How to call AWS KMS APIs for a Nitro enclave AWS KMS condition keys for AWS Nitro Enclaves Monitoring requests for Nitro enclaves

How AWS Nitro Enclaves uses AWS KMS

AWS KMS supports cryptographic attestation for AWS Nitro Enclaves. Applications that support AWS Nitro Enclaves call the following AWS KMS cryptographic operations with a signed attestation document for the enclave. These AWS KMS APIs verify that the attestation document came from a Nitro enclave. Then, instead of returning plaintext data in the response, these APIs encrypt the plaintext with the public key from the attestation document and return ciphertext that can be decrypted only by the corresponding private key in the enclave.

The following table shows how the response to Nitro enclave requests differs from the standard response for each API operation.

AWS KMS operation	Standard response	Response for AWS Nitro Enclaves
`Decrypt`	Returns plaintext data	Returns the plaintext data encrypted by the public key from the attestation document
`GenerateDataKey`	Returns a plaintext copy of the data key (Also returns a copy of the data key encrypted by a KMS key)	Returns a copy of the data key encrypted by the public key from the attestation document (Also returns a copy of the data key encrypted by a KMS key)
`GenerateDataKeyPair`	Returns a plaintext copy of the private key (Also returns the public key and a copy of the private key encrypted by a KMS key)	Returns a copy of the private key encrypted by the public key from the attestation document (Also returns the public key and a copy of the private key encrypted by a KMS key)
`GenerateRandom`	Returns a random byte string	Returns the random byte string encrypted by the public key from the attestation document

AWS KMS supports policy condition keys that you can use to allow or deny enclave operations with an AWS KMS key based on the content of the attestation document. You can also monitor requests to AWS KMS for your Nitro enclave in your AWS CloudTrail logs.

Topics

How to call AWS KMS APIs for a Nitro enclave
AWS KMS condition keys for AWS Nitro Enclaves
Monitoring requests for Nitro enclaves

How to call AWS KMS APIs for a Nitro enclave

To call AWS KMS APIs for a Nitro enclave, use the Recipient parameter in the request to provide the signed attestation document for the enclave and the encryption algorithm to use with the enclave's public key. When a request includes the Recipient parameter with a signed attestation document, the response includes a CiphertextForRecipient field with the ciphertext encrypted by the public key. The plaintext field is null or empty.

The Recipient parameter must specify a signed attestation document from an AWS Nitro enclave. AWS KMS relies on the digital signature for the enclave’s attestation document to prove that the public key in the request came from a valid enclave. You cannot supply your own certificate to digitally sign the attestation document.

To specify the Recipient parameter, use the AWS Nitro Enclaves SDK or any AWS SDK. The AWS Nitro Enclaves SDK, which is supported only within a Nitro enclave, automatically adds the Recipient parameter and its values to every AWS KMS request. To make requests for Nitro enclaves in the AWS SDKs, you have to specify the Recipient parameter and its values. Support for Nitro enclave cryptographic attestation in the AWS SDKs was introduced in March 2023.

For detailed information about the Recipient parameter and the AWS CiphertextForRecipient response field, see the Decrypt, GenerateDataKey, GenerateDataKeyPair, and GenerateRandom topics in the AWS Key Management Service API Reference, the AWS Nitro Enclaves SDK, or any AWS SDK. For information about setting up your data and data keys for encryption, see Using cryptographic attestation with AWS KMS.

AWS KMS condition keys for AWS Nitro Enclaves

You can specify condition keys in the key policies and IAM policies that control access to your AWS KMS resources. Policy statements that includes a condition key are effective only when its conditions are satisfied.

AWS KMS provides condition keys that limit the permissions for the Decrypt, GenerateDataKey, GenerateDataKeyPair, and GenerateRandom operations based on the contents of the signed attestation document in the request. These condition keys that work only when a request for an AWS KMS operation includes the Recipient parameter with a valid attestation document from an AWS Nitro enclave. To specify the Recipient parameter, use the AWS Nitro Enclaves SDK or any AWS SDK.

The enclave-specific AWS KMS condition keys are valid in key policy statements and IAM policy statements even though they do not appear in the IAM console or the IAM Service Authorization Reference.

kms:RecipientAttestation:ImageSha384

AWS KMS Condition Keys Condition Type Value type API Operations Policy Type

AWS KMS Condition Keys	Condition Type	Value type	API Operations	Policy Type
`kms:RecipientAttestation:ImageSha384`	String	Single-valued	`Decrypt` `GenerateDataKey` `GenerateDataKeyPair` `GenerateRandom`	Key policies and IAM policies

kms:RecipientAttestation:ImageSha384

String

Single-valued

Decrypt

GenerateDataKey

GenerateDataKeyPair

GenerateRandom

Key policies and IAM policies

The kms:RecipientAttestation:ImageSha384 condition key controls access to Decrypt, 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 AWS Nitro enclave.

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

Note

This condition key is valid in key policy statements and IAM policy statements even though it does not appear in the IAM console or the IAM Service Authorization Reference.

For example, the following key policy statement allows the data-processing role to use the KMS key for Decrypt, 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 AWS Nitro enclave.

If the request does not include a valid attestation document from an AWS 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:GenerateDataKey",
    "kms:GenerateDataKeyPair",
    "kms:GenerateRandom"
  ],
  "Resource" : "*",
  "Condition": {
    "StringEqualsIgnoreCase": {
      "kms:RecipientAttestation:ImageSha384": "9fedcba8abcdef7abcdef6abcdef5abcdef4abcdef3abcdef2abcdef1abcdef1abcdef0abcdef1abcdef2abcdef3abcdef4abcdef5abcdef6abcdef7abcdef99"
    }
  }
}

kms:RecipientAttestation:PCR<PCR_ID>

AWS KMS Condition Keys Condition Type Value type API Operations Policy Type

AWS KMS Condition Keys	Condition Type	Value type	API Operations	Policy Type
`kms:RecipientAttestation:PCR<PCR_ID>`	String	Single-valued	`Decrypt` `GenerateDataKey` `GenerateDataKeyPair` `GenerateRandom`	Key policies and IAM policies

kms:RecipientAttestation:PCR<PCR_ID>

String

Single-valued

Decrypt

GenerateDataKey

GenerateDataKeyPair

GenerateRandom

Key policies and IAM policies

The kms:RecipientAttestation:PCR<PCR_ID> condition key controls access to Decrypt, 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 AWS Nitro enclave.

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

Note

This condition key is valid in key policy statements and IAM policy statements even though it does not appear in the IAM console or the IAM Service Authorization Reference.

To specify a PCR value, use the following format. Concatenate the PCR ID to the condition key name. 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"
    }
  }
}

Monitoring requests for Nitro enclaves

You can use your AWS CloudTrail logs to monitor Decrypt, GenerateDataKey, GenerateDataKeyPair, and GenerateRandom operations for an AWS Nitro enclave. In these log entries, the additionalEventData field has a recipient field with the module ID (attestationDocumentModuleId), image digest (attestationDocumentEnclaveImageDigest), and platform configuration registers (PCRs) from the attestation document in the request. These fields are included only when the Recipient parameter in the request specifies a signed attestation document from an AWS Nitro enclave.

The module ID is the enclave ID of the Nitro enclave. The image digest is the SHA384 hash of the enclave image. You can use the image digest and PCR values in conditions for key policies and IAM policies. For information about the PCRs, see Where to get an enclave's measurements in the AWS Nitro Enclaves User Guide.

This section shows an example CloudTrail log entry for each of the supported Nitro enclave requests to AWS KMS.

Decrypt (for an enclave)

The following example shows an AWS CloudTrail log entry of a Decrypt operation for an AWS Nitro enclave.


{
    "eventVersion": "1.05",
    "userIdentity": {
        "type": "IAMUser",
        "principalId": "EX_PRINCIPAL_ID",
        "arn": "arn:aws:iam::111122223333:user/Alice",
        "accountId": "111122223333",
        "accessKeyId": "EXAMPLE_KEY_ID",
        "userName": "Alice"
    },
    "eventTime": "2020-07-27T22:58:24Z",
    "eventSource": "kms.amazonaws.com",
    "eventName": "Decrypt",
    "awsRegion": "us-west-2",
    "sourceIPAddress": "192.0.2.0",
    "userAgent": "AWS Internal",
    "requestParameters": {
        "encryptionAlgorithm": "SYMMETRIC_DEFAULT",
        "keyId": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab"
    },
    "responseElements": null,
    "additionalEventData": {
        "recipient": {
            "attestationDocumentModuleId": "i-123456789abcde123-enc123456789abcde12",
            "attestationDocumentEnclaveImageDigest": "<AttestationDocument.PCR0>",
            "attestationDocumentEnclavePCR1": "<AttestationDocument.PCR1>",
            "attestationDocumentEnclavePCR2": "<AttestationDocument.PCR2>",
            "attestationDocumentEnclavePCR3": "<AttestationDocument.PCR3>",
            "attestationDocumentEnclavePCR4": "<AttestationDocument.PCR4>",
            "attestationDocumentEnclavePCR8": "<AttestationDocument.PCR8>"
        }
    },
    "requestID": "b4a65126-30d5-4b28-98b9-9153da559963",
    "eventID": "e5a2f202-ba1a-467c-b4ba-f729d45ae521",
    "readOnly": true,
    "resources": [
        {
            "accountId": "111122223333",
            "type": "AWS::KMS::Key",
            "ARN": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab"
        }
    ],
    "eventType": "AwsApiCall",
    "recipientAccountId": "111122223333"
}

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GenerateDataKey (for an enclave)

The following example shows an AWS CloudTrail log entry of a GenerateDataKey operation for an AWS Nitro enclave.


{
    "eventVersion": "1.02",
    "userIdentity": {
        "type": "IAMUser",
        "principalId": "EX_PRINCIPAL_ID",
        "arn": "arn:aws:iam::111122223333:user/Alice",
        "accountId": "111122223333",
        "accessKeyId": "EXAMPLE_KEY_ID",
        "userName": "Alice"
    },
    "eventTime": "2014-11-04T00:52:40Z",
    "eventSource": "kms.amazonaws.com",
    "eventName": "GenerateDataKey",
    "awsRegion": "us-east-1",
    "sourceIPAddress": "192.0.2.0",
    "userAgent": "AWS Internal",
    "requestParameters": {
        "keyId": "1234abcd-12ab-34cd-56ef-1234567890ab",
        "numberOfBytes": 32
    },
    "responseElements": null,
    "additionalEventData": {
        "recipient": {
            "attestationDocumentModuleId": "i-123456789abcde123-enc123456789abcde12",
            "attestationDocumentEnclaveImageDigest": "<AttestationDocument.PCR0>",
            "attestationDocumentEnclavePCR1": "<AttestationDocument.PCR1>",
            "attestationDocumentEnclavePCR2": "<AttestationDocument.PCR2>",
            "attestationDocumentEnclavePCR3": "<AttestationDocument.PCR3>",
            "attestationDocumentEnclavePCR4": "<AttestationDocument.PCR4>",
            "attestationDocumentEnclavePCR8": "<AttestationDocument.PCR8>"
        }
    },
    "requestID": "e0eb83e3-63bc-11e4-bc2b-4198b6150d5c",
    "eventID": "a9dea4f9-8395-46c0-942c-f509c02c2b71",
    "readOnly": true,
    "resources": [{
        "ARN": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab",
        "accountId": "111122223333"
    }],
    "eventType": "AwsApiCall",
    "recipientAccountId": "111122223333"
}

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GenerateDataKeyPair (for an enclave)

The following example shows an AWS CloudTrail log entry of a GenerateDataKeyPair operation for an AWS Nitro enclave.


{
    "eventVersion": "1.05",
    "userIdentity": {
            "type": "IAMUser",
            "principalId": "EX_PRINCIPAL_ID",
            "arn": "arn:aws:iam::111122223333:user/Alice",
            "accountId": "111122223333",
            "accessKeyId": "EXAMPLE_KEY_ID",
            "userName": "Alice"
    },
    "eventTime": "2020-07-27T18:57:57Z",
    "eventSource": "kms.amazonaws.com",
    "eventName": "GenerateDataKeyPair",
    "awsRegion": "us-west-2",
    "sourceIPAddress": "192.0.2.0",
    "userAgent": "AWS Internal",
    "requestParameters": {
        "keyPairSpec": "RSA_3072",
        "encryptionContext": {
            "Project": "Alpha"
        },
        "keyId": "1234abcd-12ab-34cd-56ef-1234567890ab"
    },
    "responseElements": null,
    "additionalEventData": {
        "recipient": {
            "attestationDocumentModuleId": "i-123456789abcde123-enc123456789abcde12",
            "attestationDocumentEnclaveImageDigest": "<AttestationDocument.PCR0>",
            "attestationDocumentEnclavePCR1": "<AttestationDocument.PCR1>",
            "attestationDocumentEnclavePCR2": "<AttestationDocument.PCR2>",
            "attestationDocumentEnclavePCR3": "<AttestationDocument.PCR3>",
            "attestationDocumentEnclavePCR4": "<AttestationDocument.PCR4>",
            "attestationDocumentEnclavePCR8": "<AttestationDocument.PCR8>"
        }
    },
    "requestID": "52fb127b-0fe5-42bb-8e5e-f560febde6b0",
    "eventID": "9b6bd6d2-529d-4890-a949-593b13800ad7",
    "readOnly": true,
    "resources": [
        {
            "accountId": "111122223333",
            "type": "AWS::KMS::Key",
            "ARN": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab"
        }
    ],
    "eventType": "AwsApiCall",
    "recipientAccountId": "111122223333"
}

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GenerateRandom (for an enclave)

The following example shows an AWS CloudTrail log entry of a GenerateRandom operation for an AWS Nitro enclave.


{
    "eventVersion": "1.02",
    "userIdentity": {
        "type": "IAMUser",
        "principalId": "EX_PRINCIPAL_ID",
        "arn": "arn:aws:iam::111122223333:user/Alice",
        "accountId": "111122223333",
        "accessKeyId": "EXAMPLE_KEY_ID",
        "userName": "Alice"
    },
    "eventTime": "2014-11-04T00:52:37Z",
    "eventSource": "kms.amazonaws.com",
    "eventName": "GenerateRandom",
    "awsRegion": "us-east-1",
    "sourceIPAddress": "192.0.2.0",
    "userAgent": "AWS Internal",
    "requestParameters": null,
    "responseElements": null,
    "additionalEventData": {
        "recipient": {
            "attestationDocumentModuleId": "i-123456789abcde123-enc123456789abcde12",
            "attestationDocumentEnclaveImageDigest": "<AttestationDocument.PCR0>",
            "attestationDocumentEnclavePCR1": "<AttestationDocument.PCR1>",
            "attestationDocumentEnclavePCR2": "<AttestationDocument.PCR2>",
            "attestationDocumentEnclavePCR3": "<AttestationDocument.PCR3>",
            "attestationDocumentEnclavePCR4": "<AttestationDocument.PCR4>",
            "attestationDocumentEnclavePCR8": "<AttestationDocument.PCR8>"
        }
    },
    "requestID": "df1e3de6-63bc-11e4-bc2b-4198b6150d5c",
    "eventID": "239cb9f7-ae05-4c94-9221-6ea30eef0442",
    "readOnly": true,
    "resources": [],
    "eventType": "AwsApiCall",
    "recipientAccountId": "111122223333"
}

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