Self-managed certificate signing using AWS IoT Core certificate provider - AWS IoT Core

Self-managed certificate signing using AWS IoT Core certificate provider

You can create an AWS IoT Core certificate provider to sign certificate signing requests (CSRs) in AWS IoT fleet provisioning. A certificate provider references a Lambda function and the CreateCertificateFromCsr MQTT API for fleet provisioning. The Lambda function accepts a CSR and returns a signed client certificate.

When you don't have a certificate provider with your AWS account, the CreateCertificateFromCsr MQTT API is called in fleet provisioning to generate the certificate from a CSR. After you create a certificate provider, the behavior of the CreateCertificateFromCsr MQTT API will change and all calls to this MQTT API will invoke the certificate provider to issue the certificate.

With AWS IoT Core certificate provider, you can implement solutions that utilize private certificate authorities (CAs) such as AWS Private CA, other publicly trusted CAs, or your own Public Key Infrastructure (PKI) to sign the CSR. In addition, you can use certificate provider to customize your client certificate's fields such as validity periods, signing algorithms, issuers, and extensions.

Important

You can only create one certificate provider per AWS account. The signing behavior change applies to the entire fleet that calls the CreateCertificateFromCsr MQTT API until you delete the certificate provider from your AWS account.

How self-managed certificate signing works in fleet provisioning

Key concepts

The following concepts provide details that can help you understand how self-managed certificate signing works in AWS IoT fleet provisioning. For more information, see Provisioning devices that don't have device certificates using fleet provisioning.

AWS IoT fleet provisioning

With AWS IoT fleet provisioning (short for fleet provisioning), AWS IoT Core generates and securely delivers device certificates to your devices when they connect to AWS IoT Core for the first time. You can use fleet provisioning to connect devices that don't have device certificates to AWS IoT Core.

Certificate signing request (CSR)

In the process of fleet provisioning, a device makes a request to AWS IoT Core through the fleet provisioning MQTT APIs. This request includes a certificate signing request (CSR), which will be signed to create a client certificate.

AWS managed certificate signing in fleet provisioning

AWS managed is the default setting for certificate signing in fleet provisioning. With AWS managed certificate signing, AWS IoT Core will sign CSRs using its own CAs.

Self-managed certificate signing in fleet provisioning

Self-managed is another option for certificate signing in fleet provisioning. With self-managed certificate signing, you create an AWS IoT Core certificate provider to sign CSRs. You can use self-managed certificate signing to sign CSRs with a CA generated by AWS Private CA, other publicly trusted CA, or your own Public Key Infrastructure (PKI).

AWS IoT Core certificate provider

AWS IoT Core certificate provider (short for certificate provider) is a customer-managed resource that's used for self-managed certificate signing in fleet provisioning.

Diagram

The following diagram is a simplified illustration of how self-certificate signing works in AWS IoT fleet provisioning.


                        AWS IoT Core certificate provider for fleet provisioning
  • When a new IoT device is manufactured or introduced to the fleet, it needs client certificates to authenticate itself with AWS IoT Core.

  • As part of the fleet provisioning process, the device makes a request to AWS IoT Core for client certificates through the fleet provisioning MQTT APIs. This request includes a certificate signing request (CSR).

  • AWS IoT Core invokes the certificate provider and passes the CSR as input to the provider.

  • The certificate provider takes the CSR as input and issues a client certificate.

    For AWS managed certificate signing, AWS IoT Core signs the CSR using its own CA and issues a client certificate.

  • With the issued client certificate, the device will continue the fleet provisioning and establish a secure connection with AWS IoT Core.

Certificate provider Lambda function input

AWS IoT Core sends the following object to the Lambda function when a device registers with it. The value of certificateSigningRequest is the CSR in Privacy-Enhanced Mail (PEM) format that's provided in the CreateCertificateFromCsr request. The principalId is the ID of the principal used to connect to AWS IoT Core when making the CreateCertificateFromCsr request. clientId is the client ID set for the MQTT connection.

{ "certificateSigningRequest": "string", "principalId": "string", "clientId": "string" }

Certificate provider Lambda function return value

The Lambda function must return a response that contains the certificatePem value. The following is an example of a successful response. AWS IoT Core will use the return value (certificatePem) to create the certificate.

{ "certificatePem": "string" }

If the registration is successful, CreateCertificateFromCsr will return the same certificatePem in the CreateCertificateFromCsr response. For more information, see the response payload example of CreateCertificateFromCsr.

Example Lambda function

Before creating a certificate provider, you must create a Lambda function to sign a CSR. The following is an example Lambda function in Python. This function calls AWS Private CA to sign the input CSR, using a private CA and the SHA256WITHRSA signing algorithm. The returned client certificate will be valid for one year. For more information about AWS Private CA and how to create a private CA, see What is AWS Private CA? and Creating a private CA.

import os import time import uuid import boto3 def lambda_handler(event, context): ca_arn = os.environ['CA_ARN'] csr = (event['certificateSigningRequest']).encode('utf-8') acmpca = boto3.client('acm-pca') cert_arn = acmpca.issue_certificate( CertificateAuthorityArn=ca_arn, Csr=csr, Validity={"Type": "DAYS", "Value": 365}, SigningAlgorithm='SHA256WITHRSA', IdempotencyToken=str(uuid.uuid4()) )['CertificateArn'] # Wait for certificate to be issued time.sleep(1) cert_pem = acmpca.get_certificate( CertificateAuthorityArn=ca_arn, CertificateArn=cert_arn )['Certificate'] return { 'certificatePem': cert_pem }
Important
  • Certificates returned by the Lambda function must have the same subject name and public key as the Certificate Signing Request (CSR).

  • The Lambda function must finish running in 5 seconds.

  • The Lambda function must be in the same AWS account and Region as the certificate provider resource.

  • The AWS IoT service principal must be granted the invoke permission to the Lambda function. To avoid confused deputy issues, we recommend that you set sourceArn and sourceAccount for the invoke permissions. For more information, see Cross-service confused deputy prevention.

The following resource-based policy example for Lambda grants AWS IoT the permission to invoke the Lambda function:

{ "Version": "2012-10-17", "Id": "InvokePermission", "Statement": [ { "Sid": "LambdaAllowIotProvider", "Effect": "Allow", "Principal": { "Service": "iot.amazonaws.com" }, "Action": "lambda:InvokeFunction", "Resource": "arn:aws:lambda:us-east-1:123456789012:function:my-function", "Condition": { "StringEquals": { "AWS:SourceAccount": "123456789012" }, "ArnLike": { "AWS:SourceArn": "arn:aws:iot:us-east-1:123456789012:certificateprovider:my-certificate-provider" } } } ] }

Self-managed certificate signing for fleet provisioning

You can choose self-managed certificate signing for fleet provisioning using AWS CLI or AWS Management Console.

To choose self-managed certificate signing, you must create an AWS IoT Core certificate provider to sign CSRs in fleet provisioning. AWS IoT Core invokes the certificate provider, which takes a CSR as input and returns a client certificate. To create a certificate provider, use the CreateCertificateProvider API operation or the create-certificate-provider CLI command.

Note

After you create a certificate provider, the behavior of CreateCertificateFromCsr API for fleet provisioning will change so that all calls to CreateCertificateFromCsr will invoke the certificate provider to create the certificates. It can take a few minutes for this behavior to change after a certificate provider is created.

aws iot create-certificate-provider \ --certificateProviderName my-certificate-provider \ --lambdaFunctionArn arn:aws:lambda:us-east-1:123456789012:function:my-function-1 \ --accountDefaultForOperations CreateCertificateFromCsr

The following shows an example output for this command:

{ "certificateProviderName": "my-certificate-provider", "certificateProviderArn": "arn:aws:iot:us-east-1:123456789012:certificateprovider:my-certificate-provider" }

For more information, see CreateCertificateProvider from the AWS IoT API Reference.

To choose self-managed certificate signing using AWS Management Console, follow the steps:

  1. Go to the AWS IoT console.

  2. On the left navigation, under Security, choose Certificate signing.

  3. On the Certificate signing page, under Certificate signing details, choose Edit certificate signing method.

  4. On the Edit certificate signing method page, under Certificate signing method, choose Self-managed.

  5. In the Self-managed settings section, enter a name for certificate provider, then create or choose a Lambda function.

  6. Choose Update certificate signing.

AWS CLI commands for certificate provider

Create certificate provider

To create a certificate provider, use the CreateCertificateProvider API operation or the create-certificate-provider CLI command.

Note

After you create a certificate provider, the behavior of CreateCertificateFromCsr API for fleet provisioning will change so that all calls to CreateCertificateFromCsr will invoke the certificate provider to create the certificates. It can take a few minutes for this behavior to change after a certificate provider is created.

aws iot create-certificate-provider \ --certificateProviderName my-certificate-provider \ --lambdaFunctionArn arn:aws:lambda:us-east-1:123456789012:function:my-function-1 \ --accountDefaultForOperations CreateCertificateFromCsr

The following shows an example output for this command:

{ "certificateProviderName": "my-certificate-provider", "certificateProviderArn": "arn:aws:iot:us-east-1:123456789012:certificateprovider:my-certificate-provider" }

For more information, see CreateCertificateProvider from the AWS IoT API Reference.

Update certificate provider

To update a certificate provider, use the UpdateCertificateProvider API operation or the update-certificate-provider CLI command.

aws iot update-certificate-provider \ --certificateProviderName my-certificate-provider \ --lambdaFunctionArn arn:aws:lambda:us-east-1:123456789012:function:my-function-2 \ --accountDefaultForOperations CreateCertificateFromCsr

The following shows an example output for this command:

{ "certificateProviderName": "my-certificate-provider", "certificateProviderArn": "arn:aws:iot:us-east-1:123456789012:certificateprovider:my-certificate-provider" }

For more information, see UpdateCertificateProvider from the AWS IoT API Reference.

Describe certificate provider

To describe a certificate provider, use the DescribeCertificateProvider API operation or the describe-certificate-provider CLI command.

aws iot describe-certificate-provider --certificateProviderName my-certificate-provider

The following shows an example output for this command:

{ "certificateProviderName": "my-certificate-provider", "lambdaFunctionArn": "arn:aws:lambda:us-east-1:123456789012:function:my-function", "accountDefaultForOperations": [ "CreateCertificateFromCsr" ], "creationDate": "2022-11-03T00:15", "lastModifiedDate": "2022-11-18T00:15" }

For more information, see DescribeCertificateProvider from the AWS IoT API Reference.

Delete certificate provider

To delete a certificate provider, use the DeleteCertificateProvider API operation or the delete-certificate-provider CLI command. If you delete the certificate provider resource, the behavior of CreateCertificateFromCsr will resume, and AWS IoT will create certificates signed by AWS IoT from a CSR.

aws iot delete-certificate-provider --certificateProviderName my-certificate-provider

This command doesn't produce any output.

For more information, see DeleteCertificateProvider from the AWS IoT API Reference.

List certificate provider

To list the certificate providers within your AWS account, use the ListCertificateProviders API operation or the list-certificate-providers CLI command.

aws iot list-certificate-providers

The following shows an example output for this command:

{ "certificateProviders": [ { "certificateProviderName": "my-certificate-provider", "certificateProviderArn": "arn:aws:iot:us-east-1:123456789012:certificateprovider:my-certificate-provider" } ] }

For more information, see ListCertificateProvider from the AWS IoT API Reference.