Seppan: 2人のための、シンプル家計管理

"I paid for lunch today."
"I covered your Amazon purchases from last week."

Are you tired of the constant calculations and reimbursements that arise in living with your partner?

Seppan is a simple payment management app for couples, married couples, and roommates living together. Simply record your payments, and it automatically calculates who is paying how much more. Manage splitting expenses and reimbursements without actually exchanging money.

■ Recommended for those who:

・Want to share financial records with their partner/spouse

・Are tired of calculating in their heads who paid how much

・Want a simple, ad-free household budgeting app

・Are tired of complicated household budget books

・Prioritize privacy

■ Main Features

・Easy linking with your partner via QR code

Start using it immediately in just a few steps

・Easy payment entry

Record amount, date, payer, and contribution rate with one tap

・Automatic balance calculation

See at a glance who is paying how much more at any time

・Monthly summary by category

Visualize spending breakdown with graphs to prevent overspending

・History management

Review past payments anytime and freely edit or delete them

・No ads, no in-app purchases

All features are available for free

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■ Privacy First Design (End-to-End Encryption)

All sensitive data such as payment amounts, categories, and notes are encrypted using AES-256-GCM on your device before being stored on the server. On the server side, only ciphertext is stored; third parties, including developers, cannot view the plaintext data.

* Encryption of payment data using AES-256-GCM
* Secure key exchange between partners using X25519 ECDH
* Detection of man-in-the-middle attacks using fingerprinting (6-digit verification code)
* Password protection using Argon2id (65MB, 3 iterations)
* Decryption impossible without a password even if the device is lost

Because we do not compromise on privacy, you can record sensitive information such as money with peace of mind.

■ Open Source

Seppan is an open-source application with all source code publicly available on GitHub. Anyone can read the code and verify the encryption implementation and data handling.

https://github.com/YohYamasaki/Seppan

■ Feature requests and bug reports are welcome

Please feel free to submit your suggestions, such as "It would be convenient to have this feature" or "This behavior is strange," via GitHub Issues or Pull Requests. Contributions are also welcome.

■ Contact Us

Please send your questions and requests to the following address:

yohei.yamasaki.yayo1@gmail.com