# A Deep-dive into FROST

Flexible Round-Optimized Schnorr Threshold (FROST) underpins the security and decentralization of the Bitcoin side of BitSafe CBTC. As a threshold signature scheme, FROST enables a group of participants to collectively generate a single Schnorr signature, without any single participant ever having access to the full private key.

This document provides a comprehensive technical overview of FROST, its integration with CBTC, and the significant advantages it offers for institutional Bitcoin custody.

## 1. Understanding FROST

### 1.1. What is FROST?

FROST is a threshold signature scheme that allows for the creation of Schnorr signatures from a distributed set of key shares.

### 1.2. Why FROST for CBTC?

The selection of FROST for decentralized control of the BTC in our on-chain Bitcoin network vault was a deliberate choice.

## 2. How FROST Works

### 2.1. Key Generation

FROST supports two primary methods: Trusted Dealer Generation and Distributed Key Generation (DKG).

### 2.2. The Signing Process

The FROST signing process is a two-round protocol coordinated by a designated entity.

### 2.3. Signature Aggregation and Verification

Once the Coordinator has received a threshold of valid signature shares, it can aggregate them into a single, final Schnorr signature.

## 3. Advanced Features and Security

### 3.1. Share Resharing and Revocation

One of the most powerful features of FROST is the ability to perform Verifiable Secret Resharing (VSR).

### 3.2. Security Model

The security of FROST is based on strong cryptographic assumptions.

## 4. FROST in CBTC: Implementation Details

### 4.1. Attestor Network Architecture

The CBTC system operates through a decentralized network of institutional-grade Attestors.

### 4.2. Coordinator and Governance Integration

The system employs a Coordinator that executes periodic checks every 60-120 seconds.

### 4.3. Threshold Signing Process

FROST enables the Attestor network to collectively authorize Bitcoin transactions.

### 4.4. Dual-Network Security Model

The CBTC system security relies on coordination between two networks.

## 5. More Reading

RFC 9591, Zcash Foundation FROST docs, Cryptology ePrint Archive Report 2020/852