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[ aws . kms ]

decrypt

Description

Decrypts ciphertext. Ciphertext is plaintext that has been previously encrypted by using any of the following operations:

  • GenerateDataKey
  • GenerateDataKeyWithoutPlaintext
  • Encrypt

Whenever possible, use key policies to give users permission to call the Decrypt operation on the CMK, instead of IAM policies. Otherwise, you might create an IAM user policy that gives the user Decrypt permission on all CMKs. This user could decrypt ciphertext that was encrypted by CMKs in other accounts if the key policy for the cross-account CMK permits it. If you must use an IAM policy for Decrypt permissions, limit the user to particular CMKs or particular trusted accounts.

The result of this operation varies with the key state of the CMK. For details, see How Key State Affects Use of a Customer Master Key in the AWS Key Management Service Developer Guide .

See also: AWS API Documentation

See 'aws help' for descriptions of global parameters.

Synopsis

  decrypt
--ciphertext-blob <value>
[--encryption-context <value>]
[--grant-tokens <value>]
[--cli-input-json <value>]
[--generate-cli-skeleton <value>]

Options

--ciphertext-blob (blob)

Ciphertext to be decrypted. The blob includes metadata.

--encryption-context (map)

The encryption context. If this was specified in the Encrypt function, it must be specified here or the decryption operation will fail. For more information, see Encryption Context .

Shorthand Syntax:

KeyName1=string,KeyName2=string

JSON Syntax:

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

--grant-tokens (list)

A list of grant tokens.

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

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

The following command demonstrates the recommended way to decrypt data with the AWS CLI.

aws kms decrypt --ciphertext-blob fileb://ExampleEncryptedFile --output text --query Plaintext | base64 --decode > ExamplePlaintextFile

The command does several things:

  1. Uses the fileb:// prefix to specify the --ciphertext-blob parameter.

    The fileb:// prefix instructs the CLI to read the encrypted data, called the ciphertext, from a file and pass the file's contents to the command's --ciphertext-blob parameter. If the file is not in the current directory, type the full path to file. For example: fileb:///var/tmp/ExampleEncryptedFile or fileb://C:\Temp\ExampleEncryptedFile.

    For more information about reading AWS CLI parameter values from a file, see Loading Parameters from a File in the AWS Command Line Interface User Guide and Best Practices for Local File Parameters on the AWS Command Line Tool Blog.

    The command assumes the ciphertext in ExampleEncryptedFile is binary data. The encrypt examples demonstrate how to save a ciphertext this way.

  2. Uses the --output and --query parameters to control the command's output.

    These parameters extract the decrypted data, called the plaintext, from the command's output. For more information about controlling output, see Controlling Command Output in the AWS Command Line Interface User Guide.

  3. Uses the base64 utility.

    This utility decodes the extracted plaintext to binary data. The plaintext that is returned by a successful decrypt command is base64-encoded text. You must decode this text to obtain the original plaintext.

  4. Saves the binary plaintext to a file.

    The final part of the command (> ExamplePlaintextFile) saves the binary plaintext data to a file.

Example: Using the AWS CLI to decrypt data from the Windows command prompt

The preceding example assumes the base64 utility is available, which is commonly the case on Linux and Mac OS X. For the Windows command prompt, use certutil instead of base64. This requires two commands, as shown in the following examples.

aws kms decrypt --ciphertext-blob fileb://ExampleEncryptedFile --output text --query Plaintext > ExamplePlaintextFile.base64
certutil -decode ExamplePlaintextFile.base64 ExamplePlaintextFile

Output

KeyId -> (string)

ARN of the key used to perform the decryption. This value is returned if no errors are encountered during the operation.

Plaintext -> (blob)

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