Add reproducible build verification

[0xh3rman]

Summary

This PR adds reproducible build verification infrastructure to enable independent auditors and researchers to verify that published APKs match the source code. It implements Gradle dependency verification, a Docker-based verification script, and optimized tooling for maintaining verification metadata.

Key Changes

🔐 Gradle Dependency Verification

• Enabled dependencyLocking.lockAllConfigurations() for all projects
• Generated gradle/verification-metadata.xml with SHA-256 checksums for all dependencies

🐳 Reproducible Build Verification

• Added scripts/verify_apk.sh - a Docker-based script to rebuild and verify APKs
• Supports rebuilding any git tag in a clean Docker environment
• Generates diffoscope reports to analyze byte-level differences
• Configurable via environment variables (VERIFY_GRADLE_TASK, VERIFY_APK_SUBDIR, etc.)

⚡ Optimized Verification Metadata Generation

• Added just generate-verification-metadata task that:
  • Uses debug builds instead of release builds (faster)
  • Runs in Docker for Linux artifact generation
  • Automatically reads GitHub credentials from local.properties
  • No manual environment variable setup required

📚 Documentation

• Added "Reproducible Release Verification" section to README.md
• Provided clear usage examples with specific version (v1.3.48)
• Documented all configuration options and environment variables

🛠️ Code Quality

• Refactored verify_apk.sh with main function for better readability
• Organized into logical sections (Helper Functions, Docker Build, Diffoscope Report)
• Improved function signatures with explicit parameters
• Added inline comments for clarity

Verification Example

# Download official APK
curl -L --fail -o official.apk http://apk.gemwallet.com/gem_wallet_universal_v1.3.48.apk

# Verify it matches the source code
./scripts/verify_apk.sh v1.3.48 official.apk

Benefits

• Transparency: Anyone can verify that published APKs match the source code
• Security: Dependency checksums prevent supply chain attacks
• Reproducibility: Builds are deterministic and verifiable in isolated environments
• Trust: Users and auditors can independently verify app integrity

Testing

• ✅ Generated complete verification-metadata.xml for all platforms
• ✅ Docker build produces identical APKs
• ✅ diffoscope reports work correctly for mismatch analysis

[gemini-code-assist]

Summary of Changes

Hello @0xh3rman, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a robust mechanism to ensure the reproducibility of the Android application's builds. By providing a script and documentation, it empowers users to independently verify that the publicly distributed APKs are byte-for-byte identical to those built from the source code, thereby enhancing transparency and trust in the release process.

Highlights

• Reproducible Build Verification Script: A new shell script, scripts/verify_apk.sh, has been added to automate the process of verifying reproducible builds for the Android application. This script builds the APK within a Docker environment, extracts the universal APK, downloads the official APK from apk.gemwallet.com, and compares their SHA-256 hashes and raw bytes.
• Documentation Update: The README.md file has been updated with a new section titled 'Reproducible Release Verification'. This section provides detailed instructions on how to use the verify_apk.sh script, including its purpose, steps, and available command-line options for customization.
• Git Ignore Configuration: The .gitignore file has been updated to include artifacts/, ensuring that the output directory for the reproducible build verification process (which stores rebuilt and official APKs) is not committed to the repository.

Ignored Files

• Ignored by pattern: .github/workflows/** (1)
  • .github/workflows/docker.yml

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[gemini-code-assist]

Code Review

This pull request introduces a robust mechanism for reproducible build verification, which is a great addition for transparency and security. The new verify_apk.sh script is well-structured, using Docker to create a consistent build environment and then comparing the locally built APK with the official one. The documentation in README.md is clear and provides good examples. I have one suggestion to improve the clarity of a command-line option in the script.