How to use the AWS Encryption CLI

This topic explains how to use the parameters in the AWS Encryption CLI. For examples, see Examples of the AWS Encryption CLI. For complete documentation, see Read the Docs. The syntax shown in these examples is for AWS Encryption CLI version 2.1.x and later.

Note

Versions of the AWS Encryption CLI earlier than 4.0.0 are in the end-of-support phase.

You can safely update from version 2.1.x and later to the latest version of the AWS Encryption CLI without any code or data changes. However, new security features introduced in version 2.1.x are not backward-compatible. To update from version 1.7.x or earlier, you must first update to the latest 1.x version of the AWS Encryption CLI. For details, see Migrating your AWS Encryption SDK.

New security features were originally released in AWS Encryption CLI versions 1.7.x and 2.0.x. However, AWS Encryption CLI version 1.8.x replaces version 1.7.x and AWS Encryption CLI 2.1.x replaces 2.0.x. For details, see the relevant security advisory in the aws-encryption-sdk-cli repository on GitHub.

For an example showing how to use the security feature that limits encrypted data keys, see Limiting encrypted data keys.

For an example showing how to use AWS KMS multi-Region keys, see Using multi-Region AWS KMS keys.

How to encrypt and decrypt data

The AWS Encryption CLI uses the features of the AWS Encryption SDK to make it easy to encrypt and decrypt data securely.

Note

The --master-keys parameter is deprecated in version 1.8.x of the AWS Encryption CLI and removed in version 2.1.x. Instead, use the --wrapping-keys parameter. Beginning in version 2.1.x, the --wrapping-keys parameter is required when encrypting and decrypting. For details, see AWS Encryption SDK CLI syntax and parameter reference.

• When you encrypt data in the AWS Encryption CLI, you specify your plaintext data and a wrapping key (or master key), such as an AWS KMS key in AWS Key Management Service (AWS KMS). If you are using a custom master key provider, you also need to specify the provider. You also specify output locations for the encrypted message and for metadata about the encryption operation. An encryption context is optional, but recommended.

  In version 1.8.x, the --commitment-policy parameter is required when you use the --wrapping-keys parameter; otherwise it's not valid. Beginning in version 2.1.x, the --commitment-policy parameter is optional, but recommended.

  aws-encryption-cli --encrypt --input myPlaintextData \
                     --wrapping-keys key=1234abcd-12ab-34cd-56ef-1234567890ab \
                     --output myEncryptedMessage \
                     --metadata-output ~/metadata \
                     --encryption-context purpose=test \
                     --commitment-policy require-encrypt-require-decrypt

  The AWS Encryption CLI encrypts your data under a unique data key. Then it encrypts the data key under the wrapping keys you specify. It returns an encrypted message and metadata about the operation. The encrypted message contains your encrypted data (ciphertext) and an encrypted copy of the data key. You don't have to worry about storing, managing, or losing the data key.

   

• When you decrypt data, you pass in your encrypted message, the optional encryption context, and location for the plaintext output and the metadata. You also specify the wrapping keys that the AWS Encryption CLI can use to decrypt the message, or tell the AWS Encryption CLI it can use any wrapping keys that encrypted the message.

  Beginning in version 1.8.x, the --wrapping-keys parameter is optional when decrypting, but recommended. Beginning in version 2.1.x, the --wrapping-keys parameter is required when encrypting and decrypting.

  When decrypting, you can use the key attribute of the --wrapping-keys parameter to specify the wrapping keys that decrypt your data. Specifying an AWS KMS wrapping key when decrypting is optional, but it's a best practice that prevents you from using a key you didn't intend to use. If you're using a custom master key provider, you must specify the provider and wrapping key.

  If you don't use the key attribute, you must set the discovery attribute of the --wrapping-keys parameter to true, which lets the AWS Encryption CLI decrypt using any wrapping key that encrypted the message.

  As a best practice, use the --max-encrypted-data-keys parameter to avoid decrypting a malformed message with an excessive number of encrypted data keys. Specify the expected number of encrypted data keys (one for each wrapping key used in encryption) or a reasonable maximum (such as 5). For details, see Limiting encrypted data keys.

  The --buffer parameter returns plaintext only after all input is processed, including verifying the digital signature if one is present.

  The --decrypt-unsigned parameter decrypts ciphertext and ensures that messages are unsigned before decryption. Use this parameter if you used the --algorithm parameter and selected an algorithm suite without digital signing to encrypt data. If the ciphertext is signed, decryption fails.

  You can use --decrypt or --decrypt-unsigned for decryption but not both.

  aws-encryption-cli --decrypt --input myEncryptedMessage \
                     --wrapping-keys key=1234abcd-12ab-34cd-56ef-1234567890ab \
                     --output myPlaintextData \
                     --metadata-output ~/metadata \
                     --max-encrypted-data-keys 1 \
                     --buffer \
                     --encryption-context purpose=test \ 
                     --commitment-policy require-encrypt-require-decrypt

  The AWS Encryption CLI uses the wrapping key to decrypt the data key in the encrypted message. Then it uses the data key to decrypt your data. It returns your plaintext data and metadata about the operation.

How to specify wrapping keys

When you encrypt data in the AWS Encryption CLI, you need to specify at least one wrapping key (or master key). You can use AWS KMS keys in AWS Key Management Service (AWS KMS), wrapping keys from a custom master key provider, or both. The custom master key provider can be any compatible Python master key provider.

To specify wrapping keys in versions 1.8.x and later, use the --wrapping-keys parameter (-w). The value of this parameter is a collection of attributes with the attribute=value format. The attributes that you use depend on the master key provider and the command.

• AWS KMS. In encrypt commands, you must specify a --wrapping-keys parameter with a key attribute. Beginning in version 2.1.x, the --wrapping-keys parameter is also required in decrypt commands. When decrypting, the --wrapping-keys parameter must have a key attribute or a discovery attribute with a value of true (but not both). Other attributes are optional.

• Custom master key provider. You must specify a --wrapping-keys parameter in every command. The parameter value must have key and provider attributes.

You can include multiple --wrapping-keys parameters and multiple key attributes in the same command.

Wrapping key parameter attributes

The value of the --wrapping-keys parameter consists of the following attributes and their values. A --wrapping-keys parameter (or --master-keys parameter) is required in all encrypt commands. Beginning in version 2.1.x, the --wrapping-keys parameter is also required when decrypting.

If an attribute name or value includes spaces or special characters, enclose both the name and value in quotation marks. For example, --wrapping-keys key=12345 "provider=my cool provider".

Key: Specify a wrapping key

Use the key attribute to identify a wrapping key. When encrypting, the value can be any key identifier that the master key provider recognizes.

--wrapping-keys key=1234abcd-12ab-34cd-56ef-1234567890ab

In an encrypt command, you must include at least one key attribute and value. To encrypt your data key under multiple wrapping keys, use multiple key attributes.

aws-encryption-cli --encrypt --wrapping-keys key=1234abcd-12ab-34cd-56ef-1234567890ab key=1a2b3c4d-5e6f-1a2b-3c4d-5e6f1a2b3c4d

In encrypt commands that use AWS KMS keys, the value of key can be the key ID, its key ARN, an alias name, or alias ARN. For example, this encrypt command uses an alias ARN in the value of the key attribute. For details about the key identifiers for an AWS KMS key, see Key Identifiers in the AWS Key Management Service Developer Guide.

aws-encryption-cli --encrypt --wrapping-keys key=arn:aws:kms:us-west-2:111122223333:alias/ExampleAlias

In decrypt commands that use a custom master key provider, key and provider attributes are required.

\\ Custom master key provider
aws-encryption-cli --decrypt --wrapping-keys provider='myProvider' key='100101'

In decrypt commands that use AWS KMS, you can use the key attribute to specify the AWS KMS keys to use for decrypting, or the discovery attribute with a value of true, which lets the AWS Encryption CLI use any AWS KMS key that was used to encrypt the message. If you specify an AWS KMS key, it must be one of the wrapping keys used to encrypt the message.

Specifying the wrapping key is an AWS Encryption SDK best practice. It assures that you use the AWS KMS key you intend to use.

In a decrypt command, the value of the key attribute must be a key ARN.

\\ AWS KMS key
aws-encryption-cli --decrypt --wrapping-keys key=arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab

Discovery: Use any AWS KMS key when decrypting

If you don't need to limit the AWS KMS keys to use when decrypting, you can use the discovery attribute with a value of true. A value of true allows the AWS Encryption CLI to decrypt using any AWS KMS key that encrypted the message. If you don't specify a discovery attribute, discovery is false (default). The discovery attribute is valid only in decrypt commands and only when the message was encrypted with AWS KMS keys.

The discovery attribute with a value of true is an alternative to using the key attribute to specify AWS KMS keys. When decrypting a message encrypted with AWS KMS keys, each --wrapping-keys parameter must have a key attribute or a discovery attribute with a value of true, but not both.

When discovery is true, it's a best practice to use the discovery-partition and discovery-account attributes to limit the AWS KMS keys used to those in the AWS accounts you specify. In the following example, the discovery attributes allow the AWS Encryption CLI to use any AWS KMS key in the specified AWS accounts.

aws-encryption-cli --decrypt --wrapping-keys \
    discovery=true \
    discovery-partition=aws \
    discovery-account=111122223333 \
    discovery-account=444455556666

Provider: Specify the master key provider

The provider attribute identifies the master key provider. The default value is aws-kms, which represents AWS KMS. If you are using a different master key provider, the provider attribute is required.

--wrapping-keys key=12345 provider=my_custom_provider

For more information about using custom (non-AWS KMS) master key providers, see the Advanced Configuration topic in the README file for the AWS Encryption CLI repository.

Region: Specify an AWS Region

Use the region attribute to specify the AWS Region of an AWS KMS key. This attribute is valid only in encrypt commands and only when the master key provider is AWS KMS.

--encrypt --wrapping-keys key=alias/primary-key region=us-east-2

AWS Encryption CLI commands use the AWS Region that is specified in the key attribute value if it includes a region, such as an ARN. if the key value specifies a AWS Region, the region attribute is ignored.

The region attribute takes precedence over other region specifications. If you don't use a region attribute, AWS Encryption CLI commands uses the AWS Region specified in your AWS CLI named profile, if any, or your default profile.

Profile: Specify a named profile

Use the profile attribute to specify an AWS CLI named profile. Named profiles can include credentials and an AWS Region. This attribute is valid only when the master key provider is AWS KMS.

--wrapping-keys key=alias/primary-key profile=admin-1

You can use the profile attribute to specify alternate credentials in encrypt and decrypt commands. In an encrypt command, the AWS Encryption CLI uses the AWS Region in the named profile only when the key value does not include a region and there is no region attribute. In a decrypt command, the AWS Region in the name profile is ignored.

How to specify multiple wrapping keys

You can specify multiple wrapping keys (or master keys) in each command.

If you specify more than one wrapping key, the first wrapping key generates and encrypts the data key that is used to encrypt your data. The other wrapping keys encrypt the same data key. The resulting encrypted message contains the encrypted data ("ciphertext") and a collection of encrypted data keys, one encrypted by each wrapping key. Any of the wrapping can decrypt one encrypted data key and then decrypt the data.

There are two ways to specify multiple wrapping keys:

• Include multiple key attributes in the --wrapping-keys parameter value.

  $key_oregon=arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab
  $key_ohio=arn:aws:kms:us-east-2:111122223333:key/0987ab65-43cd-21ef-09ab-87654321cdef
  
  --wrapping-keys key=$key_oregon key=$key_ohio

• Include multiple --wrapping-keys parameters in the same command. Use this syntax when the attribute values that you specify do not apply to all of the wrapping keys in the command.

  --wrapping-keys region=us-east-2 key=alias/test_key \
  --wrapping-keys region=us-west-1 key=alias/test_key

The discovery attribute with a value of true lets the AWS Encryption CLI use any AWS KMS key that encrypted the message. If you use multiple --wrapping-keys parameters in the same command, using discovery=true in any --wrapping-keys parameter effectively overrides the limits of the key attribute in other --wrapping-keys parameters.

For example, in the following command, the key attribute in the first --wrapping-keys parameter limits the AWS Encryption CLI to the specified AWS KMS key. However, the discovery attribute in the second --wrapping-keys parameter lets the AWS Encryption CLI use any AWS KMS key in the specified accounts to decrypt the message.

aws-encryption-cli --decrypt \
    --wrapping-keys key=arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab \
    --wrapping-keys discovery=true \
                    discovery-partition=aws \
                    discovery-account=111122223333 \
                    discovery-account=444455556666

How to provide input

The encrypt operation in the AWS Encryption CLI takes plaintext data as input and returns an encrypted message. The decrypt operation takes an encrypted message as input and returns plaintext data.

The --input parameter (-i) , which tells the AWS Encryption CLI where to find the input, is required in all AWS Encryption CLI commands.

You can provide input in any of the following ways:

• Use a file.

  --input myData.txt

• Use a file name pattern.

  --input testdir/*.xml

• Use a directory or directory name pattern. When the input is a directory, the --recursive parameter (-r, -R) is required.

  --input testdir --recursive

• Pipe input to the command (stdin). Use a value of - for the --input parameter. (The --input parameter is always required.)

  echo 'Hello World' | aws-encryption-cli --encrypt --input -

How to specify the output location

The --output parameter tells the AWS Encryption CLI where to write the results of the encryption or decryption operation. It is required in every AWS Encryption CLI command. The AWS Encryption CLI creates a new output file for every input file in the operation.

If an output file already exists, by default, the AWS Encryption CLI prints a warning, then overwrites the file. To prevent overwriting, use the --interactive parameter, which prompts you for confirmation before overwriting, or --no-overwrite, which skips the input if the output would cause an overwrite. To suppress the overwrite warning, use --quiet. To capture errors and warnings from the AWS Encryption CLI, use the 2>&1 redirection operator to write them to the output stream.

Note

Commands that overwrite output files begin by deleting the output file. If the command fails, the output file might already be deleted.

You can the output location in several ways.

• Specify a file name. If you specify a path to the file, all directories in the path must exist before the command runs.

  --output myEncryptedData.txt

• Specify a directory. The output directory must exist before the command runs.

  If the input contains subdirectories, the command reproduces the subdirectories under the specified directory.

  --output Test

  When the output location is a directory (without file names), the AWS Encryption CLI creates output file names based on the input file names plus a suffix. Encrypt operations append .encrypted to the input file name and the decrypt operations append .decrypted. To change the suffix, use the --suffix parameter.

  For example, if you encrypt file.txt, the encrypt command creates file.txt.encrypted. If you decrypt file.txt.encrypted, the decrypt command creates file.txt.encrypted.decrypted.

   

• Write to the command line (stdout). Enter a value of - for the --output parameter. You can use --output - to pipe output to another command or program.

  --output -

How to use an encryption context

The AWS Encryption CLI lets you provide an encryption context in encrypt and decrypt commands. It is not required, but it is a cryptographic best practice that we recommend.

An encryption context is a type of arbitrary, non-secret additional authenticated data. In the AWS Encryption CLI, the encryption context consists of a collection of name=value pairs. You can use any content in the pairs, including information about the files, data that helps you to find the encryption operation in logs, or data that your grants or policies require.

In an encrypt command

The encryption context that you specify in an encrypt command, along with any additional pairs that the CMM adds, is cryptographically bound to the encrypted data. It is also included (in plaintext) in the encrypted message that the command returns. If you are using an AWS KMS key, the encryption context also might appear in plaintext in audit records and logs, such as AWS CloudTrail.

The following example shows an encryption context with three name=value pairs.

--encryption-context purpose=test dept=IT class=confidential 

In a decrypt command

In a decrypt command, the encryption context helps you to confirm that you are decrypting the right encrypted message.

You are not required to provide an encryption context in a decrypt command, even if an encryption context was used on encrypt. However, if you do, the AWS Encryption CLI verifies that every element in the encryption context of the decrypt command matches an element in the encryption context of the encrypted message. If any element does not match, the decrypt command fails.

For example, the following command decrypts the encrypted message only if its encryption context includes dept=IT.

aws-encryption-cli --decrypt --encryption-context dept=IT ...

An encryption context is an important part of your security strategy. However, when choosing an encryption context, remember that its values are not secret. Do not include any confidential data in the encryption context.

To specify an encryption context

• In an encrypt command, use the --encryption-context parameter with one or more name=value pairs. Use a space to separate each pair.

  --encryption-context name=value [name=value] ...

• In a decrypt command, the --encryption-context parameter value can include name=value pairs, name elements (with no values), or a combination of both.

  --encryption-context name[=value] [name] [name=value] ...

If the name or value in a name=value pair includes spaces or special characters, enclose the entire pair in quotation marks.

--encryption-context "department=software engineering" "AWS Region=us-west-2"

For example, this encrypt command includes an encryption context with two pairs, purpose=test and dept=23.

aws-encryption-cli --encrypt --encryption-context purpose=test dept=23 ...

These decrypt command would succeed. The encryption context in each commands is a subset of the original encryption context.

\\ Any one or both of the encryption context pairs
aws-encryption-cli --decrypt --encryption-context dept=23 ...

\\ Any one or both of the encryption context names
aws-encryption-cli --decrypt --encryption-context purpose ...

\\ Any combination of names and pairs
aws-encryption-cli --decrypt --encryption-context dept purpose=test ...

However, these decrypt commands would fail. The encryption context in the encrypted message does not contain the specified elements.

aws-encryption-cli --decrypt --encryption-context dept=Finance ...
aws-encryption-cli --decrypt --encryption-context scope ...

How to specify a commitment policy

To set the commitment policy for the command, use the --commitment-policy parameter. This parameter is introduced in version 1.8.x. It is valid in encrypt and decrypt commands. The commitment policy you set is valid only for the command in which it appears. If you do not set a commitment policy for a command, the AWS Encryption CLI uses the default value.

For example, the following parameter value sets the commitment policy to require-encrypt-allow-decrypt, which always encrypts with key commitment, but will decrypt a ciphertext that was encrypted with or without key commitment.

--commitment-policy require-encrypt-allow-decrypt

How to store parameters in a configuration file

You can save time and avoid typing errors by saving frequently used AWS Encryption CLI parameters and values in configuration files.

A configuration file is a text file that contains parameters and values for an AWS Encryption CLI command. When you refer to a configuration file in a AWS Encryption CLI command, the reference is replaced by the parameters and values in the configuration file. The effect is the same is if you typed the file content at the command line. A configuration file can have any name and it can be located in any directory that the current user can access.

The following example configuration file, key.conf, specifies two AWS KMS keys in different Regions.

--wrapping-keys key=arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab
--wrapping-keys key=arn:aws:kms:us-east-2:111122223333:key/0987ab65-43cd-21ef-09ab-87654321cdef

To use the configuration file in a command, prefix the file name with an at sign (@). In a PowerShell console, use a backtick character to escape the at sign (`@).

This example command uses the key.conf file in an encrypt command.

Bash

$ aws-encryption-cli -e @key.conf -i hello.txt -o testdir  

PowerShell

PS C:\> aws-encryption-cli -e `@key.conf -i .\Hello.txt -o .\TestDir

Configuration file rules

The rules for using configuration files are as follows:

• You can include multiple parameters in each configuration file and list them in any order. List each parameter with its values (if any) on a separate line.

• Use # to add a comment to all or part of a line.

• You can include references to other configuration files. Do not use a backtick to escape the @ sign, even in PowerShell.

• If you use quotes in a configuration file, the quoted text cannot span multiple lines.

For example, this is the contents of an example encrypt.conf file.

# Archive Files
--encrypt
--output /archive/logs
--recursive
--interactive
--encryption-context class=unclassified dept=IT
--suffix  # No suffix
--metadata-output ~/metadata
@caching.conf  # Use limited caching  

You can also include multiple configuration files in a command. This example command uses both the encrypt.conf and master-keys.conf configurations files.

Bash

$  aws-encryption-cli -i /usr/logs @encrypt.conf @master-keys.conf

PowerShell

PS C:\> aws-encryption-cli -i $home\Test\*.log `@encrypt.conf `@master-keys.conf

Next: Try the AWS Encryption CLI examples