Applied Cryptography Engineering

What this service covers

I integrate cryptographic building blocks into software with explicit identity, key and failure rules.

• End-to-end encryption flows and secure message formats
• Key exchange, derivation and lifecycle design
• Digital signature integration and verification
• Secure storage and protocol validation
• Post-quantum signature integration where requirements justify it
• Implementation review against a concrete threat model

How I build it

Cryptography work starts with what needs protection, who can observe or change traffic, and what each party trusts. The algorithm choice is only one part of the protocol; identity, key management and rejection behavior matter too.

Gumnam combines Ed25519/X25519, ChaCha20-Poly1305 and HKDF in an encrypted messaging protocol over Tor. Qbitcoin integrates Falcon-512 signatures into transaction validation and node-facing flows.

Engineering decisions

I prefer established libraries and narrow, testable protocol boundaries. Failed verification must reject the operation rather than leaving an ambiguous state.

A post-quantum choice has practical effects on key sizes, signatures and interoperability. Those trade-offs should be evaluated against the product's threat model.

Related project work

Gumnam and Qbitcoin provide two different examples: encrypted communications and post-quantum blockchain signatures. These examples do not imply an independent security audit.

Gumnam ↗ · Qbitcoin ↗

Technology and scope

Rust, Tor, Ed25519, X25519, ChaCha20-Poly1305, HKDF, Python and Falcon-512 are documented in the linked work.

Getting started

Share the assets to protect, adversaries, participants, platforms and any compatibility requirements. I can help turn those into a protocol and implementation scope.