The 28-year-old woman was in her tent at the Bloodstock Festival, in Catton Park, sometime between 2.50pm and 3.20pm on Sunday, August 14.
A man came into the tent and sexually assaulted her. She struck his hand with a torch and the man left.
She has described the man as being white with a tanned complexion and in his late 20s. He has mousey hair, which was around three inches long and has grey eyes with blue flecks in.
His teeth are uneven and he has acne scars on his face. He wore tan shorts and a black t-shirt with the name of a band on, although the victim cannot recall which band.
Police are appealing for anyone with information to get in touch and are asking people to share this appeal, as the man involved may not come from Derbyshire.
He may have complained to friends and family about a pain in his hand.
Detective Sergeant Jim Shinfield said: “This was an isolated incident at what was otherwise an uneventful festival.
“If the description of this man matches that of someone you know who went to the festival, please get in touch.”
Witnesses or anyone with information should call DS Jim Shinfield on 101, quoting reference 16000235606.
Here is the official statement from Bloodstock organizers:
“As you all know, Bloodstock is one of the safest and friendliest festivals in the country, and this is primarily because of the sense of community that you help create.