Ubuntu Manpage: lacme - ACME client written with process isolation and minimal privileges in mind

NAME

       lacme - ACME client written with process isolation and minimal privileges in mind

SYNOPSIS

       lacme [--config=FILENAME] [--socket=PATH] [OPTION ...] COMMAND [ARGUMENT ...]

DESCRIPTION

lacme is a small ACME client written with process isolation and minimal privileges in mind. It is divid‐
ed into four components, each with its own executable:

1. A lacme-accountd(1) process to manage the account key and issue SHA-256 signatures needed for each
ACME command. (This process binds to a UNIX-domain socket to reply to signature requests from the
ACME client.) One can use the UNIX-domain socket forwarding facility of OpenSSH 6.7 and later to run
lacme-accountd(1) and lacme on different hosts. Alternatively, the lacme-accountd(1) process can be
spawned by the “master” lacme process below; in that case, the two processes communicate through a
socket pair.

2. A “master” lacme process, which runs as root and is the only component with access to the private key
material of the server keys. It is used to fork the ACME client (and optionally the ACME webserver)
after dropping root privileges. For certificate issuances (new-cert command), it also generates Cer‐
tificate Signing Requests, then verifies the validity of the issued certificate, and optionally re‐
loads or restarts services when the notify option is set.

3. An actual ACME client (specified with the command option of the [client] section of the configuration
file), which builds ACME commands and dialogues with the remote ACME server. Since ACME commands need
to be signed with the account key, the “master” lacme process passes the lacme-accountd(1) UNIX-domain
socket to the ACME client: data signatures are requested by writing the data to be signed to the sock‐
et.

4. For certificate issuances (new-cert command), an optional webserver (specified with the command option
of the [webserver] section of the configuration file), which is spawned by the “master” lacme. (The
only challenge type currently supported by lacme is http-01, which requires a webserver to answer
challenges.) That webserver only processes GET and HEAD requests under the /.well-known/acme-chal‐
lenge/ URI. Moreover temporary iptables(8) rules can be automatically installed to open the HTTP
port.

COMMANDS

       lacme [--agreement-uri=URI] new-reg [CONTACT ...]
              Register  the  account  key  managed by lacme-accountd(1).  A list of CONTACT information (such as
              maito: URIs) can be specified in order for the server to contact the client for issues related  to
              this registration (such as notifications about server-initiated revocations).

              --agreement-uri= can be used to specify a URI referring to a subscriber agreement or terms of ser‐
              vice  provided by the server; adding this options indicates the client's agreement with the refer‐
              enced terms.  Note that the server might require the client to agree to subscriber  agreement  be‐
              fore performing any further actions.

              If  the  account  key is already registered, lacme prints the URI of the existing registration and
              aborts.

       lacme [--agreement-uri=URI] reg=URI [CONTACT ...]
              Dump or edit the registration URI (relative to the ACME server URI, which is  specified  with  the
              server option of the [client] section of the configuration file).

              When  specified,  the  list of CONTACT information and the agreement URI are sent to the server to
              replace the existing values.

       lacme [--config-certs=FILE] [--min-days=INT] new-cert [SECTION ...]
              Read the certificate configuration FILE (see the certificate configuration file section below  for
              the  configuration options), and request new Certificate Issuance for each of its sections (or the
              given list of SECTIONs).

       lacme revoke-cert FILE [FILE ...]
              Request that the given certificate(s) FILE(s) be revoked.  For this command, lacme-accountd(1) can
              be pointed to either the account key or the server's private key.

GENERIC OPTIONS

       --config=filename
              Use filename as configuration file.  See the configuration file section below for  the  configura‐
              tion options.

       --socket=path
              Use path as the lacme-accountd(1) UNIX-domain socket to connect to for signature requests from the
              ACME client.  lacme aborts if path is readable or writable by other users, or if its parent direc‐
              tory  is  writable  by  other  users.  This command-line option overrides the socket option of the
              [client] section of the configuration file.  Moreover this option is ignored when  the  configura‐
              tion  file  has  an  [accountd]  section; in that case lacme spawns lacme-accountd(1), and the two
              processes communicate through a socket pair.

       -h, --help
              Display a brief help and exit.

       -q, --quiet
              Be quiet.

       --debug
              Turn on debug mode.

CONFIGURATION FILE

If --config= is not given, lacme uses the first existing configuration file among ./lacme.conf, $XDG_CON‐
FIG_HOME/lacme/lacme.conf (or ~/.config/lacme/lacme.conf if the XDG_CONFIG_HOME environment variable is
not set), and /etc/lacme/lacme.conf. Valid options are:

DEFAULT SECTION
config-certs
For certificate issuances (new-cert command), specify the space-separated list of certificate con‐
figuration files or directories to use (see the certificate configuration file section below for
the configuration options).

Paths not starting with / are relative to the directory name of the configuration filename. The
list of files and directories is processed in order, with the later items taking precedence.
Files in a directory are processed in lexicographic order, only considering the ones with suffix
.conf.

Default: lacme-certs.conf lacme-certs.conf.d/.

[client] SECTION
This section is used for configuring the ACME client (which takes care of ACME commands and dialogues
with the remote ACME server).

socket See --socket=. Default: $XDG_RUNTIME_DIR/S.lacme if the XDG_RUNTIME_DIR environment variable is
set.

user The username to drop privileges to (setting both effective and real uid). Preserve root privi‐
leges if the value is empty (not recommended). Default: nobody.

group The groupname to drop privileges to (setting both effective and real gid, and also setting the
list of supplementary gids to that single group). Preserve root privileges if the value is empty
(not recommended). Default: nogroup.

command
Path to the ACME client executable. Default: /usr/lib/lacme/client.

server Root URI of the ACME server. Default: https://acme-v01.api.letsencrypt.org/.

timeout
Timeout in seconds after which the client stops polling the ACME server and considers the request
failed. Default: 10.

SSL_verify
Whether to verify the server certificate chain. Default: Yes.

SSL_version
Specify the version of the SSL protocol used to transmit data.

SSL_cipher_list
Specify the cipher list for the connection, see ciphers(1ssl) for more information.

[webserver] SECTION
This section is used to configure how ACME challenge responses are served during certificate issuance.

listen Comma- or space-separated list of addresses to listen on. Valid addresses are of the form
IPV4:PORT, [IPV6]:PORT (where the :PORT suffix is optional and defaults to the HTTP port 80), or
an absolute path of a UNIX-domain socket (created with mode 0666). Default:
/var/run/lacme-www.socket.

Note: The default value is only suitable when an external HTTP daemon is publicly reachable and
passes all ACME challenge requests to the webserver component through the UNIX-domain socket
/var/run/lacme-www.socket (for instance using the provided /etc/lacme/apache2.conf or
/etc/lacme/nginx.conf configuration snippets for each virtual host requiring authorization). If
there is no HTTP daemon bound to port 80 one needs to set listen to [::] (or 0.0.0.0 [::] when
dual IPv4/IPv6 stack is disabled or unavailable), and possibly also set iptables to Yes.

challenge-directory
Specify a non-existent directory under which an external HTTP daemon is configured to serve GET
requests for challenge files under /.well-known/acme-challenge/ (for each virtual host requiring
authorization) as static files. This option is required when listen is empty.

user The username to drop privileges to (setting both effective and real uid). Preserve root privi‐
leges if the value is empty (not recommended). Default: www-data.

command
Path to the ACME webserver executable. A separate process is spawned for each address to listen
on. (In particular no webserver process is forked when the listen option is empty.) Default:
/usr/lib/lacme/webserver.

iptables
Whether to automatically install temporary iptables(8) rules to open the ADDRESS[:PORT] specified
with listen. The rules are automatically removed once lacme exits. Default: No.

[accountd] SECTION
This section is used for configuring the lacme-accountd(1) process. If the section (including its head‐
er) is absent or commented out, lacme connects to an existing UNIX-domain socket bound by a running
lacme-accountd(1) process.

user The username to drop privileges to (setting both effective and real uid). Preserve root privi‐
leges if the value is empty.

group The groupname to drop privileges to (setting both effective and real gid, and also setting the
list of supplementary gids to that single group). Preserve root privileges if the value is empty.

command
Path to the lacme-accountd(1) executable. Default: /usr/bin/lacme-accountd.

config Path to the lacme-accountd(1) configuration file. Default: /etc/lacme/lacme-accountd.conf.

privkey
The (private) account key to use for signing requests. See lacme-accountd(1) for details.

quiet Be quiet. Possible values: Yes/No.

CERTIFICATE CONFIGURATION FILE

For certificate issuances (new-cert command), a separate file is used to configure paths to the certifi‐
cate and key, as well as the subject, subjectAltName, etc. to generate Certificate Signing Requests.
Each section denotes a separate certificate issuance. Valid options are:

certificate
Where to store the issued certificate (in PEM format). At least one of certificate or certifi‐
cate-chain is required.

certificate-chain
Where to store the issued certificate, concatenated with the content of the file specified speci‐
fied with the CAfile option (in PEM format). At least one of certificate or certificate-chain is
required.

certificate-key
Path the service's private key. This option is required. The following command can be used to
generate a new 4096-bits RSA key in PEM format with mode 0600:

openssl genrsa 4096 | install -m0600 /dev/stdin /path/to/srv.key

min-days
For an existing certificate, the minimum number of days before its expiration date the section is
considered for re-issuance. A negative value forces reissuance, while the number 0 limits reis‐
suance to expired certificates. Default: the value of the CLI option --min-days, or 21 if there
is no such option.

CAfile Path to the issuer's certificate. This is used for certificate-chain and to verify the validity
of each issued certificate. Specifying an empty value skip certificate validation. Default:
/usr/share/lacme/lets-encrypt-x3-cross-signed.pem.

hash Message digest algorithm to sign the Certificate Signing Request with.

keyUsage
Comma-separated list of Key Usages, see x509v3_config(5ssl).

subject
Subject field of the Certificate Signing Request, in the form /type0=value0/type1=val‐
ue1/type2=.... This option is required.

subjectAltName
Comma-separated list of Subject Alternative Names, in the form type0:value1,type1:value1,type2:...
The only type currently supported is DNS, to specify an alternative domain name.

chown An optional username[:groupname] to chown the issued certificate and certificate-chain to.

chmod An optional octal mode to chmod the issued certificate and certificate-chain to.

notify Command to pass the the system's command shell (/bin/sh -c) after successful installation of the
certificate and/or certificate-chain.

EXAMPLES

              ~$ sudo lacme new-reg mailto:noreply@example.com
              ~$ sudo lacme reg=/acme/reg/123456 --agreement-uri=https://letsencrypt.org/documents/LE-SA-v1.1.1-August-1-2016.pdf
              ~$ sudo lacme new-cert
              ~$ sudo lacme revoke-cert /path/to/server/certificate.pem

BUGS AND FEEDBACK

       Bugs or  feature  requests  for  lacme  should  be  filed  with  the  Debian  project's  bug  tracker  at
       <https://www.debian.org/Bugs/>.

AUTHORS

       Guilhem Moulin (mailto:guilhem@fripost.org).

                                                  December 2015                                         lacme(1)