CentoOS 7 python-cryptography package is at version 0.8.2
It has a build-requires for python-cryptography-vectors of the same version (but different source tarball apparently)
There is no python-cryptography-vectors in CentOS 7 base or updates.
There is one in EPEL but it is version 0.8
If you relax the BuildRequires to just require python-cryptography-vectors then the build fails because the build script itself checks to see if it is the same version.