Q-Paste
Q-Paste is a zero-knowledge secure exchange designed to resist long-term cryptographic compromise, including harvest-now, decrypt-later attacks by future quantum adversaries.
Security Model
Our security architecture is built on zero-trust principles where the server is never trusted with plaintext data.
The server is assumed to be honest-but-curious or fully compromised. No confidentiality depends on server secrecy.
Plaintext data, encryption keys, and passwords are never transmitted or stored server-side. All cryptographic operations occur exclusively in the client browser.
Decryption keys are embedded in the URL fragment and never sent over the network to any server.
Cryptographic Construction
Q-Paste uses a hybrid encryption scheme to ensure confidentiality as long as at least one cryptographic primitive remains secure.
Attack Surface & Data Flow
All cryptographic operations occur exclusively in the client's browser.
Formal Guarantees vs. Non-Goals
What Q-Paste Guarantees
| Guarantee | Scope | Assumptions |
|---|---|---|
| ✓ End-to-End Encryption | All data in transit and at rest | Browser crypto APIs uncompromised |
| ✓ Post-Quantum Confidentiality | Protection against future quantum decryption | ML-KEM-768 remains secure |
| ✓ Server Zero-Knowledge | Server never obtains plaintext or keys | Client-side encryption working correctly |
| ✓ Key Isolation | Decryption keys never leave client device | URL fragment not logged by intermediaries |
| ✓ Metadata Privacy Shield | No automated link analysis by scanners | Privacy controls properly configured |
What Q-Paste Explicitly Does NOT Protect Against
Client-Side Malware
If your endpoint is compromised with a keylogger or browser extension, Q-Paste cannot protect plaintext being typed.
Endpoint Forensics
Memory forensics or behavioral analysis on the client can reveal content after decryption and display.
Server Infrastructure Attacks
Denial-of-service, rate limiting, or resource exhaustion attacks on server infrastructure are not mitigated.
Network-Level Timing Attacks
Adversaries observing traffic patterns can infer some information about data size and timing.
Browser Zero-Days
Unpatched vulnerabilities in the JavaScript engine or Web Crypto API can be exploited before disclosure.
Social Engineering
No protection against phishing, credential theft, or users intentionally sharing decryption links.
Client Integrity Verification
Q-Paste uses Subresource Integrity (SRI) with SHA-384 hashing to cryptographically verify that JavaScript and client-side code has not been tampered with.
✓ How SRI Works
The server provides a cryptographic hash of the expected JavaScript bundle. Your browser automatically verifies that the downloaded code matches this hash before executing it. If even one byte is modified, the script fails to load.
Example SRI attribute:
Benefits: Protects against CDN hijacking, ISP injection, and network-level tampering.
Threats Addressed
An adversary records encrypted traffic today and decrypts it using quantum computers in the future. Q-Paste mitigates this via post-quantum hybrid encryption (ML-KEM-768 + AES-256-GCM).
If the server is breached, attackers gain access to encrypted data, but not the decryption keys (which are embedded in URL fragments). Encrypted data remains unintelligible.
Email clients, chat platforms, and web crawlers auto-preview links. Q-Paste's privacy shield prevents automated analysis through explicit user action requirement.
TLS 1.3 provides authenticated encryption in transit. Client-side encryption adds an additional layer: even if TLS is broken, plaintext is not exposed.
Deployment Models
Q-Paste supports three deployment architectures to meet your security, compliance, and operational requirements.
Pricing Plans
Choose the plan that fits your security and scale requirements. All plans include full post-quantum encryption.
Standard
Cloud-Hosted · Standard limits
- Up to 10 pastes/month
- 5GB storage
- 7-day retention
- Email support
- HTTPS + TLS
Professional
Higher limits · Priority support
- Unlimited pastes
- 100GB storage
- 90-day retention
- Priority email & Slack
- HTTPS + TLS + ML-KEM
- Private instances available
Enterprise
Dedicated · SLA guaranteed
- Unlimited everything
- On-premises deployment
- Air-gap configuration
- 24/7 support
- Custom integrations
- Dedicated infrastructure