rpmbuild: handle naming differences of packages in different distributions

I'm writing a RPM spec file for building my software. The software depends on [Crypto++](http://cryptopp.com) . Crypto++ is named differently on different distributions, for example, on OpenSUSE, I should write

BuildRequires: libcryptopp-devel

But on Fedora, it should be

BuildRequires: cryptopp-devel

Now, how can I unify the two in a single spec file?