I'm using Dropbear as an SSH server in my embedded system.
I want to know if Dropbear supports SSH key revocation? If yes, how I can do it?
SSH public key authentication does not support anything like key revocation. The list of "allowed" keys is store in the
~/.ssh/authorized_keys and if you remove the key from there, you revoke the access (if this is what you want to hear).
Revocation list is related to Public Key Infrastructure usually based on the X.509 certificates with certificate authorities, which is really overkill to implement in lightweight Dropbear. SSH keys are standalone cryptographic primitives and they do not use anything like this. There is possibility to use certificates in OpenSSH, but not with Dropbear.