Install bitcoin core on debian jessie error 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?
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! :)