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Vsevolod Trofimov

@vsevolodtrofimov

Mobile Tech Lead at Crossbar, delivering an MPC wallet across Flutter apps and a Kotlin Multiplatform SDK.

At Crossbar, I lead delivery for a self-custody Web3 wallet with MPC signing, Flutter mobile apps, and a Kotlin Multiplatform SDK. I work across Dart, Kotlin, and Swift to integrate the SDK and resolve release-critical native issues.

I owned core wallet architecture and execution for signing, passkey onboarding, Active Card pairing, and recovery flows. I also delivered wallet creation and restore, transfers, asset views, and multi-network support.

At PashaPay, I delivered international transfers, KYC and face-recognition flows, and payment and card capabilities. I also implemented Python backend components for OCR/HTR and LLM-powered features.

Earlier, I contributed to a real-time P2P messenger and built Flutter features for fintech, digital health, logistics, and trading products at Startup (NDA), ID Finance, Innowise Group, HERE Technologies, and Deriv.

Experience

Work history, roles, and key accomplishments

Current

Tech Lead

Current

Crossbar

Oct 2025 - Present (1 year 1 month)

Led end-to-end delivery of a self-custody Web3 wallet with MPC signing, passkeys, and Active Card flows. Owned core wallet architecture and execution for MPC signing flows, and worked hands-on across Dart, Kotlin, and Swift to integrate and harden the KMP SDK inside Flutter apps.

Technical Leadership Solutions Architect Delivery Management MPC Wallets Rust Self Custody WebAuthn BLE Device Flows Web3 Flutter Kotlin Multiplatform Jetpack Compose Coroutines Kotlin Swift API Design CI CD Analytics Observability

Senior Mobile Engineer

PashaPay

Sep 2023 - Oct 2025 (2 years 1 month)

Delivered international transfers, KYC and Face Recognition flows, and payments and card capabilities for a mobile wallet super-app. Strengthened client security and reliability with device binding, jailbreak/root detection, certificate pinning, and performance tuning.

Mobile/Native Engineer

Startup (NDA)

Nov 2022 - Sep 2023 (10 months)

Developed a cross-platform real-time messenger with a shared C++ core, WebSocket/TLS 1.3, and Protocol Buffers. Implemented real-time robustness, storage and search, multi-device sync, media pipeline, and push bridge.

C++ (NDK)Kotlin Java Swift Obj C Flutter WebSocket GRPC Protocol Buffers SQLCipher Room CoreData Push Deep Links CI CD

Flutter Developer

ID Finance

Oct 2021 - Nov 2022 (1 year 1 month)

Implemented payment flows, P2P and cards/limits for a consumer fintech app. Improved reliability with circuit breaker, graceful degradation, and local send queues, and enhanced cold-start and reduced UI jank.

Flutter Dart Firebase REST GraphQL OpenAPI 3DS2 Secure Data Storage Feature Flags CI CD

Flutter Mobile Developer

Innowise Group

May 2020 - Oct 2021 (1 year 5 months)

Developed a digital-health app for lab test booking, trends tracking, and wearables integration. Implemented patient portal features, AI modules, and integrations with Apple Health and Google Fit, ensuring GDPR compliance.

Flutter Dart FHIR REST GraphQL OIDC Background Tasks Push PDF

Flutter Developer

HERE Technologies

May 2019 - May 2020 (1 year)

Developed a courier/last-mile app with barcode/QR scanning, Proof-of-Delivery, and task status tracking. Implemented offline-first features, maps and logistics, and observability.

Flutter Dart Map SDKs BG Location Camera Barcode Firebase

Flutter Mobile Developer

Deriv

Jan 2018 - May 2019 (1 year 4 months)

Developed a retail trading app with real-time quotes, charts, and order book. Implemented risk and orders features, security measures, and unit/integration tests.

Flutter Dart WebSocket REST Charts Secure Data Storage Firebase CI CD