How can I use message signing to prove that I have private keys for many different accounts?

Question

I want to prove the total sum of BTC I have access to. Therefore I think if I use message signing to assert "owned by makerofthings7" in each address, then anyone can compute the total coins in my wallet based on that assertion.

• If we only focus on the encryption part (and not what the QT client permits), what is the most efficient way to prove that I control the funds of many addresses?

• Are all addresses in my wallet that contain coins available for signing & verification? In particular what happens to the "change" addresses that are dynamically created when sending and receiving Tx?

• Can I have a single signed message that is signed by all the keys in my wallet?

Answer 1

You can sign a message or export the private key of all the addresses in your wallet, including change addresses.

If you want to have a single message signed by all your keys the only solution I see would be to sign a message with the first key, then sign the signed message with a second key, ad nauseam.

Strictly from an encryption point of view I don't believe it is possible with ECDSA to sign with multiple keys in the same signature, I might be wrong here though.

As you may already have guessed, the most practical solution would probably be to consolidate your funds into a single address and sign a message with its private key. But it has a privacy tradeoff.