<p>Returns the public key of an asymmetric KMS key. Unlike the private key of a asymmetric KMS key, which never leaves KMS unencrypted, callers with <code>kms:GetPublicKey</code> permission can download the public key of an asymmetric KMS key. You can share the public key to allow others to encrypt messages and verify signatures outside of KMS. For information about asymmetric KMS keys, see <a href="https://docs.aws.amazon.com/kms/latest/developerguide/symmetric-asymmetric.html">Asymmetric KMS keys</a> in the <i>Key Management Service Developer Guide</i>.</p> <p>You do not need to download the public key. Instead, you can use the public key within KMS by calling the <a>Encrypt</a>, <a>ReEncrypt</a>, or <a>Verify</a> operations with the identifier of an asymmetric KMS key. When you use the public key within KMS, you benefit from the authentication, authorization, and logging that are part of every KMS operation. You also reduce of risk of encrypting data that cannot be decrypted. These features are not effective outside of KMS.</p> <p>To help you use the public key safely outside of KMS, <code>GetPublicKey</code> returns important information about the public key in the response, including:</p> <ul> <li> <p> <a href="https://docs.aws.amazon.com/kms/latest/APIReference/API_GetPublicKey.html#KMS-GetPublicKey-response-KeySpec">KeySpec</a>: The type of key material in the public key, such as <code>RSA_4096</code> or <code>ECC_NIST_P521</code>.</p> </li> <li> <p> <a href="https://docs.aws.amazon.com/kms/latest/APIReference/API_GetPublicKey.html#KMS-GetPublicKey-response-KeyUsage">KeyUsage</a>: Whether the key is used for encryption or signing.</p> </li> <li> <p> <a href="https://docs.aws.amazon.com/kms/latest/APIReference/API_GetPublicKey.html#KMS-GetPublicKey-response-EncryptionAlgorithms">EncryptionAlgorithms</a> or <a href="https://docs.aws.amazon.com/kms/latest/APIReference/API_GetPublicKey.html#KMS-GetPublicKey-response-SigningAlgorithms">SigningAlgorithms</a>: A list of the encryption algorithms or the signing algorithms for the key.</p> </li> </ul> <p>Although 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 KMS. You can also avoid errors, such as using the wrong signing algorithm in a verification operation.</p> <p>To verify a signature outside of KMS with an SM2 public key (China Regions only), you must specify the distinguishing ID. By default, KMS uses <code>1234567812345678</code> as the distinguishing ID. For more information, see <a href="https://docs.aws.amazon.com/kms/latest/developerguide/asymmetric-key-specs.html#key-spec-sm-offline-verification">Offline verification with SM2 key pairs</a>.</p> <p>The KMS key that you use for this operation must be in a compatible key state. For details, see <a href="https://docs.aws.amazon.com/kms/latest/developerguide/key-state.html">Key states of KMS keys</a> in the <i>Key Management Service Developer Guide</i>.</p> <p> <b>Cross-account use</b>: Yes. To perform this operation with a KMS key in a different Amazon Web Services account, specify the key ARN or alias ARN in the value of the <code>KeyId</code> parameter.</p> <p> <b>Required permissions</b>: <a href="https://docs.aws.amazon.com/kms/latest/developerguide/kms-api-permissions-reference.html">kms:GetPublicKey</a> (key policy)</p> <p> <b>Related operations</b>: <a>CreateKey</a> </p>

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