[ aws . kms ]

get-public-key

Description

Returns the public key of an asymmetric CMK. Unlike the private key of a asymmetric CMK, which never leaves AWS KMS unencrypted, callers with kms:GetPublicKey permission can download the public key of an asymmetric CMK. You can share the public key to allow others to encrypt messages and verify signatures outside of AWS KMS. For information about symmetric and asymmetric CMKs, see Using Symmetric and Asymmetric CMKs in the AWS Key Management Service Developer Guide .

You do not need to download the public key. Instead, you can use the public key within AWS KMS by calling the Encrypt , ReEncrypt , or Verify operations with the identifier of an asymmetric CMK. When you use the public key within AWS KMS, you benefit from the authentication, authorization, and logging that are part of every AWS KMS operation. You also reduce of risk of encrypting data that cannot be decrypted. These features are not effective outside of AWS KMS. For details, see Special Considerations for Downloading Public Keys .

To help you use the public key safely outside of AWS KMS, GetPublicKey returns important information about the public key in the response, including:

• CustomerMasterKeySpec : The type of key material in the public key, such as RSA_4096 or ECC_NIST_P521 .

• KeyUsage : Whether the key is used for encryption or signing.

• EncryptionAlgorithms or SigningAlgorithms : A list of the encryption algorithms or the signing algorithms for the key.

Although AWS KMS cannot enforce these restrictions on external operations, it is crucial that you use this information to prevent the public key from being used improperly. For example, you can prevent a public signing key from being used encrypt data, or prevent a public key from being used with an encryption algorithm that is not supported by AWS KMS. You can also avoid errors, such as using the wrong signing algorithm in a verification operation.

The CMK that you use for this operation must be in a compatible key state. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide .

Cross-account use : Yes. To perform this operation with a CMK in a different AWS account, specify the key ARN or alias ARN in the value of the KeyId parameter.

Required permissions : kms:GetPublicKey (key policy)

Related operations : CreateKey

See also: AWS API Documentation

See ‘aws help’ for descriptions of global parameters.

Synopsis

  get-public-key
--key-id <value>
[--grant-tokens <value>]
[--cli-input-json | --cli-input-yaml]
[--generate-cli-skeleton <value>]

Options

--key-id (string)

Identifies the asymmetric CMK that includes the public key.

To specify a CMK, use its key ID, Amazon Resource Name (ARN), alias name, or alias ARN. When using an alias name, prefix it with "alias/" . To specify a CMK in a different AWS account, you must use the key ARN or alias ARN.

For example:

• Key ID: 1234abcd-12ab-34cd-56ef-1234567890ab

• Key ARN: arn:aws:kms:us-east-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab

• Alias name: alias/ExampleAlias

• Alias ARN: arn:aws:kms:us-east-2:111122223333:alias/ExampleAlias

To get the key ID and key ARN for a CMK, use ListKeys or DescribeKey . To get the alias name and alias ARN, use ListAliases .

--grant-tokens (list)

A list of grant tokens.

For more information, see Grant Tokens in the AWS Key Management Service Developer Guide .

(string)

Syntax:

"string" "string" ...

--cli-input-json | --cli-input-yaml (string) Reads arguments from the JSON string provided. The JSON string follows the format provided by --generate-cli-skeleton. If other arguments are provided on the command line, those values will override the JSON-provided values. It is not possible to pass arbitrary binary values using a JSON-provided value as the string will be taken literally. This may not be specified along with --cli-input-yaml.

--generate-cli-skeleton (string) Prints a JSON skeleton to standard output without sending an API request. If provided with no value or the value input, prints a sample input JSON that can be used as an argument for --cli-input-json. Similarly, if provided yaml-input it will print a sample input YAML that can be used with --cli-input-yaml. If provided with the value output, it validates the command inputs and returns a sample output JSON for that command.

See ‘aws help’ for descriptions of global parameters.

Examples

Example 1: To download the public key of an asymmetric CMK

The following get-public-key example downloads the public key of an asymmetric CMK.

In addition to returning the public key, the output includes information that you need to use the public key safely outside of AWS KMS, including the key usage and supported encryption algorithms.

Before running this command, replace the example key ID with a valid key ID from your AWS account.

aws kms get-public-key \
    --key-id 1234abcd-12ab-34cd-56ef-1234567890ab

Output:

{
    "KeyId": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab",
    "PublicKey": "jANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEAl5epvg1/QtJhxSi2g9SDEVg8QV/...",
    "CustomerMasterKeySpec": "RSA_4096",
    "KeyUsage": "ENCRYPT_DECRYPT",
    "EncryptionAlgorithms": [
        "RSAES_OAEP_SHA_1",
        "RSAES_OAEP_SHA_256"
    ]
}

For more information about using asymmetric CMKs in AWS KMS, see Using Symmetric and Asymmetric Keys in the AWS Key Management Service API Reference.

Example 2: To convert a public key to DER format (Linux and macOS)

The following get-public-key example downloads the public key of an asymmetric CMK and saves it in a DER file.

When you use the get-public-key command in the AWS CLI, it returns a DER-encoded X.509 public key that is Base64-encoded. This example gets the value of the PublicKey property as text. It Base64-decodes the PublicKey and saves it in the public_key.der file. The output parameter returns the output as text, instead of JSON. The --query parameter gets only the PublicKey property, not the properties that you need to use the public key safely outside of AWS KMS.

Before running this command, replace the example key ID with a valid key ID from your AWS account.

aws kms get-public-key \
    --key-id 1234abcd-12ab-34cd-56ef-1234567890ab \
    --output text \
    --query PublicKey | base64 --decode > public_key.der

This command produces no output.

For more information about using asymmetric CMKs in AWS KMS, see Using Symmetric and Asymmetric Keys in the AWS Key Management Service API Reference.

Output

KeyId -> (string)

The Amazon Resource Name (key ARN ) of the asymmetric CMK from which the public key was downloaded.

PublicKey -> (blob)

The exported public key.

The value is a DER-encoded X.509 public key, also known as SubjectPublicKeyInfo (SPKI), as defined in RFC 5280 . When you use the HTTP API or the AWS CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded.

CustomerMasterKeySpec -> (string)

The type of the of the public key that was downloaded.

KeyUsage -> (string)

The permitted use of the public key. Valid values are ENCRYPT_DECRYPT or SIGN_VERIFY .

This information is critical. If a public key with SIGN_VERIFY key usage encrypts data outside of AWS KMS, the ciphertext cannot be decrypted.

EncryptionAlgorithms -> (list)

The encryption algorithms that AWS KMS supports for this key.

This information is critical. If a public key encrypts data outside of AWS KMS by using an unsupported encryption algorithm, the ciphertext cannot be decrypted.

This field appears in the response only when the KeyUsage of the public key is ENCRYPT_DECRYPT .

(string)

SigningAlgorithms -> (list)

The signing algorithms that AWS KMS supports for this key.

This field appears in the response only when the KeyUsage of the public key is SIGN_VERIFY .

(string)