# Summary and Key Takeaways

Cryptographic functions form the security foundation of Bitcoin Script. **Hash functions** create unforgeable fingerprints that detect data modification, while **signature verification** proves transaction authorization.

**Core Concepts:**

**Hash Functions:**

* Double-hash operations provide enhanced security
* Each hash function offers different output sizes, security levels, and performance characteristics

**Digital Signatures:**

* **OP\_CHECKSIG** verifies single signatures to prove ownership and authorization
* **OP\_CHECKMULTISIG** enables M-of-N threshold signatures for shared control
* **OP\_CODESEPARATOR** enables selective signing for advanced contract patterns


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