README

AWS KMS signing adapter for the Chronicle audit ledger.

Signs Chronicle checkpoints and exports via AWS KMS (ECDSA P-256). Verification is always offline — no AWS API call needed — using a cached public key.

Installation

composer require laravel-chronicle/kms-aws

The package auto-discovers its service provider via Laravel's package discovery.

Requirements

PHP 8.2+
ext-openssl
laravel-chronicle/core ^1.10
AWS SDK for PHP ^3.0

AWS Setup

Create a KMS key

Create an asymmetric KMS key with:

Key type: Asymmetric
Key spec: ECC_NIST_P256
Key usage: SIGN_VERIFY

Required IAM actions

Attach the following IAM policy to the role that runs your application:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "kms:Sign",
        "kms:DescribeKey"
      ],
      "Resource": "arn:aws:kms:REGION:ACCOUNT_ID:key/KEY_ID"
    }
  ]
}

kms:GetPublicKey is not required at runtime — the public key is cached in your application config and never fetched from KMS during verification.

Retrieve and cache the public key

Retrieve your KMS key's public key once and store it in your config:

aws kms get-public-key \
  --key-id arn:aws:kms:REGION:ACCOUNT_ID:key/KEY_ID \
  --query 'PublicKey' --output text | base64 -d | \
  openssl pkey -pubin -inform DER -outform PEM

This outputs a PEM string like:

-----BEGIN PUBLIC KEY-----
MFkwEwYH...
-----END PUBLIC KEY-----

Store this as the public_key in your Chronicle signing config (see below).

Configuration

use Chronicle\KmsAws\AwsKmsSigningProvider;

'signing' => [
    'active' => env('CHRONICLE_ACTIVE_KEY', 'kms-production'),

    'keys' => [
        'kms-production' => [
            'provider'   => AwsKmsSigningProvider::class,
            'algorithm'  => 'ecdsa-p256',
            'key_arn'    => env('CHRONICLE_KMS_KEY_ARN'),
            'public_key' => env('CHRONICLE_KMS_PUBLIC_KEY'),  // PEM string
        ],
    ],
],

Set the corresponding environment variables:

AWS_DEFAULT_REGION=eu-west-1
CHRONICLE_ACTIVE_KEY=kms-production
CHRONICLE_KMS_KEY_ARN=arn:aws:kms:eu-west-1:123456789012:key/your-key-id
CHRONICLE_KMS_PUBLIC_KEY="-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE...
-----END PUBLIC KEY-----
"

How it works

Operation	Where it runs
`sign()`	Remote — calls KMS `Sign` API with `MessageType: DIGEST`
`verify()`	Local — `openssl_verify` against the cached PEM public key

The private key never leaves AWS KMS. Verification is offline and instant.

Key rotation

Chronicle's key rotation works identically for KMS-backed keys. Retire the old key by keeping only its public_key in the ring (omit key_arn), then add the new KMS key as active. Historic checkpoints and exports continue to verify offline against the retained public key.

Example two-key ring after rotation:

'signing' => [
    'active' => 'kms-2026',
    'keys' => [
        // Retired — switch to EcdsaSigningProvider (from core) for verify-only mode.
        // AwsKmsSigningProvider requires key_arn and cannot be verify-only.
        'kms-2025' => [
            'provider'   => \Chronicle\Signing\EcdsaSigningProvider::class,
            'algorithm'  => 'ecdsa-p256',
            'public_key' => env('CHRONICLE_KMS_2025_PUBLIC_KEY'),
        ],
        // Active
        'kms-2026' => [
            'provider'   => AwsKmsSigningProvider::class,
            'algorithm'  => 'ecdsa-p256',
            'key_arn'    => env('CHRONICLE_KMS_KEY_ARN'),
            'public_key' => env('CHRONICLE_KMS_PUBLIC_KEY'),
        ],
    ],
],

Note: AwsKmsSigningProvider requires key_arn at construction — it cannot be used as a verify-only provider. For retired KMS keys, switch the entry to Chronicle\Signing\EcdsaSigningProvider (from core) with only public_key set, as shown above. Core's EcdsaSigningProvider handles the local-verify-only case.

License

MIT

laravel-chronicle / kms-aws

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