# Merkle Trees & Digital Signatures
Besides the use for data integrity and data storage/retrieval, hash functions are used for two key concepts in BSV: **Merkle Trees and Digital signatures**
### Merkle Trees
#### What Are Merkle Trees?
The BSV blockchain makes extensive use of Merkle Trees.
A Merkle Tree is a **binary tree structure** (each branch splits into two nodes) that is made entirely of **hashes**.
#### How They Are Built
* The **leaf nodes** at the bottom layer of the tree are the **hash values of raw Bitcoin transaction data**.
* Each successive layer is created by **concatenating two hashes** from the layer below and hashing them together.
* This process continues until reaching the **root node**, which represents the entire tree with a **single hash value**.
#### Why They Matter
This structure makes it:
* **Easy to find data** stored at the bottom of the tree.
* **Efficient to prove** that specific data exists in the tree.
* **Critical for scaling** the BSV system, since data integrity can be verified quickly without re-checking the entire dataset.
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### Digital Signatures
#### What Are Digital Signatures?
Although hash tables and Merkle Trees are powerful uses of hash functions, the most **widely recognized use** is in **cryptography**.
* Digital signatures, alongside encryption and key exchange, **rely heavily on hash functions**.
* Like a **physical signature**, a digital signature **associates an identity** with a document or message.
* To keep them secure, digital signatures use **well-tested algorithms** for both creation and verification.
#### Digital Signatures in BSV
On the BSV blockchain, digital signatures are most commonly used in **Pay-to-Public-Key-Hash (P2PKH) transactions**— the standard template where **ownership of funds** is transferred from a sender to a receiver.
* Digital signatures let someone **prove they created a transaction** without ever revealing their **private key**.
#### How It Works
1. Instead of signing the **entire transaction data** (which may be large and inefficient), the data is first run through a **cryptographic hash function**.
2. This produces a **short, fixed-size digest** that uniquely represents the transaction.
3. The **sender signs this digest** with their **private key**.
4. Anyone can then use the **sender’s public key** to:
* Verify the signature matches the digest (**authenticity**)
* Confirm the data hasn’t been altered (**integrity**)
#### Key Learning
✅ **Digital signatures prove authorship and integrity without exposing private keys** — a foundation of security in Bitcoin transactions.
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