Administrator cannot encrypt/decrypt in AWS KMS

user_1039462 0
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I am using the Key Management service (KMS) in AWS and am currently setting up key policies.

I created two roles KmsUser and KmsAdmin and attached the following key policy to my CMK:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "KMS KeyAdmin access",
      "Effect": "Allow",
      "Principal": {"AWS": [
          "arn:aws:iam::1234567890:role/KmsAdmin",
      "arn:aws:iam::1234567890:user/myadmin"
      ]},
      "Action": [
        "kms:Create*",
        "kms:Describe*",
        "kms:Enable*",
        "kms:List*",
        "kms:Put*",
        "kms:Update*",
        "kms:Revoke*",
        "kms:Disable*",
        "kms:Get*",
        "kms:Delete*",
        "kms:TagResource",
        "kms:UntagResource",
        "kms:ScheduleKeyDeletion",
        "kms:CancelKeyDeletion"
      ],
    "Resource": "*"
    },
    {
      "Sid": "KMS KeyUser access",
      "Effect": "Allow",
      "Principal": {"AWS": [
          "arn:aws:iam::1234567890:role/KmsUser"
      ]},
      "Action": [
        "kms:Encrypt",
        "kms:Decrypt",
        "kms:ReEncrypt*",
        "kms:GenerateDataKey*",
        "kms:DescribeKey"
      ],
      "Resource": "*"
    }
  ]
}

The problem is that now if I try to use my key as the myadmin user (which has the AdministratorAccess policy attached) I get an error in the CLI:

$ aws kms encrypt --key-id "alias/test-key" --plaintext fileb:///tmp/plaintext.dat

An error occurred (AccessDeniedException) when calling the Encrypt operation: User: arn:aws:iam::1234567890:user/myadmin is not authorized to perform: kms:Encrypt on resource: arn:aws:kms:eu-north-1:1234567890:key/99999999-9999-9999-9999-99999999999

What is especially strange, is that the IAM policy simulator tells me that everything should work as expected:

enter image description here

If I manually add the myadmin user as a pricipal to the Key User policy, everything works fine.

aws-policies amazon-iam aws-kms amazon-web-services
2 Answers

You need to add a statement like this to your key policy:

        {
            "Sid": "Enable IAM User Permissions",
            "Effect": "Allow",
            "Principal": {
                "AWS": "arn:aws:iam::1234567890:root"
            },
            "Action": "kms:*",
            "Resource": "*"
        }

This allows the account to have access to the key, which is required to enable IAM access to it.

user_28600320

If you're creating the KMS construct using AWS CDK then make sure to set the trustAccountIdentities to true. Example in TypeScript

const passwordEncryptionKey = new kms.Key(this, 'MyKey', {
  enabled: true,
  trustAccountIdentities: true,
});

Docs are here

user_61066410
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