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[ aws . kms ]

re-encrypt

Description

Decrypts ciphertext and then reencrypts it entirely within KMS. You can use this operation to change the KMS key under which data is encrypted, such as when you manually rotate a KMS key or change the KMS key that protects a ciphertext. You can also use it to reencrypt ciphertext under the same KMS key, such as to change the encryption context of a ciphertext.

The ReEncrypt operation can decrypt ciphertext that was encrypted by using an KMS KMS key in an KMS operation, such as Encrypt or GenerateDataKey . It can also decrypt ciphertext that was encrypted by using the public key of an asymmetric KMS key outside of KMS. However, it cannot decrypt ciphertext produced by other libraries, such as the Amazon Web Services Encryption SDK or Amazon S3 client-side encryption . These libraries return a ciphertext format that is incompatible with KMS.

When you use the ReEncrypt operation, you need to provide information for the decrypt operation and the subsequent encrypt operation.

  • If your ciphertext was encrypted under an asymmetric KMS key, you must use the SourceKeyId parameter to identify the KMS key that encrypted the ciphertext. You must also supply the encryption algorithm that was used. This information is required to decrypt the data.
  • If your ciphertext was encrypted under a symmetric KMS key, the SourceKeyId parameter is optional. KMS can get this information from metadata that it adds to the symmetric ciphertext blob. This feature adds durability to your implementation by ensuring that authorized users can decrypt ciphertext decades after it was encrypted, even if they've lost track of the key ID. However, specifying the source KMS key is always recommended as a best practice. When you use the SourceKeyId parameter to specify a KMS key, KMS uses only the KMS key you specify. If the ciphertext was encrypted under a different KMS key, the ReEncrypt operation fails. This practice ensures that you use the KMS key that you intend.
  • To reencrypt the data, you must use the DestinationKeyId parameter specify the KMS key that re-encrypts the data after it is decrypted. You can select a symmetric or asymmetric KMS key. If the destination KMS key is an asymmetric KMS key, you must also provide the encryption algorithm. The algorithm that you choose must be compatible with the KMS key.

Warning

When you use an asymmetric KMS key to encrypt or reencrypt data, be sure to record the KMS key and encryption algorithm that you choose. You will be required to provide the same KMS key and encryption algorithm when you decrypt the data. If the KMS key and algorithm do not match the values used to encrypt the data, the decrypt operation fails. You are not required to supply the key ID and encryption algorithm when you decrypt with symmetric KMS keys because KMS stores this information in the ciphertext blob. KMS cannot store metadata in ciphertext generated with asymmetric keys. The standard format for asymmetric key ciphertext does not include configurable fields.

The KMS key that you use for this operation must be in a compatible key state. For details, see Key state: Effect on your KMS key in the Key Management Service Developer Guide .

Cross-account use : Yes. The source KMS key and destination KMS key can be in different Amazon Web Services accounts. Either or both KMS keys can be in a different account than the caller. To specify a KMS key in a different account, you must use its key ARN or alias ARN.

Required permissions :

To permit reencryption from or to a KMS key, include the "kms:ReEncrypt*" permission in your key policy . This permission is automatically included in the key policy when you use the console to create a KMS key. But you must include it manually when you create a KMS key programmatically or when you use the PutKeyPolicy operation to set a key policy.

Related operations:
  • Decrypt
  • Encrypt
  • GenerateDataKey
  • GenerateDataKeyPair

See also: AWS API Documentation

See 'aws help' for descriptions of global parameters.

Synopsis

  re-encrypt
--ciphertext-blob <value>
[--source-encryption-context <value>]
[--source-key-id <value>]
--destination-key-id <value>
[--destination-encryption-context <value>]
[--source-encryption-algorithm <value>]
[--destination-encryption-algorithm <value>]
[--grant-tokens <value>]
[--cli-input-json <value>]
[--generate-cli-skeleton <value>]

Options

--ciphertext-blob (blob)

Ciphertext of the data to reencrypt.

--source-encryption-context (map)

Specifies the encryption context to use to decrypt the ciphertext. Enter the same encryption context that was used to encrypt the ciphertext.

An encryption context is a collection of non-secret key-value pairs that represents additional authenticated data. When you use an encryption context to encrypt data, you must specify the same (an exact case-sensitive match) encryption context to decrypt the data. An encryption context is optional when encrypting with a symmetric KMS key, but it is highly recommended.

For more information, see Encryption Context in the Key Management Service Developer Guide .

key -> (string)

value -> (string)

Shorthand Syntax:

KeyName1=string,KeyName2=string

JSON Syntax:

{"string": "string"
  ...}

--source-key-id (string)

Specifies the KMS key that KMS will use to decrypt the ciphertext before it is re-encrypted. Enter a key ID of the KMS key that was used to encrypt the ciphertext.

This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key. If you used a symmetric KMS key, KMS can get the KMS key from metadata that it adds to the symmetric ciphertext blob. However, it is always recommended as a best practice. This practice ensures that you use the KMS key that you intend.

To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/" . To specify a KMS key in a different Amazon Web Services 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 KMS key, use ListKeys or DescribeKey . To get the alias name and alias ARN, use ListAliases .

--destination-key-id (string)

A unique identifier for the KMS key that is used to reencrypt the data. Specify a symmetric or asymmetric KMS key with a KeyUsage value of ENCRYPT_DECRYPT . To find the KeyUsage value of a KMS key, use the DescribeKey operation.

To specify a KMS key, use its key ID, key ARN, alias name, or alias ARN. When using an alias name, prefix it with "alias/" . To specify a KMS key in a different Amazon Web Services 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 KMS key, use ListKeys or DescribeKey . To get the alias name and alias ARN, use ListAliases .

--destination-encryption-context (map)

Specifies that encryption context to use when the reencrypting the data.

A destination encryption context is valid only when the destination KMS key is a symmetric KMS key. The standard ciphertext format for asymmetric KMS keys does not include fields for metadata.

An encryption context is a collection of non-secret key-value pairs that represents additional authenticated data. When you use an encryption context to encrypt data, you must specify the same (an exact case-sensitive match) encryption context to decrypt the data. An encryption context is optional when encrypting with a symmetric KMS key, but it is highly recommended.

For more information, see Encryption Context in the Key Management Service Developer Guide .

key -> (string)

value -> (string)

Shorthand Syntax:

KeyName1=string,KeyName2=string

JSON Syntax:

{"string": "string"
  ...}

--source-encryption-algorithm (string)

Specifies the encryption algorithm that KMS will use to decrypt the ciphertext before it is reencrypted. The default value, SYMMETRIC_DEFAULT , represents the algorithm used for symmetric KMS keys.

Specify the same algorithm that was used to encrypt the ciphertext. If you specify a different algorithm, the decrypt attempt fails.

This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key.

Possible values:

  • SYMMETRIC_DEFAULT
  • RSAES_OAEP_SHA_1
  • RSAES_OAEP_SHA_256

--destination-encryption-algorithm (string)

Specifies the encryption algorithm that KMS will use to reecrypt the data after it has decrypted it. The default value, SYMMETRIC_DEFAULT , represents the encryption algorithm used for symmetric KMS keys.

This parameter is required only when the destination KMS key is an asymmetric KMS key.

Possible values:

  • SYMMETRIC_DEFAULT
  • RSAES_OAEP_SHA_1
  • RSAES_OAEP_SHA_256

--grant-tokens (list)

A list of grant tokens.

Use a grant token when your permission to call this operation comes from a new grant that has not yet achieved eventual consistency . For more information, see Grant token and Using a grant token in the Key Management Service Developer Guide .

(string)

Syntax:

"string" "string" ...

--cli-input-json (string) Performs service operation based on the JSON string provided. The JSON string follows the format provided by --generate-cli-skeleton. If other arguments are provided on the command line, the CLI 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.

--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. 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 re-encrypt an encrypted message under a different symmetric CMK (Linux and macOS).

The following re-encrypt command example demonstrates the recommended way to re-encrypt data with the AWS CLI.

  • Provide the ciphertext in a file.

    In the value of the --ciphertext-blob parameter, use the fileb:// prefix, which tells the CLI to read the data from a binary file. If the file is not in the current directory, type the full path to file. For more information about reading AWS CLI parameter values from a file, see Loading AWS CLI parameters from a file <https://docs.aws.amazon.com/cli/latest/userguide/cli-usage-parameters-file.html> in the AWS Command Line Interface User Guide and Best Practices for Local File Parameters<https://aws.amazon.com/blogs/developer/best-practices-for-local-file-parameters/> in the AWS Command Line Tool Blog.

  • Specify the source CMK, which decrypts the ciphertext.

    The --source-key-id parameter is not required when decrypting with symmetric CMKs. AWS KMS can get the CMK that was used to encrypt the data from the metadata in the ciphertext blob. But it's always a best practice to specify the CMK you are using. This practice ensures that you use the CMK that you intend, and prevents you from inadvertently decrypting a ciphertext using a CMK you do not trust.

  • Specify the destination CMK, which re-encrypts the data.

    The --destination-key-id parameter is always required. This example uses a key ARN, but you can use any valid key identifier.

  • Request the plaintext output as a text value.

    The --query parameter tells the CLI to get only the value of the Plaintext field from the output. The --output parameter returns the output as text.

  • Base64-decode the plaintext and save it in a file.

    The following example pipes (|) the value of the Plaintext parameter to the Base64 utility, which decodes it. Then, it redirects (>) the decoded output to the ExamplePlaintext file.

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

aws kms re-encrypt \
    --ciphertext-blob fileb://ExampleEncryptedFile \
    --source-key-id 1234abcd-12ab-34cd-56ef-1234567890ab \
    --destination-key-id 0987dcba-09fe-87dc-65ba-ab0987654321 \
    --query CiphertextBlob \
    --output text | base64 --decode > ExampleReEncryptedFile

This command produces no output. The output from the decrypt command is base64-decoded and saved in a file.

For more information, see `Using symmetric and asymmetric keys <https://docs.aws.amazon.com/kms/latest/developerguide/symmetric-asymmetric.html`__ in the AWS KMS Developer Guide.

Example 2: To re-encrypt an encrypted message under a different symmetric CMK (Windows command prompt).

The following re-encrypt command example is the same as the previous one except that it uses the certutil utility to Base64-decode the plaintext data. This procedure requires two commands, as shown in the following examples.

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

aws kms re-encrypt ^
    --ciphertext-blob fileb://ExampleEncryptedFile ^
    --source-key-id 1234abcd-12ab-34cd-56ef-1234567890ab ^
    --destination-key-id 0987dcba-09fe-87dc-65ba-ab0987654321 ^
    --query CiphertextBlob ^
    --output text > ExampleReEncryptedFile.base64

Then use the certutil utility

certutil -decode ExamplePlaintextFile.base64 ExamplePlaintextFile

Output:

Input Length = 18
Output Length = 12
CertUtil: -decode command completed successfully.

For more information, see `Using symmetric and asymmetric keys <https://docs.aws.amazon.com/kms/latest/developerguide/symmetric-asymmetric.html`__ in the AWS KMS Developer Guide.

Output

CiphertextBlob -> (blob)

The reencrypted data. When you use the HTTP API or the Amazon Web Services CLI, the value is Base64-encoded. Otherwise, it is not Base64-encoded.

SourceKeyId -> (string)

Unique identifier of the KMS key used to originally encrypt the data.

KeyId -> (string)

The Amazon Resource Name (key ARN ) of the KMS key that was used to reencrypt the data.

SourceEncryptionAlgorithm -> (string)

The encryption algorithm that was used to decrypt the ciphertext before it was reencrypted.

DestinationEncryptionAlgorithm -> (string)

The encryption algorithm that was used to reencrypt the data.