Cisco Security Monitoring, Analysis and Response System

Document ID: 99790

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Problem
Solution
Related Information

Introduction

This document describes the error message in the Cisco Security Monitoring, Analysis, and Response System (CS-MARS) when you try to add a device such as an IOS^® router or switch with Secure Shell (SSH).

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on the Cisco Secure MARS Version 4.2x/5.2x.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Problem

In the CS-MARS, when you try to add a device such as an IOS router or switch, this error message appears:

ssh_rsa_verify: n too small: 512 bits 
key_verify failed for server_host_key

Solution

Use this solution to resolve the problem.

The cause for this error message is due to a 512-bit key that is generated by a router (device), but MARS expects a 1024-bit or higher key.

In order to resolve this issue, zeroize the key and generate a 1024-bit key in the router:

Router#config terminal
Router(config)#crypto key zeroize rsa 
Router(config)#crypto key generate rsa general-keys modulus 1024

Warning: Cisco recommends that you use labeled key pairs instead of the default key pairs because the zeroizing of the default key pairs can lead to VPN tunnel termination. It can also affect the Certificate Authority (CA) data that relies on your default keys, for example:

 
Router(config)#crypto key generate rsa general-keys label sshkey modulus 1024 exportable
Router(config)#ip ssh rsa keypair-name sshkey

Refer to the Cisco IOS Security Command Reference for more information.

Related Information

• Technical Support & Documentation - Cisco Systems