Janko is available for hire

Janko Krstic

Verified Expert in Engineering

Software Engineer and Web Developer

Belgrade, Serbia

Toptal member since July 27, 2018

Expertise

Ethereum Blockchain Python Golang Bitcoin ÐApp NFT Ethereum Smart Contract Hyperledger Solidity Kubernetes Agile Development Docker Rust

Bio

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.

Portfolio

X-Margin INC

Web3, Blockchain, Smart Contracts, Front-end Development, Back-end Development...

PollPapa Inc.

Blockchain, Cosmos SDK, Tendermint

Divine Ray

Blockchain, Cosmos, Go, Cryptocurrency

Experience

Blockchain - 8 years
Python - 8 years
Smart Contracts - 7 years
Hyperledger - 6 years
Solidity - 6 years
Go - 6 years
IPFS - 1 year
Rust - 1 year

Availability

Full-time

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.

Work Experience

Blockchain Developer

2024 - PRESENT

X-Margin INC

Integrated decentralized finance metrics providers into the Credora metrics system.
Wrote Credora metrics smart contracts for the Ethereum blockchain.
Conducted research on liquid staking and verified smart contracts.

Technologies: Web3, Blockchain, Smart Contracts, Front-end Development, Back-end Development, React, Python, Data Science, Node.js, TypeScript

Cosmos Developer

2024 - PRESENT

PollPapa Inc.

Reviewed blockchain architecture for the PollPapa system.
Created the blockchain network architecture for the production network.
Set up the security and performance requirements for the blockchain network.

Technologies: Blockchain, Cosmos SDK, Tendermint

Cosmos Blockchain Developer

2023 - 2024

Divine Ray

Developed the application-specific blockchain using Tendermint and Cosmos SDK.
Developed blockchain integration service, which interacts with the Cosmos SDK-built blockchain using the Go programming language.
Integrated the blockchain monitoring service to oversee the blockchain.

Technologies: Blockchain, Cosmos, Go, Cryptocurrency

DLT Engineer

2020 - 2023

ASU Pocket - University Technology Office

Built a web service that integrated Hyperledger Aries and the university's system, allowing it to issue verifiable credentials to its students.
Guided the SSI implementation process of the entire project.
Built several proof-of-concept applications that showcase the usage of verifiable credentials in education.

Technologies: Blockchain, Distributed Ledgers, Web3.js, Hashgraph

Blockchain and SSI Engineer

2020 - 2023

Pocket (Arizona State Univesity)

Created a self-sovereign identity (SSI) wallet that stores students' verifiable credentials.
Wrote a back-end system for issuing verifiable credentials to the institution's users.
Designed and researched self-sovereign identity libraries to use.
Architected the platform that issues verifiable credentials to students.

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), Smart Contracts, Ethereum Smart Contracts

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, Smart Contracts, Ethereum Smart Contracts

Blockchain Engineer

2019 - 2020

Pharmwerks

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, Smart Contracts, Ethereum Smart Contracts

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, Smart Contracts, Ethereum Smart Contracts

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, Smart Contracts, Ethereum Smart Contracts

Software Engineer

2018 - 2019

Evernym

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

TeleSign

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

BEST

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

Self-employed

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, Jakarta Server Pages (JSP), Java, Pyramid, Django, Flask, Python

Experience

Hyperledger Indy Crypto Wallet

https://github.com/hyperledger/indy-sdk

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

https://www.telesign.com/products/sms-api/

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

Phone ID Service

https://www.telesign.com/products/phone-id/

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

Education

2012 - 2016

Bachelor's Degree in Software Engineering

University in Belgrade - Belgrade, Serbia

Skills

Libraries/APIs

Beautiful Soup, Gevent, Bottle.py, Node.js, Web3.js, React

Tools

Hyperledger Indy, Git, Stellar SDK

Languages

Go, Python, Solidity, Rust, Erlang, JavaScript, Java, TypeScript

Platforms

Blockchain Platforms, Ethereum, Blockchain, Hyperledger, Kubernetes, Docker, Hyperledger Fabric, Linux, Hedera Hashgraph, Amazon Web Services (AWS)

Frameworks

Tendermint, Cosmos SDK, Pyramid, Jakarta Server Pages (JSP), Flask, Django

Paradigms

Concurrent Programming, Agile, Functional Programming

Storage

Relational Databases, Cassandra, BigchainDB

Other

Distributed Ledger Technology (DLT), Distributed Ledgers, Decentralized Applications, Distributed Systems, Self-sovereign Identity (SSI), Web3, 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), ÐApp, DApps, Cosmos, APIs, ERC-721, Hashgraph Technology, EOSIO, EOS, Cryptography, Hashgraph, Machine Learning, Artificial Intelligence (AI), Data Science, Front-end Development, Back-end Development

Collaboration That Works

How to Work with Toptal

Toptal matches you directly with global industry experts from our network in hours—not weeks or months.

Share your needs

Discuss your requirements and refine your scope in a call with a Toptal domain expert.

Choose your talent

Get a short list of expertly matched talent within 24 hours to review, interview, and choose from.

Start your risk-free talent trial

Work with your chosen talent on a trial basis for up to two weeks. Pay only if you decide to hire them.

Top talent is in high demand.

Start hiring