user7144: I've made an offline address and only have the key stored on 2 encrypted flash drives stored in different locations with the private key written physically on paper and stored in 2 locations. Do I ever have to worry about my coins? That is, could theyever be lost in software changes or is that as big of a never-going-to-happen as the 21 million limit being lifted? I'm pretty sure I'm not touching that wallet for a long time. Is there any benefit to repeating this process for a more "fresh" address ever or does that not make sense?

user403: They could be lost in a few rare scenarios. For example:

If substantial weaknesses are found in Bitcoin's crypto, or if quantum computing becomes usable on a large scale, your coins could be stolen. Most likely, the crypto will simply be weakened and attacks will still be very slow, so you'll have some time to send your coins to new addresses that use improved crypto.
When you go to redeem your coins, your CPU may err in a way that causes Bitcoin to send your coins into oblivion. There are no known cases of this actually happening, but CPUs are not perfect, and it is possible.
If Bitcoin develops critical scalability problems, and nothing else solves it, one "nuclear option" for improving things would be to require everyone to "renew" their coins every few months (or whatever). Old coins that that aren't renewed would be destroyed. If this policy is implemented, you will have to follow it. You'd have plenty of warning if something like this was approaching.

To protect yourself against these things and other possibilities, you should:

Not store too much in any one address.
Not send huge amounts at once.
Never send from any high-value address more than once. The best way to do this is to only pay to an address once.
Make sure that you're able to access your wallet with only a few days of notice.

There isn't any value in moving coins before you need to.

user1409: I'll go through your question clause by clause:

I've made an offline address

You're doing good.

and only have the key stored on 2 encrypted flash drives stored in different locations 

As long as only you know the password and the password is sufficiently strong, this is probably secure.

with the private key written physically on paper and stored in 2 locations. 

If either of these two locations are accessible by anyone other than you, then they are vulnerable. If someone else found either paper, and your keys are in plain text, then you could consider them compromised.

Do I ever have to worry about my coins? 

Yes.

That is, could they ever be lost in software changes 

Extremely unlikely, as the whole of Bitcoin depends on the safety of balances through upgrades. There are people who have very vested in ensuring that this never happens. Even a bug in the protocol could not erase history in an unrecoverable way, as a single offline client copied online or bootstrap.dat would refresh anyone affected.

or is that as big of a never-going-to-happen as the 21 million limit being lifted? 

Pretty much.

I'm pretty sure I'm not touching that wallet for a long time. Is there any benefit to repeating this process for a more "fresh" address ever or does that not make sense?

Theoretically, you would never need to regenerate keys unless some kind of vulnerability was found in the software that generated your key, ala the Android random number generator flaw.
An unlikely occurrence would be some kind of change to the way private keys are imported, and your private key generated in 2013 cannot be securely converted to whatever format is expected in 2063, or whenever. I wouldn't get too paranoid about this.

7144: <p>I've made an offline address and only have the key stored on 2 encrypted flash drives stored in different locations with the private key written physically on paper and stored in 2 locations. Do I ever have to worry about my coins? That is, could theyever be lost in software changes or is that as big of a never-going-to-happen as the 21 million limit being lifted? I'm pretty sure I'm not touching that wallet for a long time. Is there any benefit to repeating this process for a more "fresh" address ever or does that not make sense?</p>
 403: <p>They could be lost in a few rare scenarios. For example:</p>

<ul>
<li>If substantial weaknesses are found in Bitcoin's crypto, or if quantum computing becomes usable on a large scale, your coins could be stolen. Most likely, the crypto will simply be weakened and attacks will still be very slow, so you'll have some time to send your coins to new addresses that use improved crypto.</li>
<li>When you go to redeem your coins, your CPU may err in a way that causes Bitcoin to send your coins into oblivion. There are no known cases of this actually happening, but CPUs are not perfect, and it is possible.</li>
<li>If Bitcoin develops critical scalability problems, and nothing else solves it, one "nuclear option" for improving things would be to require everyone to "renew" their coins every few months (or whatever). Old coins that that aren't renewed would be destroyed. If this policy is implemented, you will have to follow it. You'd have plenty of warning if something like this was approaching.</li>
</ul>

<p>To protect yourself against these things and other possibilities, you should:</p>

<ul>
<li>Not store too much in any one address.</li>
<li>Not send huge amounts at once.</li>
<li>Never send <em>from</em> any high-value address more than once. The best way to do this is to only pay to an address once.</li>
<li>Make sure that you're able to access your wallet with only a few days of notice.</li>
</ul>

<p>There isn't any value in moving coins before you need to.</p>
 1409: <p>I'll go through your question clause by clause:</p>

<blockquote>
  <p>I've made an offline address</p>
</blockquote>

<p>You're doing good.</p>

<blockquote>
  <p>and only have the key stored on 2 encrypted flash drives stored in different locations </p>
</blockquote>

<p>As long as only you know the password and the password is sufficiently strong, this is <em>probably</em> secure.</p>

<blockquote>
  <p>with the private key written physically on paper and stored in 2 locations. </p>
</blockquote>

<p>If either of these two locations are accessible by anyone other than you, then they are vulnerable. If someone else found either paper, and your keys are in plain text, then you could consider them compromised.</p>

<blockquote>
  <p>Do I ever have to worry about my coins? </p>
</blockquote>

<p>Yes.</p>

<blockquote>
  <p>That is, could they ever be lost in software changes </p>
</blockquote>

<p>Extremely unlikely, as the whole of Bitcoin depends on the safety of balances through upgrades. There are people who have very vested in ensuring that this never happens. Even a bug in the protocol could not erase history in an unrecoverable way, as a single offline client copied online or bootstrap.dat would refresh anyone affected.</p>

<blockquote>
  <p>or is that as big of a never-going-to-happen as the 21 million limit being lifted? </p>
</blockquote>

<p>Pretty much.</p>

<blockquote>
  <p>I'm pretty sure I'm not touching that wallet for a long time. Is there any benefit to repeating this process for a more "fresh" address ever or does that not make sense?</p>
</blockquote>

<p>Theoretically, you would never need to regenerate keys unless some kind of vulnerability was found in the software that generated your key, ala the <a href="http://arstechnica.com/security/2013/08/google-confirms-critical-android-crypto-flaw-used-in-5700-bitcoin-heist/" rel="nofollow">Android random number generator flaw</a>.</p>

<p>An unlikely occurrence would be some kind of change to the way private keys are imported, and your private key generated in 2013 cannot be <em>securely</em> converted to whatever format is expected in 2063, or whenever. I wouldn't get too paranoid about this.</p>
