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