# Digital Signatures: Proving Ownership

<figure><img src="/files/dTWb9kQHk4fWF4lfshGJ" alt=""><figcaption></figcaption></figure>

While hash functions verify **data integrity**, digital signatures verify **authorization**—whether someone has the right to spend funds. Bitcoin uses **Elliptic Curve Digital Signature Algorithm (ECDSA)** with the **secp256k1 curve**.

**Important Identity Distinction:** Digital signatures alone do not establish human identity. They only prove that someone possessing a specific private key authorized a transaction.

#### Single Signature Verification:&#x20;

#### OP\_CHECKSIG

| Opcode             | Input      | Output         | Description                                                               |
| ------------------ | ---------- | -------------- | ------------------------------------------------------------------------- |
| OP\_CHECKSIG       | sig pubkey | TRUE / FALSE   | Verifies the signature against the public key for the current transaction |
| OP\_CHECKSIGVERIFY | sig pubkey | Nothing / fail | Same as OP\_CHECKSIG, but executes OP\_VERIFY afterward                   |

**Pay-to-Public-Key-Hash (P2PKH) Example:**

```
<signature> <public_key> 
OP_DUP OP_HASH160 <pubkey_hash> OP_EQUALVERIFY OP_CHECKSIG 
```

This pattern ensures both that the correct public key is provided and that a valid signature for that key is present.


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