for rbd, how to use qmp directly to add dick

Hi, all:     in my case, i need to add device via qmp.  but for rbd  drive needs a secret object. how to produce secret object. 'base64 -d' outputs unreadable code . -object secret,id=virtio-disk0-secret0,data=2YVH6svMZa42RfVx8MbIIVjtU6iGO8QzFADuDnLk7BU=,keyid=masterKey0,iv=/m3QyHQ33NeMEfDDMuDEeg==,format=base64 thanks