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https://en.wikipedia.org/wiki/Ransomware#File_decryption_and_recovery

But, it only works when the cipher the attacker used was weak to begin with, being vulnerable to known-plaintext attack); recovery of the key, if it is possible, may take several days. Free ransomware decryption tools can help decrypt files encrypted by the following forms of ransomware: AES_NI, Alcatraz Locker, Apocalypse, BadBlock, Bart, BTCWare, Crypt888, CryptoMix, CrySiS, EncrypTile, FindZip, Globe, Hidden Tear, Jigsaw, LambdaLocker, Legion, NoobCrypt, Stampado, SZFLocker, TeslaCrypt, XData.