In the subroutine responsible for generating encryption key in Acronis True Image 2017 i found interesting OpenSSL library calls (EVP_PKEY_, d2i_X509). These are used for encrypting "something" which appears to be randomly generated encryption key with public key embedded inside Acronis.
The use of public key encryption inside function responsible for generating secure random encryption key is rather suspicious. There's possibility that after the "random" key is generated - it's then encrypted using acronis public key and stored inside TIB file. Which means the owner of corresponding private key (Acronis), might in theory decrypt that data, and gain access to the real "random" encryption key.
The functionality is currently disabled at least in 2017 version of acronis, however presence of such code might mean that it can be reenabled in custom builds in some regions and countries.
By default, the public key encryption is skipped for now and following code at the bottom is executed:
Full decompilation results are available here: https://pastebin.com/3x0WnGiF
So based on that, you can decide whether acronis encryption is secure or not.