Git GPG Signing

Comprehensive guidance for setting up, configuring, and troubleshooting GPG commit signing across all platforms.

Overview
When to Use This Skill
Quick Start
Platform-Specific Setup
Key Generation
Git Configuration
Passphrase Caching
GitHub Integration
Troubleshooting
GPG Signing Methods Comparison
Security Best Practices
Resources
Related Skills

Overview

Git commit signing provides cryptographic proof that commits came from you. This skill helps you:

Install and configure GPG tools on Windows, macOS, and Linux
Set up commit signing with proper key management
Configure passphrase caching for better workflow
Troubleshoot common GPG signing issues
Understand security trade-offs and best practices

When to Use This Skill

This skill should be used when:

Setting up GPG commit signing for the first time
Configuring GPG tools (Gpg4win, GPG Suite, gnupg)
Troubleshooting GPG signing errors ("gpg: signing failed", "inappropriate ioctl", etc.)
Troubleshooting keyboxd daemon startup issues (Windows race condition)
Determining which GPG installation Git is using
Understanding Windows daemon startup behavior vs. official design
Configuring passphrase caching to reduce prompts
Understanding GPG vs SSH vs S/MIME signing methods
Adding GPG keys to GitHub/GitLab/Bitbucket
Resolving "Unverified" commits on GitHub
Working with .gnupg/gpg-agent.conf configuration

Quick Start

Basic Setup (Single Personal Key):

# 1. Install GPG (see Platform-Specific Setup below)

# 2. Generate key
gpg --full-generate-key
# Select: (9) ECC (sign and encrypt) → Curve 25519
# Expiration: 0 (no expiration)
# Passphrase: Strong 20+ character passphrase

# 3. Get key ID
gpg --list-secret-keys --keyid-format=long
# Look for "sec   ed25519/<KEY_ID>"

# 4. Configure Git
git config --global user.signingkey <KEY_ID>
git config --global commit.gpgsign true

# 5. Export public key and add to GitHub
gpg --armor --export <KEY_ID>
# Paste at: https://github.com/settings/keys

Platform-Specific Setup

Windows: Gpg4win Installation

For detailed Windows setup, see references/windows-setup.md.

Quick install:

# Option 1: Download installer
# https://gpg4win.org/thanks-for-download.html

# Option 2: winget
winget install --id GnuPG.Gpg4win -e --source winget

# Configure Git to use Gpg4win (adjust path if installed elsewhere)
git config --global gpg.program "C:/Program Files (x86)/GnuPG/bin/gpg.exe"

macOS: GPG Suite / Homebrew

# Option 1: Homebrew (recommended)
brew install gnupg

# Option 2: GPG Suite
# Download from: https://gpgtools.org/

# Configure Git (if needed)
git config --global gpg.program $(which gpg)

Linux: GnuPG

# Debian/Ubuntu
sudo apt update && sudo apt install gnupg

# Fedora/RHEL
sudo dnf install gnupg2

# Arch
sudo pacman -S gnupg

WSL: Follow Linux Instructions

WSL users: Follow the Linux setup instructions above (WSL runs Linux). See troubleshooting section for WSL-specific issues if needed.

Key Generation

Personal Development Key (Interactive)

# Generate key interactively
gpg --full-generate-key

# Follow prompts:
# 1. Key type: (9) ECC (sign and encrypt) *default*
# 2. Curve: (1) Curve 25519 *default*
# 3. Expiration: 0 = no expiration (or 2y for 2 years)
# 4. Real name: Your Name
# 5. Email: your.verified@email.com
# 6. Comment: (optional, can leave blank)
# 7. Passphrase: Strong 20+ character passphrase

# List keys to get KEY_ID
gpg --list-secret-keys --keyid-format=long
# Look for "sec   ed25519/<KEY_ID>"

Recommended algorithm: EdDSA using Curve25519 (Ed25519) - modern, fast, small keys, excellent security

Alternative: RSA 4096-bit (traditional, widely compatible)

Exporting Keys

# Export public key (for GitHub)
gpg --armor --export <KEY_ID>

# Export private key (for backup only - KEEP SECURE!)
gpg --armor --export-secret-keys <KEY_ID>

Git Configuration

Enable Commit Signing

# Global (all repositories)
git config --global user.signingkey <KEY_ID>
git config --global commit.gpgsign true
git config --global tag.gpgSign true

# Repository-local (specific repo)
cd /path/to/repo
git config user.signingkey <KEY_ID>
git config commit.gpgsign true

Verify Configuration

# Check configured key
git config --global user.signingkey

# Test signing
git commit --allow-empty -m "Test GPG signing"

# Verify signature
git log --show-signature -1

Passphrase Caching

GPG agent caches passphrases to reduce how often you're prompted.

Check if config exists:

ls ~/.gnupg/gpg-agent.conf

Create or edit ~/.gnupg/gpg-agent.conf:

# Cache passphrase for 8 hours of inactivity
default-cache-ttl 28800

# Maximum cache time of 24 hours regardless of use
max-cache-ttl 86400

# Allow pinentry to cache the passphrase
allow-preset-passphrase

Apply changes:

gpgconf --kill gpg-agent
gpgconf --launch gpg-agent

For comprehensive caching configuration, including security scenarios, testing procedures, and troubleshooting, see references/passphrase-caching.md.

Windows-Specific: Dual GPG Installation Issue

CRITICAL for Windows users: Windows typically has two separate GPG installations (Gpg4win and Git Bash GPG), each with different config file locations:

Gpg4win: %APPDATA%\gnupg\gpg-agent.conf (typically C:\Users\<Username>\AppData\Roaming\gnupg\gpg-agent.conf)
Git Bash GPG: ~/.gnupg/gpg-agent.conf (resolves to C:\Users\<Username>\.gnupg\gpg-agent.conf)

Common problem: Configuring ~/.gnupg/gpg-agent.conf (Git Bash GPG) when Git is configured to use Gpg4win. Result: configuration silently ignored, caching doesn't work.

Verify which GPG Git is using:

# Check Git's GPG configuration
git config --global gpg.program

# If output is "C:/Program Files (x86)/GnuPG/bin/gpg.exe":
# → Use: %APPDATA%\gnupg\gpg-agent.conf

# Verify GPG's config directory
gpgconf --list-dirs homedir

Windows configuration must include pinentry-program:

# Example: %APPDATA%\gnupg\gpg-agent.conf
default-cache-ttl 28800
max-cache-ttl 86400
allow-preset-passphrase

# REQUIRED for Windows:
pinentry-program C:/Program Files (x86)/GnuPG/bin/pinentry-basic.exe

See: Windows Setup Guide - Dual GPG Installations for detailed explanation.

Recommended Cache Durations

Scenario	default-cache-ttl	max-cache-ttl	Rationale
High Security	900 (15 min)	3600 (1 hour)	Prompt frequently, short window
Balanced	3600 (1 hour)	28800 (8 hours)	Prompt every ~hour, expires by end of day
Convenience	28800 (8 hours)	86400 (24 hours)	Prompt once per workday, expires daily

GitHub Integration

Adding GPG Key to GitHub

Export public key:
```
gpg --armor --export <KEY_ID>
```
Add to GitHub:
- Go to: https://github.com/settings/keys
- Click "New GPG key"
- Paste ASCII-armored public key
- Click "Add GPG key"

Verify email matches:

Git email must match GPG key email
Email must be verified in GitHub account

# Check Git email
git config --global user.email

# Check GPG key email
gpg --list-keys <KEY_ID>

Troubleshooting "Unverified" Commits

Possible causes:

Public key not added to GitHub → Add key at Settings → SSH and GPG keys
Email mismatch → Ensure Git email = GPG key email = GitHub verified email
Key expired → Extend expiration or generate new key
Key revoked → Generate new key (cannot un-revoke)

Troubleshooting

For comprehensive troubleshooting, see references/troubleshooting.md.

"gpg: signing failed: No secret key"

Cause: Git configured to use key ID that doesn't exist in keyring.

Solution:

# List available keys
gpg --list-secret-keys --keyid-format=long

# Verify Git config matches available key
git config --global user.signingkey

# If mismatch, update config
git config --global user.signingkey <CORRECT_KEY_ID>

"gpg: signing failed: Inappropriate ioctl for device"

Cause: GPG agent cannot prompt for passphrase (terminal issue).

Solution (Linux/macOS/WSL):

# Set GPG_TTY environment variable
export GPG_TTY=$(tty)

# Add to shell profile (e.g., ~/.bashrc, ~/.zshrc)
echo 'export GPG_TTY=$(tty)' >> ~/.bashrc

Solution (Windows with Gpg4win):

# Use GUI pinentry (adjust path to match your Gpg4win installation)
echo 'pinentry-program "C:/Program Files (x86)/GnuPG/bin/pinentry-basic.exe"' >> ~/.gnupg/gpg-agent.conf
gpgconf --kill gpg-agent

"error: gpg failed to sign the data"

Debug steps:

# Test GPG signing directly
echo "test" | gpg --clearsign

# Check GPG agent status
gpgconf --list-components

# Check key expiration
gpg --list-keys --keyid-format=long <KEY_ID>

# Restart GPG agent
gpgconf --kill gpg-agent
gpgconf --launch gpg-agent

# Try commit again
git commit -m "test"

Passphrase Prompt Every Commit (Cache Not Working)

Windows users: This is commonly caused by dual GPG installation issues. See Windows Setup - Passphrase Caching Troubleshooting and Troubleshooting - Windows Caching Issue for detailed diagnosis.

Possible causes:

Wrong config file location (Windows):

# Verify which GPG Git is using
git config --global gpg.program

# Check GPG's config directory
gpgconf --list-dirs homedir

# Ensure config exists at correct location
# Windows (Gpg4win): %APPDATA%\gnupg\gpg-agent.conf
# Windows (Git Bash): ~/.gnupg/gpg-agent.conf
# Linux/macOS/WSL: ~/.gnupg/gpg-agent.conf

gpg-agent.conf not loaded:

# Restart agent to load config
gpgconf --kill gpg-agent
gpgconf --launch gpg-agent

# Verify config loaded
gpgconf --list-options gpg-agent | grep cache-ttl

Cache TTL set too low → Increase cache time in ~/.gnupg/gpg-agent.conf

Multiple GPG agents running:

# Kill all agents
pkill gpg-agent

# Launch single agent
gpgconf --launch gpg-agent

GPG Signing Methods Comparison

Method	Best For	Setup Complexity	Key Management
GPG	Full-featured, supports expiration/revocation	Medium	Most flexible
SSH	Simplest, reuses existing SSH keys	Low	Limited features
S/MIME	Enterprise with X.509 certificates	High	Org-managed

SSH Signing (Alternative)

When to use SSH instead of GPG:

Simple personal projects
Already have SSH key setup
Don't need expiration/revocation features
Want minimal configuration

Setup:

# Configure Git to use SSH signing
git config --global gpg.format ssh
git config --global user.signingkey ~/.ssh/id_ed25519.pub
git config --global commit.gpgsign true

# Add SSH key to GitHub as "Signing Key"

Limitations:

No key expiration support
No revocation tracking
Requires Git 2.34+ (2021)

Security Best Practices

For comprehensive security guidance, see references/security-best-practices.md.

Quick recommendations:

✅ Use passphrase protection on personal keys (minimum 20 characters)
✅ Configure caching to balance security and convenience (4-8 hours)
✅ Consider key expiration: No expiration for personal projects, 1-year for enterprise work
✅ Backup private key to encrypted vault or password manager's Secure Documents
⚠️ Never store unencrypted keys in Git repos, cloud storage, or email

Resources

Reference Documentation

Quick Command Reference - Quick lookup for common GPG and Git signing commands
Windows Setup Guide - Gpg4win installation, Git Bash paths, security considerations
Passphrase Caching Configuration - Cache strategies, security trade-offs
Security Best Practices - Passphrase protection, key expiration, backup strategies
Troubleshooting Guide - Common issues and solutions
GPG Agent Configuration Example - Sample configuration file
Test Scenarios - Skill activation validation scenarios

Official Documentation

Related Skills

git-commit: Use for complete git commit workflow with Conventional Commits format, safety protocols, and attribution requirements
git-identity: Use for multi-identity GPG key isolation -- scoping different GPG keys to different directories using includeIf conditional includes
config: Advanced Git configuration including aliases, credentials, and performance tuning
setup: Prerequisite for Git installation and configuration

Version History

v1.1.1 (2025-11-25): Progressive disclosure optimization - extracted Test Scenarios to reference file, removed redundant Quick Command Reference section, reduced SKILL.md to under 500 lines
v1.1.0 (2025-11-22): Enhanced troubleshooting - added keyboxd daemon race condition troubleshooting (T7777/T7829), dynamic GPG detection workflow, Windows startup best practices with official design vs. reality analysis
v1.0.5 (2025-11-19): Optimization improvements - added table of contents to SKILL.md, extracted Essential Commands Reference to quick-reference.md, reduced line count from 530 to 522
v1.0.4 (2025-11-17): Progressive disclosure improvement - extracted Security Best Practices to separate reference file
v1.0.3 (2025-11-17): Validated against official documentation - fixed tag.gpgSign capitalization, updated Last Verified dates
v1.0.2 (2025-11-12): Enhanced documentation - added TOCs to long references, documented test scenarios
v1.0.1 (2025-11-13): Added cross-reference to git-commit skill
v1.0.0 (2025-01-09): Initial release migrated from repository documentation

Last Updated

Date: 2025-11-28 Model: claude-opus-4-5-20251101

gpg-signing