user38652: I have to install bitcoin core to use op_return library. 
But I have difficulties to install correctly bitcoin core. 
First I run the command sudo apt-add-repository ppa:bitcoin/bitcoin
Second I enter this command: apt-get update
But I have error : 
 Err http://ppa.launchpad.net jessie/main amd64 Packages                
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                                                     
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                               
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                               
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                               
404  Not Found

 W: Failed to fetch http:/ppa.launchpad.net/bitcoin/bitcoin/ubuntu/dists/jessie/main/binary-amd64/Packages  404  Not Found

 E: Some index files failed to download. They have been ignored, or old ones used instead.

So when I want to do this : apt-get install bitcoin-qt
I have : E: Unable to locate package bitcoin-qt
What can I do? 

user33314: The repository is for ubuntu and you're on debian.
So it doesn't have packages for jessie.
Use this instead: https://github.com/bitcoin/bitcoin/blob/master/doc/build-unix.md
Hope this helps! :)

38652: <p>I have to install bitcoin core to use op_return library. 
But I have difficulties to install correctly bitcoin core. </p>

<p>First I run the command <code>sudo apt-add-repository ppa:bitcoin/bitcoin</code></p>

<p>Second I enter this command: <code>apt-get update</code></p>

<p>But I have error : </p>

<pre><code> Err http://ppa.launchpad.net jessie/main amd64 Packages                
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                                                     
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                               
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                               
 Err http://ppa.launchpad.net jessie/main amd64 Packages                                               
404  Not Found

 W: Failed to fetch http:/ppa.launchpad.net/bitcoin/bitcoin/ubuntu/dists/jessie/main/binary-amd64/Packages  404  Not Found

 E: Some index files failed to download. They have been ignored, or old ones used instead.
</code></pre>

<p>So when I want to do this : <code>apt-get install bitcoin-qt</code>
I have : <code>E: Unable to locate package bitcoin-qt</code></p>

<p>What can I do? </p>
 33314: <p>The repository is for ubuntu and you're on debian.<br>
So it doesn't have packages for jessie.<br>
Use this instead: <a href="https://github.com/bitcoin/bitcoin/blob/master/doc/build-unix.md" rel="nofollow">https://github.com/bitcoin/bitcoin/blob/master/doc/build-unix.md</a><br>
Hope this helps! :)<br></p>
