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11.1.4.1. Creating certificates
Generating suitable certificates can be a painful experience for the uninitiated, so we have provided some useful
tools which can be downloaded from the FireBrick website. These are bash scripts which use the OpenSSL
tools, and can be run on Linux or MacOS systems, or on Windows using Cygwin. They should be downloaded
and saved locally (eg by cut-and-paste from the displayed web page text, or using the browser save source
function). If invoked with no arguments usage information is displayed.
Use the make-key script to generate a new public/private key pair. This is available as http://
www.firebrick.co.uk/tools/make-key. By default an RSA key of 2048 bits is generated, but this can be changed
by supplying suitable parameters.
Use the make-cert script to generate a new certificate. This is available as http://www.firebrick.co.uk/tools/
make-cert. It can be used to generate a CA or an end-entity certificate, and can make a self-signed certificate
or make one signed by an existing CA. The private key to be associated with the certificate must be supplied,
and if the certificate is not self-signed the CA certificate and its associated private key must be supplied. When
making an end-entity certificate the IKE identity should be built into the certificate as a subjectAltName field,
using one of the IP, FQDN or EMAIL keywords.
As an example, consider the company Paradigm Ltd. who wish to set up a certificate suitable for authenticating
one of their servers using IKE identity FQDN:vpn.server42.paradigm.co.uk. To make a suitable CA and end-
entity certificate run the following commands:
# Note that trailing backslash characters have been used below
# to split commands over multiple lines for readability.
# Generate a new key for the CA certificate
./make-key paradigm-ca-key.pem
# Generate the CA certificate
# Note that the DN setting can be freely chosen.
./make-cert CA DN="/C=UK/ST=Midsomer/O=Paradigm Ltd/CN=paradigm.co.uk" \
KEY=paradigm-ca-key.pem paradigm-ca.pem
# Generate a new key for the end-entity certificate for server42
./make-key paradigm42-key.pem
# Generate the end-entity certificate
# Note that the FQDN= parameter is used to set the certificate's SubjectAltName
# and this will correspond to the server's local-ID setting
./make-cert DN=/CN=server42 KEY=paradigm42-key.pem \
ISSUER-KEY=paradigm-ca-key.pem ISSUER=paradigm-ca.pem \
FQDN=vpn.server42.paradigm.co.uk paradigm42.pem
The paradigm-ca-key.pem file should be stored safely offline. The paradigm-ca.pem, paradigm42.pem and
paradigm42-key.pem files should be uploaded to the FireBrick certificate store. The paradigm-ca.pem file
should be installed on the peer(s) wishing to connect.
11.1.5. Choice of algorithms
The following types of algorithm are used:
• Integrity: used to perform integrity checking of the control or data channels
• Encryption: used to perform encryption of the control or data channels
• DHGroup: used to select the Diffie-Hellman group to be used to agree a mutually-agreed secret key
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