Homework 1: Signature Verification Discovery

← Back to Cryptography I: Blockchain Security and Cryptographic Foundations

---

Objective

This homework deepens your understanding of how Rippled verifies transaction signatures. You will explore the codebase to trace the signature verification pipeline and analyze cryptographic operations step by step.

Format: Written report (PDF or Markdown) including diagrams, code snippets, and explanations.

---

Task

Perform a hands-on exploration of Rippled’s transaction processing code and trace how a transaction’s signature is verified from submission to final cryptographic validation.

Requirements

1. Setup

   • Optionally run Rippled in standalone mode for testing

   • Select a transaction to analyze (e.g., Payment, OfferCreate)

   • Trace the transaction through the signature verification process in the codebase

2. Code Exploration

   • Identify the entry point: Transactor::apply()

   • Document the call to preflight() and its parameters

   • Follow the verification chain to checkSign() functions

     • Distinguish between Transactor::checkSign() and STTx::checkSign()

     • Identify which function performs actual cryptographic verification

   • Explore STTx::checkSign() and trace the call to verify()

   • Determine how the signature algorithm (secp256k1 or ed25519) is detected

   • Document differences in the verification flow for each algorithm

3. Documentation

   • Create a call chain diagram from Transactor::apply() to the final verify() function

   • Prepare a function analysis table including:

     • Function name

     • File location

     • Purpose

     • Key parameters

     • Return values

   • Explain error handling for failed signature verification

   • Include relevant code snippets (5–10 lines) for:

     • Signature verification calls

     • Algorithm detection logic

     • Final cryptographic verification

---

Deliverable

A written report containing:

• Call chain diagram

• Function analysis table

• Explanation of algorithm handling (secp256k1 vs ed25519)

• Error handling details

• Code snippets illustrating the verification process

Tips

• Use grep or your IDE to locate function definitions

• Follow #include statements to understand dependencies

• Check return types to understand success/failure patterns

• Use git log to examine history of cryptographic changes

Learning Goals

By completing this homework, you should be able to:

• Navigate Rippled’s transaction processing code

• Understand the signature verification pipeline

• Identify where cryptographic operations occur

• Explain the difference between permission checks and signature verification