Sia Network Integration - Milestone 1 Research Summary

Technical Research Completed

1. Protocol Analysis

• V2 Transaction Format: Analyzed current Sia V2 transaction specifications post-hardfork
• Cryptographic Requirements: Ed25519 signatures, Blake2b hashing, BIP44 derivation with coin type 1991
• API Integration: Studied current Sia protocol specifications

2. Library Selection

• Firmware: Selected trezor-crypto for Ed25519/Blake2b operations (audited, embedded-optimized)
• Protocol: Identified need for custom V2 transaction parsing due to memory constraints

3. API Research & Integration Challenge

Initial Challenge: During research phase, we discovered that official walletd infrastructure recommended in Sia documentation was not publicly accessible for development and testing purposes.

Research Response: Conducted comprehensive API analysis to identify alternative blockchain interaction methods. Collaborated with Sia Foundation team who provided access to Siascan's production APIs as a viable integration target.

API Requirements Analysis & Validation:

Researched and tested all blockchain operations required for full wallet functionality:

Operation	Endpoint	Validation Status	Purpose
Balance Check	GET /addresses/{addr}/balance	✓ Tested	Portfolio display
UTXO Retrieval	GET /addresses/{addr}/outputs/siacoin	✓ Tested	Transaction construction
Transaction History	GET /addresses/{addr}/events	✓ Tested	Transaction list
Pending Transactions	GET /addresses/{addr}/events/unconfirmed	✓ Tested	Mempool status
Transaction Details	GET /events/{txid}	✓ Tested	Detailed transaction view
Fee Estimation	GET /txpool/fee	✓ Tested	Dynamic fee calculation
Network Status	GET /consensus/network	✓ Tested	Network connectivity
Blockchain Tip	GET /consensus/tip	✓ Tested	Confirmation tracking
Transaction Broadcasting	POST /txpool/broadcast	✓ Tested	Post-signing submission

Key Research Findings:

• All APIs confirmed compatible with V2 transaction format
• Response formats provide necessary data fields for wallet implementation
• Broadcasting endpoint accepts V2 transaction structure as documented
• Fee estimation API provides real-time network fee data for optimal user experience

Integration Decision: Siascan APIs provide complete coverage for all required wallet operations, enabling full Sia integration without dependency on self-hosted walletd infrastructure.

Planned Repository Structure (Milestone 2)

1. Firmware Integration: x1_wallet_firmware

Following the existing XRP app pattern:

apps/sia_app/
├── sia_api.c
├── sia_api.h
├── sia_context.h
├── sia_helpers.c
├── sia_helpers.h
├── sia_main.c
├── sia_main.h
├── sia_priv.h
├── sia_pub_key.c
├── sia_txn_helpers.c
├── sia_txn_helpers.h
└── sia_txn.c

common/proto-options/sia/
├── core.options
├── error.options
├── get_public_key.options
└── sign_txn.options

2. Protocol Definitions: cypherock-common

proto/sia/
├── core.proto
├── get_public_keys.proto
└── sign_txn.proto

File Structure Overview

Firmware Application Files (apps/sia_app/):

• API Layer (sia_api.c/h): Device communication handlers for host requests
• Context Management (sia_context.h): State management and transaction context storage
• Cryptographic Operations (sia_helpers.c/h): Ed25519 key derivation, address generation using trezor-crypto
• Main Logic (sia_main.c/h): Application entry points and command routing
• Private Definitions (sia_priv.h): Internal constants and private function declarations
• Public Key Operations (sia_pub_key.c): BIP44 key derivation and address generation
• Transaction Processing (sia_txn.c, sia_txn_helpers.c/h): UTXO-based transaction parsing and signing

Protocol Buffer Files:

• Core Definitions (core.proto): Basic data structures and error handling
• Address Generation (get_public_keys.proto): Public key derivation and address requests
• Transaction Signing (sign_txn.proto): Transaction data structures and signing requests
• Options Files (.options): Protocol buffer compilation settings for embedded constraints

Firmware Signing Process for UTXO-Based Cryptocurrencies

Technical Challenge: The firmware implementation represents the most complex aspect of Sia integration. Unlike host-side software that can leverage existing libraries and APIs, the hardware wallet operates in an extremely constrained environment:

• No External Libraries: Cannot utilize high-level Sia protocol libraries available for desktop applications
• Manual Transaction Parsing: Must parse and validate complex V2 transaction structures byte-by-byte
• Memory Constraints: Limited RAM requires meticulous implementations of all required buffers and data structures to hold relevant data.
• Cryptographic Isolation: All operations must occur within secure element boundaries

UTXO Model Complexity: Sia's UTXO-based architecture adds additional complexity compared to account-based cryptocurrencies, requiring careful tracking of input-output relationships and change calculations.

Cypherock X1 implements a secure signing process specifically designed for UTXO-based ledgers like Sia:

1. Transaction Construction (Host-Side)

• Host application constructs unsigned transaction with selected UTXOs as inputs
• Transaction includes recipient addresses, amounts, and calculated fees
• Raw transaction data is serialized and sent to hardware wallet via USB

2. On-Device Processing (Manual Implementation)

• Custom Parser: Firmware implements custom parser for V2 transaction format without external dependencies
• Bit-Level Validation: Every transaction field validated manually according to Sia protocol specifications
• UTXO Verification: Referenced UTXOs validated against expected format and spending conditions
• Memory Management: Firmware needs to be implemented in a memory optimized way, as the hardware has limited memory of 98kb.

3. User Verification (WYSIWYS - What You See Is What You Sign)

• Output Display: Each transaction output is displayed with recipient address and amount
• Fee Confirmation: Total transaction fee is calculated and displayed for user approval
• Input Summary: Total input amount and change calculations are shown
• Sequential Approval: User must physically confirm each element using device buttons

4. Cryptographic Signing (Hardware-Isolated)

• Key Derivation: Private key derived from master seed using BIP44 path m/44'/1991'/i'/0/j
• Manual Hash Generation: V2 transaction hash calculated manually using Blake2b-256 algorithm
• Signature Creation: Ed25519 signature generated using secure element with trezor-crypto primitives
• Air-Gap Maintained: Private key never leaves secure hardware boundary

5. Transaction Return

• Signed transaction returned to host for network broadcasting
• Device clears all transaction context and sensitive data from memory
• Host broadcasts completed transaction to Sia network via established APIs

Key Technical Decisions

Coin Support Scope

• Basic transfers: Siacoin send/receive operations
• Portfolio features: Balance tracking, transaction history, price integration
• Future extensibility: Architecture supports Siafund transactions

Security Approach

• Hardware isolation: All private key operations in secure element
• On-device verification: Transaction confirmation on hardware wallet
• Air-gapped signing: Host constructs, device signs after user approval

Protocol Compliance

• V2 transactions: Full support for current Sia protocol post-hardfork
• Standard derivation: BIP44 path m/44'/1991'/i'/0/j
• Address compatibility: SpendPolicy-based address generation

Research Deliverables Completed

• Milestone 1 completion report with technical specifications
• Cryptographic library evaluation (trezor-crypto selection)
• Repository integration planning for existing Cypherock architecture
• API research and validation for blockchain interaction