Authenticating to Cisco devices using SSH and your RSA Public Key

Using an RSA Public/Private key pair instead of a password to authenticate an SSH session is popular on Linux/Unix boxes. Digital Ocean, a Virtual Private Server (VPS) provider, has this advice on how you should log into their Droplets:  "you should use public key authentication instead of passwords, if at all possible. This is because SSH keys provide a more secure way of logging in compared to using a password alone. While a password can eventually be cracked with a brute-force attack, SSH keys are nearly impossible to decipher by brute force alone." Plus, it means you never have to type C!$c0 again!

Cisco IOS now has support for using SSH with RSA keys. There are many resources showing how to configure SSH with RSA keys on the Internet and I have included several in the references section to give you more information. In this blog I am going to show how to configure a switch and create the public/private key pair using Puttygen for Windows.

OpenSSH ships with most *nix OS's like Mac OSX and Ubuntu so you don't need a separate program to generate the key pair. There are resources in the reference section on how to create the keys using OpenSSH. As a side note, Microsoft announced that it is going to build OpenSSH support into Powershell so you may be able to log into the next release of Windows server using SSH.

Download Puttygen

Recently there was some malware floating around using the name putty.exe. Make sure that you download putty and puttygen from http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html

The MD5 check sums are at this link - checksums.  On Windows you can use the official MS tool FCIV to check the MD5 sums. You can also use the certutil tool built into windows:
certutil -hashfile <filename> md5

If you prefer a GUI Hashtab is a nice tool that integrates into the right click menu. It's free but does require registration and an email address.

On Linux:
md5sum <filename>

Once you have Puttygen double click to start it up. Enter a description for your key and a passphrase. I recommend storing your passphrase in a password manager so that you don't for get it. Select SSH-2 RSA and enter 2048 for bits. Enter a comment for your key pair and click Generate. You will be asked to move the mouse around to generate some entropy.

Once the key is done you can select it and paste it into the switch. You should also save the public and private keys to a file.

Open Putty and create a session. Click on Auth under the SSH menu. Under Authentication parameters click Browse and select your private key. Click on Session and save your session.

You can also click on Data under Connection and set up an Auto-login username:

Don't forget to save your session. If you always log in using the same settings you can set all of them and then save the session as the default session.

Setup the Cisco Device

I'm using a 3750X-48P-L running IOS Version 15.2(3)E1 for this example.

Configure a time server

While this isn't absolutely necessary it's the first thing I do on any production device.
3750x(config)#ntp server 129.6.15.29 prefer
3750x(config)#clock timezone PST -8 0
3750x(config)#clock summer-time PDT recurring

Configure an IP domain name, create the RSA private key and enable SSH

3750x(config)ip domain-name pu.pri
3750x(config)crypto key generate rsa modulus 2048 exportable
3750x(config)ip ssh version 2

Note the "exportable" parameter. This isn't required but I wanted to point that out that you can make the keys exportable. It's not so important in this case but if you have setup GetVPN on a router you absolutely want to export the keys used for the tunnels. If you don't and the router fails you will have to touch EVERY tunnel once you replace the hardware. If you have exported the keys you just reload them on the new hardware and call it a day.

I have a link to a Cisco TAC podcast on GetVPN and DMVPN in the references that does a great job of explaining how to use RSA key pairs and why you MUST export them. If you don't want to listen to the entire podcast jump to minute 40 or so and listen from there. I highly recommend listening to all the TAC Security podcasts.

View the key

3750x#sh crypto key mypubkey rsa
% Key pair was generated at: 22:53:25 PDT Jul 16 2015
Key name: 3750x.pu.pri
Key type: RSA KEYS
 Storage Device: not specified
 Usage: General Purpose Key
 Key is exportable. Redundancy enabled.
 Key Data:
  30820122 300D0609 2A864886 F70D0101 01050003 82010F00 3082010A 02820101
  00ABDBCC B2C31B8F 264A92D0 8C56D9F2 B5B2E8E3 354BDA0E A3C6F287 5D5A66D4
  5BDF9E25 A866E5CA 3B6641CB 375410E9 4F142169 8334C1DC 88F8BC34 80129A62
  F59E0B90 B329A728 93F96C32 EE2AF78A DFF692A0 1649D911 F8DA728B 108B2790
  4954B60D 62999C52 2F832900 61A654A3 938EF6FB EB85F88F 2A3740D6 BE57B4C8
  C55EE8A0 4F6A23AB 416CB6F3 9F211B2E 2640ED4E 7AB03B6F 4B982F91 4965B834
  DB00254F F00E5D4D D3C102AA 75A78903 862D22AF 290D85B2 09D1D8A6 4A5D66C4
  4B7A2E0F 437A4566 864130ED 82411160 4198AFC1 AC0C8946 2FE181A5 6AFBD4AF
  20E8D5A5 83BA182F A5FA8352 48E55CF5 1A5C2F38 B61A57A1 DC7229F8 994C87B2
  C5020301 0001

Export the key

3750x(config)#crypto key export rsa 3750x.pu.pri pem terminal 3des SecurePassPhrase
% Key name: 3750x.pu.pri
   Usage: General Purpose Key
   Key data:
-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAq9vMssMbjyZKktCMVtny
tbLo4zVL2g6jxvKHXVpm1FvfniWoZuXKO2ZByzdUEOlPFCFpgzTB3Ij4vDSAEppi
9Z4LkLMppyiT+Wwy7ir3it/2kqAWSdkR+NpyixCLJ5BJVLYNYpmcUi+DKQBhplSj
k472++uF+I8qN0DWvle0yMVe6KBPaiOrQWy2858hGy4mQO1OerA7b0uYL5FJZbg0
2wAlT/AOXU3TwQKqdaeJA4YtIq8pDYWyCdHYpkpdZsRLei4PQ3pFZoZBMO2CQRFg
QZivwawMiUYv4YGlavvUryDo1aWDuhgvpfqDUkjlXPUaXC84thpXodxyKfiZTIey
xQIDAQAB
-----END PUBLIC KEY-----
-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED
DEK-Info: DES-EDE3-CBC,3E0EAC17DCDE45B0
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-----END RSA PRIVATE KEY-----

Configure AAA authentication

The aaa new-model command causes the local username and password on the router to be used in the absence of other AAA statements. Once you enter "aaa new-model" you will not be able to enter "login local" on vty line configuration. If you had login local configured it will be removed.

When you create the username be sure to include a secret. I you don't anyone will be able to login with just the username. As always, create a strong secret and use a password manager to store it.

3750x(config)#username cisco privilege 15 secret ^8(nn-!#who
3750x(config)#aaa new-model
3750x(config)#aaa authentication login default local
3750x(config)#aaa authorization exec default local

(Authentication through the line password is not possible with SSH)

Configure the line

3750x(config)#line vty 0 4
3750x(config-line)#transport input ssh
3750x(config-line)#logging sync (prevents console messages from interfering with your inputs)

Add your PUBLIC key to the device.

Open the public key file you created in puttygen. Copy the text between the comments. If you generated a 2048 bit key you will need to paste it into notepad and break it into smaller pieces or you may see "%SSH: Failed to decode the Key Value" when you exit:
3750x(config)#ip ssh pubkey-chain
3750x(conf-ssh-pubkey)#username hubbard
3750x(conf-ssh-pubkey-user)#key-string
3750x(conf-ssh-pubkey-data)#$QAAAQEAkp2EDdpi86+h2aygSIYLt6DvoeFVKYJ1S/Zr
3750x(conf-ssh-pubkey-data)#$ylIDAzWA+G9TolxvWTLzTcUR/+Ykk74mqQbuGTxpteP
3750x(conf-ssh-pubkey-data)#$IStVVjycGYHRSJv9H2C8OQYMcHCR7yM/36TTFRIjLfV
3750x(conf-ssh-pubkey-data)#$PaWM45mr8DI2/sJkwESLWWGJKYiaSxEG6h+gLA5DePj
3750x(conf-ssh-pubkey-data)#$SP4zpktK7KD51NQDy8vx3jVVhkkANGbFfz/uWk2Uhno
3750x(conf-ssh-pubkey-data)#$DQeBxtZbxEGU4tXDZmRbPGVmk8DtFh9LVRCxUTQ==
3750x(conf-ssh-pubkey-data)#exit

3750x#sh run | sec ssh
ip ssh version 2
ip ssh pubkey-chain
  username hubbard
   key-hash ssh-rsa 0C029272CF23E61C4315A0D59E565B76
 transport input telnet ssh
3750x#
3750x#sh run | b 0 4
line vty 0 4
 transport input ssh
line vty 5 15

Note - You can use the HASH instead of the key for the next devices you setup. Instead of using "Key-string" in the ip ssh pubkey-chain statement use "key-hash ssh-rsa 0C029272CF23E61C4315A0D59E565B76".

Login using your SSH Keys!

References

SSH RSA authentication works in IOS release 15.0M
Secure Shell Version 2 Support in IOS 15
TAC Security Podcast Episode #25 - GETVPN and DMVPN
SSH/OpenSSH/Keys - A good Ubuntu article on OpenSSH
How to create ssh keys with putty to connect to a virtual private server (VPS) - The Digital Ocean Tutorial. They have a lot of good tutorials.
Using SSH/SCP on Mac OS X in the Terminal app
Kali Linux remote SSH – How to configure openSSH server - A great tutorial.
SSH using public key authentication to IOS and big outputs - A Cisco Support Forum article. It includes a Bash script for remotely executing commands.

SSH with key authentication on Cisco IOS devices - A good blog for Windows users
How To Protect SSH with fail2ban on Ubuntu 12.04
Synchronise remote SSH authorised_keys
Configure SSH in IOS - For IOx devices such as ISR819(C819), CGR1120/1240, and IR829/809.

Basic Authentication on Cisco Network Devices

In this blog I want to go over basic authentication on a Cisco device because I see a lot of questions on authentication on the Cisco Support forums. Here I have cleared the configuration on a 3750-48PS running IOS 12.2.55-SE10. Once the switch rebooted I connected with a console cable and answered No to the wizard. Then I added an IP address to vlan 1.

interface Vlan1
 ip address 192.168.10.50 255.255.255.0
 no ip redirects
end

Here is what a login session looked like:

As you can see you can't log in using telnet because the vty lines aren't configured. This is really a problem if you forget and leave the site. You will have to return and configure the vty lines before you can log in remotely.

Here is the configuration required to use telnet:
Switch(config)#line vty 0 15
Switch(config-line)#password cisco1
Switch(config-line)#login
Switch(config-line)#end

Switch#sh run | b 0 4
line vty 0 4
 password cisco1
 login
line vty 5 15
 password cisco1
 login
!

Here is what a login session looked like:

Notice that you are placed into user mode. Since we didn't create an "enable secret" password we cannot change to enable mode.

To create an enable secret:
Switch(config)#enable secret 9x3kaqq!!
Switch(config)#end

Using login local

Now we will add "login local" to the vty lines.
Switch(config)#line vty 0 15
Switch(config-line)#login local
Switch(config-line)#end

Switch#sh run | b 0 4
line vty 0 4
 password cisco1
 login local
line vty 5 15
 password cisco1
 login local
!
end

Once login local is added you must create a local user or you will not be able to login. To create the user:
Switch(config)#username cisco privilege 15 secret 9x3kaqq
Switch(config)#end
Switch#sh run | i username
username cisco privilege 15 secret 5 $1$T6mv$85a/oQ3sWiyxKd/yQ9Sh3/


Here is what a login session looked like:

Notice that you are logged directly to enable mode. 

Now we will add a "aaa new-model" command:

aaa new-model

aaa authentication login default local

aaa authorization exec default local

end

Switch#

!Note that login local is removed from vty configuration. You cannot use login local

!once you add the aaa new-model command.

Switch#sh run | b 0 4

line vty 0 4

 password cisco1

line vty 5 15

 password cisco1

!

Switch#sh run | i aaa

aaa new-model

aaa authentication login default local

aaa authorization exec default local

aaa session-id common

Here is what a login session looked like:

Customize the prompts

You can customize the login prompts for username and password. The is helpful if you have a mix of devices using local databases and RADIUS or Tacacs. One caution though, be careful if you are using Cisco Prime Infrastructure or other tool that logs into the devices. I had a bunch of devices with custom prompts one time using local database authentication. I then tried to add the devices to Prime and it failed on the authentication. It turns out that I had miss-spelled password and Prime was looking for Password in the prompt from the switch.

Switch(config)#aaa authentication password-prompt "Enter Local Password: "

Switch(config)#aaa authentication username-prompt "Enter Local username: "

Switch(config)#end

Conclusions

• It's easy to forget to set up telnet or SSH correctly and not be able to log in remotely once you deploy the switch so pick an authentication method and add it to your basic configuration script.
• To use RADIUS or TACACS+ you must create a new-model.
• Don't use telnet unless your device doesn't support encryption. Once you have a username, enable secret and login local, setting up SSH is easy. 

Here are the steps to enable SSH:

Add a hostname to the device - hostname sw1

Add a domain name - ip domain-name mylab.pri

Create the RSA keys - crypto key generate rsa general-keys modulus 2048 (depending on your IOS version this command my be different. Use the ? to work your way through.

enable SSH - ip ssh ver 2
save the configuration - wr mem

The first time your computer connects to a device with SSH enabled you will be asked to verify the host keys. This is because the RSA keys the device offers to you are not known to your host yet. If you are sure that you entered the IP address correctly accept the keys. If you are on Windows using Putty this is what the message looks like:

Checking Server Cipher Suites with Nmap

Ok, one more blog on cipher suites and then I'm finished (for a while!). Last night I was reading  Testing for Weak SSL/TLS Ciphers on the OWASP site and found an nmap script that gives you a quick and dirty way to check ciphers. One advantage over cipherscan is that nmap runs on almost every OS.

I ran the script against the same servers as in the cipherscan blog. You can see that you don't get quite as much information but if you updating your server's list of ciphers or inspecting a new version of IOS you get enough and it's pretty quick. Notice that you can test any port. In the OWASP example they were testing a mail server so they included smtps, imaps and pop3s ports.

Here is nmap running against my ISE server. The scan took 1.53 seconds:

1S1K-930:~ mhubbard$ nmap --script ssl-cert,ssl-enum-ciphers -p 443,465,993,995 192.168.10.21

Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-13 18:48 PDT
Nmap scan report for 192.168.10.21
Host is up (0.00091s latency).
PORT    STATE    SERVICE
443/tcp open     https
| ssl-cert: Subject: commonName=RANISE01.pu.pri
| Issuer: commonName=ProgrammingUnlimited
| Public Key type: rsa
| Public Key bits: 2048
| Not valid before: 2015-07-12T02:38:27+00:00
| Not valid after:  2017-07-11T02:38:27+00:00
| MD5:   fab4 235e fa7d 9f4a d10a 6b24 9764 0cdd
|_SHA-1: 539e 2a03 14b3 c265 1e41 ebf9 c987 77e5 8d63 783c
| ssl-enum-ciphers:
|   SSLv3:
|     ciphers:
|       TLS_DHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_DHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA - strong
|     compressors:
|       NULL
|   TLSv1.0:
|     ciphers:
|       TLS_DHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_DHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA - strong
|     compressors:
|       NULL
|_  least strength: strong
465/tcp filtered smtps
993/tcp filtered imaps
995/tcp filtered pop3s

Nmap done: 1 IP address (1 host up) scanned in 1.53 seconds

*****************************************

Here is the HP OfficeJet Pro 8600. The scan took .75 seconds.

1S1K-930:~ mhubbard$ nmap --script ssl-cert,ssl-enum-ciphers -p 443,465,993,995 192.168.10.239

Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-13 18:39 PDT

Nmap scan report for 192.168.10.239

Host is up (0.0015s latency).

PORT    STATE  SERVICE

443/tcp open   https

| ssl-cert: Subject: commonName=HP6544E8/organizationName=HP/stateOrProvinceName=Washington/countryName=US

| Issuer: commonName=HP6544E8/organizationName=HP/stateOrProvinceName=Washington/countryName=US

| Public Key type: rsa

| Public Key bits: 1024

| Not valid before: 2014-08-28T13:09:39+00:00

| Not valid after:  2034-08-23T13:09:39+00:00

| MD5:   ac97 99b1 8ed9 b0c5 8d38 fcb4 764e f4dd

|_SHA-1: 982e ea57 c19c 6cde 38bc f9eb 523f 274e f837 dc93

| ssl-enum-ciphers: 

|   SSLv3: 

|     ciphers: 

|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong

|       TLS_RSA_WITH_AES_128_CBC_SHA - strong

|       TLS_RSA_WITH_AES_256_CBC_SHA - strong

|       TLS_RSA_WITH_DES_CBC_SHA - weak

|       TLS_RSA_WITH_RC4_128_MD5 - strong

|       TLS_RSA_WITH_RC4_128_SHA - strong

|     compressors: 

|       NULL

|   TLSv1.0: 

|     ciphers: 

|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong

|       TLS_RSA_WITH_AES_128_CBC_SHA - strong

|       TLS_RSA_WITH_AES_256_CBC_SHA - strong

|       TLS_RSA_WITH_DES_CBC_SHA - weak

|       TLS_RSA_WITH_RC4_128_MD5 - strong

|       TLS_RSA_WITH_RC4_128_SHA - strong

|     compressors: 

|       NULL

|_  least strength: weak

465/tcp closed smtps

993/tcp closed imaps

995/tcp closed pop3s

Nmap done: 1 IP address (1 host up) scanned in 0.75 seconds

*****************************************

And finally mail.google.com. Notice that the smtps, imaps and pop3s are filtered. You have to have a gmail account and set it specifically before you can use "The less secure Protocols" like imaps. This scan was much larger and took 85 seconds.

C:\Windows\system32>nmap --script ssl-cert,ssl-enum-ciphers -p 443,465,993,995 mail.google.com

Starting Nmap 6.47 ( http://nmap.org ) at 2015-07-12 21:02 Pacific Daylight Time
Nmap scan report for mail.google.com (173.194.219.18)
Host is up (0.0090s latency).
Other addresses for mail.google.com (not scanned): 173.194.219.17 173.194.219.83 173.194.219.19
rDNS record for 173.194.219.18: ya-in-f18.1e100.net
PORT    STATE    SERVICE
443/tcp open     https
| ssl-cert: Subject: commonName=mail.google.com/organizationName=Google Inc/stateOrProvinceName=California/countryName=US
| Issuer: commonName=Google Internet Authority G2/organizationName=Google Inc/countryName=US
| Public Key type: rsa
| Public Key bits: 2048
| Not valid before: 2015-07-01T19:53:43+00:00
| Not valid after:  2015-09-28T23:00:00+00:00
| MD5:   1b61 b9fb ee8c 6735 f5bf 414b 5b8a ce81
|_SHA-1: b434 c59a 0926 b380 d4d2 8002 0870 4ee5 87e1 1945
| ssl-enum-ciphers:
|   SSLv3:
|     ciphers:
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_RC4_128_SHA - strong
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_RC4_128_MD5 - strong
|       TLS_RSA_WITH_RC4_128_SHA - strong
|     compressors:
|       NULL
|   TLSv1.0:
|     ciphers:
|       TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_RC4_128_SHA - strong
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_RC4_128_SHA - strong
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_RC4_128_MD5 - strong
|       TLS_RSA_WITH_RC4_128_SHA - strong
|     compressors:
|
|   TLSv1.1:
|     ciphers:
|       TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_RC4_128_SHA - strong
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_RC4_128_SHA - strong
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_RC4_128_MD5 - strong
|       TLS_RSA_WITH_RC4_128_SHA - strong
|     compressors:
|
|   TLSv1.2:
|     ciphers:
|       TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256 - strong
|       TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 - strong
|       TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 - strong
|       TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 - strong
|       TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 - strong
|       TLS_ECDHE_ECDSA_WITH_RC4_128_SHA - strong
|       TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 - strong
|       TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 - strong
|       TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 - strong
|       TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 - strong
|       TLS_ECDHE_RSA_WITH_RC4_128_SHA - strong
|       TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA - strong
|       TLS_RSA_WITH_AES_128_CBC_SHA256 - strong
|       TLS_RSA_WITH_AES_128_GCM_SHA256 - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA - strong
|       TLS_RSA_WITH_AES_256_CBC_SHA256 - strong
|       TLS_RSA_WITH_AES_256_GCM_SHA384 - strong
|       TLS_RSA_WITH_RC4_128_MD5 - strong
|       TLS_RSA_WITH_RC4_128_SHA - strong
|     compressors:
|       NULL
|_  least strength: strong
465/tcp filtered smtps
993/tcp filtered imaps
995/tcp filtered pop3s

Nmap done: 1 IP address (1 host up) scanned in 84.99 seconds

References

ssl-enum-ciphers man page
ssl-cert man page
NMAP Scripts page - There are 498 scripts on the nmap site!  If you need a script and can't find one on the nmap site you can google the protocol and nmap.

Recently I was investigating a Linksys router that a friend bought. I googled nmap and HNAP and found a script that locates routers running the Home Network Administration Protocol. Another example, HD Moore has an enhanced version of the nmap banner script called banner-plus on github.
More on HNAP - What is it, How to Use it, How to Find it

Checking Browser Cipher Suites

My previous blog showed you an easy way to check the cipher suites offered by a server. Now I will show you an easy way to check your browser's cipher suites.

The team at the  "Distributed Computing & Security (DCSec) Research Group" of the Leibniz Universität Hannover have created a web page that pulls all of the cipher suites out of your browser - Cipher Suites Supported by Your Browser (ordered by preference). A big thank you to the team that created this site! 

NOTE: the German site is no longer up. Please use Qualys.com instead

Qualys Client Test


I wanted to see how bad IE6 on Windows XP really was so I fired up my XP SP3 Virtual Machine and went to the site. Yikes it's bad! My favorite cipher in the list is RC2 with 40 bit key size!

I highlighted the connection that my browser made in red, it's SSL3.0 with RC4 and SHA1. Well, at least it isn't vulnerable to BEAST!

For all of the corporate IT folks that have to run IE6 because of legacy applications here are the results:

Spec	Cipher_Suite_Name	Key_Siz	Description
(00,04)	RSA-RC4128-MD5	128 Bit	Key exchange: RSA, encryption: RC4, MAC: MD5.
(00,05)	RSA-RC4128-SHA	128 Bit	Key exchange: RSA, encryption: RC4, MAC: SHA1
(00,0a)	RSA-3DES-EDE-SHA	168 Bit	Key exchange: RSA, encryption: 3DES, MAC: SHA1.
(01,0080)	RC4128-MD5	128 Bit	Key exchange: RC4, encryption algorithm is unknown, MAC: MD5.
(07,00c0)	DES192-EDE3-MD5	168 Bit	Key exchange: Data Encryption Standard (DES), encryption algorithm is unknown, MAC: MD5.
(03,0080)	RC2128-MD5	128 Bit	Key exchange: RC2, encryption algorithm is unknown, MAC: MD5.
(00,09)	RSA-DES-SHA	56 Bit	Key exchange: RSA, encryption: DES, MAC: SHA1.
(06,0040)	DES64-MD5	56 Bit	Key exchange: Data Encryption Standard (DES), encryption algorithm is unknown, MAC: MD5.
(00,64)	RSA-EXPORT1024-RC456-SHA	56 Bit	Key exchange: RSA, encryption: RC4, MAC: SHA1.
(00,62)	RSA-EXPORT1024-DES-SHA	56 Bit	Key exchange: RSA, encryption: DES, MAC: SHA1.
(00,03)	RSA-EXPORT-RC440-MD5	40 Bit	Key exchange: RSA, encryption: RC4, MAC: MD5.
(00,06)	RSA-EXPORT-RC2-CBC40-MD5	40 Bit	Key exchange: RSA, encryption: RC2, MAC: MD5.
(02,0080)	RC4128-EXPORT40-MD5	40 Bit	Key exchange: RC4, encryption algorithm is unknown, MAC: MD5.
(04,0080)	RC2128-EXPORT40-MD5	40 Bit	Key exchange: RC2, encryption algorithm is unknown, MAC: MD5.
(00,13)	DHE-DSS-3DES-EDE-SHA	168 Bit	Key exchange: DH, encryption: 3DES, MAC: SHA1.
(00,12)	DHE-DSS-DES-SHA	56 Bit	Key exchange: DH, encryption: DES, MAC: SHA1.
(00,63)	DHE-DSS-EXPORT1024-DES-SHA	56 Bit	Key exchange: DH, encryption: DES, MAC: SHA1.

User-Agent:Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; .NET4.0C; .NET4.0E)Preferred SSL/TLS version: SSLv3SNI information: Your
browser did not send SNI information.SSL stack current time: The TLS stack of your browser did not send a time value.

This connection uses SSLv3 with RC4-SHA and a 128 Bit key for encryption.
Raw: Version: 3.0 Ciphers:04,05,0a,010080,0700c0,030080,09,060040,64,62,03,06,020080,040080,13,12,63 Extensions: The TLS stack of your browser did not send
extensions.Remote Time: The TLS stack of your browser did not send a time value.

This service is provided by the DCSEC research group at Leibniz University Hannover. Imprint
If you have any comments or questions please contact Sascha Fahl
***************************************

Next I went to the site with Firefox 39 on XP SP3 and the results were much different! Even running on XP SP3 Firefox provided modern cipher suites and didn't offer the "Export Grade" suites used by Logjam.

The connection negotiated was the latest TLSv1.2 with Elliptic Curve DH Ephemeral to give Perfect Forward Secrecy and SHA 256 for the MAC! Again, I highlighted the connection in red.
***************************************

Spec	Cipher Suite Name	Key Size	Description
(c0,2b)	ECDHE-ECDSA-AES128-GCM-SHA256	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA256.
(c0,2f)	ECDHE-RSA-AES128-GCM-SHA256	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA256.
(c0,0a)	ECDHE-ECDSA-AES256-SHA	256 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(c0,09)	ECDHE-ECDSA-AES128-SHA	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(c0,13)	ECDHE-RSA-AES128-SHA	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(c0,14)	ECDHE-RSA-AES256-SHA	256 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(00,33)	DHE-RSA-AES128-SHA	128 Bit	Key exchange: DH, encryption: AES, MAC: SHA1.
(00,39)	DHE-RSA-AES256-SHA	256 Bit	Key exchange: DH, encryption: AES, MAC: SHA1.
(00,2f)	RSA-AES128-SHA	128 Bit	Key exchange: RSA, encryption: AES, MAC: SHA1.
(00,35)	RSA-AES256-SHA	256 Bit	Key exchange: RSA, encryption: AES, MAC: SHA1.
(00,0a)	RSA-3DES-EDE-SHA	168 Bit	Key exchange: RSA, encryption: 3DES, MAC: SHA1.

Further information:
User-Agent:
Mozilla/5.0 (Windows NT 5.1; rv:39.0) Gecko/20100101 Firefox/39.0
Preferred SSL/TLS version:
TLSv1
SNI information:
cc.dcsec.uni-hannover.de
SSL stack current time:
The TLS stack of your browser did not send a time value.

This connection uses TLSv1.2 with ECDHE-RSA-AES128-GCM-SHA256 and a 128 Bit key for encryption.

Raw:
Version:
3.1
Ciphers:
c02b,c02f,c00a,c009,c013,c014,33,39,2f,35,0a
Extensions:
0000,ff01,000a,000b,0023,3374,0010,0005,000d
Remote Time:
The TLS stack of your browser did not send a time value.

This service is provided by the DCSEC research group at Leibniz University Hannover. Imprint
If you have any comments or questions please contact Sascha Fahl
***************************************

Next I tried my Samsung s5 running Google Chorme. To my surprise it supported the latest cipher suites and no "Export Grade" ciphers.

***************************************

Spec	Cipher Suite Name	Key Size	Description
(cc,14)	ECDHE-ECDSA-CHACHA20-POLY1305-SHA256	128 Bit	Key exchange: ECDH, encryption: ChaCha20 Poly1305, MAC: SHA256.
(cc,13)	ECDHE-RSA-CHACHA20-POLY1305-SHA256	128 Bit	Key exchange: ECDH, encryption: ChaCha20 Poly1305, MAC: SHA256.
(cc,15)	DHE-RSA-CHACHA20-POLY1305-SHA256	128 Bit	Key exchange: DH, encryption: ChaCha20 Poly1305, MAC: SHA256.
(c0,2b)	ECDHE-ECDSA-AES128-GCM-SHA256	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA256.
(c0,2f)	ECDHE-RSA-AES128-GCM-SHA256	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA256.
(00,9e)	DHE-RSA-AES128-GCM-SHA256	128 Bit	Key exchange: DH, encryption: AES, MAC: SHA256.
(c0,0a)	ECDHE-ECDSA-AES256-SHA	256 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(c0,14)	ECDHE-RSA-AES256-SHA	256 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(00,39)	DHE-RSA-AES256-SHA	256 Bit	Key exchange: DH, encryption: AES, MAC: SHA1.
(c0,09)	ECDHE-ECDSA-AES128-SHA	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(c0,13)	ECDHE-RSA-AES128-SHA	128 Bit	Key exchange: ECDH, encryption: AES, MAC: SHA1.
(00,33)	DHE-RSA-AES128-SHA	128 Bit	Key exchange: DH, encryption: AES, MAC: SHA1.
(00,9c)	RSA-AES128-GCM-SHA256	128 Bit	Key exchange: RSA, encryption: AES, MAC: SHA256.
(00,35)	RSA-AES256-SHA	256 Bit	Key exchange: RSA, encryption: AES, MAC: SHA1.
(00,2f)	RSA-AES128-SHA	128 Bit	Key exchange: RSA, encryption: AES, MAC: SHA1.
(00,0a)	RSA-3DES-EDE-SHA	168 Bit	Key exchange: RSA, encryption: 3DES, MAC: SHA1.
(00,ff)	EMPTY-RENEGOTIATION-INFO-SCSV	0 Bit	Used for secure renegotation.

Further information:

User-Agent:Mozilla/5.0 (Linux; Android 5.0; SM-G900V Build/LRX21T) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.93 Mobile

Safari/537.36
Preferred SSL/TLS version: TLSv1
SNI information: cc.dcsec.uni-hannover.de
SSL stack current time: The TLS stack of your browser did not send a time value.

This connection uses TLSv1.2 with ECDHE-RSA-AES128-GCM-SHA256 and a 128 Bit key for encryption.

***************************************

Conclusions

• Don't use IE6 for anything you don't have too!  
• Keep your browser updated. Firefox and Chrome especially are rapidly upgrading their cipher suites.
• If you use Firefox install the Calomel Addon to quickly see what ciphers a connection is using.
• If you are responsible for maintaining a web server read the Mozilla Wiki on Server Side Security and make sure you have the best cipher suites that your clients can use.
• If you are responsible for a Windows IIS web server use Steve Gibson's Ordered and Curated cipher suite list
• Read the ars Technica blog on Massive leak reveals Hacking Team’s most private moments in messy detail to see how dangerous the Internet really is.

Checking Server Cipher Suites with Cipherscan

Unless you have been living under a rock for the last year you have heard about many of the flaws with SSL - Heartbleed, Logjam, Poodle, etc.

And then there is the ars technica article on the breach at the infamous organization "The Hacking Team" . Here is a disturbing paragraph from the article:

******************************************
Still another document boasts of Hacking Team's ability to bypass certificate pinning and the HTTP strict transport security mechanisms that are designed to make HTTPS website encryption more reliable and secure. "Our solution is the only way to intercept TOR traffic at the moment," the undated PowerPoint presentation went on to say.
******************************************

For a network engineer there is also the problem that Firefox and Chrome are going to stop allowing you to go to servers with weak security. Here is a screen shot of the message I received in Firefox 39 this morning when I tried to log into my Cisco ISE server:

Firefox 39 connecting to Cisco ISE 1.2

I put the message into Google and found this on the Firefox support site:

It makes you wish you had an easy way to know what cipher suites a server can provide! Well lucky for us there is a project on Github called Cipherscan that does just that! They created a customized version of OpenSSL and a script for Linux. You just download the custom OpenSSL package, install it in a private directory, save the script to the apps directory and execute the script. It's that easy and in my opinion it is a great tool to have in your toolbox, a big thank you to the developers!

*********************************************
From the cipherscan readme file:
Cipherscan tests the ordering of the SSL/TLS ciphers on a given target, for all major versions of SSL
and TLS. It also extracts some certificates informations, TLS options, OCSP stapling and more. Cipherscan is a wrapper above the openssl s_client command line.

Cipherscan is meant to run on all flavors of unix. It ships with its own built of OpenSSL for
Linux/64 and Darwin/64. On other platform, it will use the openssl version provided by the operating
system (which may have limited ciphers support), or your own version provided in the -o command line flag.

*********************************************

Script Output

I have been running the script against a lot of different servers and the results are interesting.

For example, here is the output from my ISE server:
root@kali:~/Desktop/openssl/apps# ./cipherscan 192.168.10.21
......
Target: 192.168.10.21:443

prio	ciphersuite	protocols	pfs	curves
1	DHE-RSA-AES256-SHA	SSLv3,TLSv1	DH,768bits	None
2	AES256-SHA	SSLv3,TLSv1	None	None
3	DHE-RSA-AES128-SHA	SSLv3,TLSv1	DH,768bits	None
4	AES128-SHA	SSLv3,TLSv1	None	None
5	DES-CBC3-SHA	SSLv3,TLSv1	None	None

Certificate: UNTRUSTED, 2048 bit, sha1WithRSAEncryption signature
TLS ticket lifetime hint: None
OCSP stapling: not supported
Cipher ordering: client

You can see that the Diffe-Hellman Ephemeral key is only 768 bits.

Then I ran it on an HP officeJet pro 8600. Firefox 39 will open this page because the printer doesn't offer a weak Diffe-Hellman Ephemeral key but the Calomel SSL extension turns red.

If you aren't running the Calomel extension for Firefox I highly recommend it. Calomel checks the certificate on every site and gives you a Red, Yellow or Green shield depending on the strength of the certificate. See the "References" section below for their site. They have a lot of good information about SSL on their site.

root@kali:~/Desktop/openssl/apps# ./cipherscan 192.168.10.239
.......
Target: 192.168.10.239:443

prio	ciphersuite	protocols	pfs	curves
1	AES256-SHA	SSLv3,TLSv1	None	None
2	AES128-SHA	SSLv3,TLSv1	None	None
3	RC4-SHA	SSLv3,TLSv1	None	None
4	RC4-MD5	SSLv3,TLSv1	None	None
5	DES-CBC3-SHA	SSLv3,TLSv1	None	None
6	DES-CBC-SHA	SSLv3,TLSv1	None	None

Certificate: UNTRUSTED, 1024 bit, md5WithRSAEncryption signature
TLS ticket lifetime hint: None
OCSP stapling: not supported
Cipher ordering: client

Here is the output from https://mail.google.com.

root@kali:~/Desktop/openssl/apps# ./cipherscan mail.google.com
...................
Target: mail.google.com:443

prio	ciphersuite	protocols	pfs	curves
1	ECDHE-RSA-CHACHA20-POLY1305	TLSv1.2	ECDH,P-256,256bits	prime256v1
2	ECDHE-RSA-AES128-GCM-SHA256	TLSv1.2	ECDH,P-256,256bits	prime256v1
3	ECDHE-RSA-AES128-SHA	TLSv1.1,TLSv1.2	ECDH,P-256,256bits	prime256v1
4	ECDHE-RSA-RC4-SHA	SSLv3,TLSv1,TLSv1.1,TLSv1.2	ECDH,P-256,256bits	prime256v1
5	AES128-GCM-SHA256	TLSv1.2	None	None
6	AES128-SHA256	TLSv1.2	None	None
7	AES128-SHA	TLSv1.1,TLSv1.2	None	None
8	RC4-SHA	SSLv3,TLSv1,TLSv1.1,TLSv1.2	None	None
9	RC4-MD5	SSLv3,TLSv1,TLSv1.1,TLSv1.2	None	None
10	ECDHE-RSA-AES256-GCM-SHA384	TLSv1.2	ECDH,P-256,256bits	prime256v1
11	ECDHE-RSA-AES256-SHA384	TLSv1.2	ECDH,P-256,256bits	prime256v1
12	ECDHE-RSA-AES256-SHA	SSLv3,TLSv1,TLSv1.1,TLSv1.2	ECDH,P-256,256bits	prime256v1
13	AES256-GCM-SHA384	TLSv1.2	None	None
14	AES256-SHA256	TLSv1.2	None	None
15	AES256-SHA	SSLv3,TLSv1,TLSv1.1,TLSv1.2	None	None
16	ECDHE-RSA-AES128-SHA256	TLSv1.2	ECDH,P-256,256bits	prime256v1
17	ECDHE-RSA-DES-CBC3-SHA	SSLv3,TLSv1,TLSv1.1,TLSv1.2	ECDH,P-256,256bits	prime256v1
18	DES-CBC3-SHA	SSLv3,TLSv1,TLSv1.1,TLSv1.2	None	None

Certificate: trusted, 2048 bit, sha256WithRSAEncryption signature
TLS ticket lifetime hint: 100800
OCSP stapling: not supported
Cipher ordering: server

Here is Calomel's view of the certificate:

Installing Cipherscan

Open a terminal on kali or your favorite Linux distro.
Switch to the directory you want to install Cipherscan into.

• run git clone https://github.com/PeterMosmans/openssl.git --depth 1 -b 1.0.2-chacha
• cd openssl
• ./Configure zlib no-shared experimental-jpake enable-md2 enable-rc5 \ enable-rfc3779 enable-gost 
• enable-static-engine linux-x86_64
• make depend
• make
• make report

Get the script from https://github.com/jvehent/cipherscan.

To copy the script click in the page and press ctrl+a on Linux\Windows or command+a on Max OSX. Paste the script into your editor of choice, verify that you copied it correctly, then save it to the apps folder.

The Mozilla Wiki article on Sever Side TLS

The Mozilla Wiki has a great article on TLS. It explains Forward Secrecy, Diffie\Hellman Ephemeral key exchange, OCSP Stapling and much more for just about every browser and OS. It is also where I found cipherscan!

If you are responsible for an Apache, Haproxy or Nginx server the Mozilla wiki article is a must read. It even has a configuration generator for these servers that will create a configuration based on which generation browsers you must support.

References:

Cipherscan on Github

Mozilla Wiki - Security/Server Side TLS
Calomel Firefox Addon
ars technica - Massive leak reveals Hacking Team’s most private moments in messy detail
Defensive Security Episode 122 - Discussion on the breach at The Hacking Team
Testing for Weak SSL/TLS Ciphers - OWASP
SSL Cipher Suites Supported By Your Browser
How to restrict the use of certain cryptographic algorithms and protocols in Schannel.dll