From an article by Mark Wyciślik-Wilson in the BetaNews web site:
“The Petya ransomware — and several variants — wreaked havoc with data around the world, but now the author of the original malware has released the master decryption key.
“Janus Cybercrime Solutions has provided a key that work with all “official” variants of Petya (meaning NotPetya is not included). The key was released to — of all places — Mega, and its authenticity has been verified. While Petya has already been cracked, the key offers the fastest and most reliable decryption method yet.”
The brief, but full, article may be found at: https://betanews.com/2017/07/07/petya-universal-decryptor/.