You're missing the --gen-amalgamation flag. Your command should look like: python configure.py --cc=msvc --gen-amalgamation --single-amalgamation-file ...
In the documentation, SymmetricKey (which is just a typedef for OctetString) can take a byte array and length as constructor. Alternatively, you can encode the key as a hex string. If you already have the key as std::vector<byte>, then this should suffice: std::vector<byte> keybytes; // ...fill the vector... SymmetricKey key(...
I just checked and looks like Botan v. 1.10.9 doesn’t have unlock. You have two options. The version 1.10.9 has another final method where you can pass a vector of byte as reference to get the return. Something like: byte out[hash.output_length()]; hash.final(out); Another option is to convert from SecureVector to...