Yossef E.

I build crypto wallets in Flutter — and the apps I've shipped are live with 100K+, 10K+ and 5K+ installs. I built the swap flow inside ChangeNOW, a six-chain wallet with Safe multi-sig, and ISLAMIwallet across 9 languages. If you're shipping a wallet, an exchange, or a dApp to iOS and Android, that's the exact problem I've spent five years on. What I build - Crypto wallets — HD wallets (BIP-39/44, Trust Wallet Core), on-device key derivation, biometric-gated signing, WalletConnect v2 sessions, Safe multi-sig. The app never holds a key the user didn't authorize. - DeFi & exchanges — token swaps (1inch), staking and on-chain rewards, lending with collateral vaults, cross-chain bridges, token sales. - Multi-chain — Ethereum, Polygon, BSC, Solana, TRON, and custom L1s. Contract integration, gas-aware UX, in-app dApp browsers. - Production Flutter — BLoC + clean architecture, offline-first, CI/CD to both stores. Marketplaces, delivery platforms, custom EPUB/audio engines. How I work Clear updates, honest estimates, no surprises. I flag problems before they become delays, not after. You'll get a written approach before I write code, and I'll tell you when something you've asked for is a bad idea. Straight about my Upwork record: I've spent the last four years in full-time engineering roles building the wallets above, not on this platform. My Upwork history is one contract, rated 5.0. I'm priced at $35/hr while I rebuild that history — you're getting senior wallet work at a rate that reflects my Upwork tenure, not my experience. That won't last long. Send me what you're building and the deadline. I'll reply within hours with a concrete approach — scope, risks, and what I'd do first.