Crypto Key Generate Rsa 1024 Command

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Crypto Key Generate Rsa 1024 Command Rating: 4,8/5 8179 votes
  • October 2, 2015
  • Posted by: Syed Shujaat
  • Category: Cisco, Networking Solutions
  1. Step 4: Erase existing key pairs on the router. R1(config)# crypto key zeroize rsa Note: If no keys exist, you might receive this message:% No Signature RSA Keys found in configuration. Step 5: Generate the RSA encryption key pair for the router. The router uses the RSA key pair for authentication and encryption of transmitted SSH data.
  2. The label is important, I'll tell you! In a minute why C1801(config)# crypto key generate rsa modulus 1024 label C1801 The name for the keys will be: C1801% The key modulus size is 1024 bits% Generating 1024 bit RSA keys, keys will be non-exportable.OK C1801(config)#.Jan 6 15:22:25.339:%SSH-5-ENABLED: SSH 1.99 has been enabled!
  3. Device-1(config)# crypto key generate rsa label myKey exportable modulus 1024 Device-1(config)# do show crypto key mypubkey rsa key label: myKey key size: 1024 exportable: yes Step 5 Associate the RSA key pair to the trustpoint. Device-1(config)# crypto ca trustpoint myCA Device-1(config-trustpoint)# rsakeypair myKey.
  4. Nov 23, 2011 Hi, i have a switch 2960 24TC-L with c2960-lanbasek9-mz.150-1.SE.bin and SSH v1 enabled. When i try to enable SSH v2 the swith tell me that i have to create a crypto key rsa. I generated the crypto key rsa with 1024 bits and when i try to enable the SSH v2 i receive the same message.
  5. To generate a key pair, select the bit length of your key pair and click Generate key pair. Depending on length, your browser may take a long time to generate the key pair. A 1024-bit key will usually be ready instantly, while a 4096-bit key may take up to several minutes. For a faster and more secure method, see Do It Yourself below.
  6. When you use the crypto key generate rsa command, it will ask you how many bits you want to use for the key size. How much should you pick? It’s best to check the next generation encryption article from Cisco for this. At this moment, a key size of 2048 bits is acceptable. Key sizes of 1024 or smaller should be avoided.

The simplest way to generate a key pair is to run ssh-keygen without arguments. In this case, it will prompt for the file in which to store keys. Here's an example: klar (11:39) ssh-keygen Generating public/private rsa key pair.

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

router (Config)# crypto key generate rsa

how many bits in the modulus [512] :1024

router (Config)# ip ssh version2

router (Config)# CTRL Z


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 “,” the key name is “”

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.

Router360 bits512 bits1024 bits2048 bits (maximum)
Cisco 250011 seconds20 seconds4 minutes, 38 secondsMore than 1 hour
Cisco 4700Less than 1 second1 second4 seconds50 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.
Note Effective with Cisco IOS XE Release 2.4 and Cisco IOS Release 15.1(1)T, the maximum key size was expanded to 4096 bits for private key operations. The maximum for private key operations prior to these releases was 2048 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.
copyCopies any file from a source to a destination, use the copy command in privileged EXEC mode.
cryptokeystorageSets the default storage location for RSA key pairs.
debugcryptoengineDisplays debug messages about crypto engines.
hostnameSpecifies or modifies the hostname for the network server.
ipdomain-nameDefines a default domain name to complete unqualified hostnames (names without a dotted-decimal domain name).
showcryptokeymypubkeyrsaDisplays the RSA public keys of your router.
show crypto pki certificatesDisplays information about your PKI certificate, certification authority, and any registration authority certificates.

Crypto Key Generate Rsa Ssh

Telnet versus SSH

Many people continue to use Telnet for sensitive applications or access to critical systems. Telnet is CLEARTEXT, so all the data, including the login id is visible is someone intercepts that session

Crypto Key Generate Rsa 1024

Here’s what this looks like using Wireshark an Open Source Protocol Analyzer when we use the Follow TCP Stream feature in Wireshark.

The next characters are red (the character I typed) and blue (the characters echoed back)

You clearly see the User Verification Prompt.Here's the telnet trace file.

Below you can see me typing in my username;

In this screenshot below you can see me entering the commandenable and the the enable password.

How to Enable SSH Version 1 on Cisco

Before you can enable SSH you need to assign individual (or group) user IDs and passwords.

These are just login id's and are required regardless if you use Telnet or SSH.

To enable locally administered user IDs, use the following set of configuration commands. I would not suggest using the nopassword parameter.

Put your own data in the italized text.

Now when you telnet into the device you should see the Username prompt

User Access Verification
Username: fortunato

Now that you have login id's created you can turn on SSH version 1.

To enable SSH, use the following set of configuration commands. I would not suggest using the nopassword parameter.

Put your own data in the italized text.

foghorn#configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

foghorn(config)#crypto key generate rsa

% Please define a domain-name first.! common mistake when you do not the IP domain-name created

foghorn(config)#ip domain-name

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foghorn(config)#crypto key generate rsa

The name for the keys will be:

Choose the size of the key modulus in the range of 360 to 2048 for your

General Purpose Keys. Choosing a key modulus greater than 512 may take a few minutes.

How many bits in the modulus [512]: 1024

% Generating 1024 bit RSA keys ..[OK]

foghorn(config)#ip ssh time-out 120

foghorn(config)#ip ssh authentication-retries 5


Now we'll try to capture the SSH login and as you can see the login data is no longer in clear text. Here's the SSH 1 trace file.

The moral of the story is not to use Cleartext logins if the device or application is sensitive.

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To upgrade to even more secure SSH version 2, type in the following commands

foghorn(config)#ip ssh version 2
foghorn(config)#no ip ssh version 1

Cisco Generate Crypto Key

the SSH version 2 trace files are here

In this write up I used;

  • Wireshark Protocol Analyzer(free)

  • Putty Telnet/SSH Client(free)

  • Cisco Switch(not free)