Jun 28, 2007 Zeroize the RSA keys and re-generate the keys. Crypto key zeroize rsa label keyname crypto key generate rsa label keyname modulus keysize; If the previous workaround does not work, try these steps: Zeroize all RSA keys. Reload the device. Create new labeled keys for SSH.
- October 2, 2015
- Posted by: Syed Shujaat
- Category: Cisco, Networking Solutions
Use this command to generate RSA key pairs for your Cisco device (such as a router). keys are generated in pairs–one public RSA key and one private RSA key.
If your router already has RSA keys when you issue this command, you will be warned and prompted to replace the existing keys with new keys.
NOTE: Before issuing this command, ensure that your router has a hostname and IP domain name configured (with the hostname and ipdomain-name commands).
You will be unable to complete the cryptokeygeneratersacommand without a hostname and IP domain name. (This situation is not true when you generate only a named key pair.)
Here are the steps to Enable SSH and Crypto Key setup : 2 config must requried for SSH
1 Setup Local VTY line User ID and password
router (Config) # Line VTY 0 15
router (Config-line)# login local
router (Config-line)# Exit
!!! create local login ID/Pass
router (Config)# username [loginid] password [cisco]
router (Config)# username loginid1 password cisco1
2. router (Config)# ip domain-name example.com
router (Config)# crypto key generate rsa
how many bits in the modulus [512] :1024
router (Config)# ip ssh version2 Generate custom certificate and key store.
router (Config)# CTRL Z
Note | Secure Shell (SSH) may generate an additional RSA key pair if you generate a key pair on a router having no RSA keys. The additional key pair is used only by SSH and will have a name such as {router_FQDN }.server. For example, if a router name is “router1.cisco.com,” the key name is “router1.cisco.com.server.” |
This command is not saved in the router configuration; however, the RSA keys generated by this command are saved in the private configuration in NVRAM (which is never displayed to the user or backed up to another device) the next time the configuration is written to NVRAM.
Modulus Length
When you generate RSA keys, you will be prompted to enter a modulus length. The longer the modulus, the stronger the security. However, a longer modules take longer to generate (see the table below for sample times) and takes longer to use.
The size of Key Modulus range from 360 to 2048. Choosing modulus greater than 512 will take longer time.
| Router | 360 bits | 512 bits | 1024 bits | 2048 bits (maximum) |
|---|---|---|---|---|
| Cisco 2500 | 11 seconds | 20 seconds | 4 minutes, 38 seconds | More than 1 hour |
| Cisco 4700 | Less than 1 second | 1 second | 4 seconds | 50 seconds |
Cisco IOS software does not support a modulus greater than 4096 bits. A length of less than 512 bits is normally not recommended. In certain situations, the shorter modulus may not function properly with IKE, so we recommend using a minimum modulus of 2048 bits.
Syntax Description : Optional Strings to embed with SSH Crypto key
| general-keys | (Optional) Specifies that a general-purpose key pair will be generated, which is the default. | ||
| usage-keys | (Optional) Specifies that two RSA special-usage key pairs, one encryption pair and one signature pair, will be generated. | ||
| signature | (Optional) Specifies that the RSA public key generated will be a signature special usage key. | ||
| encryption | (Optional) Specifies that the RSA public key generated will be an encryption special usage key. | ||
| labelkey-label | (Optional) Specifies the name that is used for an RSA key pair when they are being exported.If a key label is not specified, the fully qualified domain name (FQDN) of the router is used. | ||
| exportable | (Optional) Specifies that the RSA key pair can be exported to another Cisco device, such as a router. | ||
| modulusmodulus-size | (Optional) Specifies the IP size of the key modulus.By default, the modulus of a certification authority (CA) key is 1024 bits. The recommended modulus for a CA key is 2048 bits. The range of a CA key modulus is from 350 to 4096 bits.
| ||
| storagedevicename: | (Optional) Specifies the key storage location. The name of the storage device is followed by a colon (:). | ||
| redundancy | (Optional) Specifies that the key should be synchronized to the standby CA. | ||
| ondevicename: | (Optional) Specifies that the RSA key pair will be created on the specified device, including a Universal Serial Bus (USB) token, local disk, or NVRAM. The name of the device is followed by a colon (:).Keys created on a USB token must be 2048 bits or less. |
| Command | Description |
|---|---|
| copy | Copies any file from a source to a destination, use the copy command in privileged EXEC mode. |
| cryptokeystorage | Sets the default storage location for RSA key pairs. |
| debugcryptoengine | Displays debug messages about crypto engines. |
| hostname | Specifies or modifies the hostname for the network server. |
| ipdomain-name | Defines a default domain name to complete unqualified hostnames (names without a dotted-decimal domain name). |
| showcryptokeymypubkeyrsa | Displays the RSA public keys of your router. |
| show crypto pki certificates | Displays information about your PKI certificate, certification authority, and any registration authority certificates. |
Q: I have a Cisco switch in my network, which I can access by hooking up a console cable directly to the device. I like to access the switch remotely using SSH. How can I enable ssh on my Cisco 3750 Catalyst Switch?
A: By default, when you configure a Cisco device, you have to use the console cable and connect directly to the system to access it. Follow the steps mentioned below, which will enable SSH access to your Cisco devices. Once you enable SSH, you can access it remotely using PuTTY or any other SSH client.
1. Setup Management IP
First, make sure you have performed basic network configurations on your switch. For example, assign default gateway, assign management ip-address, etc. If this is already done, skip to the next step.
In the following example, the management ip address is set as 192.168.101.2 in the 101 VLAN. The default gateway points to the firewall, which is 192.168.101.1
2. Set hostname and domain-name
Next, make sure the switch has a hostname and domain-name set properly.
3. Generate the RSA Keys
The switch or router should have RSA keys that it will use during the SSH process. So, generate these using crypto command as shown below.
Also, if you are running on an older Cisco IOS image, it is highly recommended that you upgrade to latest Cisco IOS.
4. Setup the Line VTY configurations
Setup the following line vty configuration parameters, where input transport is set to SSH. Set the login to local, and password to 7.
If you have not set the console line yet, set it to the following values.
5. Create the username password
If you don’t have an username created already, do it as shown below.
Note: If you don’t have the enable password setup properly, do it now.
Make sure the password-encryption service is turned-on, which will encrypt the password, and when you do “sh run”, you’ll seee only the encrypted password and not clear-text password.
5. Verify SSH access
From the switch, if you do ‘sh ip ssh’, it will confirm that the SSH is enabled on this cisco device.
After the above configurations, login from a remote machine to verify that you can ssh to this cisco switch.
Crypto Key Generate Rsa 1024
In this example, 192.168.101.2 is the management ip-address of the switch.
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