sign¶

Description¶

Creates a digital signature for a message or message digest by using the private key in an asymmetric signing KMS key. To verify the signature, use the Verify operation, or use the public key in the same asymmetric KMS key outside of KMS. For information about asymmetric KMS keys, see Asymmetric KMS keys in the Key Management Service Developer Guide .

Digital signatures are generated and verified by using asymmetric key pair, such as an RSA or ECC pair that is represented by an asymmetric KMS key. The key owner (or an authorized user) uses their private key to sign a message. Anyone with the public key can verify that the message was signed with that particular private key and that the message hasn’t changed since it was signed.

To use the Sign operation, provide the following information:

Use the KeyId parameter to identify an asymmetric KMS key with a KeyUsage value of SIGN_VERIFY . To get the KeyUsage value of a KMS key, use the DescribeKey operation. The caller must have kms:Sign permission on the KMS key.
Use the Message parameter to specify the message or message digest to sign. You can submit messages of up to 4096 bytes. To sign a larger message, generate a hash digest of the message, and then provide the hash digest in the Message parameter. To indicate whether the message is a full message or a digest, use the MessageType parameter.
Choose a signing algorithm that is compatible with the KMS key.

Warning

When signing a message, be sure to record the KMS key and the signing algorithm. This information is required to verify the signature.

Note

Best practices recommend that you limit the time during which any signature is effective. This deters an attack where the actor uses a signed message to establish validity repeatedly or long after the message is superseded. Signatures do not include a timestamp, but you can include a timestamp in the signed message to help you detect when its time to refresh the signature.

To verify the signature that this operation generates, use the Verify operation. Or use the GetPublicKey operation to download the public key and then use the public key to verify the signature outside of KMS.

The KMS key that you use for this operation must be in a compatible key state. For details, see Key states of KMS keys 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:Sign (key policy)

Related operations : Verify

Synopsis¶

  sign
--key-id <value>
--message <value>
[--message-type <value>]
[--grant-tokens <value>]
--signing-algorithm <value>
[--cli-input-json | --cli-input-yaml]
[--generate-cli-skeleton <value>]

Options¶

--key-id (string)

Identifies an asymmetric KMS key. KMS uses the private key in the asymmetric KMS key to sign the message. The KeyUsage type of the KMS key must be SIGN_VERIFY . To find the KeyUsage of a KMS key, use the DescribeKey operation.

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 .

--message (blob)

Specifies the message or message digest to sign. Messages can be 0-4096 bytes. To sign a larger message, provide the message digest.

If you provide a message, KMS generates a hash digest of the message and then signs it.

--message-type (string)

Tells KMS whether the value of the Message parameter is a message or message digest. The default value, RAW, indicates a message. To indicate a message digest, enter DIGEST .

Possible values:

RAW

DIGEST

--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" ...

--signing-algorithm (string)

Specifies the signing algorithm to use when signing the message.

Choose an algorithm that is compatible with the type and size of the specified asymmetric KMS key.

Possible values:

RSASSA_PSS_SHA_256

RSASSA_PSS_SHA_384

RSASSA_PSS_SHA_512

RSASSA_PKCS1_V1_5_SHA_256

RSASSA_PKCS1_V1_5_SHA_384

RSASSA_PKCS1_V1_5_SHA_512

ECDSA_SHA_256

ECDSA_SHA_384

ECDSA_SHA_512

SM2DSA

--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. The generated JSON skeleton is not stable between versions of the AWS CLI and there are no backwards compatibility guarantees in the JSON skeleton generated.

See ‘aws help’ for descriptions of global parameters.

Examples¶

Note

To use the following examples, you must have the AWS CLI installed and configured. See the Getting started guide in the AWS CLI User Guide for more information.

Unless otherwise stated, all examples have unix-like quotation rules. These examples will need to be adapted to your terminal’s quoting rules. See Using quotation marks with strings in the AWS CLI User Guide .

Example 1: To generate a digital signature for a message

The following sign example generates a cryptographic signature for a short message. The output of the command includes a base-64 encoded Signature field that you can verify by using the verify command.

You must also specify a signing algorithm that your asymmetric KMS key supports. To get the signing algorithms for your KMS key, use the describe-key command.

Before running this command, replace the example key ID with a valid key ID from your AWS account. The key ID must represent an asymmetric KMS key with a key usage of SIGN_VERIFY.

aws kms sign \
    --key-id 1234abcd-12ab-34cd-56ef-1234567890ab \
    --message 'hello world' \
    --message-type RAW \
    --signing-algorithm RSASSA_PKCS1_V1_5_SHA_256

Output:

{
    "KeyId": "arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab",
    "Signature": "ABCDEFhpyVYyTxbafE74ccSvEJLJr3zuoV1Hfymz4qv+/fxmxNLA7SE1SiF8lHw80fKZZ3bJ...",
    "SigningAlgorithm": "RSASSA_PKCS1_V1_5_SHA_256"
}

For more information about using asymmetric KMS keys in AWS KMS, see Asymmetric keys in AWS KMS in the AWS Key Management Service Developer Guide.

Example 2: To save a digital signature in a file (Linux and macOs)

The following sign example generates a cryptographic signature for a short message stored in a local file. The command also gets the Signature property from the response, Base64-decodes it and saves it in the ExampleSignature file. You can use the signature file in a verify command that verifies the signature.

The sign command requires a signing algorithm. To get the signing algorithms that your KMS key supports, use the describe-key command.

Before running this command, replace the example key ID with a valid key ID from your AWS account. The key ID must represent an asymmetric KMS key with a key usage of SIGN_VERIFY.

aws kms sign \
    --key-id 1234abcd-12ab-34cd-56ef-1234567890ab \
    --message fileb://originalString \
    --message-type RAW \
    --signing-algorithm RSASSA_PKCS1_V1_5_SHA_256 \
    --output text \
    --query Signature | base64 --decode > ExampleSignature

This command produces no output. This example extracts the Signature property of the output and saves it in a file.

For more information about using asymmetric KMS keys in AWS KMS, see Asymmetric keys in AWS KMS in the AWS Key Management Service Developer Guide.

Output¶

KeyId -> (string)

The Amazon Resource Name (key ARN ) of the asymmetric KMS key that was used to sign the message.

Signature -> (blob)

The cryptographic signature that was generated for the message.

When used with the supported RSA signing algorithms, the encoding of this value is defined by PKCS #1 in RFC 8017 .

When used with the ECDSA_SHA_256 , ECDSA_SHA_384 , or ECDSA_SHA_512 signing algorithms, this value is a DER-encoded object as defined by ANS X9.62–2005 and RFC 3279 Section 2.2.3 . This is the most commonly used signature format and is appropriate for most uses.

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

SigningAlgorithm -> (string)

The signing algorithm that was used to sign the message.

Table of Contents

Feedback

User Guide