Similar to Cerber (Ferber) ransomware, Spora has its own intricate encryption file format and does not encrypt the whole file. The encryption block size varies depending on a file size.
Read our analysis of Spora ransomware for Acronis https://www.acronis.com/en-us/blog/posts/spora-gets-update-youre-safe-acronis-active-protection
Article Link: http://nioguard.blogspot.com/2017/08/spora-ransomware-analysis.html