Bitcoin client backward compatible w/ older wallet.dat?

[Stephen Gornick]

Saw this Twitter status update:
  Does the #bitcoin protocol have a version number that allows to upgrade if someone leaves the system for 5 - 10 years?
  http://twitter.com/stephanwehner/statuses/16224034316361728

I think what is being asked is, if a client were not upgraded for a very long time, could it still communicate?

Either way, will the future clients be backward compatible as far as being able to access today's wallet.dat?

A lot can happen in 5 to 10 years. 

  IPv6, various vulnerabilities discovered, encrypted wallet.dat, etc.

(Incidentally, ... isn't the reason most who have left the system for 5 - 10 years due to being incarcerated?)

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[theymos]

The public/private keys are in there, so it should always be possible to recover them, even if Bitcoin can't do it automatically.

[Stephen Gornick]

How would I merge the keys from an old wallet.dat into current.  If I can launch the client, I can just transfer to address from a new wallet, but is it possible to add those keys into another wallet?

[theymos]

is it possible to add those keys into another wallet?

It's possible, but Bitcoin doesn't do it. A future version of Bitcoin might do it, though. In any case, it will be possible to manually extract keys from an old wallet and insert them into a new one.

[Stephen Gornick]

A future version of Bitcoin might do it, though.

Just to bookend this thread:
  Pull #220, Wallet and key import and export
  - https://github.com/bitcoin/bitcoin/pull/220