Elliptic Curve Cryptography

Public-key cryptography is a cryptographic system that requires a secret key and a public key that are mathematically linked with each other. One key encrypts the plain text while the other decrypts the cipher text. RSA is the most widely used public-key algorithm.

Elliptic Curve Cryptography (ECC) were introduced as an alternative to RSA in public key cryptography. One advantage of ECC over RSA is key size versus strength. For example, a security strength of 80 bits can be achieved through an ECC key size of 160 bits, whereas RSA requires a key size of 1024. With a 112-bit strength, the ECC key size is 224 bits and the RSA key size is 2048 bits.

The most popular signature scheme that uses elliptic curves is called the Elliptic Curve Digital Signature Algorithm (ECDSA). The most popular key agreement scheme is called Elliptic Curve Diffie-Hellman (ECDH). An ECDH exchange is a variant of the Diffie-Hellman (DH) protocol and is an integral part of the Suite B cryptography standards proposed by the National Security Agency (NSA) for protecting both classified and unclassified information.

The Advanced Encryption Standard (AES) is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001. Because a single encryption algorithm cannot satisfy all of the needs of the national security community, NSA created a larger set of cryptographic algorithms, called Suite B, which can be used along with AES in systems used by national security users. In addition to AES, Suite B includes cryptographic algorithms for hashing, digital signatures, and key exchanges.

Per RFC 6460, to be Suite B TLS 1.2 compliant the server and client should negotiate with the following ciphers:

Clients and servers that do not yet support Suite B TLS 1.2 should negotiate with the following ciphers:

Clients and servers that do not yet support Suite B TLS 1.3 should negotiate with the following ciphers:

ECC certificates are currently supported only on the ISA Series Gateways and virtual appliance platforms. As with RSA certificates, ECC certificates are associated with a network port. You can create multiple virtual ports on the server with each port supporting a specific certificate. For example, external virtual port 1 can use a 1024-bit RSA while external virtual port 2 uses ECC P-256 and external virtual port 3 uses ECC P-384. Only clients that support ECC cipher suites can connect to the web server on that network port.

When an Elliptic Curve Cryptography (ECC) certificate is associated with a network port, only clients that support ECC cipher suites can connect to the Web server on that network port.

Except for the key and certificate generation process, the use of ECC certificates is basically the same as using RSA certificates.

This example outlines the general steps for creating an external port and assigning an ECC P-256 certificate. The steps are generally the same as assigning an RSA certificate to a port.

The external port handles all requests from users signed into the server from outside the customer LAN, for example, from the Internet.

To configure the external port:

A virtual port is an IP alias bound to a physical port. It shares all of the network settings, except IP address, with the associated physical port. You can use virtual ports for different purposes, depending on the physical port or the VLAN on which you base the virtual port. In this example, we are configuring the virtual port on the external port to support external sign-ins. This is an optional step that shows one way of allowing multiple certificates on the device.

To configure the external virtual port:

A certificate signing request (CSR) is a message sent from an applicant to a certificate authority (CA) to apply for a digital identity certificate. You create a CSR through the admin console. When you create a CSR, a private key is created locally that corresponds to the CSR. If you delete the CSR at any point, the private key is deleted too, prohibiting you from installing a signed certificate generated from the CSR.

In this example, a CSR for an ECC P-256 certificate is requested.

To create a CSR for a new certificate:

CSR Successfully Created

Once your CA has sent your signed certificate, you must import that into the pending CSR.

To import a signed device certificate created from a CSR:

You can present a certificate many ways, depending on your configuration. For example, you can present the certificate to one or more virtual ports or on an internal or external port. In this example, the ECC P-256 certificate is presented on the external virtual port p1.

To present a certificate on an external virtual port:

To specify the cipher suites for the incoming connection to the Web server, use the SSL Options page and select the Custom SSL Cipher Selection option. This step is required in our example to give Suite B cipher suites preference. If you do not want to give Suite B cipher suites preference, you do not have to perform this step.

Only when FIPS mode is turned on, the FIPS compliant ciphers are available to be chosen from the Supported Ciphers panel. FIPS mode is editable only on the inbound option page.

To set the security options with Inbound SSL Options:

Only for Outbound SSL Settings, we can configure Non FIPS Ciphers when FIPS is Enabled using Custom Cipher Selection Option. Now, there are options to change different SSL/TLS versions and different encryptions in the Outbound SSL Settings. Outbound SSL Settingsshows the Outbound SSL Settings.

Outbound SSL Settings

End users can check which certificate their browser is using to connect to the server. In the following example, the end user connects to server port p3, which uses an ECC curve P-256 certificate. See the following figure.

Connecting to a Port Using an ECC Curve P-256 Certificate

To view the certificate from an Internet Explorer 8 browser:

You can use the TCP Dump tool to view which cipher each client uses to connect to the server. TCP Dump is a packet analyzer that intercepts (sniffs) and displays TCP/IP and other packets transmitted or received between the server and clients.

To capture packet headers: