Zen Crypted Client Developer

client.txt

Zen Crypted Backend Developer
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Statement of Work – Client Developer (Swift / iOS / ASN.1)

*Project*: Development and enhancement of secure military-grade iOS chat client
*Position*: iOS Developer (Swift, security-focused)
*Project context*: The client is based on the open-source Chat X.509 for iOS, a server-less proof-of-concept using multicast UDP + X.509 certs for local encrypted messaging. The goal is to evolve it into a full client for the custom Elixir server (TCP/QUIC + ASN.1/DER protocol), with end-to-end X.509 CMS encryption and military-grade security.
Scope of Work (main deliverables):

Scope of Work (main deliverables):

* Migration & refactoring from multicast UDP to client-server model:
* Replace UDP multicast with TCP/QUIC transport
* Implement full ASN.1/DER parser & serializer (using existing CHAT.asn1 schema)
* Integrate with backend protocol (AUTH, PRESENCE, MESSAGE, ROSTER, PROFILE, etc.)

Cryptographic core implementation:

* X.509 certificate handling (import, validation, chain building, OCSP stapling)
* CMS envelope encrypt/decrypt + sign/verify for every message
* Key management (private key in Secure Enclave, biometric protection)
* Support for ДСТУ national algorithms if required by client

UI/UX for military use case:

* Secure chat interface (threads, roster, presence, read receipts)
* Offline message queue + synchronization
* Minimalist, high-contrast UI suitable for field/gloved use
* Ephemeral / self-destructing messages support

Security & hardening:

* App Transport Security (ATS) compliance + custom pinning
* Jailbreak / debugger detection
* Data protection (NSFileProtectionCompleteUnlessOpen)
* Secure local storage (Keychain + encrypted SQLite / DataProtection)

Testing & release:

* Unit tests for crypto & ASN.1 logic (> 80% coverage)
* Integration tests with backend server
* Prepare for TestFlight / enterprise distribution
* Documentation for crypto verification / licensing needs

Required skills & experience (for job/CV screening):

* 4+ years commercial iOS development (Swift 5+)
* Strong experience with Security framework, CommonCrypto, CryptoKit
* Practical work with X.509 certificates, ASN.1 parsing (e.g. via Swift-ASN.1 or custom)
* Understanding of end-to-end encryption protocols (Signal-like, CMS/S-MIME)
* Experience with networking (URLSession, NWConnection, QUIC if possible)
* Familiarity with Secure Enclave, biometric auth (Face ID / Touch ID)
* English (Upper-Intermediate) + Ukrainian (advantage)

Nice to have:

* Experience with military/government/defense apps (secure comms, STIG compliance)
* Background in cryptography / PKI on mobile
* Previous work with multicast UDP or local-network protocols
* Knowledge of Swift Package Manager for crypto libs

Estimated engagement: Full-time / 6–12 months initial contract with extension option
Success criteria: Fully functional iOS client connecting to the custom server,
  passing end-to-end encryption verification, ready for security audit / field testing.