[csense]

With this approach, the first partner who reveals their offer will be at a disadvantage. If they want to buy, they can offer (otherguy + epsilon), and if they want to sell, they can offer (otherguy - epsilon). (Where "otherguy" is the other cofounder's price, and epsilon is a small number like $0.01.)

To fix this, you need to have both parties commit to their prices before anyone learns anyone else's price. For example, you could require both parties to mail their offers to the company lawyer, who is only allowed to reveal them when both offers have arrived.

Of course, with the above solution, you have to trust a human being (the lawyer) to be impartial and not collude with one of the cofounders against the other. For the paranoid, you can instead use a protocol that trusts cryptography instead of humans. You could have each person choose a random nonce, publish H(price + "#" + nonce). When everybody's published a hash, everyone then reveals their price and their nonce -- you know the price was chosen without knowledge of the other party's offer. (Of course each person needs a public key to sign the hash as well, to make sure a participant can't legitimately claim "I didn't send that.")

[TheCapn]

Seems overly complicated... couldn't you just meet with the lawyer, each sit at one end of the table then write your price down and hand it to the lawyer all in person?

[ronaldx]

Slightly easier fix that doesn't immediately require a trusted middleman: swap pieces of paper after committing that anyone who doesn't reveal loses his stake in the company for 0.