yao.md

Yao's Millionaire Problem 💵

This is a really classic MPC problem posed by Andrew Yao in 1982. The premise is that two millionaires wish to identify who is richest but do not wish to disclose their wealth to one another. Traditionally, this is solved using a variant of oblivious transfer (FYI: where our company got its name), but in our setting, we'll use an enclave.

In settings like this, we must be careful who inputs what and who receives what. Input validation, the frequency a party can call an API endpoint, the time it takes to respond, and more should all be considered.

We give a simple demonstration of this, where the path /submit_value can only be called once by each party (ensured by their username not being in the dictionary keys of the uploaded dictionary):

@router.get("/submit_value")
def submit_value(
    value: int,
    x_oblv_user_name: str = Header(default=None)
):
    if x_oblv_user_name is None:
        raise HTTPException(401, "No X-OBLV-User-Name provided.")
    
    if x_oblv_user_name in router.uploaded.keys():
        raise HTTPException(401, f"Path only available for one time use. Value already uploaded by {x_oblv_user_name}.")

    router.uploaded[x_oblv_user_name] = value

    return f"Successfully saved {value} as value for {x_oblv_user_name}."

Give it a go yourself with a friend if you like! The code can be seen here.