# Tekkoh: An Open-Source Encrypted Journal for iPhone A privacy-focused digital notebook that automatically logs your daily activity and movements. - **Source:** [Stripe CTO Blog](https://blog.singleton.io) - **Published:** 2026-11-08 - **Topic:** [technology](https://brifing.si/c/technology) - **Original article:** - **On Brifing:** https://brifing.si/s/ce2b2689-3abc-45bf-999f-22c229f1f885 ## Automated Daily Journaling Tekkoh is a new iPhone journal application designed to reduce the friction of writing by pre-filling pages. It automatically pulls data from Apple Health and Maps, including step counts, workout summaries, visited locations, and sunrise or sunset times. Users simply add their personal thoughts to these automatically generated daily summaries. ## Design and Aesthetic The app draws inspiration from the Japanese word techō, referring to traditional paper planners. Its interface features a cream-colored paper background, fine grid lines, and serif typography. A vermillion accent and a brush-drawn ensō symbol track user streaks, providing a tactile, notebook-like experience that opens flat on the iPhone Duo. ## End-to-End Encryption Privacy is central to the app, utilizing AES-256-GCM encryption on the device before any data is transmitted. Keys are stored in the user's iCloud Keychain, ensuring that even the server hosting the data cannot access the content. Page identifiers are derived from the user's key, effectively hiding the dates of entries. ## Recovery and Security Data recovery on new devices is managed via a six-digit PIN protected by 600,000 rounds of PBKDF2. The server limits recovery attempts to ten, with increasing delays between each, before destroying the copy. The developer explicitly notes that a six-digit PIN has limitations against sophisticated attacks targeting both database and server secrets. ## Agent Integration Support Tekkoh includes a command-line tool allowing personal AI agents to interact with the journal. By linking an agent, users can grant it permission to read entries or add notes about tasks performed on their behalf. This feature is designed for users running agents in controlled environments, such as a confidential virtual machine. ## Development and Tools The project was developed rapidly starting November 7th, utilizing Claude Code for the SwiftUI app, Go server, and web interface. The developer also open-sourced Berth, a platform-as-a-service tool running on a Mac mini, which powers the server infrastructure. All components are available under the MIT license for public review. ## Cross-Platform Consistency The system ensures cryptographic consistency across Swift, Go, and JavaScript implementations by using shared test vectors. A web version allows for reading and writing on computers, linked securely via a QR code scan. This ensures that the encryption key remains strictly within the user's trusted devices during the initial pairing process. ## Current Status and Audit While the project has undergone one independent review, it has not yet received a formal security audit. The developer advises users to consult the provided security notes before storing highly sensitive information. The app is currently on its way to the App Store, with updates promised once it goes live. ## Sources covering this story - https://blog.singleton.io/posts/2026-11-08-introducing-tekkoh/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._