GPG Encryption and Signing Explained | Generated by AI

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GPG Basics: Encryption vs. Signing

You’re mixing a couple of concepts here—GPG (GNU Privacy Guard) can do encryption (to protect file contents) and signing (to verify identity and integrity)—but they’re separate features. I’ll break it down step by step, confirm your points, and clarify where things overlap or differ. This is based on standard GPG usage (which hasn’t changed much as of 2025).

1. Generating Keys and Your Info (Name/Email)

• When you first set up GPG, you generate a key pair: a private key (kept secret) and a public key (shared with others).
• During generation, you provide your name and email as part of the key’s “user ID” (e.g., gpg --gen-key). This ties the key to your identity.
• You also set a passphrase to protect your private key. This passphrase is not used for encrypting files—it’s just to unlock your private key when needed.
• Command example:

  gpg --gen-key
  

  Follow the prompts for RSA/RSA, key size, expiration, and your name/email.

2. Encrypting a File

• With a password (symmetric encryption): This doesn’t involve keys or your identity—it’s quick for sharing a file securely. GPG uses the passphrase to create a single key for encryption.
  • Command: gpg -c filename.txt (prompts for passphrase, outputs filename.txt.gpg).
  • Anyone with the passphrase can decrypt: gpg -d filename.txt.gpg.
  • No public/private keys here; no identity verification.
• With public keys (asymmetric encryption): To encrypt for someone specific, use their public key. Your name/email isn’t directly involved in the encryption output.
  • Command: gpg -e -r recipient@example.com filename.txt (outputs filename.txt.gpg).
  • Only the recipient’s private key can decrypt it.
• Encryption output is a .gpg file, but it’s not a signature—it’s just encrypted data. No “GPG signature” from encryption alone.

3. Signing a File (What You’re Describing)

• Signing attaches a digital signature to a file (or its hash) to prove it came from you and hasn’t been tampered with. This is where your private key and identity come in.
• Yes, you must use your private key to generate the signature. GPG unlocks it with your passphrase.
  • Command for a detached signature: gpg --detach-sign filename.txt (outputs filename.txt.sig).
  • Or inline (signs and encrypts in one): gpg -s filename.txt (outputs filename.txt.gpg with signature embedded).
• The signature is a cryptographic “value” (like a hash signed with your private key) that includes your key ID and user ID (name/email).
• Others verify with your public key: They import your public key (e.g., from a keyserver: gpg --keyserver keys.openpgp.org --recv-keys YOUR_KEY_ID), then run gpg --verify filename.txt.sig filename.txt.
  • If it matches, it says something like “Good signature from ‘Your Name '".
• Yes, this matches identity and builds trust:
  • The signature proves the file is from the key owner (you).
  • If you’ve shared your public key via a trusted channel (e.g., your website) and the key is signed by others you trust, you can “trust” the chain.
  • It doesn’t encrypt the file—just verifies it. Combine with encryption for full security (sign then encrypt).

Key Differences and Your Questions

Feature	Encryption (Password)	Encryption (Public Key)	Signing
Uses Passphrase?	Yes, for symmetric key	No (uses recipient’s public key)	Yes, to unlock your private key
Involves Your Name/Email?	No	Indirectly (via your key for decryption response)	Yes, embedded in signature
Output	.gpg file (encrypted data)	.gpg file (encrypted data)	.sig or embedded in .gpg (signature value)
Private Key Needed?	No	No (for encrypting to others)	Yes, to generate
Verification	Passphrase to decrypt	Recipient’s private key	Anyone with your public key
Purpose	Hide contents	Secure sharing	Prove identity/integrity

• Right on the private key: Yes, you must use your private key (unlocked by passphrase) to sign. Never share it!
• Right on trust: Exactly—if the signature verifies against your public key, and you trust that key belongs to the claimed author (via name/email and trust web), you can trust the file is authentic and unaltered. It’s like a digital notary.

Tips

• Always back up your keys: gpg --export-secret-keys --armor > private.asc (store securely).
• For passwords only (no keys), tools like age or openssl are simpler alternatives, but GPG is great for identity-linked stuff.
• Common pitfall: Forgetting to export/share your public key means others can’t verify.

If you meant a specific command or scenario (e.g., encrypting and signing), share more details!

References
GPG Documentation: Encrypting and Signing
GPG Quick Start Guide

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