BSV

SHA-256

32 Bytes

Generates unique 256-bit value from input string

1. Proof-of-work algorithm 2. Address Creation

RIPEMD-160

20 Bytes

Generates unique 160-bit value from an input string

Address creation

HASH-256

32 Bytes

SHA256 hash of a SHA256 hash

1. Blocks 2. Transactions

HASH-160

20 Bytes

RIPEMD160 hash of a SHA256 hash

Address creation

SHA512

64 Bytes

Generates unique 512-bit value from input string

Wallet encryption (AES)

SHA256HMAC/SHA512HMAC

32 Bytes

HMAC Prevents length extension attacks and can be used with any hash function

Address Creation

The first two Merkle-Damgård hash functions to gain widespread adoption were Ron Rivest's MD4 and MD5. First specified in 1992 in the Internet Engineering Task Force (IETF) Request For Comments (RFCs) and , respectively, MD4 and MD5 were the first hash functions to use a 448 congruent to 512 message block padding scheme with the remaining 64 bits left for Merkle-Damgård strengthening.

As already mentioned, the two hash functions found in the BSV system are SHA-256 and RIPEMD-160. For reasons explored further in Chapter 7, Bitcoin uses SHA-256 and RIPEMD-160 in double hash forms: SHA-256(SHA-256) and RIPEMD-160(SHA-256) – often abstracted and referred to as HASH-256 and HASH-160, respectively, following the convention set out in the .

1320
1321
original bitcoin code