mirror of
https://gitlab.com/veilid/veilid.git
synced 2024-12-18 04:04:43 -05:00
98 lines
4.8 KiB
Markdown
98 lines
4.8 KiB
Markdown
Introduction to PKI
|
|
===================
|
|
|
|
This document is designed to give you a brief introduction into how a PKI, or
|
|
Public Key Infrastructure, works.
|
|
|
|
Terminology Used
|
|
----------------
|
|
|
|
To avoid confusion, the following terms will be used throughout the Easy-RSA
|
|
documentation. Short forms may be substituted for longer forms as convenient.
|
|
|
|
* **PKI**: Public Key Infrastructure. This describes the collection of files
|
|
and associations between the CA, keypairs, requests, and certificates.
|
|
* **CA**: Certificate Authority. This is the "master cert" at the root of a
|
|
PKI.
|
|
* **cert**: Certificate. A certificate is a request that has been signed by a
|
|
CA. The certificate contains the public key, some details describing the
|
|
cert itself, and a digital signature from the CA.
|
|
* **request**: Certificate Request (optionally 'req'.) This is a request for a
|
|
certificate that is then send to a CA for signing. A request contains the
|
|
desired cert information along with a digital signature from the private
|
|
key.
|
|
* **keypair**: A keypair is an asymmetric cryptographic pair of keys. These
|
|
keys are split into two parts: the public and private keys. The public key
|
|
is included in a request and certificate.
|
|
|
|
The CA
|
|
------
|
|
|
|
The heart of a PKI is the CA, or Certificate Authority, and this is also the
|
|
most security-sensitive. The CA private key is used to sign all issued
|
|
certificates, so its security is critical in keeping the entire PKI safe. For
|
|
this reason, it is highly recommended that the CA PKI structure be kept on a
|
|
system dedicated for such secure usage; it is not a great idea to keep the CA
|
|
PKI mixed in with one used to generate end-entity certificates, such as clients
|
|
or servers (VPN or web servers.)
|
|
|
|
To start a new PKI, the CA is first created on the secure environment.
|
|
Depending on security needs, this could be managed under a locked down account,
|
|
dedicated system, or even a completely offline system or using removable media
|
|
to improve security (after all, you can't suffer an online break-in if your
|
|
system or PKI is not online.) The exact steps to create a CA are described in a
|
|
separate section. When creating a new CA, the CA keypair (private and public
|
|
keys) are created, as well as the file structure necessary to support signing
|
|
issued certificates.
|
|
|
|
Once a CA has been created, it can receive certificate requests from
|
|
end-entities. These entity certificates are issued to consumers of X509
|
|
certificates, such as a client or server of a VPN, web, or email system. The
|
|
certificate requests and certificates are not security-sensitive, and can be
|
|
transferred in whatever means convenient, such as email, flash drive, etc. For
|
|
better security, it is a good idea to verify the received request matches the
|
|
sender's copy, such as by verifying the expected checksum against the sender's
|
|
original.
|
|
|
|
Keypairs and requests
|
|
---------------------
|
|
|
|
Individual end-entities do not need a full CA set up and will only need to
|
|
create a keypair and associated certificate request. The private key is not used
|
|
anywhere except on this entity, and should never leave that system. It is wise
|
|
to secure this private key with a strong passphrase, because if lost or stolen
|
|
the holder of the private key can make connections appearing as the certificate
|
|
holder.
|
|
|
|
Once a keypair is generated, the certificate request is created and digitally
|
|
signed using the private key. This request will be sent to a CA for signing, and
|
|
a signed certificate will be returned.
|
|
|
|
How requests become certificates
|
|
--------------------------------
|
|
|
|
After a CA signs the certificate request, a signed certificate is produced. In
|
|
this step, the CA's private key is used to digitally sign the entity's public
|
|
key so that any system trusting the CA certificate can implicitly trust the
|
|
newly issued certificate. This signed certificate is then sent back to the
|
|
requesting entity. The issued certificate is not security-sensitive and can be
|
|
sent over plaintext transmission methods.
|
|
|
|
Verifying an issued certificate
|
|
-------------------------------
|
|
|
|
After 2 entities have created keypairs, sent their requests to the CA, and
|
|
received a copy of their signed certificates and the CA's own certificate, they
|
|
can mutually authenticate with one-another. This process does not require the 2
|
|
entities to have previously exchanged any kind of security information directly.
|
|
|
|
During a TLS handshake each side of the connection presents their own cert chain
|
|
to the remote end. Each side checks the validity of the cert received against
|
|
their own copy of the CA cert. By trusting the CA root cert, the peer they are
|
|
talking to can be authenticated.
|
|
|
|
The remote end proves it "really is" the entity identified by the cert by
|
|
signing a bit of data using its own private key. Only the holder of the private
|
|
key is able to do this, allowing the remote end to verify the authenticity of
|
|
the system being connected to.
|