AWS CLI Command Reference

[ aws . kms ]

decrypt

Description

Decrypts ciphertext that was encrypted by a KMS key using any of the following operations:

  • Encrypt

  • GenerateDataKey

  • GenerateDataKeyPair

  • GenerateDataKeyWithoutPlaintext

  • GenerateDataKeyPairWithoutPlaintext

You can use this operation to decrypt ciphertext that was encrypted under a symmetric or asymmetric KMS key. When the KMS key is asymmetric, you must specify the KMS key and the encryption algorithm that was used to encrypt the ciphertext. For information about symmetric and asymmetric KMS keys, see Using Symmetric and Asymmetric KMS keys in the Key Management Service Developer Guide .

The Decrypt operation also decrypts ciphertext that was encrypted outside of KMS by the public key in an KMS asymmetric KMS key. 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.

If the ciphertext was encrypted under a symmetric KMS key, the KeyId 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 KMS key is always recommended as a best practice. When you use the KeyId parameter to specify a KMS key, KMS only uses the KMS key you specify. If the ciphertext was encrypted under a different KMS key, the Decrypt operation fails. This practice ensures that you use the KMS key that you intend.

Whenever possible, use key policies to give users permission to call the Decrypt operation on a particular KMS key, instead of using IAM policies. Otherwise, you might create an IAM user policy that gives the user Decrypt permission on all KMS keys. This user could decrypt ciphertext that was encrypted by KMS keys in other accounts if the key policy for the cross-account KMS key permits it. If you must use an IAM policy for Decrypt permissions, limit the user to particular KMS keys or particular trusted accounts. For details, see Best practices for IAM policies in the Key Management Service Developer Guide .

Applications in Amazon Web Services Nitro Enclaves can call this operation by using the Amazon Web Services Nitro Enclaves Development Kit . For information about the supporting parameters, see How Amazon Web Services Nitro Enclaves use KMS in the Key Management Service Developer Guide .

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. 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 KeyId parameter.

Required permissions : kms:Decrypt (key policy)

Related operations:

  • Encrypt

  • GenerateDataKey

  • GenerateDataKeyPair

  • ReEncrypt

See also: AWS API Documentation

See ‘aws help’ for descriptions of global parameters.

Synopsis

  decrypt
--ciphertext-blob <value>
[--encryption-context <value>]
[--grant-tokens <value>]
[--key-id <value>]
[--encryption-algorithm <value>]
[--cli-input-json | --cli-input-yaml]
[--generate-cli-skeleton <value>]

Options

--ciphertext-blob (blob)

Ciphertext to be decrypted. The blob includes metadata.

--encryption-context (map)

Specifies the encryption context to use when decrypting the data. An encryption context is valid only for cryptographic operations with a symmetric KMS key. The standard asymmetric encryption algorithms that KMS uses do not support an encryption context.

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"
  ...}

--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" ...

--key-id (string)

Specifies the KMS key that KMS uses to decrypt the ciphertext. 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 .

--encryption-algorithm (string)

Specifies the encryption algorithm that will be used to decrypt the ciphertext. Specify the same algorithm that was used to encrypt the data. If you specify a different algorithm, the Decrypt operation fails.

This parameter is required only when the ciphertext was encrypted under an asymmetric KMS key. The default value, SYMMETRIC_DEFAULT , represents the only supported algorithm that is valid for symmetric KMS keys.

Possible values:

  • SYMMETRIC_DEFAULT

  • RSAES_OAEP_SHA_1

  • RSAES_OAEP_SHA_256

--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 decrypt an encrypted message with a symmetric CMK (Linux and macOS)

The following decrypt command example demonstrates the recommended way to decrypt data with the AWS CLI. This version shows how to decrypt data under a symmetric customer master key (CMK).

  • 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 CMK to decrypt the ciphertext.

    The --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.

  • 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 ID with a valid key ID from your AWS account.

aws kms decrypt \
    --ciphertext-blob fileb://ExampleEncryptedFile \
    --key-id 1234abcd-12ab-34cd-56ef-1234567890ab \
    --output text \
    --query Plaintext | base64 \
    --decode > ExamplePlaintextFile

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

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

Example 2: To decrypt an encrypted message with a symmetric CMK (Windows command prompt)

The following 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 decrypt ^
    --ciphertext-blob fileb://ExampleEncryptedFile ^
    --key-id 1234abcd-12ab-34cd-56ef-1234567890ab ^
    --output text ^
    --query Plaintext > ExamplePlaintextFile.base64

Run the certutil command.

certutil -decode ExamplePlaintextFile.base64 ExamplePlaintextFile

Output:

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

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

Output

KeyId -> (string)

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

Plaintext -> (blob)

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

EncryptionAlgorithm -> (string)

The encryption algorithm that was used to decrypt the ciphertext.

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