TL;DR
PGP is a decades-old ecosystem of protocols, formats and tools whose core design predates modern cryptography. The system exhibits deep structural, usability and security problems that the installed base and backward-compatibility choices have left largely unaddressed.
What happened
The PGP ecosystem — covering the OpenPGP standards and common implementations such as GnuPG — contains many long-standing flaws rooted in its 1990s-era design. Its on-disk and on-wire formats are extremely complex and fragile, with multiple packet encodings and nested packet types that have produced parser bugs and practical attacks (for example, a GnuPG keyserver parsing issue that went quadratic). PGP attempts to be a multipurpose tool for signing, encrypting and identity management, but that generality results in mediocre or unsafe behavior across use cases. The protocol preserves obsolete cryptographic primitives and modes for backward compatibility, leading to unpredictably weak choices in real installs. Usability problems are severe, key management encourages long-lived root keys, and mechanisms such as the MDC for ciphertext authentication are brittle and easy to misuse. PGP also leaks metadata and lacks forward secrecy for typical use patterns.
Why it matters
- Outdated defaults and format complexity leave users exposed to avoidable cryptographic weaknesses.
- Poor usability and key-management patterns increase the likelihood of long-lived, easily exploited secrets.
- Compatibility-driven decisions make it hard to deploy modern authenticated-encryption and key-rotation practices across the installed base.
- Metadata leakage and lack of forward secrecy undermine confidentiality guarantees expected in contemporary secure messaging.
Key facts
- PGP’s message format is a packet archive with multiple overlapping length encodings and nested subpackets, creating implementation difficulty.
- A GnuPG keyserver parsing bug caused quadratic behavior when handling keys, illustrating practical harms from format complexity.
- PGP aggregates many functions (signing, file encryption, messaging, identity) but does each poorly compared with purpose-built modern alternatives.
- Backward compatibility maintains legacy primitives such as 64-bit-block ciphers, RSA defaults and older KDFs that cryptographers avoid today.
- Ad hoc extensions can add modern primitives (for example AEAD modes), but those are rarely supported across the installed user base.
- PGP’s MDC mechanism for authenticating ciphertext is fragile: it can be removed or mis-signaled in ways that bypass checks.
- The web-of-trust, keyservers and key-signing practices create an incoherent identity model that does not reliably bind keys to people.
- PGP usage patterns commonly rely on long-lived root keys, increasing compromise blast radius instead of promoting frequent key rotation.
- PGP messages and keyserver usage can expose metadata linking user identities and their correspondents.
What to watch next
- Whether efforts to push AEAD and modern cipher defaults into widely deployed PGP implementations gain traction; not confirmed in the source
- The presence or absence of a sustained research and engineering effort to replace or significantly revise OpenPGP — the source says serious cryptographers largely stopped publishing on PGP, with exceptions
- Adoption of alternative, purpose-built cryptographic tools for messaging, backups and package signing instead of multi-purpose PGP; not confirmed in the source
Quick glossary
- PGP / OpenPGP: A family of protocols, formats and implementations for encrypting, signing and managing cryptographic keys, originating in the 1990s.
- AEAD: Authenticated Encryption with Associated Data: an encryption mode that provides confidentiality and integrity checks together.
- KDF: Key Derivation Function: an algorithm that derives cryptographic keys from passwords or other inputs; modern designs may be time- and memory-hard.
- Forward secrecy: A property of a communication protocol where compromise of long-term keys does not allow decryption of past recorded sessions.
- MDC: Modification Detection Code: an OpenPGP mechanism that appends a checksum of plaintext prior to encryption to detect tampering; the source notes it is brittle.
Reader FAQ
Is PGP insecure?
The source argues PGP has many structural, cryptographic and usability weaknesses stemming from its age and compatibility choices.
Does PGP provide forward secrecy?
No — the source states that PGP lacks forward secrecy in typical usage patterns.
Will modern primitives solve PGP’s problems?
Partial updates exist (for example AEAD extensions), but the source emphasizes that installed base compatibility often prevents effective deployment of modern defaults.
Does storing keys on hardware tokens like YubiKey fix PGP’s issues?
The source says relying on hardware tokens is not a complete solution and notes most users do not use such devices.
▶ Table of Contents (21 sections) Cryptography engineers have been tearing their hair out over PGP’s deficiencies for (literally) decades. When other kinds of engineers get wind of this, they’re…
Sources
- The PGP Problem (2019)
- What's the matter with PGP?
- We're calling it: PGP is dead
- The PGP Problem: A Critique (2020)
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