user26366: I was thinking around http://lightning.network/ .
My problem is Alice sending coins to Bob via Eve: A -- tx1 -> E -- tx2 -> B
Is there a way to condition tx1 on Eve signing tx2?

user2306: Not directly, but you could do something similar by combining tx1 and tx2 into a single transaction.
So, instead of:

tx1:
Input         | Output
Alice (1 BTC) | Eve (1 BTC)

tx2:
Input          | Output
Eve (0.99 BTC) | Bob (0.99 BTC)


you could use:

tx:
Input          | Output
Alice (1 BTC)  | Eve (0.01 BTC)
               | Bob (0.99 BTC)


This doesn't seem useful for the lightning network, because you really don't want to have a payment fail just because a settlement somewhere along the path failed.

26366: <p>I was thinking around <a href="http://lightning.network/" rel="nofollow">http://lightning.network/</a> .</p>

<p>My problem is Alice sending coins to Bob via Eve: <code>A -- tx1 -&gt; E -- tx2 -&gt; B</code></p>

<p>Is there a way to condition tx1 on Eve signing tx2?</p>
 2306: <p>Not directly, but you could do something similar by combining tx1 and tx2 into a single transaction.</p>
<p>So, instead of:</p>
<blockquote>
<p>tx1:</p>
<pre><code>Input         | Output
Alice (1 BTC) | Eve (1 BTC)
</code></pre>
<p>tx2:</p>
<pre><code>Input          | Output
Eve (0.99 BTC) | Bob (0.99 BTC)
</code></pre>
</blockquote>
<p>you could use:</p>
<blockquote>
<p>tx:</p>
<pre><code>Input          | Output
Alice (1 BTC)  | Eve (0.01 BTC)
               | Bob (0.99 BTC)
</code></pre>
</blockquote>
<p>This doesn't seem useful for the lightning network, because you really don't want to have a payment fail just because a settlement somewhere along the path failed.</p>
