Pebble

A miniature version of Boulder, Pebble is a small ACME test server not suited for use as a production CA.

!!! WARNING !!!

Pebble is NOT INTENDED FOR PRODUCTION USE. Pebble is for testing only.

By design Pebble will drop all of its state between invocations and will randomize keys/certificates used for issuance.

Goals

Pebble has several top level goals:

1. Provide a simplified ACME testing front end
2. Provide a test-bed for new and compatibility breaking ACME features
3. Encourage ACME client best-practices
4. Aggressively build in guardrails against non-testing usage

Pebble aims to address the need for ACME clients to have an easier to use, self-contained version of Boulder to test their clients against while developing ACME v2 support. Boulder is multi-process, requires heavy dependencies (MariaDB, gRPC, etc), and is operationally complex to integrate with other projects.

Where possible Pebble aims to be a test-bed for new ACME protocol features that can be used to inform later Boulder support. Pebble provides a way for Boulder developers to test compatibility breaking changes more aggressively than is appropriate for Boulder.

In places where the ACME specification allows customization/CA choice Pebble aims to make choices different from Boulder. For instance, Pebble changes the path structures for its resources and directory endpoints to differ from Boulder. The goal is to emphasize client specification compatibility and to avoid "over-fitting" on Boulder and the Let's Encrypt production service.

Lastly, Pebble will enforce it's test-only usage by aggressively building in guardrails that make using it in a production setting impossible or very inconvenient. Pebble will not support non-volatile storage or persistence between executions. Pebble will also randomize keys/certificates used for issuance. Where possible Pebble will make decisions that force clients to implement ACME correctly (e.g. randomizing /directory endpoint URLs to ensure clients are not hardcoding URLs.)

Limitations

Pebble is missing some ACME features (PRs are welcome!). It does not presently support subproblems, or pre-authorization. Pebble does not support revoking a certificate issued by a different ACME account by proving authorization of all of the certificate's domains.

Pebble does not perform all of the same input validation as Boulder. Some domain names that would be rejected by Boulder/Let's Encrypt may work with Pebble.

Pebble does not enforce any rate limits. It is not presently an appropriate tool for testing that your client handles Boulder/Let's Encrypt rate limits correctly.

Install

1. Set up Go
2. Add ~/go/bin to your $PATH, or set GOBIN to a directory that is in your $PATH already, so that pebble will be in your $PATH for easy execution.
   • One way to do this is to add export PATH=$PATH:$HOME/go/bin to your ~/.profile
3. git clone https://github.com/letsencrypt/pebble/
4. cd pebble
5. go install ./cmd/pebble

Usage

Binary

Assuming pebble is easily accessible in your $PATH:

pebble -config ./test/config/pebble-config.json

(otherwise replace pebble with ~/go/bin/pebble or $GOBIN/pebble)

Afterwards you can access the Pebble server's ACME directory at https://localhost:14000/dir.

Docker

Pebble includes a docker-compose file that will create a pebble instance that uses a pebble-challtestsrv instance for DNS resolution.

To download and start the containers run:

docker-compose up

Afterwards you can access the ACME API from your host machine at https://localhost:14000/dir, pebble's management interface at https://localhost:15000 and the pebble-challtestsrv's management interface at http://localhost:8055.

To get started you may want to update the pebble-challtestsrv mock DNS data with a new default IPv4 address to use to respond to A queries from pebble:

curl --request POST --data '{"ip":"172.20.0.1"}' http://localhost:8055/set-default-ipv4

See the pebble-challtestsrv README for more information.

Prebuilt Docker Images

Pebble releases are published as Docker images to the Github Container Registry

With a docker-compose file:

version: '3'

services:
 pebble:
  image: ghcr.io/letsencrypt/pebble:latest
  command: pebble -config /test/my-pebble-config.json
  ports:
    - 14000:14000  # ACME port
    - 15000:15000  # Management port
  environment:
    - PEBBLE_VA_NOSLEEP=1
  volumes:
    - ./my-pebble-config.json:/test/my-pebble-config.json

With a Docker command:

docker run -e "PEBBLE_VA_NOSLEEP=1" ghcr.io/letsencrypt/pebble
# or
docker run -e "PEBBLE_VA_NOSLEEP=1" --mount src=$(pwd)/my-pebble-config.json,target=/test/my-pebble-config.json,type=bind letsencrypt/pebble pebble -config /test/my-pebble-config.json

Default validation ports

To make it easier to test ACME clients and run challenge response servers without root privileges Pebble defaults to validating ACME challenges using unprivileged high ports:

• Default HTTP-01 Port: 5002
• Default TLS-ALPN-01 Port: 5001

These ports can be changed by editing the "httpPort" and "tlsPort" values of the Pebble -config file provided to pebble.

Strict Mode

Pebble's goal to aggressively support new protocol features and backwards compatibility breaking changes is slightly at odds with its goal to provide a simple, light-weight ACME test server for clients to use in integration tests. On the one hand we want to introduce breaking changes quickly and use Pebble as a test-bed for this. On the other we want to make sure we don't break client integration tests using Pebble too often.

As a balance to meet these two needs Pebble supports a -strict flag. By running Pebble with -strict false changes known to break client compatibility are disabled.

Presently we default -strict to false but this will change in the future. If you are using Pebble for integration tests and favour reliability over learning about breaking changes ASAP please explicitly run Pebble with -strict false.

DNS Server

By default Pebble uses the system DNS resolver, this may mean that caching causes problems with DNS-01 validation. It may also mean that no DNSSEC validation is performed. You should configure your system's recursive DNS resolver according to your needs or use the -dnsserver flag to define an address to a DNS server.

pebble -dnsserver 10.10.10.10:5053
pebble -dnsserver 8.8.8.8:53
pebble -dnsserver :5053

You may find it useful to set pebble's -dnsserver to the address you used as the -dns01 argument when starting up a pebble-challtestsrv instance. This will let you easily mock DNS data for Pebble. See the included docker-compose.yml and the pebble-challtestsrv README for more information.

Testing at full speed

By default Pebble will sleep a random number of seconds (from 0 to 15) between individual challenge validation attempts. This ensures clients don't make assumptions about when the challenge is solved from the CA side by observing a single request for a challenge response. Instead clients must poll the challenge to observe the state since the CA may send many validation requests.

To test issuance "at full speed" with no artificial sleeps set the environment variable PEBBLE_VA_NOSLEEP to 1. E.g.

PEBBLE_VA_NOSLEEP=1 pebble -config ./test/config/pebble-config.json

The maximal number of seconds to sleep can be configured by defining PEBBLE_VA_SLEEPTIME. It must be set to a positive integer.

Skipping Validation

If you want to avoid the hassle of having to stand up a challenge response server for real HTTP-01, DNS-01 or TLS-ALPN-01 validation requests Pebble supports a mode that always treats challenge validation requests as successful. By default this mode is disabled and challenge validation is performed.

To have all challenge POST requests succeed without performing any validation run:

PEBBLE_VA_ALWAYS_VALID=1 pebble

Invalid Anti-Replay Nonce Errors

The urn:ietf:params:acme:error:badNonce error type is meant to be retry-able. When receiving this error a client should make a subsequent request to the /new-nonce endpoint (or use the nonce from the error response) to retry the failed request, rather than quitting outright.

Experience from Boulder indicates that many ACME clients do not gracefully retry on invalid nonce errors. To help ensure future ACME clients are able to gracefully handle these errors by default Pebble rejects 5% of all valid nonces as invalid.

The percentage of valid nonces that are rejected can be configured using the environment variable PEBBLE_WFE_NONCEREJECT. E.g. to reject 90% of good nonces as invalid instead of 15% run:

PEBBLE_WFE_NONCEREJECT=90 pebble

To never reject a valid nonce as invalid run:

PEBBLE_WFE_NONCEREJECT=0 pebble

Object Reuse

The RFC allows for several objects to be re-used.

Clients should be prepared an ACME server may re-use any given object type, regardless of Pebble implementing a reuse policy for that object.

Pebble and Boulder may or may not implement the same object re-use policies at any given time. There exists an ACME Implementation Details document for Boulder which contains some information on how Boulder handles this.

Order Reuse

The RFC allows ACME servers to reuse an Order. Pebble does not reuse Orders at this time; however Boulder does reuse Orders in at least one scenario:

• If an Account requests a new Order that is identical to an already existing "pending" or "ready" Order for that same Account, the Order will be re-used.

Authorization Reuse

ACME servers may choose to reuse authorizations from previous orders in new orders. ACME clients should always check the status of a new order and its authorizations to confirm whether they need to respond to any challenges.

Valid Authorization Reuse

Pebble will reuse valid authorizations in new orders, if they exist, 50% of the time.

The percentage may be controlled with the environment variable PEBBLE_AUTHZREUSE, e.g. to always reuse authorizations:

PEBBLE_AUTHZREUSE=100 pebble

Pending Authorization Reuse

Pebble does not currently reuse Pending Authorizations across Orders, however other ACME servers - notably Boulder - will reuse Pending Authorizations.

Avoiding Client HTTPS Errors

Pebble is accessible over HTTPS only and uses a test certificate generated using a test CA (See the test/certs/ directory for more information).

Since the Pebble test CA isn't part of any default CA trust stores you must add the test/certs/pebble.minica.pem certificate to your client's trusted root configuration to avoid HTTPS errors. Your client should offer a runtime option to specify a list of trusted root CAs.

IMPORTANT: Do not add the pebble.minica.pem CA to the system-wide trust store or to any production systems/codebases. The private key for this CA is intentionally made publicly available in this repo.

Management interface

In order to ease the interaction of Pebble with testing systems, a specific HTTP management interface is exposed on a different port than the ACME protocol, and offers several useful testing endpoints.

These endpoints are specific to Pebble and its internal behavior, and are not part of the RFC 8555 that defines the ACME protocol.

The management interface is configured by the managementListenAddress field in pebble-config.json that defines the address and the port on which the management interface will listen on. Set managementListenAddress to an empty string or null to disable it.

The default configuration for this management interface as defined in test/config/pebble-config.json is to listen on any address on port 15000:

  "managementListenAddress": "0.0.0.0:15000",

CA Root and Intermediate Certificates

Note that the CA's root and intermediate certificates are regenerated on every launch. They can be retrieved by a GET request to https://localhost:15000/roots/0 and https://localhost:15000/intermediates/0 respectively.

You might need the root certificate to verify the complete trust chain of generated certificates, for example in end-to-end tests.

The private keys of these certificates can also be retrieved by a GET request to https://localhost:15000/root-keys/0 and https://localhost:15000/intermediate-keys/0 respectively.

IMPORTANT: Do not add Pebble's root or intermediate certificate to a trust store that you use for ordinary browsing or that is used for non-testing purposes, since Pebble and its generated keys are not audited or held to the same standards as the Let's Encrypt production CA and their keys. Moreover these keys are exposed by Pebble and will be lost as soon as the process terminates: so they are not safe to use for anything other than testing.

In case alternative root chains are enabled by setting PEBBLE_ALTERNATE_ROOTS to a positive integer, the root certificates for these can be retrieved by doing a GET request to https://localhost:15000/roots/0, https://localhost:15000/root-keys/1 https://localhost:15000/intermediates/2, https://localhost:15000/intermediate-keys/3 etc. These endpoints also send Link HTTP headers for all alternative root and intermediate certificates and keys.

The length of certificate chains can be controlled using PEBBLE_CHAIN_LENGTH, which has a default and minimum value of 1 (leaf + 1 intermediate). For higher values, Pebble will include extra intermediate certificates between the leaf and the root. Extra intermediate certificates are not exposed via the management interface.

Certificate Status

The certificate (in PEM format) and its revocation status can be queried by sending a GET request to https://localhost:15000/cert-status-by-serial/<serial>, where <serial> is the hexadecimal representation of the certificate's serial number (no 0x prefix). It can be obtained via:

openssl x509 -in cert.pem -noout -serial | cut -d= -f2

The endpoint returns the information as a JSON object:

$ curl -ki https://127.0.0.1:15000/cert-status-by-serial/66317d2e02f5d3d6
HTTP/2 200
cache-control: public, max-age=0, no-cache
content-type: application/json; charset=utf-8
link: <https://127.0.0.1:15000/dir>;rel="index"
content-length: 1740
date: Fri, 12 Jul 2019 22:14:21 GMT

{
   "Certificate": "-----BEGIN CERTIFICATE-----\nMIIEVz...tcw=\n-----END CERTIFICATE-----\n",
   "Reason": 4,
   "RevokedAt": "2019-07-13T00:13:20.418489956+02:00",
   "Serial": "66317d2e02f5d3d6",
   "Status": "Revoked"
}

OCSP Responder URL

Pebble does not support the OCSP protocol as a responder and so does not set the OCSP Responder URL in the issued certificates. However, if you setup a proper OCSP Responder run side by side with Pebble, you may want to set this URL. This is possible by setting the field ocspResponderURL of the pebble-config.json consummed by Pebble to a non empty string: in this case, this string will be use in the appropriate field of all issued certificates.

For instance, to have Pebble issue certificates that instruct a client to check the URL http://127.0.0.1:4002 to retrieve the OCSP status of a certificate, run Pebble with a pebble-config.json that includes:

  "ocspResponderURL": "http://127.0.0.1:4002",

Listing orders

Pebble has support for enumerating all orders for an ACME account object according to RFC 8555, Section 7.1.2. By default, three orders are returned per page, to make it easy to test pagination. This number can be modified by setting the PEBBLE_WFE_ORDERS_PER_PAGE environment variable to a positive integer. For example, to have 15 orders per page, run

PEBBLE_WFE_ORDERS_PER_PAGE=15 pebble