Kalle Rosenbaum
Bitcoin Consultant at Popeller AB
Greater Linköping Metropolitan Area Sweden
Summary
👤
Senior🎓
Top SchoolKalle Rosenbaum is a Bitcoin-focused software engineer and consultant with 11+ years of experience building secure, production-grade systems and wallets. Based in Sweden, he combines deep Java and Linux expertise with hands-on Bitcoin protocol work—authoring Grokking Bitcoin and contributing Taproot and signing-support code to Ledger's JavaScript libraries. He has implemented non-custodial and multisig wallet integrations (e.g., BitGo) and added Proof-of-Payment features to the Mycelium Android wallet, demonstrating both backend crypto plumbing and mobile UX integration. Kalle advises, trains and develops Bitcoin software through his consultancy Popeller AB, bridging developer education and real-world deployment. Colleagues praise his easygoing style and steady focus on pragmatic, secure implementations of complex cryptographic flows.
11 years of coding experience
12 years of employment as a software developer
M.Sc., Computer science, M.Sc., Computer science at Linköping University
English, Swedish
Github Skills (25)
apim10
javascript10
pst10
mobile-development10
bitcoin10
bitcoins10
android-development10
java10
javas10
api10
android10
cryptography10
ps10
native-android10
unit-testing9
Programming languages (17)
Github contributions (5)
LedgerHQ/ledgerjs
Sep 2021 - Nov 2021
⛔️ DEPRECATED - Ledger's JavaScript libraries
Role in this project:
Back-end Developer
Back-end DeveloperContributions:53 commits, 5 PRs, 2 comments in 2 months
Contributions summary:Kalle primarily worked on the `BtcNew.ts` file, which seems to be a core component of the Bitcoin library. Their contributions focused on implementing new features and fixing compatibility issues related to getting wallet public keys and signing transactions, specifically related to the new hardware app v2+ protocol. They added support for Taproot transactions and refactored the code to move account-specific behavior to separate classes. Furthermore, the user introduced the use of callbacks to help track progress.
ethereumjavascriptblockchainwalletbitcoin
mycelium-com/wallet-android
Mar 2015 - Oct 2015
Mycelium Bitcoin Wallet for Android
Role in this project:Mobile Developer (Android)
Mobile Developer (Android)Contributions:23 commits, 1 PR, 1 comment in 6 months
Contributions summary:Kalle primarily contributed to the Mycelium Bitcoin Wallet for Android, focusing on the implementation of PoP (Proof of Payment) functionality. Their work involved creating and modifying activities, such as `PopActivity` for handling PoP requests, and integrating it with the wallet's core features. They also created unit tests related to the `PopRequest` functionality. The user demonstrated proficiency in Android development, UI interactions, and the integration of PoP-related features within the Mycelium Bitcoin Wallet.
androidwalletcryptocurrencymyceliumbitcoin
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