LITE Bootstrap Server

A proof-of-concept certificate authority (CA) and bootstrap server written in Go.

This utility provides an authenticated REST API that can be used to:

• Validate and sign certificate signing requests (CSRs)
• Register devices on a 3rd party cloud service during certificate registration
• Provision devices with basic connection details (MQTT broker domain/port)
• List previously registered devices
• Check certificate validity

Certificate requests are logged to a local SQLite database (CADB.db).

Device registration hooks to cloud services and returned MQTT broker details are currently based on Azure IoT Hub, which may be extended to other providers in the future.

It also enables a basic TCP server (mTLS TCP server) that requests a client certificate during the TLS handshake, verifying that the certificate has been signed by the CA. This is only used for testing and proof of concept purposes.

The REST API will only accept requests from client devices with access to the bootstrap certificate and private key generated by setup-bootstrap.sh further below in this guide. It's assumed that this certificate and key pair will be provisioned to devices in the factory. This only provides a nominal level of protection, but demonstrates a starting point for securing the server from unwanted access.

Prerequisites

This project requires a recent version of go to compile and debug the server.

For platform-specific details on installing go, see: https://go.dev/doc/install

Quick Setup

0. Build the App

If you haven't already, the first step is to clone and build the app locally:

$ git clone https://github.com/Linaro/lite_bootstrap_server.git
$ cd lite_bootstrap_server
$ go build -o liteboot

The -o liteboot is optional, but will cause the compiled app to have the shorter liteboot name instead of the cumbersome default of lite_bootstrap_server.

1. Add a Config File

You can override various config settings with a .liteboot.toml file in the application root folder.

The [server] settings, which map to the command-line parameters shown with liteboot server --help, must be populated to set the ports used by the utility, as well as to provide a response to the ccs endpoint:

[server]
# Azure IoT Hub Settings
hubname = "azure-hub-name"
resourcegroup = "azure-resource-group"
mqttport = 8883

# Set the server hostname explicitly
# hostname = "myhostname.local"

# CA port number (REST API)
port = 1443

# mTLS port number
mport = 8443

2. Set the Hostname

The hostname is important since it will be included in the subject line of certificates signed by liteboot, and be part of the SERVER certificate used to establish a TLS connection to the server.

The same hostname must be used in the SERVER certificate or the TLS connection will be refused.

This application will attempt to determine the hostname to use for the server(s) based on the following order of precedence:

1. Via the --hostname parameter in the server command
2. Via a hostname entry in the .liteboot.toml config file (see step 1 above)
3. Check for the $CAHOSTNAME environment variable
4. Check the system hostname (same value as hostname in shell)
5. Default to localhost as a last resort

For example, set the hostname before starting the server via:

$ export CAHOSTNAME='myhostname.local'

Which could also be overridden via:

$ ./liteboot server start --hostname="localhost"

For local development, this can usually be set to localhost, but will need to be changed when working with multiple machines or containers.

3. Run Setup Scripts

First, create the HTTP and CA keys and certificates via setup-ca.sh.

This should only need to be run once, and, in fact, will require existing certs to have to be removed manually before it can be run again:

If you haven't set the hostname via the CAHOSTNAME environment variable, and wish to use a hostname other than what the hostname command resolves to, this script should be called with the hostname as the first parameter. Run the script with -h for details.

$ ./setup-ca.sh

Next, setup the bootstrap key pair via setup-bootstrap.sh.

This key pair is required to authenticate with the CA server, and the data placed in bootstrap_crt.txt and bootstrap_key.txt will need to be included in the client device, or included in any attempts to connect to the REST API using curl, wget, etc.

The script can be run multiple times (after removing the generated files), but only would need to be rerun after regenerating the CA cert.

$ ./setup-bootstrap.sh

4. Start the Server

Run run-server.sh to start the CA server on port 1443, or whatever port you set in the config file:

This script also accepts an optional hostname override as the first parameter. Run the script with -h for details.

$ ./run-server.sh

5. Optional Steps

Generate Test Device(s)

You can optionally run new-device.sh to create a new device, and registers it with this CA.

The certificates for the device will be placed in the 'certs' directory, along with the certificates above.

This certificate is only useful for testing the CA, and generally will not be used in a production setting.

This script also accepts an optional hostname override as the first parameter. Run the script with -h for details.

$ ./new-device.sh

Cleanup

You can remove all existing certificate artifacts via:

$ rm CADB.rb
$ rm -rf certs

REST API

The REST API is a work in progress, and may be changed in the future!

/api/v1/cr Certification Request: POST

Request a certificate for a new device, based on the provided certificate signing request (CSR).

The CA will assign and record a unique serial number for this certificate, which can later be used to check the certificate status via the cs/{serial} endpoint.

This API requires the Content-Type to be set on the post data, and must be set to either application/cbor or application/json. A request made in cbor will have a cbor reply, json will reply with a json encoded response.

Request with application/cbor

The CSR payload should be wrapped in a single CBOR array:

[ bstr ]

Example

See the new-device.sh script for an example of generating an appropriate request from the shell, and saving the response.

Response

Replies with a CBOR array containing the following fields:

{
   1 => int,   ; Status.
   2 => bstr,  ; Certificate
}

• Status is an error code where 0 indicates success, and non-zero values should be treated as an error.
• Certificate contains the BASE64-encoded DER format certificate.

Request with application/json

Takes a BASE64-encoded CSR payload in a JSON wrapper as follows:

{
  "CSR":"MIH9MIGlAgEAMEMxEjAQBgNVBAoMCWxvY2FsaG9zdDEtMCsGA1UEAwwkZThjNDdiNDItZjdmYy00ZGM4LWI1MzgtOTM0OTZiNjE5YTNjMFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEJ5aLGLJID8MVHCHEzQOlO63RvBaTy8lRbtkDODYPgDKBOuAHWXbytgjO32K8O282BK/Hl5eEKqcXcHerlxE2xKAAMAoGCCqGSM49BAMCA0cAMEQCIEFoH+NV9jXJA0PmctbCQ7FOBnE/aT9hmqBuvBq2kIhuAiAyKGAUIAzHDBZ+lY6WaJGh/56rzr4KprVtNYFGLHLs1g=="
}

⚠️ The CSR field in the JSON request payload is a BASE64 encoded byte array from a DER file. This paylaod doesn't include the text headers present in the PEM files generated by openssl req -new -key UUID.key -out UUID.csr in new-device.sh.

Response

Replies with a JSON array containing Status, and Cert fields:

• Status is an error code where 0 indicates success, and non-zero values should be treated as an error.
• Cert contains the BASE64-encoded DER format certificate.

{
  "Status":0,
  "Cert":"MIIBtjCCAVugAwIBAgIIFrKA6WV+D5gwCgYIKoZIzj0EAwIwOjEUMBIGA1UEChMLTGluYXJvLCBMVEQxIjAgBgNVBAMTGUxpbmFyb0NBIFJvb3QgQ2VydCAtIDIwMjAwHhcNMjExMDI5MTI0MjM0WhcNMjIxMDI5MTI0MjM0WjBDMRIwEAYDVQQKEwlsb2NhbGhvc3QxLTArBgNVBAMTJGU4YzQ3YjQyLWY3ZmMtNGRjOC1iNTM4LTkzNDk2YjYxOWEzYzBZMBMGByqGSM49AgEGCCqGSM49AwEHA0IABCeWixiySA/DFRwhxM0DpTut0bwWk8vJUW7ZAzg2D4AygTrgB1l28rYIzt9ivDtvNgSvx5eXhCqnF3B3q5cRNsSjQjBAMB0GA1UdDgQWBBSCv0wCNUXMXavfi15AbcCclDvfkzAfBgNVHSMEGDAWgBSxhUrvHyyKgHn5/FaoKd761df1tjAKBggqhkjOPQQDAgNJADBGAiEAjDVYvr1qBfvc0VFZcFLxwO/5XvnBh2jZFpL9ykKsCw8CIQDF3ne7yokRAHt0nn35CW/J3FclGYH9rBVCZr7FU+pzHg==",
}

/api/v1/p10cr Certification Request from PKCS10: POST

This endpoint is used to request a certificate for a new device, posting a PKCS#10 CSR file in PEM format.

The CA will assign and record a unique serial number for this certificate, which can later be used to check the certificate status via the cs/{serial} endpoint.

It will reply with a certificate file in PEM format or a status error in JSON, depending on the input CSR provided.

Testing this endpoint with:

The example belows assumes MBP2021.lan as the local hostname. This value will vary from one machine to another.

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          -F csrfile=@USER.csr       \
          --output USER.crt          \
          https://MBP2021.lan:1443/api/v1/p10cr

should give you a USER.crt file in PEM format, which you can view via:

$ openssl x509 -in USER.crt -noout -text

api/v1/ds/{uuid} Device Status Request: GET

Checks if any valid certificates are associated with the specified device UUID. If any valid certificates are found, their serial number will be returned in the response payload.

This endpoint accepts requests in cbor (application/cbor) or json (application/json), defaulting to JSON responses if no Content-Type is provided. The response Content-Type will match the request type used.

Request with application/json

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          https://MBP2021.lan:1443/api/v1/ds/56d38f73-3f6f-4a59-86bc-d315a1ccc634

Request with application/cbor

You can send a status request via:

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          -H 'Content-Type: application/cbor' \
          https://MBP2021.lan:1443/api/v1/ds/56d38f73-3f6f-4a59-86bc-d315a1ccc634 \
          -o cbor_enc.raw

CBOR requests receive binary responses, which curl will print as an unknown symbol on the console. Pass the -o <filename> argument to store the binary output in a file, and execute go run cbor_decoder.go -i cbor_enc.raw -r ds to decode the binary output response and print in the JSON format.

Responses

This endpoint will return the following responses, in JSON or CBOR encoding depening on the Content-Type used:

• HTTP response code 200
  • {"Status":0,"Serials":null}: No valid certs found for UUID
  • {"Status":1,"Serials":[1649073924922206000]}: Valid cert(s) found for UUID
• HTTP response code 400 + {"error": "<error msg>"}, where error msg is:
  • need a valid UUID: Invalid or improperly formatted UUID was provided
  • unable to query db for UUID: error querying for database UUID (fatal)
  • bad request: Content-Type must be ...: Invalid Content-Type provided

api/v1/cs/{serial} Certificate Status Request: GET

Requests the certificate status based on the supplied certificate serial number.

The serial number is generated by the CA during the certificate generation process (/ap1/v1/cr), and is a unique timestamp-based 64-bit integer (ex. 1635511354607407000) that is added to the certificate before sending it back to the requesting device.

It can be retrieved using the /api/v1/ds/{uuid} endpoint, or from a certificate file directly via the serial number field, for example:

The example belows assumes a specific device UUID, and MBP2021.lan as the local hostname. These values will vary from one machine to another.

$ openssl x509 -in certs/a8c6f808-b659-4f88-affb-40498834c572.crt -noout -text
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 1648935985023194000 (0x16e2328abcaa9390)
    Signature Algorithm: ecdsa-with-SHA256
        Issuer: O=Linaro, LTD, CN=LRC - 20220330062226
        Validity
            Not Before: Apr  2 21:46:25 2022 GMT
            Not After : Apr  2 21:46:25 2023 GMT
        Subject: O=MBP2021.lan, OU=LinaroCA Device Cert - Signing, CN=a8c6f808-b659-4f88-affb-40498834c572
        ...

Once you have the serial number, you can send a status request via:

Request with application/json (default)

You can send a status request via:

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          https://MBP2021.lan:1443/api/v1/cs/1648935985023194000

Request with application/cbor

You can send a status request via:

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          -H 'Content-Type: application/cbor' \
          https://MBP2021.lan:1443/api/v1/cs/1648935985023194000 \
          -o cbor_enc.raw

CBOR requests receive binary responses, which curl will print as an unknown symbol on the console. Pass the -o <filename> argument to store the binary output in a file, and execute go run cbor_decoder.go -i cbor_enc.raw -r cs to decode the binary output response and print in the JSON format.

Responses

This endpoint will return the following responses, in JSON or CBOR depending on the Content-Type used:

• HTTP response code 200
  • {"status": "1"}: Indicates that the serial number exists, and that the certificate is marked as valid in the CA database.
  • {"status": "0"}: Indicates that the serial number exists, but that the certificate is marked as invalid in the CA database (i.e., it has been revoked).
• HTTP response code 400 + {"error": "<error msg>"}, where error msg is:
  • invalid request: Poorly formatted serial number was provided
  • invalid serial number: No certificate matching supplied serial found
  • bad request: Content-Type must be ...: Invalid Content-Type provided

api/v1/cc/{serial} X509 Certificate Copy Request: GET

Requests a copy of the x509 certificate associated with the supplied serial number. If found, the certificate data is returned in PEM format (BASE64 ASCII).

See the cs endpoint for details on retrieving a certificate serial number.

Request with application/json (default)

You can send the x509 certificate copy request via:

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          https://MBP2021.lan:1443/api/v1/cc/1664276589086394391

Request with application/cbor

You can send the x509 certificate copy request via:

$ curl -v --cacert certs/CA.crt  \          
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          -H 'Content-Type: application/cbor' \
          https://MBP2021.lan:1443/api/v1/cc/1664276589086394391 \
          -o cbor_enc.raw

CBOR requests receive binary responses, which curl will print as an unknown symbol on the console. Pass the -o <filename> argument to store the binary output in a file, and execute go run cbor_decoder.go -i cbor_enc.raw -r cc to decode the binary output response and print in the JSON format.

Response

Replies with a JSON or CBOR array containing Status, and Cert fields:

• Status is an error code where 0 indicates success, and non-zero values should be treated as an error.
• Cert contains the string type x509 pem format certificate.

For example, if the Content-Type is set to the default application/json:

{
  "Status":0,
  "Cert":"-----BEGIN CERTIFICATE-----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\nKKmII4ZjIWrZs7Qr/A==\n-----END CERTIFICATE-----\n"
}

api/v1/ccs Cloud Connectvity Settings: GET

Requests the cloud connectivity details for the MQTT broker associated with your cloud infrastructure.

This endpoint allows device to retrieve details about the MQTT broker, etc., that they should connect to, and is usually retrieved during the provisioning process, or when an alert is received by the client device that the cloud connectivity settings have changed.

Request with application/cbor

You can send a status request via:

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          -H 'Content-Type: application/cbor' \
          -H 'Accept: application/cbor' \
          https://MBP2021.lan:1443/api/v1/ccs \
          -o cbor_enc.raw

CBOR requests receive binary responses, which curl will print as an unknown symbol on the console. Pass the -o <filename> argument to store the binary output in a file, and execute go run cbor_decoder.go -i cbor_enc.raw -r ccs to decode the binary output response and print in the JSON format.

Request with application/json (default)

You can send a status request via:

$ curl -v --cacert certs/CA.crt  \
          --cert certs/BOOTSTRAP.crt \
          --key certs/BOOTSTRAP.key  \
          https://MBP2021.lan:1443/api/v1/ccs

Response

Replies with a JSON array containing the following fields:

{
  "Hubname":"azure_hubname",
  "Port":8883
}

• Hubname contains the Azure IoT Hub hubname string.
• Port contains the Azure IoT Hub MQTT port number.

api/v1/kur Key Update Request: POST (TODO)

Request an update to an existing (non-revoked and non-expired) certificate. An update is a replacement certificate containing either a new subject public key or the current subject public key.

api/v1/krr Key Revocation Request: POST (TODO)

Requests the revocation of an existing certificate registration.

Mutual TLS Test Server

A secondary TCP server is started up along with the main CA server to test mutual TLS authentication using client certificates.

mutual TLS authentication requests a certificate from the connecting client device that has been signed with the CA, adding an additional level of trust on behalf of the server concerning the client device.

Using a CA-signed client certificate

Once a user certificate has been generated (via new-device.sh), you can test mTLS connections via:

The example belows assumes a specific device UUID, and MBP2021.lan as the local hostname. These values will vary from one machine to another.

$ openssl s_client \
  -cert certs/f269528d-ff66-4fb0-83d8-e449e0038010.crt \
  -key certs/f269528d-ff66-4fb0-83d8-e449e0038010.key \
  -CAfile certs/CA.crt \
  -connect MBP2021.lan:8443

• The cert and key fields indicate the client certificate and key
• The CAfile field is the CA certificate

If the connection is successful, you should get the following response at the end of the outptut:

Verify return code: 0 (ok)

And liteboot will display details about the client cert in the log output:

$ ./liteboot server start
Starting mTLS TCP server on MBP2021.lan:8443
Starting CA server on port https://MBP2021.lan:1443
Connection accepted from 127.0.0.1:60510
[Certificate 0]
  - Subject: CN=f269528d-ff66-4fb0-83d8-e449e0038010,OU=Signing,O=Linaro\, LTD
  - Serial:  1671014018808547000
[Certificate 1]
  - Subject: CN=LRC - 20221129052020,O=Linaro\, LTD
  - Serial:  2022001129172020

• Certificate 0 is the device certificate
• Certificate 1 is the CA certificate used to sign certificate 0.

Using an invalid client certificate

To test with an invalid user certificate, generate a new cert:

$ openssl ecparam -name prime256v1 -genkey -out USERBAD.key
$ openssl req -new -x509 -sha256 -days 365 \
  -key USERBAD.key -out USERBAD.crt \
  -subj "/O=Linaro, LTD/CN=MBP2021.lan"

Then try the request again:

$ openssl s_client \
  -cert USERBAD.crt -key USERBAD.key \
  -CAfile certs/CA.crt \
  -connect MBP2021.lan:8443

You should get the following error from liteboot, since the device certificate has not been signed by our CA:

Connection accepted from 127.0.0.1:50443
Client handshake error: tls: failed to verify client certificate: x509: certificate signed by unknown authority

Troubleshooting

FAQs

setup-bootstrap.sh causes Can't load /home/user/.rnd into RNG

Run openssl rand -writerand .rnd to generate the missing .rnd file.