An implementation of the Enrollment over Secure Transport (EST) certificate enrollment protocol as defined by RFC7030.

The implementation provides:

• An EST client library;
• An EST client command line utility using the client library; and
• An EST server which can be used for testing and development purposes.

The implementation is intended to be mostly feature-complete, including support for:

• The optional /csrattrs and /serverkeygen operations, with support for server-generated private keys returned with or without additional encryption
• The optional additional path segment
• Optional HTTP-based client authentication on top of certificate-based TLS authentication

In addition, a non-standard operation is implemented enabling EST-like enrollment using the privacy preserving protocol for distributing credentials for keys on a Trusted Platform Module (TPM) 2.0 device, as described in Part 1, section 24 of the Trusted Platform Module 2.0 Library specification.

go install github.com/globalsign/est/cmd/estserver@latest
go install github.com/globalsign/est/cmd/estclient@latest

When started with no configuration file, the EST server listens on localhost:8443 and generates a random, transient Certificate Authority (CA) which can be used for testing:

user@host:$ estserver &
[1] 62405

Refer to the documentation for more details on using a configuration file.

Because we're using a random, transient CA, we must retrieve the CA certificates in insecure mode to establish an explicit trust anchor for subsequent EST operations. Since we only need the root CA certificate to establish a trust anchor, we use the -rootout flag:

user@host:$ estclient cacerts -server localhost:8443 -insecure -rootout -out anchor.pem

We will also obtain and store the full CA certificates chain, since we'll use it shortly to demonstrate reenrollment. Since we now have an explicit trust anchor, we can use it instead of the -insecure option. Since we're storing the full chain, we don't use the -rootout option here:

user@host:$ estclient cacerts -server localhost:8443 -explicit anchor.pem -out cacerts.pem

First we generate a new private key, here using openssl:

user@host:$ openssl genrsa 4096 > key.pem
Generating RSA private key, 4096 bit long modulus
.................+++
.............+++
e is 65537 (0x10001)

Then we generate a PKCS#10 certificate signing request, and enroll using the explicit trust anchor we previously obtained:

user@host:$ estclient csr -key key.pem -cn 'John Doe' -emails 'john@doe.com' -out csr.pem
user@host:$ estclient enroll -server localhost:8443 -explicit anchor.pem -csr csr.pem -out cert.pem

Using a configuration file, we can enroll with a private key resident on a hardware module, such as a hardware security module (HSM) or a Trusted Platform Module 2.0 (TPM) device. Refer to the documentation for more details.

If we're unable or unwilling to create our own private key, the EST server can generate one for us, and return it along with our certificate:

user@host:$ estclient serverkeygen -server localhost:8443 -explicit anchor.pem -cn 'Jane Doe' -out cert.pem -keyout key.pem

Note that we can omit the -csr option when enrolling and the EST client can dynamically generate a CSR for us using fields passed at the command line and the private key we specified, or an automatically-generated ephemeral private key if we are requesting server-side private key generation.

Whichever way we generated our private key, we can now use it to reenroll.

To reenroll a previously obtained certificate, we must use it to authenticate ourselves during the TLS handshake with the EST server. Since our random, transient CA uses an intermediate CA certificate, we must provide a chain of certificates to the EST client, or the TLS handshake may fail.

Although providing the root CA certificate is optional for a TLS handshake, the simplest option is to provide the certificate we received along with the full chain of CA certificates which we previously obtained. To do this, we can just append those CA certificates to the certificate we received, and use that chain to reenroll:

user@host:$ cat cert.pem cacerts.pem >> certs.pem
user@host:$ estclient reenroll -server localhost:8443 -explicit anchor.pem -key key.pem -certs certs.pem -out newcert.pem

Note that when we omit the -csr option when reenrolling, the EST client automatically generates a CSR for us by copying the subject field and subject alternative name extension from the certificate we're renewing.