Why not use a stripped down version of the bitcoin code? Each share is a coin, no decimal places allowed, and blocks can be generated using the issuers signing key instead of mining. Shares can be traded p2p and transactions confirmed by the issuer.
Why would you want to give issuers the power to veto transactions?
1) Possibly there are legal reasons they must.
2) ASICMINER has that power right now.
3) An issuer in general always has the ultimate power: they can inflate their own shares, or simply stop producing useful revenue.
1) Why should we care about that? We have the means of making a better system. Law always plays catch-up anyway.
2) True. And before they had the sole ability, GLBSE had it. All of the "stock exchanges" are just ledger books, even MPEX. By and large, we don't accept money that is only ours because someone says it is ours, we prefer money that is cryptographically ours. Why do we still accept fiat securities while we reject fiat money?
3) They always have the ability to do things globally. Why should they also have the ability to selectively veto private transfers?
I worked out a system (probably like the 50th person to do so, but whatever) with a merged mine chain that was a bit like namecoin, but with quantities. Totally decentralized, like bitcoin. You'd need brokers still, but that's pretty much the case when trading bitcoin also.