This is a small RSA key management package,
based on the openssl command line tool, that
can be found in the easy-rsa subdirectory
of the OpenVPN distribution.
These are reference notes. For step
by step instructions, see the HOWTO:
http://openvpn.net/howto.html
INSTALL
1. Edit vars.
2. Set KEY_CONFIG to point to the openssl.cnf file
included in this distribution.
3. Set KEY_DIR to point to a directory which will
contain all keys, certificates, etc. This
directory need not exist, and if it does,
it will be deleted with rm -rf, so BE
CAREFUL how you set KEY_DIR.
4. (Optional) Edit other fields in vars
per your site data. You may want to
increase KEY_SIZE to 2048 if you are
paranoid and don't mind slower key
processing, but certainly 1024 is
fine for testing purposes. KEY_SIZE
must be compatible across both peers
participating in a secure SSL/TLS
connection.
5 . vars
6. ./clean-all
7. As you create certificates, keys, and
certificate signing requests, understand that
only .key files should be kept confidential.
.crt and .csr files can be sent over insecure
channels such as plaintext email.
8. You should never need to copy a .key file
between computers. Normally each computer
will have its own certificate/key pair.
BUILD YOUR OWN ROOT CERTIFICATE AUTHORITY (CA) CERTIFICATE/KEY
1. ./build-ca
2. ca.crt and ca.key will be built in your KEY_DIR
directory
BUILD AN INTERMEDIATE CERTIFICATE AUTHORITY CERTIFICATE/KEY (optional)
1. ./build-inter inter
2. inter.crt and inter.key will be built in your KEY_DIR
directory and signed with your root certificate.
BUILD DIFFIE-HELLMAN PARAMETERS (necessary for
the server end of a SSL/TLS connection).
1. ./build-dh
BUILD A CERTIFICATE SIGNING REQUEST (If
you want to sign your certificate with a root
certificate controlled by another individual
or organization, or residing on a different machine).
1. Get ca.crt (the root certificate) from your
certificate authority. Though this
transfer can be over an insecure channel, to prevent
man-in-the-middle attacks you must confirm that
ca.crt was not tampered with. Large CAs solve this
problem by hardwiring their root certificates into
popular web browsers. A simple way to verify a root
CA is to call the issuer on the telephone and confirm
that the md5sum or sha1sum signatures on the ca.crt
files match (such as with the command: "md5sum ca.crt").
2. Choose a name for your certificate such as your computer
name. In our example we will use "mycert".
3. ./build-req mycert
4. You can ignore most of the fields, but set
"Common Name" to something unique such as your
computer's host name. Leave all password
fields blank, unless you want your private key
to be protected by password. Using a password
is not required -- it will make your key more secure
but also more inconvenient to use, because you will
need to supply your password anytime the key is used.
NOTE: if you are using a password, use ./build-req-pass
instead of ./build-req
5. Your key will be written to $KEY_DIR/mycert.key
6. Your certificate signing request will be written to
to $KEY_DIR/mycert.csr
7. Email mycert.csr to the individual or organization
which controls the root certificate. This can be
done over an insecure channel.
8. After the .csr file is signed by the root certificate
authority, you will receive a file mycert.crt
(your certificate). Place mycert.crt in your
KEY_DIR directory.
9. The combined files of mycert.crt, mycert.key,
and ca.crt can now be used to secure one end of
an SSL/TLS connection.
SIGN A CERTIFICATE SIGNING REQUEST
1. ./sign-req mycert
2. mycert.crt will be built in your KEY_DIR
directory using mycert.csr and your root CA
file as input.
BUILD AND SIGN A CERTIFICATE SIGNING REQUEST
USING A LOCALLY INSTALLED ROOT CERTIFICATE/KEY -- this
script generates and signs a certificate in one step,
but it requires that the generated certificate and private
key files be copied to the destination host over a
secure channel.
1. ./build-key mycert (no password protection)
2. OR ./build-key-pass mycert (with password protection)
3. OR ./build-key-pkcs12 mycert (PKCS #12 format)
4. OR ./build-key-server mycert (with nsCertType=server)
5. mycert.crt and mycert.key will be built in your
KEY_DIR directory, and mycert.crt will be signed
by your root CA. If ./build-key-pkcs12 was used a
mycert.p12 file will also be created including the
private key, certificate and the ca certificate.
IMPORTANT
To avoid a possible Man-in-the-Middle attack where an authorized
client tries to connect to another client by impersonating the
server, make sure to enforce some kind of server certificate
verification by clients. There are currently four different ways
of accomplishing this, listed in the order of preference:
(1) Build your server certificates with the build-key-server
script. This will designate the certificate as a
server-only certificate by setting nsCertType=server.
Now add the following line to your client configuration:
ns-cert-type server
This will block clients from connecting to any
server which lacks the nsCertType=server designation
in its certificate, even if the certificate has been
signed by the CA which is cited in the OpenVPN configuration
file (--ca directive).
(2) Use the --tls-remote directive on the client to
accept/reject the server connection based on the common
name of the server certificate.
(3) Use a --tls-verify script or plugin to accept/reject the
server connection based on a custom test of the server
certificate's embedded X509 subject details.
(4) Sign server certificates with one CA and client certificates
with a different CA. The client config "ca" directive should
reference the server-signing CA while the server config "ca"
directive should reference the client-signing CA.
NOTES
Show certificate fields:
openssl x509 -in cert.crt -text
