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Support for an Openssl based CA stored on local file system

The openssl CA handler is rather for testing and lab usage. I strongly recommend not to reuse it in production environments without reviewing local system configuration and hardening state

Prerequisites

You need to create a certificate authority on the local file-system.

I did it by running the below command:

root@rlh:~# openssl req -x509 -new -extensions v3_ca -newkey rsa:4096 -keyout ca-key.pem -out ca-cert.pem -days 3650

Configuration

• create a directory to store the (ca) certificate(s), key and CRL(s)

root@rlh:~# mkdir acme_srv/ca
root@rlh:~# mkdir acme_srv/ca/certs

• place the above generated key and cert into the "ca" directory

root@rlh:~# mv ca-key.pem acme_srv/ca/
root@rlh:~# mv ca-cert.pem acme_srv/ca/

• modify the server configuration (/acme_srv/acme_srv.cfg) and add the following parameters

[CAhandler]
handler_file: examples/ca_handler/openssl_ca_handler.py
issuing_ca_key: acme_srv/ca/ca-key.pem
issuing_ca_key_passphrase: Test1234
issuing_ca_cert: acme_srv/ca/ca-cert.pem
issuing_ca_crl: acme_srv/ca/crl.pem
cert_validity_days: 30
cert_validity_adjust: True
cert_save_path: acme_srv/ca/certs
ca_cert_chain_list: []
openssl_conf: acme_srv/ca/openssl.conf
allowed_domainlist: ["foo.bar\\$", "foo1.bar.local"]
blocked_domainlist: ["google.com.foo.bar\\$", "host.foo.bar$", "\\*.foo.bar"]
save_cert_as_hex: True
cn_enforce: True

• issuing_ca_key - private key of the issuing CA (in PEM format) used to sign certificates and CRLs
• issuing_ca_key_passphrase - password to access the private key
• issuing_ca_key_passphrase_variable - optional - name of the environment variable containing the passphrase to access the CA key (a configured issuing_ca_key_passphrase parameter in acme_srv.cfg takes precedence)
• issuing_ca_cert - Certificate of issuing CA in PEM format
• issuing_ca_crl - CRL of issuing CA in PEM format
• ca_cert_chain_list - List of root and intermediate CA certificates to be added to the bundle return to an ACME-client (the issueing CA cert must not be included)
• cert_validity_days - optional - certificate lifetime in days (default 365)
• cert_save_path - optional - directory to store then enrolled certificates
• openssl_conf - optional - file in openssl.conf format containing certificate extensions to be applied
• allowed_domainlist - optional - list of allowed common names and sans. Format per entry must follow the regular expression syntax- To be stored in json format
• blocked_domainlist - optional - list of prohibited common names and sans. Format per entry must follow the regular expression syntax. To be stored in json format
• save_cert_as_hex - optional - serialnumber in hex format will be used as filename to save enrolled certificates - default is False
• cn_enforce - optional - use first SAN as CN in case there is no CN included in CSR - default is False
• cert_validity_adjust - optional - limit on the "valid until" field, so that a certificate is never valid longer than any other certificate in the certificate chain - default is set to False

allowed_domainlist and blocked_domainlist options can be used independently from each other. When used together please note that that a positive result of a blocked_domainlist check takes precedence over the positive result of a allowed_domainlist check.

The openssl_conf file allows customization of the certificate profile and must contain a section [extensions] containing the certificate extensions to be inserted. If not specified the following extensions will be applied.

[extensions]
subjectKeyIdentifier    = hash, issuer:always
keyUsage                = digitalSignature, keyEncipherment
basicConstraints        = critical, CA:FALSEerr
authorityKeyIdentifier  = keyid:always, issuer:always
extendedKeyUsage        = critical, clientAuth, serverAuth

Enjoy enrolling and revoking certificates

some remarks:

• certificates and CRLs will be signed with sha256
• during enrollment all extensions included in the csr will be copied to the certificate. Don’t tell me that this is a bad idea. Read the first two sentences of this page instead.
• the CRL "next update interval" is 7days