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Amazon KMS condition keys for Amazon Nitro Enclaves

Amazon Nitro Enclaves is an Amazon EC2 capability that lets you create isolated compute environments called enclaves to protect and process highly sensitive data. Amazon KMS provides condition keys to support Amazon Nitro Enclaves. These conditions keys are effective only for requests to Amazon KMS for a Nitro Enclave.

When you call the Decrypt, DeriveSharedSecret, GenerateDataKey, GenerateDataKeyPair, or GenerateRandom API operations with the signed attestation document from an enclave, these APIs encrypt the plaintext in the response under the public key from the attestation document, and return ciphertext instead of plaintext. This ciphertext can be decrypted only by using the private key in the enclave. For more information, see Cryptographic attestation for Amazon Nitro Enclaves.

The following condition keys let you limit the permissions for these operations based on the contents of the signed attestation document. Before allowing an operation, Amazon KMS compares the attestation document from the enclave to the values in these Amazon KMS condition keys.

kms:RecipientAttestation:ImageSha384

The kms:RecipientAttestation:ImageSha384 condition key controls access to Decrypt, DeriveSharedSecret, GenerateDataKey, GenerateDataKeyPair, and GenerateRandom with a KMS key when the image digest from the signed attestation document in the request matches the value in the condition key. The ImageSha384 value corresponds to PCR0 in the attestation document. This condition key is effective only when the Recipient parameter in the request specifies a signed attestation document for an Amazon Nitro enclave.

This value is also included in CloudTrail events for requests to Amazon KMS for Nitro enclaves.

For example, the following key policy statement allows the data-processing role to use the KMS key for Decrypt, DeriveSharedSecret, GenerateDataKey, GenerateDataKeyPair, and GenerateRandom operations. The kms:RecipientAttestation:ImageSha384 condition key allows the operations only when the image digest value (PCR0) of the attestation document in the request matches the image digest value in the condition. This condition key is effective only when the Recipient parameter in the request specifies a signed attestation document for an Amazon Nitro enclave.

If the request does not include a valid attestation document from an Amazon Nitro enclave, permission is denied because this condition is not satisfied.

{
  "Sid" : "Enable enclave data processing",
  "Effect" : "Allow",
  "Principal" : {
    "AWS" : "arn:aws:iam::111122223333:role/data-processing"
  },
  "Action": [
    "kms:Decrypt",
    "kms:DeriveSharedSecret",
    "kms:GenerateDataKey",
    "kms:GenerateDataKeyPair",
    "kms:GenerateRandom"
  ],
  "Resource" : "*",
  "Condition": {
    "StringEqualsIgnoreCase": {
      "kms:RecipientAttestation:ImageSha384": "9fedcba8abcdef7abcdef6abcdef5abcdef4abcdef3abcdef2abcdef1abcdef1abcdef0abcdef1abcdef2abcdef3abcdef4abcdef5abcdef6abcdef7abcdef99"
    }
  }
}

kms:RecipientAttestation:PCR<PCR_ID>

The kms:RecipientAttestation:PCR<PCR_ID> condition key controls access to Decrypt, DeriveSharedSecret, GenerateDataKey, GenerateDataKeyPair, and GenerateRandom with a KMS key only when the platform configuration registers (PCRs) from the signed attestation document in the request match the PCRs in the condition key. This condition key is effective only when the Recipient parameter in the request specifies a signed attestation document from an Amazon Nitro enclave.

This value is also included in CloudTrail events that represent requests to Amazon KMS for Nitro enclaves.

To specify a PCR value, use the following format. Concatenate the PCR ID to the condition key name. You can specify a PCR ID that identifies one of the six enclave measurements or a custom PCR ID that you defined for a specific use case. The PCR value must be a lower-case hexadecimal string of up to 96 bytes.

"kms:RecipientAttestation:PCRPCR_ID": "PCR_value"

For example, the following condition key specifies a particular value for PCR1, which corresponds to the hash of the kernel used for the enclave and the bootstrap process.

kms:RecipientAttestation:PCR1: "0x1abcdef2abcdef3abcdef4abcdef5abcdef6abcdef7abcdef8abcdef9abcdef8abcdef7abcdef6abcdef5abcdef4abcdef3abcdef2abcdef1abcdef0abcde"

The following example key policy statement allows the data-processing role to use the KMS key for the Decrypt operation.

The kms:RecipientAttestation:PCR condition key in this statement allows the operation only when the PCR1 value in the signed attestation document in the request matches kms:RecipientAttestation:PCR1 value in the condition. Use the StringEqualsIgnoreCase policy operator to require a case-insensitive comparison of the PCR values.

If the request does not include an attestation document, permission is denied because this condition is not satisfied.

{
  "Sid" : "Enable enclave data processing",
  "Effect" : "Allow",
  "Principal" : {
    "AWS" : "arn:aws:iam::111122223333:role/data-processing"
  },
  "Action": "kms:Decrypt",
  "Resource" : "*",
  "Condition": {
    "StringEqualsIgnoreCase": {
      "kms:RecipientAttestation:PCR1": "0x1de4f2dcf774f6e3b679f62e5f120065b2e408dcea327bd1c9dddaea6664e7af7935581474844767453082c6f1586116376cede396a30a39a611b9aad7966c87"
    }
  }
}