# File lib/net/ssh/authentication/key_manager.rb, line 142
142:         def sign(identity, data)
143:           info = known_identities[identity] or raise KeyManagerError, "the given identity is unknown to the key manager"
144: 
145:           if info[:key].nil? && info[:from] == :file
146:             begin
147:               info[:key] = KeyFactory.load_private_key(info[:file], options[:passphrase])
148:             rescue Exception => e 
149:               raise KeyManagerError, "the given identity is known, but the private key could not be loaded: #{e.class} (#{e.message})"
150:             end
151:           end
152: 
153:           if info[:key]
154:             return Net::SSH::Buffer.from(:string, identity.ssh_type,
155:               :string, info[:key].ssh_do_sign(data.to_s)).to_s
156:           end
157: 
158:           if info[:from] == :agent
159:             raise KeyManagerError, "the agent is no longer available" unless agent
160:             return agent.sign(identity, data.to_s)
161:           end
162: 
163:           raise KeyManagerError, "[BUG] can't determine identity origin (#{info.inspect})"
164:         end