Configuring Secure Socket Layer HTTP

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Information about Secure Sockets Layer (SSL) HTTP

Secure HTTP Servers and Clients Overview

On a secure HTTP connection, data to and from an HTTP server is encrypted before being sent over the Internet. HTTP with SSL encryption provides a secure connection to allow such functions as configuring a switch from a Web browser. Cisco's implementation of the secure HTTP server and secure HTTP client uses an implementation of SSL Version 3.0 with application-layer encryption. HTTP over SSL is abbreviated as HTTPS; the URL of a secure connection begins with https:// instead of http://.


Note

SSL evolved into Transport Layer Security (TLS) in 1999, but is still used in this particular context.

The primary role of the HTTP secure server (the switch) is to listen for HTTPS requests on a designated port (the default HTTPS port is 443) and pass the request to the HTTP 1.1 Web server. The HTTP 1.1 server processes requests and passes responses (pages) back to the HTTP secure server, which, in turn, responds to the original request.

The primary role of the HTTP secure client (the web browser) is to respond to Cisco IOS application requests for HTTPS User Agent services, perform HTTPS User Agent services for the application, and pass the response back to the application.

Certificate Authority Trustpoints

Certificate authorities (CAs) manage certificate requests and issue certificates to participating network devices. These services provide centralized security key and certificate management for the participating devices. Specific CA servers are referred to as trustpoints.

When a connection attempt is made, the HTTPS server provides a secure connection by issuing a certified X.509v3 certificate, obtained from a specified CA trustpoint, to the client. The client (usually a Web browser), in turn, has a public key that allows it to authenticate the certificate.

For secure HTTP connections, we highly recommend that you configure a CA trustpoint. If a CA trustpoint is not configured for the device running the HTTPS server, the server certifies itself and generates the needed RSA key pair. Because a self-certified (self-signed) certificate does not provide adequate security, the connecting client generates a notification that the certificate is self-certified, and the user has the opportunity to accept or reject the connection. This option is useful for internal network topologies (such as testing).

If you do not configure a CA trustpoint, when you enable a secure HTTP connection, either a temporary or a persistent self-signed certificate for the secure HTTP server (or client) is automatically generated.

  • If the switch is not configured with a hostname and a domain name, a temporary self-signed certificate is generated. If the switch reboots, any temporary self-signed certificate is lost, and a new temporary new self-signed certificate is assigned.

  • If the switch has been configured with a host and domain name, a persistent self-signed certificate is generated. This certificate remains active if you reboot the switch or if you disable the secure HTTP server so that it will be there the next time you re-enable a secure HTTP connection.


Note

The certificate authorities and trustpoints must be configured on each device individually. Copying them from other devices makes them invalid on the switch.

When a new certificate is enrolled, the new configuration change is not applied to the HTTPS server until the server is restarted. You can restart the server using either the CLI or by physical reboot. On restarting the server, the switch starts using the new certificate.

If a self-signed certificate has been generated, this information is included in the output of the show running-config privileged EXEC command. This is a partial sample output from that command displaying a self-signed certificate. 


Device# show running-config
Building configuration...

<output truncated>

crypto pki trustpoint TP-self-signed-3080755072
 enrollment selfsigned
 subject-name cn=IOS-Self-Signed-Certificate-3080755072
 revocation-check none
 rsakeypair TP-self-signed-3080755072
!
!
crypto ca certificate chain TP-self-signed-3080755072
 certificate self-signed 01
  3082029F 30820208 A0030201 02020101 300D0609 2A864886 F70D0101 04050030
  59312F30 2D060355 04031326 494F532D 53656C66 2D536967 6E65642D 43657274
  69666963 6174652D 33303830 37353530 37323126 30240609 2A864886 F70D0109
  02161743 45322D33 3535302D 31332E73 756D6D30 342D3335 3530301E 170D3933
  30333031 30303030 35395A17 0D323030 31303130 30303030 305A3059 312F302D

<output truncated>

You can remove this self-signed certificate by disabling the secure HTTP server and entering the no crypto pki trustpoint TP-self-signed-30890755072 global configuration command. If you later re-enable a secure HTTP server, a new self-signed certificate is generated.


Note

The values that follow TP self-signed depend on the serial number of the device.

You can use an optional command (ip http secure-client-auth ) to allow the HTTPS server to request an X.509v3 certificate from the client. Authenticating the client provides more security than server authentication by itself.

CipherSuites

A CipherSuite specifies the encryption algorithm and the digest algorithm to use on a SSL connection. When connecting to the HTTPS server, the client Web browser offers a list of supported CipherSuites, and the client and server negotiate the best encryption algorithm to use from those on the list that are supported by both. For example, Netscape Communicator 4.76 supports U.S. security with RSA Public Key Cryptography, MD2, MD5, RC2-CBC, RC4, DES-CBC, and DES-EDE3-CBC.

For the best possible encryption, you should use a client browser that supports 128-bit encryption, such as Microsoft Internet Explorer Version 5.5 (or later) or Netscape Communicator Version 4.76 (or later). The SSL_RSA_WITH_DES_CBC_SHA CipherSuite provides less security than the other CipherSuites, as it does not offer 128-bit encryption.

The more secure and more complex CipherSuites require slightly more processing time. This list defines the CipherSuites supported by the switch and ranks them from fastest to slowest in terms of router processing load (speed):

  1. SSL_RSA_WITH_DES_CBC_SHA—RSA key exchange (RSA Public Key Cryptography) with DES-CBC for message encryption and SHA for message digest

  2. SSL_RSA_WITH_NULL_SHA key exchange with NULL for message encryption and SHA for message digest (only for SSL 3.0).

  3. SSL_RSA_WITH_NULL_MD5 key exchange with NULL for message encryption and MD5 for message digest (only for SSL 3.0).

  4. SSL_RSA_WITH_RC4_128_MD5—RSA key exchange with RC4 128-bit encryption and MD5 for message digest

  5. SSL_RSA_WITH_RC4_128_SHA—RSA key exchange with RC4 128-bit encryption and SHA for message digest

  6. SSL_RSA_WITH_3DES_EDE_CBC_SHA—RSA key exchange with 3DES and DES-EDE3-CBC for message encryption and SHA for message digest

  7. SSL_RSA_WITH_AES_128_CBC_SHA—RSA key exchange with AES 128-bit encryption and SHA for message digest (only for SSL 3.0).

  8. SSL_RSA_WITH_AES_256_CBC_SHA—RSA key exchange with AES 256-bit encryption and SHA for message digest (only for SSL 3.0).

  9. SSL_RSA_WITH_DHE_AES_128_CBC_SHA—RSA key exchange with AES 128-bit encryption and SHA for message digest (only for SSL 3.0).

  10. SSL_RSA_WITH_DHE_AES_256_CBC_SHA—RSA key exchange with AES 256-bit encryption and SHA for message digest (only for SSL 3.0).


Note

The latest versions of Chrome do not support the four original cipher suites, thus disallowing access to both web GUI and guest portals.

RSA (in conjunction with the specified encryption and digest algorithm combinations) is used for both key generation and authentication on SSL connections. This usage is independent of whether or not a CA trustpoint is configured.

Default SSL Configuration

The standard HTTP server is enabled.

SSL is enabled.

No CA trustpoints are configured.

No self-signed certificates are generated.

SSL Configuration Guidelines

When SSL is used in a switch cluster, the SSL session terminates at the cluster commander. Cluster member switches must run standard HTTP.

Before you configure a CA trustpoint, you should ensure that the system clock is set. If the clock is not set, the certificate is rejected due to an incorrect date.

In a switch stack, the SSL session terminates at the active switch.

How to Configure Secure HTTP Servers and Clients

Configuring a CA Trustpoint

For secure HTTP connections, we recommend that you configure an official CA trustpoint. A CA trustpoint is more secure than a self-signed certificate.

Beginning in privileged EXEC mode, follow these steps to configure a CA Trustpoint:

SUMMARY STEPS

  1. configure terminal
  2. hostname hostname
  3. ip domain-name domain-name
  4. crypto key generate rsa
  5. crypto ca trustpoint name
  6. enrollment url url
  7. enrollment http-proxy host-name port-number
  8. crl query url
  9. primary name
  10. exit
  11. crypto ca authentication name
  12. crypto ca enroll name
  13. end

DETAILED STEPS

  Command or Action Purpose
Step 1

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 2

hostname hostname

Example:


Device(config)# hostname your_hostname

Specifies the hostname of the switch (required only if you have not previously configured a hostname). The hostname is required for security keys and certificates.

Step 3

ip domain-name domain-name

Example:


Device(config)# ip domain-name your_domain

Specifies the IP domain name of the switch (required only if you have not previously configured an IP domain name). The domain name is required for security keys and certificates.

Step 4

crypto key generate rsa

Example:


Device(config)# crypto key generate rsa

(Optional) Generates an RSA key pair. RSA key pairs are required before you can obtain a certificate for the switch. RSA key pairs are generated automatically. You can use this command to regenerate the keys, if needed.

Step 5

crypto ca trustpoint name

Example:


Device(config)# crypto ca trustpoint your_trustpoint

Specifies a local configuration name for the CA trustpoint and enter CA trustpoint configuration mode.
Step 6

enrollment url url

Example:


Device(ca-trustpoint)# enrollment url http://your_server:80

Specifies the URL to which the switch should send certificate requests.
Step 7

enrollment http-proxy host-name port-number

Example:


Device(ca-trustpoint)# enrollment http-proxy your_host 49

(Optional) Configures the switch to obtain certificates from the CA through an HTTP proxy server.

  • For host-name , specify the proxy server used to get the CA.

  • For port-number, specify the port number used to access the CA.

Step 8

crl query url

Example:

Device(ca-trustpoint)# crl query ldap://your_host:49

Configures the switch to request a certificate revocation list (CRL) to ensure that the certificate of the peer has not been revoked.

Step 9

primary name

Example:


Device(ca-trustpoint)# primary your_trustpoint

(Optional) Specifies that the trustpoint should be used as the primary (default) trustpoint for CA requests.

  • For name, specify the trustpoint that you just configured.
Step 10

exit

Example:


Device(ca-trustpoint)# exit

Exits CA trustpoint configuration mode and return to global configuration mode.
Step 11

crypto ca authentication name

Example:


Device(config)# crypto ca authentication your_trustpoint

Authenticates the CA by getting the public key of the CA. Use the same name used in Step 5.
Step 12

crypto ca enroll name

Example:


Device(config)# crypto ca enroll your_trustpoint

Obtains the certificate from the specified CA trustpoint. This command requests a signed certificate for each RSA key pair.
Step 13

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Configuring the Secure HTTP Server

Beginning in privileged EXEC mode, follow these steps to configure a secure HTTP server:

Before you begin

If you are using a certificate authority for certification, you should use the previous procedure to configure the CA trustpoint on the switch before enabling the HTTP server. If you have not configured a CA trustpoint, a self-signed certificate is generated the first time that you enable the secure HTTP server. After you have configured the server, you can configure options (path, access list to apply, maximum number of connections, or timeout policy) that apply to both standard and secure HTTP servers.

To verify the secure HTTP connection by using a Web browser, enter https://URL, where the URL is the IP address or hostname of the server switch. If you configure a port other than the default port, you must also specify the port number after the URL. For example:


Note

AES256_SHA2 is not supported. 


https://209.165.129:1026

or 


https://host.domain.com:1026

SUMMARY STEPS

  1. show ip http server status
  2. configure terminal
  3. ip http secure-server
  4. ip http secure-port port-number
  5. ip http secure-ciphersuite {[3des-ede-cbc-sha] [rc4-128-md5] [rc4-128-sha] [des-cbc-sha]}
  6. ip http secure-client-auth
  7. ip http secure-trustpoint name
  8. ip http path path-name
  9. ip http access-class access-list-number
  10. ip http max-connections value
  11. ip http timeout-policy idle seconds life seconds requests value
  12. end

DETAILED STEPS

  Command or Action Purpose
Step 1

show ip http server status

Example:


Device# show ip http server status

(Optional) Displays the status of the HTTP server to determine if the secure HTTP server feature is supported in the software. You should see one of these lines in the output: 


HTTP secure server capability: Present

or 


HTTP secure server capability: Not present
Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

ip http secure-server

Example:


Device(config)# ip http secure-server

Enables the HTTPS server if it has been disabled. The HTTPS server is enabled by default.

Step 4

ip http secure-port port-number

Example:


Device(config)# ip http secure-port 443

(Optional) Specifies the port number to be used for the HTTPS server. The default port number is 443. Valid options are 443 or any number in the range 1025 to 65535.

Step 5

ip http secure-ciphersuite {[3des-ede-cbc-sha] [rc4-128-md5] [rc4-128-sha] [des-cbc-sha]}

Example:


Device(config)# ip http secure-ciphersuite rc4-128-md5

(Optional) Specifies the CipherSuites (encryption algorithms) to be used for encryption over the HTTPS connection. If you do not have a reason to specify a particularly CipherSuite, you should allow the server and client to negotiate a CipherSuite that they both support. This is the default.

Step 6

ip http secure-client-auth

Example:


Device(config)# ip http secure-client-auth

(Optional) Configures the HTTP server to request an X.509v3 certificate from the client for authentication during the connection process. The default is for the client to request a certificate from the server, but the server does not attempt to authenticate the client.

Step 7

ip http secure-trustpoint name

Example:


Device(config)# ip http secure-trustpoint your_trustpoint

Specifies the CA trustpoint to use to get an X.509v3 security certificate and to authenticate the client certificate connection.

Note 

Use of this command assumes you have already configured a CA trustpoint according to the previous procedure.

Step 8

ip http path path-name

Example:


Device(config)# ip http path /your_server:80

(Optional) Sets a base HTTP path for HTML files. The path specifies the location of the HTTP server files on the local system (usually located in system flash memory).

Step 9

ip http access-class access-list-number

Example:


Device(config)# ip http access-class 2

(Optional) Specifies an access list to use to allow access to the HTTP server.

Step 10

ip http max-connections value

Example:


Device(config)# ip http max-connections 4

(Optional) Sets the maximum number of concurrent connections that are allowed to the HTTP server. We recommend that the value be at least 10 and not less. This is required for the UI to function as expected.

Step 11

ip http timeout-policy idle seconds life seconds requests value

Example:


Device(config)# ip http timeout-policy idle 120 life 240 requests 1

(Optional) Specifies how long a connection to the HTTP server can remain open under the defined circumstances:

  • idle —the maximum time period when no data is received or response data cannot be sent. The range is 1 to 600 seconds. The default is 180 seconds (3 minutes).

  • life —the maximum time period from the time that the connection is established. The range is 1 to 86400 seconds (24 hours). The default is 180 seconds.

  • requests —the maximum number of requests processed on a persistent connection. The maximum value is 86400. The default is 1.

Step 12

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Configuring the Secure HTTP Client

Beginning in privileged EXEC mode, follow these steps to configure a secure HTTP client:

Before you begin

The standard HTTP client and secure HTTP client are always enabled. A certificate authority is required for secure HTTP client certification. This procedure assumes that you have previously configured a CA trustpoint on the switch. If a CA trustpoint is not configured and the remote HTTPS server requires client authentication, connections to the secure HTTP client fail.

SUMMARY STEPS

  1. configure terminal
  2. ip http client secure-trustpoint name
  3. ip http client secure-ciphersuite {[3des-ede-cbc-sha] [rc4-128-md5] [rc4-128-sha] [des-cbc-sha]}
  4. end

DETAILED STEPS

  Command or Action Purpose
Step 1

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 2

ip http client secure-trustpoint name

Example:


Device(config)# ip http client secure-trustpoint your_trustpoint

(Optional) Specifies the CA trustpoint to be used if the remote HTTP server requests client authentication. Using this command assumes that you have already configured a CA trustpoint by using the previous procedure. The command is optional if client authentication is not needed or if a primary trustpoint has been configured.

Step 3

ip http client secure-ciphersuite {[3des-ede-cbc-sha] [rc4-128-md5] [rc4-128-sha] [des-cbc-sha]}

Example:


Device(config)# ip http client secure-ciphersuite rc4-128-md5

(Optional) Specifies the CipherSuites (encryption algorithms) to be used for encryption over the HTTPS connection. If you do not have a reason to specify a particular CipherSuite, you should allow the server and client to negotiate a CipherSuite that they both support. This is the default.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Monitoring Secure HTTP Server and Client Status

To monitor the SSL secure server and client status, use the privileged EXEC commands in the following table.

Table 1. Commands for Displaying the SSL Secure Server and Client Status

Command

Purpose

show ip http client secure status

Shows the HTTP secure client configuration.

show ip http server secure status

Shows the HTTP secure server configuration.

show running-config

Shows the generated self-signed certificate for secure HTTP connections.