3.4 Post-Quantum Threats to Darknets

Modern hidden services rely heavily on cryptography that is secure against classical computers.
However, advances in quantum computing introduce a new category of threats that directly affect the long-term security assumptions of darknets and anonymous services.

This section explains what post-quantum threats are, which parts of darknet cryptography are affected, and why this matters for hidden services, using accepted cryptographic research and standards.

A. What Is a Post-Quantum Threat?

A post-quantum threat refers to the risk that future quantum computers could efficiently break cryptographic algorithms that are currently considered secure.

This is not science fiction.
It is a recognized cryptographic transition problem acknowledged by:

• NIST (USA)

• ETSI (EU)

• NSA (Commercial National Security Algorithm Suite)

• Academic cryptography communities

The concern is not if quantum computers arrive, but when they reach cryptographically relevant scale.

B. Why Darknets Are Especially Sensitive to Quantum Threats

Darknets and hidden services face unique risks:

1. Long-term confidentiality requirements
   Some communications must remain private for decades.

2. Passive global adversaries
   Adversaries may record traffic today and decrypt it years later.

3. Self-authenticating identities
   Onion addresses are derived directly from cryptographic keys.

4. No central revocation authority
   If cryptography breaks, recovery is harder than on the clearnet.

This makes post-quantum risk more severe for darknets than for ordinary web systems.

C. Quantum Algorithms That Matter for Darknets

Two quantum algorithms are relevant:

1. Shor’s Algorithm (Critical Threat)

Shor’s algorithm can efficiently break:

• RSA

• Diffie–Hellman

• Elliptic Curve Cryptography (ECC)

This directly impacts:

• Tor relay identity keys

• Onion service identity keys (Ed25519)

• Key exchange mechanisms

• Self-authenticating .onion addresses

If a sufficiently powerful quantum computer exists, current onion service identities could be forged.

2. Grover’s Algorithm (Moderate Threat)

Grover’s algorithm weakens:

• symmetric encryption (AES)

• hash functions (SHA-2, SHA-3)

Effect:

• halves effective key strength

Mitigation:

• larger key sizes (already mostly in place)

This threat is manageable, unlike Shor’s algorithm.

D. “Harvest Now, Decrypt Later” (HN-DL) Risk

One of the most discussed post-quantum risks is HN-DL:

1. Adversary records encrypted darknet traffic today

2. Stores it indefinitely

3. Decrypts it in the future using quantum capabilities

This is dangerous even if:

• systems are secure today

• users behave correctly

Forward secrecy helps, but identity-layer cryptography remains vulnerable.

E. Impact on Hidden Services Specifically

Post-quantum threats affect hidden services in several ways:

1. Onion Service Identity Compromise

• Onion addresses embed public keys

• Quantum attacks could allow impersonation

• Trust in self-authenticating names would fail

2. HSDir Descriptor Integrity

• Descriptor signatures rely on ECC

• Quantum adversaries could forge or manipulate descriptors

3. Long-Term Service Tracking

• Recorded metadata could be re-analyzed

• Historical service behavior may become linkable

F. What Post-Quantum Threats Do Not Immediately Break

Important clarification:

• Onion routing itself does not instantly fail

• Symmetric encryption remains strong with larger keys

• Quantum computers do not magically reveal IP addresses

The threat is cryptographic trust erosion, not immediate deanonymization.

G. Why This Is a Design Concern, Not a Panic

No known quantum computer today can:

• break ECC at required scale

• threaten Tor in real time

However:

• cryptographic systems take years to migrate

• darknets cannot rely on emergency upgrades

Therefore, post-quantum planning is a long-term architectural concern, not an operational crisis.

H. Relationship to v3 Onion Services

v3 onion services improve:

• forward secrecy

• identity rotation

• descriptor privacy

But they still rely on ECC, which is quantum-vulnerable.

So:

• v3 is quantum-aware

• not quantum-resistant

This distinction is crucial.

I. Why Darknets Must Plan Early

History shows:

• RSA-1024 was once “safe”

• SHA-1 was once “safe”

• v2 onion services were once “good enough”

Post-quantum threats reinforce a core lesson:

Cryptography ages, anonymity systems must anticipate that aging.