PGP Encryption and Signatures

Definition

PGP-style workflows use public-key encryption and signatures to protect content confidentiality and verify origin or integrity. In practice, the workflow depends on key management, trust decisions, and careful handling of metadata and endpoints.

Why it matters

PGP can be very useful for file encryption, signed releases, and long-lived trust relationships. It is also easy to misuse: bad key verification, weak backup habits, stale keys, overbroad trust, and confusing encryption with anonymity all create real risk.

How it works

Use the 4-step OpenPGP model:

1. Key generation Each user creates a public/private key pair.

2. Key distribution Public keys are shared through a channel the user must trust or verify.

3. Encryption or signing Encryption protects content to a recipient key. Signing proves control of the signing key.

4. Verification and rotation Keys must be verified, renewed, revoked, rotated, and backed up correctly.

Example:

sender -> encrypt to recipient public key -> ciphertext
sender -> sign with private key -> signature
recipient -> verify signature and decrypt locally

The bug is not PGP itself. The bug is confusing cryptographic correctness with identity, trust, and workflow safety.

Techniques / patterns

• Verify fingerprints out of band when trust matters.
• Keep signing and encryption keys protected separately where possible.
• Use revocation and expiration intentionally.
• Back up keys safely and test recovery.
• Encrypt files, not just email text, when the use case calls for it.
• Treat key servers and directories as discovery aids, not trust sources.

Variants and bypasses

Use the 6 PGP cases:

1. File encryption

Useful for protecting content at rest or in transfer.

2. Signed release artifacts

Useful for software or document authenticity.

3. Signed email

Provides authenticity but may still expose metadata and mail routing context.

4. Web of trust

Can work, but trust management is operationally demanding and often misunderstood.

5. Keyserver-discovered keys

Convenient for discovery, but keyserver presence does not prove trust.

6. Revocation and rotation failure

Expired, revoked, or replaced keys must be handled carefully or trust relationships rot.

Impact

• Strong content confidentiality and authenticity when key management is sound.
• Protection for files and signed releases.
• Operational burden around trust, backups, revocation, and fingerprint verification.
• Metadata and account identity still remain outside PGP's content protection.
• False confidence when users think PGP makes them anonymous.

Detection and defense

Ordered by effectiveness:

1. Verify fingerprints out of band Fingerprint comparison is stronger than trusting a web page or directory listing.

2. Use expiration and revocation Keys should be replaceable, and old keys should not live forever.

3. Back up keys safely Losing a private key can mean losing access to encrypted data or signing identity.

4. Separate trust from convenience A key being easy to find is not the same as it being trustworthy.

5. Keep the content/metadata distinction explicit PGP protects content, not necessarily who sent it, when, or through which provider.

What does not work as a primary defense

• PGP is not anonymity.
• A verified keyserver listing is not identity verification.
• Encrypting mail does not hide headers or subject lines.
• Signing a file does not prove the device that signed it was uncompromised.

Practical labs

Inspect a key workflow

Key fingerprint:
How verified:
Expiration:
Revocation method:
Backup location:
Used for signing:
Used for encryption:

This makes the trust model explicit.

Classify a use case

Use case:
File encryption:
Email signing:
Software release:
Long-term archive:
Anonymous use:
Suitable tool:

PGP is not the answer to every private communication problem.

Review key hygiene

Private key location:
Passphrase:
Hardware token:
Backup:
Revocation certificate:
Expiration:

Key hygiene is the control most people forget.

Compare PGP to E2EE

Property                PGP               Modern E2EE
Content confidentiality:
Identity verification:
Multi-device convenience:
Metadata privacy:
Ease of recovery:

The comparison helps place PGP in the right niche.

Practical examples

• A developer signs a release tarball so users can verify authenticity.
• A journalist encrypts a document for a known recipient.
• A team manages revocation when a key is rotated.
• A user trusts a key without verifying the fingerprint and gets the wrong identity.
• An email is encrypted but the subject line still reveals the topic.

Related notes

• End-to-End Encryption
• Secure File Sharing
• Private Email Threat Models
• Metadata and Identity Leakage
• Artifact Integrity

Suggested future atomic notes

• key-fingerprint-verification
• revocation-certificates
• web-of-trust

References

• Official Tool Docs: GnuPG Manual - https://gnupg.org/documentation/manuals/gnupg/
• Official Tool Docs: OpenPGP RFC 9580 - https://www.rfc-editor.org/rfc/rfc9580
• Threat Model: EFF Surveillance Self-Defense - https://ssd.eff.org/