Janko Krstic, Smart Contracts Developer in Belgrade, Serbia
Janko Krstic

Smart Contracts Developer in Belgrade, Serbia

Member since July 27, 2018
Janko is a software engineer and architect specializing in blockchain and focusing on decentralized finance and self-sovereign identity (SSI). He has years of experience with Bitcoin, Ethereum, Quorum, Fabric, Tendermint, Cosmos blockchains, and Hyperledger Indy and Aries SSI solutions. Janko has recently applied modern distributed systems, cryptography, and blockchain theory to solving SSI-related problems.
Janko is now available for hire




Belgrade, Serbia



Preferred Environment

Git, Erlang, Rust, Go, Python, Linux, Blockchain

The most amazing...

...project I've worked on was a secure, enterprise-level crypto wallet with tagging features for searching and filtering encrypted records.


  • Blockchain and SSI Engineer

    2020 - PRESENT
    • Created self-sovereign identity (SSI) wallet that stores students' verifiable credentials.
    • Wrote back-end system for issuing verifiable credentials to institution's users.
    • Designed and researched self-sovereign identity libraries to use.
    Technologies: Hyperledger, Hyperledger Indy, Blockchain
  • Blockchain Engineer

    2020 - 2020
    404 Publishing
    • Worked on developing features for the new DAG platform.
    • Improved the wallet capabilities of the DAG platform.
    • Created the trigger mechanism to allow smarter DAG nodes.
    Technologies: JavaScript, Node.js, Directed Acrylic Graphs (DAG)
  • Blockchain Engineer

    2020 - 2020
    Forward Edge
    • Worked on picking the correct blockchain technology for the client's needs.
    • Implemented a prototype on the Tendermint blockchain platform.
    • Wrote integration services in Golang, which serve as a blockchain's outer layer.
    Technologies: Tendermint, Go
  • Blockchain Engineer

    2019 - 2020
    • Worked on designing the prototype for a platform on top of blockchain in the pharmaceutical industry.
    • Developed prototype smart contracts on Ethereum, using Solidity.
    • Wrote an engine in Python which integrated with Ethereum.
    Technologies: Quorum, Ethereum, Python
  • Blockchain Architect

    2018 - 2019
    Tykn tech
    • Architectured the platform.
    • Implemented the solution using Hyperledger and Python.
    • Coordinated with end-user application team.
    Technologies: Hyperledger, Python
  • Senior Blockchain Developer

    2018 - 2019
    6fusion (via Toptal)
    • Wrote software in Go which interacts with a blockchain platform.
    • Worked with the Quorum platform.
    • Used Docker and kubernetes for deployment.
    Technologies: Solidity, Quorum, Ethereum, Go
  • Solidity/Blockchain Expert with Go Experience

    2018 - 2019
    Fractal Blockchain (via Toptal)
    • Contributed to software written in Go which interacts with Ethereum nodes (with geth nodes specifically).
    • Reviewed and improved smart contracts written in Solidity.
    • Reviewed and improved software interacting with the Bitcoin network.
    Technologies: Go, Bitcoin, Ethereum, Solidity, Blockchain
  • Software Engineer

    2018 - 2019
    • Developed a secure crypto-wallet intended to be used for Hyperledger Indy.
    • Supported the Indy-SDK project.
    • Created proprietary software solving SSI-related problems on top of Hyperledger Indy.
    • Bulit a system of pluggable crypto-wallet storage back-ends which allows for enterprise-scale wallets.
    Technologies: Hyperledger, Rust, Python
  • Software Engineer

    2016 - 2018
    • Developed the Number Discovery Platform using Python and Gevent.
    • Extended the PhoneID product written in Python and Bottle.
    • Created a URL-shortening service using Python and Flask.
    • Built a Number Deactivation product using Python.
    Technologies: Flask, Bottle.py, Gevent, Python
  • Web Developer

    2015 - 2016
    • Wrote an internal HR application using JSP.
    • Refactored an internal voting system written in a custom in-house framework.
    • Supported and extended an internal forum written in JSP.
    Technologies: Java, Python
  • Web Developer

    2012 - 2016
    • Wrote a web crawler and scraper using Python and Beautiful Soup.
    • Developed a custom content manager application back-end using Django.
    • Created web microservices using Python.
    Technologies: Beautiful Soup, JSP, Java, Pyramid, Django, Flask, Python


  • Hyperledger Indy Crypto Wallet

    Designed and developed a crypto wallet used in Hyperledger Indy.

    Some of the features that distinguish this wallet:
    1. mechanism for searching through encrypted entities using tags
    2. multiple encryption keys using Elliptic Curve Cryptography
    3. pluggable storage system supporting enterprise-scale crypto wallets

  • Identity Solution for Red Cross Refugees on Top of Hyperledger Indy

    Part of the team that designed and developed a solution for solving identity problems for the refugees in Red Cross centers. This was a part of Blockchaingers 2018 Hackathon, which was held in Groningen, Netherlands

  • Multichain Tracker (Blockchain Data Tracker and Aggregator)

    This project allowed the user to track through a dashboard different blockchains (and possibly even private sidechains if they exposed correct APIs), and be able to both look at the current data, as well as track data (hashes) across several blockchains.

    It integrated with most common blockchains (Bitcoin, Ethereum, etc.) through their APIs, and fed data through web sockets to a front-end dashboard.

  • Reward System on Top of Ethereum Blockchain

    Developed a part of a platform intended for rewarding loyal users of the platform and provide gamification, using Ethereum.

  • Pharmachain (Provenance and Supply Chain Blockchain)

    Blockchain for tracking provenance and ownership transfers of pharmaceutical supplies. It was intended to function on an international level and enable easier tracking of transfers across international borders, to prevent scam, and track defects and inappropriate batches.

  • Website and Web App Used in BEST

    Redesigned an old website into a current, modern version.

    Refactored and extended the internal application.

  • Number Discovery Platform

    One of the key components of the SMS platform used to discover the best routes and providers for delivering an SMS.

  • Phone ID Service

    Developed and extended existing features for a Phone ID service. It is a service intended to provide sophisticated information for phone numbers.


  • Languages

    Go, Python, Solidity, Rust, Erlang, JavaScript, Java
  • Platforms

    Blockchain Platforms, Ethereum, Blockchain, Hyperledger, Kubernetes, Docker, Hyperledger Fabric, Linux, Hedera Hashgraph
  • Other

    Distributed Ledger Technology, Distributed Ledgers, Decentralized Applications, Distributed Systems, Self-sovereign Identity (SSI), Directed Acrylic Graphs (DAG), Applied Cryptography, Ethereum Smart Contracts, Smart Contracts, Quorum, IPFS, Bitcoin, Peer-to-peer Networking, Hyperledger Aries, Cryptocurrency, Non-fungible Tokens (NFT), Hashgraph Technology, EOSIO, EOS, Cryptography
  • Frameworks

    Tendermint, Pyramid, JSP, Flask, Django
  • Tools

    Hyperledger Indy, Git, Stellar SDK
  • Paradigms

    Concurrent Programming, Agile, Functional Programming
  • Storage

    Relational Databases, Cassandra, BigchainDB
  • Libraries/APIs

    Beautiful Soup, Gevent, Bottle.py, Node.js


  • Bachelor's Degree in Software Engineering
    2012 - 2016
    University in Belgrade - Belgrade, Serbia

To view more profiles

Join Toptal
Share it with others