[ aws . kms ]

re-encrypt

Description

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

The ReEncrypt operation can decrypt ciphertext that was encrypted by using an AWS KMS CMK in an AWS KMS operation, such as Encrypt or GenerateDataKey . It can also decrypt ciphertext that was encrypted by using the public key of an asymmetric CMK outside of AWS KMS. However, it cannot decrypt ciphertext produced by other libraries, such as the AWS Encryption SDK or Amazon S3 client-side encryption . These libraries return a ciphertext format that is incompatible with AWS 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 CMK, you must use the SourceKeyId parameter to identify the CMK 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 CMK, the SourceKeyId parameter is optional. AWS 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 CMK ID. However, specifying the source CMK is always recommended as a best practice. When you use the SourceKeyId parameter to specify a CMK, AWS KMS uses only the CMK you specify. If the ciphertext was encrypted under a different CMK, the ReEncrypt operation fails. This practice ensures that you use the CMK that you intend.

• To reencrypt the data, you must use the DestinationKeyId parameter specify the CMK that re-encrypts the data after it is decrypted. You can select a symmetric or asymmetric CMK. If the destination CMK is an asymmetric CMK, you must also provide the encryption algorithm. The algorithm that you choose must be compatible with the CMK.

Warning

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

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. The source CMK and destination CMK can be in different AWS accounts. Either or both CMKs can be in a different account than the caller.

Required permissions :

• kms:ReEncryptFrom permission on the source CMK (key policy)

• kms:ReEncryptTo permission on the destination CMK (key policy)

To permit reencryption from or to a CMK, 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 CMK. But you must include it manually when you create a CMK 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 | --cli-input-yaml]
[--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 CMK, but it is highly recommended.

For more information, see Encryption Context in the AWS 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 customer master key (CMK) that AWS KMS will use to decrypt the ciphertext before it is re-encrypted. Enter a key ID of the CMK that was used to encrypt the ciphertext.

This parameter is required only when the ciphertext was encrypted under an asymmetric CMK. If you used a symmetric CMK, AWS KMS can get the CMK 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 CMK that you intend.

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 .

--destination-key-id (string)

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

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 .

--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 CMK is a symmetric CMK. The standard ciphertext format for asymmetric CMKs 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 CMK, but it is highly recommended.

For more information, see Encryption Context in the AWS 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 AWS KMS will use to decrypt the ciphertext before it is reencrypted. The default value, SYMMETRIC_DEFAULT , represents the algorithm used for symmetric CMKs.

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 CMK.

Possible values:

• SYMMETRIC_DEFAULT

• RSAES_OAEP_SHA_1

• RSAES_OAEP_SHA_256

--destination-encryption-algorithm (string)

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

This parameter is required only when the destination CMK is an asymmetric CMK.

Possible values:

• SYMMETRIC_DEFAULT

• RSAES_OAEP_SHA_1

• RSAES_OAEP_SHA_256

--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 re-encrypt encrypted data under a different CMK

The following re-encrypt example re-encrypts data that was encrypted using the encrypt operation in the AWS CLI. You can use the re-encrypt command to re-encrypt the result of any AWS KMS operation that encrypted data or data keys.

This example writes the output to the command line so you can see the all of the properties in the response. However, unless you’re testing or demonstrating this operation, you should base64-decode the encrypted data and save it in a file.

The command in this example re-encrypts the data under a different CMK, but you can re-encrypt it under the same CMK to change characteristics of the encryption, such as the encryption context.

To run this command, you must have kms:ReEncryptFrom permission on the CMK that encrypted the data and kms:ReEncryptTo permissions on the CMK that you use to re-encrypt the data.

• The --ciphertext-blob parameter identifies the ciphertext to re-encrypt. The file ExampleEncryptedFile contains the base64-decoded output of the encrypt command.

• The fileb:// prefix of the file name tells the CLI to treat the input file as binary instead of text.

• The --destination-key-id parameter specifies the CMK under which the data is to be re-encrypted. This example uses the key ID to identify the CMK, but you can use a key ID, key ARN, alias name, or alias ARN in this command.

• You do not need to specify the CMK that was used to encrypt the data. AWS KMS gets that information from metadata in the ciphertext.

  aws kms re-encrypt \
      --ciphertext-blob fileb://ExampleEncryptedFile \
      --destination-key-id 0987dcba-09fe-87dc-65ba-ab0987654321
  

The output includes the following properties:

• The SourceKeyID is the key ID of the CMK that originally encrypted the CMK.

• The KeyId is the ID of the CMK that re-encrypted the data.

• The CiphertextBlob, which is the re-encrypted data in base64-encoded format.

  {
      "CiphertextBlob": "AQICAHgJtIvJqgOGUX6NLvVXnW5OOQT...",
      "SourceKeyId": "arn:aws:kms:us-west-2:123456789012:key/1234abcd-12ab-34cd-56ef-1234567890ab",
      "KeyId": "arn:aws:kms:us-west-2:123456789012:key/0987dcba-09fe-87dc-65ba-ab0987654321"
  }
  

Example 2: To re-encrypt encrypted data under a different CMK (Linux or macOs)

The following re-encrypt example demonstrates the recommended way to re-encrypt data with the AWS CLI. This example re-encrypts the ciphertext that was encrypted by the encrypt command, but you can use the same procedure to re-encrypt data keys.

This example is the same as the previous example except that it does not write the output to the command line. Instead, after re-encrypting the ciphertext under a different CMK, it extracts the re-encrypted ciphertext from the response, base64-decodes it, and saves the binary data in a file. You can store the file safely. Then, you can use the file in decrypt or re-encrypt commands in the AWS CLI.

To run this command, you must have kms:ReEncryptFrom permission on the CMK that encrypted the data and kms:ReEncryptTo permissions on the CMK that will re-encrypt the data. The --ciphertext-blob parameter identifies the ciphertext to re-encrypt.

• The fileb:// prefix tells the CLI to treat the input file as binary instead of text.

• The --destination-key-id parameter specifies the CMK under which the data is re-encrypted. This example uses the key ID to identify the CMK, but you can use a key ID, key ARN, alias name, or alias ARN in this command.

• You do not need to specify the CMK that was used to encrypt the data. AWS KMS gets that information from metadata in the ciphertext.

• The --output parameter with a value of text directs the AWS CLI to return the output as text, instead of JSON.

• The --query parameter extracts the value of the CiphertextBlob property from the response.

• The pipe operator ( | ) sends the output of the CLI command to the base64 utility, which decodes the extracted output. The CiphertextBlob that the re-encrypt operation returns is base64-encoded text. However, the decrypt and re-encrypt commands require binary data. The example decodes the base64-encoded ciphertext back to binary and then saves it in a file. You can use the file as input to the decrypt or re-encrypt commands.

  aws kms re-encrypt \
      --ciphertext-blob fileb://ExampleEncryptedFile \
      --destination-key-id 0987dcba-09fe-87dc-65ba-ab0987654321 \
      --output text \
      --query CiphertextBlob | base64 --decode > ExampleReEncryptedFile
  

This command produces no output on screen because it is redirected to a file.

Example 3: To re-encrypted encrypted data under a different CMK (Windows Command Prompt)

This example is the same as the previous example, except that it uses the certutil utility in Windows to base64-decode the ciphertext before saving it in a file.

• The first command re-encrypts the ciphertext and saves the base64-encoded ciphertext in a temporary file named ExampleReEncryptedFile.base64.

• The second command uses the certutil -decode command to decode the base64-encoded ciphertext in the file to binary. Then, it saves the binary ciphertext in the file ExampleReEncryptedFile. This file is ready to be used in a decrypt or re-encrypt command in the AWS CLI.

  aws kms re-encrypt ^
      --ciphertext-blob fileb://ExampleEncryptedFile ^
      --destination-key-id 0987dcba-09fe-87dc-65ba-ab0987654321 ^
      --output text ^
      --query CiphertextBlob  > ExampleReEncryptedFile.base64
  certutil -decode ExampleReEncryptedFile.base64 ExampleReEncryptedFile
  

Output:

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

For more information, see ReEncrypt in the AWS Key Management Service API Reference.

Output

CiphertextBlob -> (blob)

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

SourceKeyId -> (string)

Unique identifier of the CMK used to originally encrypt the data.

KeyId -> (string)

The Amazon Resource Name (key ARN ) of the CMK 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.