Where your money is

USDC

Your balance is held in USDC, a digital dollar: a token issued to be worth one US dollar, that moves between addresses on a blockchain in minutes rather than days. When you pay in by bank transfer, the dollars or euros you sent are converted to USDC on the way in; the figure on your home screen is USDC.

Two addresses, one key

When your account is set up after verification, Sempo creates one private key for you and gives you two addresses from it: one on Ethereum, which is where a bank deposit lands as USDC, and one on Miden, the network Sempo is built on and where your balance is held. They are the same key written two ways, which is why a single key is enough: whatever arrives at either address can be signed for by that key and by nothing else.

The key itself is created and kept in a service built for holding keys, in a compartment that is yours alone, and it never leaves it. Keys and Turnkey goes into who can use it and when.

Miden, where the balance lives

Ethereum is where USDC arrives; Miden is where it stays. A deposit is bridged from your Ethereum address onto your Miden account, and that account is what the home screen shows and what a payment to another Sempo user is made from. Two properties of Miden are the reason:

• Your balance is private. A Miden account keeps its state with its owner rather than publishing it. What you hold, and what you have paid whom, is known to you and to the service that keeps your account for you — not to anyone who can read a public ledger.
• Moving money costs almost nothing. A transaction on Miden is priced in fractions of a cent. Sempo pays it, which is why a payment to another Sempo user has no fee line to show.

The road in, the road between Sempo users and the road out are drawn in Sending and withdrawing.

What the balance counts

Today the number on your home screen is the sum of the bank deposits that have completed, less any withdrawals. That is because a bank transfer is the one route we can see end to end: our banking partner tells us when a transfer has been converted and delivered.

What Sempo can and cannot do

• Sempo can open the account, receive money into it, bridge it onto Miden, and move money out at your instruction, signed with your key.
• Every transfer out is a signature from your key, made on a request you made while signed in and, for anything that moves money, recently confirmed as you. Nothing in the product sends money out on its own.
• Signing in with a Bread wallet does not move money to that wallet. It is a way in; the balance stays where it is.