Configuring code signing for AWS SAM applications

You can use AWS SAM to enable code signing with your serverless applications to help ensure that only trusted code is deployed. For more information about the code signing feature, see Configuring code signing for Lambda functions in the AWS Lambda Developer Guide.

Before you can configure code signing for your serverless application, you must create a signing profile using AWS Signer. You use this signing profile for the following tasks:

1. Creating a code signing configuration – Declare an AWS::Lambda::CodeSigningConfig resource to specify the signing profiles of trusted publishers and to set the policy action for validation checks. You can declare this object in the same AWS SAM template as your serverless function, in a different AWS SAM template, or in an AWS CloudFormation template. You then enable code signing for a serverless function by specify the CodeSigningConfigArn property the function with the Amazon Resource Name (ARN) of an AWS::Lambda::CodeSigningConfig resource.

2. Signing your code – Use the sam package or sam deploy command with the --signing-profiles option.

When you deploy a serverless application, Lambda performs validation checks on all functions that you've enabled code signing for. Lambda also performs validation checks on any layers that those functions depend on. For more information about Lambda's validation checks, see Signature validation in the AWS Lambda Developer Guide.

Example

Creating a signing profile

To create a signing profile, run the following command:

aws signer put-signing-profile --platform-id "AWSLambda-SHA384-ECDSA" --profile-name MySigningProfile

If the previous command is successful, you see the signing profile's ARN returned. For example:

{
    "arn": "arn:aws:signer:us-east-1:111122223333:/signing-profiles/MySigningProfile",
    "profileVersion": "SAMPLEverx",
    "profileVersionArn": "arn:aws:signer:us-east-1:111122223333:/signing-profiles/MySigningProfile/SAMPLEverx"
}

The profileVersionArn field contains the ARN to use when you create the code signing configuration.

Creating a code signing configuration and enabling code signing for a function

The following example AWS SAM template declares an AWS::Lambda::CodeSigningConfig resource and enables code signing for a Lambda function. In this example, there is one trusted profile, and deployments are rejected if the signature checks fail.

Resources:
  HelloWorld:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: hello_world/
      Handler: app.lambda_handler
      Runtime: python3.7
      CodeSigningConfigArn: !Ref MySignedFunctionCodeSigningConfig

  MySignedFunctionCodeSigningConfig:
    Type: AWS::Lambda::CodeSigningConfig
    Properties:
      Description: "Code Signing for MySignedLambdaFunction"
      AllowedPublishers:
        SigningProfileVersionArns:
          - MySigningProfile-profileVersionArn
      CodeSigningPolicies:
        UntrustedArtifactOnDeployment: "Enforce"

Signing your code

You can sign your code when packaging or deploying your application. Specify the --signing-profiles option with either the sam package or sam deploy command, as shown in the following example commands.

Signing your function code when packaging your application:

sam package --signing-profile HelloWorld=MySigningProfile --s3-bucket test-bucket --output-template-file packaged.yaml

Signing both your function code and a layer that your function depends on, when packaging your application:

sam package --signing-profile HelloWorld=MySigningProfile MyLayer=MySigningProfile --s3-bucket test-bucket --output-template-file packaged.yaml

Signing your function code and a layer, then performing a deployment:

sam deploy --signing-profile HelloWorld=MySigningProfile MyLayer=MySigningProfile --s3-bucket test-bucket --template-file packaged.yaml --stack-name --region us-east-1 --capabilities CAPABILITY_IAM

Providing signing profiles with sam deploy --guided

When you run the sam deploy --guided command with a serverless application that's configured with code signing, AWS SAM prompts you to provide the signing profile to use for code signing. For more information about sam deploy --guided prompts, see sam deploy in the AWS SAM CLI command reference.