source: http://openvpn.net/index.php/open-source/documentation/miscellaneous/77-rsa-key-management.html

RSA Key Management

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

easy-rsa/vars

# easy-rsa parameter settings

# NOTE: If you installed from an RPM,
# don't edit this file in place in
# /usr/share/openvpn/easy-rsa --
# instead, you should copy the whole
# easy-rsa directory to another location
# (such as /etc/openvpn) so that your
# edits will not be wiped out by a future
# OpenVPN package upgrade.

# This variable should point to
# the top level of the easy-rsa
# tree.
export D=`pwd`

# This variable should point to
# the openssl.cnf file included
# with easy-rsa.
export KEY_CONFIG=$D/openssl.cnf

# Edit this variable to point to
# your soon-to-be-created key
# directory.
#
# WARNING: clean-all will do
# a rm -rf on this directory
# so make sure you define
# it correctly!
export KEY_DIR=$D/keys

# Issue rm -rf warning
echo NOTE: when you run ./clean-all, I will be doing a rm -rf on $KEY_DIR

# Increase this to 2048 if you
# are paranoid.  This will slow
# down TLS negotiation performance
# as well as the one-time DH parms
# generation process.
export KEY_SIZE=1024

# These are the default values for fields
# which will be placed in the certificate.
# Don't leave any of these fields blank.
export KEY_COUNTRY=KG
export KEY_PROVINCE=NA
export KEY_CITY=BISHKEK
export KEY_ORG="OpenVPN-TEST"
export KEY_EMAIL="me@myhost.mydomain"

easy-rsa/clean-all

#!/bin/sh

#
# Initialize the $KEY_DIR directory.
# Note that this script does a
# rm -rf on $KEY_DIR so be careful!
#

d=$KEY_DIR

if test $d; then
 rm -rf $d
 mkdir $d && \
 chmod go-rwx $d && \
 touch $d/index.txt && \
 echo 01 >$d/serial
else
 echo you must define KEY_DIR
fi

easy-rsa/build-dh

#!/bin/sh

#
# Build Diffie-Hellman parameters for the server side
# of an SSL/TLS connection.
#

if test $KEY_DIR; then
    openssl dhparam -out ${KEY_DIR}/dh${KEY_SIZE}.pem ${KEY_SIZE}
else
    echo you must define KEY_DIR
fi

easy-rsa/build-ca

#!/bin/sh

#
# Build a root certificate
#

if test $KEY_DIR; then
 cd $KEY_DIR && \
 openssl req -days 3650 -nodes -new -x509 -keyout ca.key -out ca.crt -config $KEY_CONFIG && \
        chmod 0600 ca.key
else
 echo you must define KEY_DIR
fi

easy-rsa/build-inter

#!/bin/sh

#
# Make an intermediate CA certificate/private key pair using a locally generated
# root certificate.
#

if test $# -ne 1; then
        echo "usage: build-inter <name>";
        exit 1
fi                                                                             

if test $KEY_DIR; then
 cd $KEY_DIR && \
 openssl req -days 3650 -nodes -new -keyout $1.key -out $1.csr -config $KEY_CONFIG && \
 openssl ca -extensions v3_ca -days 3650 -out $1.crt -in $1.csr -config $KEY_CONFIG
else
 echo you must define KEY_DIR
fi

easy-rsa/build-key

#!/bin/sh

#
# Make a certificate/private key pair using a locally generated
# root certificate.
#

if test $# -ne 1; then
        echo "usage: build-key <name>";
        exit 1
fi                                                                             

if test $KEY_DIR; then
 cd $KEY_DIR && \
 openssl req -days 3650 -nodes -new -keyout $1.key -out $1.csr -config $KEY_CONFIG && \
 openssl ca -days 3650 -out $1.crt -in $1.csr -config $KEY_CONFIG && \
 chmod 0600 $1.key
else
 echo you must define KEY_DIR
fi

easy-rsa/build-key-pass

#!/bin/sh

#
# Similar to build-key, but protect the private key
# with a password.
#

if test $# -ne 1; then
        echo "usage: build-key-pass <name>";
        exit 1
fi

if test $KEY_DIR; then
 cd $KEY_DIR && \
 openssl req -days 3650 -new -keyout $1.key -out $1.csr -config $KEY_CONFIG && \
 openssl ca -days 3650 -out $1.crt -in $1.csr -config $KEY_CONFIG && \
 chmod 0600 $1.key
else
 echo you must define KEY_DIR
fi

easy-rsa/build-req

#!/bin/sh

#
# Build a certificate signing request and private key.  Use this
# when your root certificate and key is not available locally.
#

if test $# -ne 1; then
    echo "usage: build-req <name>";
    exit 1
fi                                                                             

if test $KEY_DIR; then
    cd $KEY_DIR && \
    openssl req -days 3650 -nodes -new -keyout $1.key -out $1.csr -config $KEY_CONFIG
else
    echo you must define KEY_DIR
fi

easy-rsa/build-req-pass

#!/bin/sh

#
# Like build-req, but protect your private key
# with a password.
#

if test $# -ne 1; then
    echo "usage: build-req-pass <name>";
    exit 1
fi                                                                             

if test $KEY_DIR; then
    cd $KEY_DIR && \
    openssl req -days 3650 -new -keyout $1.key -out $1.csr -config $KEY_CONFIG
else
    echo you must define KEY_DIR
fi

easy-rsa/sign-req

#!/bin/sh

#
# Sign a certificate signing request (a .csr file)
# with a local root certificate and key.
#

if test $# -ne 1; then
        echo "usage: sign-req <name>";
        exit 1
fi                                                                             

if test $KEY_DIR; then
 cd $KEY_DIR && \
 openssl ca -days 3650 -out $1.crt -in $1.csr -config $KEY_CONFIG
else
 echo you must define KEY_DIR
fi

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RSA management

RSA Key Management

easy-rsa/vars

easy-rsa/clean-all

easy-rsa/build-dh

easy-rsa/build-ca

easy-rsa/build-inter

easy-rsa/build-key

easy-rsa/build-key-pass

easy-rsa/build-req

easy-rsa/build-req-pass

easy-rsa/sign-req