I found this at cute story at Contact Music regarding how Coldplay obtained permission to use the riff:
But he was only able to obtain the riff by writing to frontman RALF HUTTER and begging him to let Coldplay use it.
He admits, "The only thing I could think of was the pen pal letters I learnt in German lessons at school. I had no idea if they knew who Coldplay were so had to explain myself like a 15 year-old school-boy.
"Dear Ralf, I sing in a band called Coldplay, blah, blah. I drew a little picture. Everyone says it's extraordinary that they said yes.'
Compare clips: Kraftwerk, Coldplay