aws-encryption-sdk-cli

This command line tool can be used to encrypt and decrypt files and directories using the AWS Encryption SDK.

The latest full documentation can be found at Read the Docs.

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See Support Policy for details on the current support status of all major versions of this library.

Getting Started

Required Prerequisites

• Python 3.8+
• aws-encryption-sdk >= 3.1.0

Installation

$ pip install aws-encryption-sdk-cli

$ cd my_project
$ python3 -m venv env
$ source env/bin/activate
$ python -m pip install aws-encryption-sdk-cli

> cd my_project
> python3 -m venv env
> .\env\Scripts\Activate.ps1
(env) > pip install aws-encryption-sdk-cli

Usage

Input and Output

For the most part, the behavior of aws-encryption-cli in handling files is based on that of GNU CLIs such as cp. A qualifier to this is that when encrypting a file, if a directory is provided as the destination, rather than creating the source filename in the destination directory, a suffix is appended to the destination filename. By default the suffix is .encrypted when encrypting and .decrypted when decrypting, but a custom suffix can be provided by the caller if desired.

If a destination file already exists, the contents will be overwritten.

If the source includes a directory and the --recursive flag is set, the entire tree of the source directory is replicated in the target directory.

Parameter Values

Some arguments accept additional parameter values. These values must be provided in the form of key=value as demonstrated below.

--encryption-context key1=value1 key2=value2 "key 3=value with spaces"
--master-keys provider=aws-kms key=$KEY_ID_1 key=$KEY_ID_2
--caching capacity=3 max_age=80.0

Encryption Context

Encrypt

The encryption context is an optional, but recommended, set of key-value pairs that contain arbitrary nonsecret data. The encryption context can contain any data you choose, but it typically consists of data that is useful in logging and tracking, such as data about the file type, purpose, or ownership.

Parameters may be provided using Parameter Values.

--encryption-context key1=value1 key2=value2 "key 3=value with spaces"

Decrypt

If an encryption context is provided on decrypt, it is instead used to require that the message being decrypted was encrypted using an encryption context that matches the specified requirements.

If key=value elements are provided, the decryption will only continue if the encryption context found in the encrypted message contains matching pairs.

--encryption-context required_key=required_value classification=secret

If bare key elements are provided, the decryption will continue if those keys are found, regardless of the values. key and key=value elements can be mixed.

--encryption-context required_key classification=secret

Output Metadata

In addition to the actual output of the operation, there is metadata about the operation that can be useful. This metadata includes some information about the operation as well as the complete header data from the ciphertext message.

The metadata for each operation is written to the specified file as a single line containing formatted JSON, so if a single command performs multiple file operations, a separate line will be written for each operation. There are three operating modes:

• --metadata-output FILE : Writes the metadata output to FILE (can be - for stdout as long as main output is not stdout). Default behavior is to append the metadata entry to the end of FILE.
• --overwrite-metadata : Force overwriting the contents of FILE with the new metadata.
• -S/--suppress-metadata : Output metadata is suppressed.

Metadata Contents

The metadata JSON contains the following fields:

• "mode" : "encrypt"/"decrypt"/"decrypt-unsigned"
• "input" : Full path to input file (or "" if stdin)
• "output" : Full path to output file (or "" if stdout)
• "header" : JSON representation of message header data
• "header_auth" : JSON representation of message header authentication data (only on decrypt)

Skipped Files

If encryption context checks fail when attempting to decrypt a file, the metadata contains additional fields:

• skipped : true
• reason : "Missing encryption context key or value"
• missing_encryption_context_keys : List of required encryption context keys that were missing from the message.
• missing_encryption_context_pairs : List of required encryption context key-value pairs missing from the message.

Master Key Provider

Information for configuring a master key provider must be provided.

Parameters may be provided using Parameter Values.

These parameters are common to all master key providers:

• provider (default: aws-encryption-sdk-cli::aws-kms) : Indicator of the master key provider to use.

  > - See Advanced Configuration for more > information on using other master key providers.

• key (on encrypt: at least one required, many allowed; on decrypt: one of key or discovery is required) : Identifier for a wrapping key to be used in the operation. Must be an identifier understood by the specified master key provider. The discovery attribute is only available if you are using an aws-kms provider.

  > - If using aws-kms to decrypt, you must specify either a key > or discovery with a value of > true. > - If using aws-kms to decrypt and specifying a key, you must > use a key ARN; key ids, alias names, and alias ARNs are not > supported.

Any additional parameters supplied are collected into lists by parameter name and passed to the master key provider class when it is instantiated. Custom master key providers must accept all arguments as prepared. See Advanced Configuration for more information.

Multiple master keys can be defined using multiple instances of the key argument.

Multiple master key providers can be defined using multiple --wrapping-keys groups.

If multiple master key providers are defined, the first one is treated as the primary.

If multiple master keys are defined in the primary master key provider, the first one is treated as the primary. The primary master key is used to generate the data key.

The following logic is used to construct all master key providers. We use StrictAwsKmsMasterKeyProvider as an example.

# With parameters:
--wrapping-keys provider=aws-kms key=$KEY_1 key=$KEY_2

# KMSMasterKeyProvider is called as:
key_provider = StrictAwsKmsMasterKeyProvider(key_ids=[$KEY_1, $KEY_2])

# Single KMS CMK
--wrapping-keys provider=aws-kms key=$KEY_ARN_1

# Two KMS CMKs
--wrapping-keys provider=aws-kms key=$KEY_ARN_1 key=$KEY_ARN_2

# KMS Alias by name in default region
--wrapping-keys provider=aws-kms key=$ALIAS_NAME

# KMS Alias by name in two specific regions
--wrapping-keys provider=aws-kms key=$ALIAS_NAME region=us-west-2
--wrapping-keys provider=aws-kms key=$ALIAS_NAME region=eu-central-1

AWS KMS

If you want to use the aws-kms master key provider, you can either specify that as the provider or simply not specify a provider and allow the default value to be used.

There are some configuration options which are unique to the aws-kms master key provider:

• profile : Providing this configuration value will use the specified named profile credentials.
• discovery (default: false; one of key or discovery with a value of true is required) : Indicates whether this provider should be in "discovery" mode. If true (enabled), the AWS Encryption CLI will attempt to decrypt ciphertexts encrypted with any AWS KMS CMK. If false (disabled), the AWS Encryption CLI will only attempt to decrypt ciphertexts encrypted with the key ARNs specified in the key attribute. Any key specified in the key attribute that is a KMS CMK Identier other than a key ARN will not be used for decryption.
• discovery-account (optional; available only when discovery=true and discovery-partition is also provided) : If discovery is enabled, limits decryption to AWS KMS CMKs in the specified accounts.
• discovery-partition (optional; available only when discovery=true and discovery-account is also provided) : If discovery is enabled, limits decryption to AWS KMS CMKs in the specified partition, e.g. "aws" or "aws-gov".
• region : This allows you to specify the target region.

The logic for determining which region to use is shown in the pseudocode below:

if key ID is an ARN:
   use region identified in ARN
else:
   if region is specified:
      use region
   else if profile is specified and profile has a defined region:
      use region defined in profile
   else:
      use system default region

Advanced Configuration

If you want to use a different master key provider, that provider must register a setuptools entry point. You can find an example of registering this entry point in the setup.py for this package.

When a provider name is specifed in a call to aws-encryption-cli, the appropriate entry point for that name is used.

Handling Multiple Entry Points

If multiple entry points are registered for a given name, you will need to specify the package that registered the entry point you want to use.

In order to specify the package name, use the format: PACKAGE_NAME::ENTRY_POINT.

• provider=aws-kms
• provider=aws-encryption-sdk-cli::aws-kms

If you supply only an entry point name and there is only one entry point registered for that name, that entry point will be used.

If you supply only an entry point name and there is more than one entry point registered for that name, an error will be raised showing you all of the packages that have an entry point registered for that name.

If you supply both a package and an entry point name, that exact entry point will be used. If it is not accessible, an error will be raised showing you all of the packages that have an entry point registered for that name.

External Master Key Providers

The entry point name use must not contain the string ::. This is used as a namespace separator as descibed in Handling Multiple Entry Points.

When called, these entry points must return an instance of a master key provider. They must accept the parameters prepared by the CLI as described in Master Key Provider.

These entry points must be registered in the aws_encryption_sdk_cli.master_key_providers group.

If the entry point raises a aws_encryption_sdk_cli.exceptions.BadUserArgumentError, the CLI will present the raised error message to the user to indicate bad user input.

Commitment Policy

The commitment policy controls which algorithms can be used in encryption and decryption. Versions 2.0.x and later of the AWS Encryption CLI use a default commitment policy of require-encrypt-require-decrypt, which ensures that only algorithms which provide key commitment can be used on both encryption and decryption. If you want to use a different commitment policy, you can do so with the --commitment-policy parameter.

For more details, see the Commitment Policy documentation.

# Use a commitment policy that requires an algorithm which provides key commitment
# on both encryption and decryption
--commitment-policy require-encrypt-require-decrypt

Data Key Caching

Data key caching is optional, but if used then the parameters noted as required must be provided. For detailed information about using data key caching with the AWS Encryption SDK, see the data key caching documentation.

Parameters may be provided using Parameter Values.

Allowed parameters:

• capacity (required) : Number of entries that the cache will hold.
• max_age (required) : Determines how long each entry can remain in the cache, beginning when it was added.
• max_messages_encrypted : Determines how long each entry can remain in the cache, beginning when it was added.
• max_bytes_encrypted : Specifies the maximum number of bytes that a cached data key can encrypt.

Logging and Verbosity

The -v argument allows you to tune the verbosity of the built-in logging to your desired level. In short, the more -v arguments you supply, the more verbose the output gets.

• unset : aws-encryption-cli logs all warnings, all dependencies only log critical messages
• -v : aws-encryption-cli performs moderate logging, all dependencies only log critical messages
• -vv : aws-encryption-cli performs detailed logging, all dependencies only log critical messages
• -vvv : aws-encryption-cli performs detailed logging, all dependencies perform moderate logging
• -vvvv : aws-encryption-cli performs detailed logging, all dependencies perform detailed logging

Configuration Files

As with any CLI where the configuration can get rather complex, you might want to use a configuration file to define some or all of your desired behavior.

Configuration files are supported using Python's native argparse file support, which allows you to write configuration files exactly as you would enter arguments in the shell. Configuration file references passed to aws-encryption-cli are identified by the @ prefix and the contents are expanded as if you had included them in line. Configuration files can have any name you desire.

For example, if I wanted to use a common master key configuration for all of my calls, I could create a file master-key.conf with contents detailing my master key configuration.

master-key.conf

--master-key key=A_KEY key=ANOTHER_KEY

Then, when calling aws-encryption-cli, I can specify the rest of my arguments and reference my new configuration file, and aws-encryption-cli will use the composite configuration.

aws-encryption-cli -e -i $INPUT_FILE -o $OUTPUT_FILE @master-key.conf

To extend the example, if I wanted a common caching configuration for all of my calls, I could similarly place my caching configuration in a configuration file caching.conf in this example and include both files in my call.

caching.conf

--caching capacity=10 max_age=60.0 max_messages_encrypted=15

aws-encryption-cli -e -i $INPUT_FILE -o $OUTPUT_FILE @master-key.conf @caching.conf

Configuration files can be referenced anywhere in aws-encryption-cli parameters.

aws-encryption-cli -e -i $INPUT_DIR -o $OUTPUT_DIR @master-key.conf @caching.conf --recursive

Configuration files can have many lines, include comments using #. Escape characters are platform-specific: \ on Linux and MacOS and ``` on Windows. Configuration files may also include references to other configuration files.

my-encrypt.config

--encrypt
@master-key.conf # Use existing master key config
@caching.conf
# Always recurse, but require interactive overwrite.
--recursive
--interactive

aws-encryption-cli @my-encrypt -i $INPUT -o $OUTPUT

Encoding

By default, aws-encryption-cli will always output raw binary data and expect raw binary data as input. However, there are some cases where you might not want this to be the case.

Sometimes this might be for convenience:

• Accepting ciphertext through stdin from a human.
• Presenting ciphertext through stdout to a human.

Sometimes it might be out of necessity:

• Saving ciphertext output to a shell variable.

  > - Most shells apply a system encoding to any data stored in a > variable. As a result, this often results in corrupted data if > binary data is stored without additional encoding.

• Piping ciphertext in PowerShell.

  > - Similar to the above, all data passed through a PowerShell > pipe is encoded using the system encoding.

In order to address these scenarios, we provide two optional arguments:

• --decode : Base64-decode input before processing.
• --encode : Base64-encode output after processing.

These can be used independently or together, on any valid input or output.

Be aware, however, that if you target multiple files either through a path expansion or by targeting a directory, the requested decoding/encoding will be applied to all files.