Whether you can recover (decrypt) your files or not depends on what ransomware infection you are dealing with, the type of encryption used by the malware writers and a variety of other factors as explained here
. All crypto malware ransomware use some form of encryption algorithms
, most of them are secure, but others are not. The possibility of decryption depends on the thoroughness of the malware creator, what algorithm the creator utilized for encryption, discovery of any flaws and sometimes just plain luck. Many ransomware variants use a public and private key system where the public key is used to encrypt and the private key is used to decrypt. The private key is stored on a central server maintained by the cyber-criminals and not available unless the victim pays the ransom or at some point, law enforcement authorities arrest the criminals...seize the C2 server and release the private RSA decryption keys to the public.