Encrypt with an asymmetric key

Encrypt plaintext using the public key portion of an asymmetric key.

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For detailed documentation that includes this code sample, see the following:

• Encrypting and decrypting data with an asymmetric key

Code sample

C#

To learn how to install and use the client library for Cloud KMS, see Cloud KMS client libraries.

To authenticate to Cloud KMS, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

using Google.Cloud.Kms.V1;
using System;
using System.Security.Cryptography;
using System.Text;

public class EncryptAsymmetricSample
{
    public byte[] EncryptAsymmetric(
      string projectId = "my-project", string locationId = "us-east1", string keyRingId = "my-key-ring", string keyId = "my-key", string keyVersionId = "123",
      string message = "Sample message")
    {
        // Create the client.
        KeyManagementServiceClient client = KeyManagementServiceClient.Create();

        // Build the key version name.
        CryptoKeyVersionName keyVersionName = new CryptoKeyVersionName(projectId, locationId, keyRingId, keyId, keyVersionId);

        // Get the public key.
        PublicKey publicKey = client.GetPublicKey(keyVersionName);

        // Split the key into blocks and base64-decode the PEM parts.
        string[] blocks = publicKey.Pem.Split("-", StringSplitOptions.RemoveEmptyEntries);
        byte[] pem = Convert.FromBase64String(blocks[1]);

        // Create a new RSA key.
        RSA rsa = RSA.Create();
        rsa.ImportSubjectPublicKeyInfo(pem, out _);

        // Convert the message into bytes. Cryptographic plaintexts and
        // ciphertexts are always byte arrays.
        byte[] plaintext = Encoding.UTF8.GetBytes(message);

        // Encrypt the data.
        byte[] ciphertext = rsa.Encrypt(plaintext, RSAEncryptionPadding.OaepSHA256);
        return ciphertext;
    }
}

Go

To learn how to install and use the client library for Cloud KMS, see Cloud KMS client libraries.

To authenticate to Cloud KMS, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

import (
	"context"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"io"

	kms "cloud.google.com/go/kms/apiv1"
	"cloud.google.com/go/kms/apiv1/kmspb"
)

// encryptAsymmetric encrypts data on your local machine using an
// 'RSA_DECRYPT_OAEP_2048_SHA256' public key retrieved from Cloud KMS.
func encryptAsymmetric(w io.Writer, name string, message string) error {
	// name := "projects/my-project/locations/us-east1/keyRings/my-key-ring/cryptoKeys/my-key/cryptoKeyVersions/123"
	// message := "Sample message"

	// Create the client.
	ctx := context.Background()
	client, err := kms.NewKeyManagementClient(ctx)
	if err != nil {
		return fmt.Errorf("failed to create kms client: %w", err)
	}
	defer client.Close()

	// Retrieve the public key from Cloud KMS. This is the only operation that
	// involves Cloud KMS. The remaining operations take place on your local
	// machine.
	response, err := client.GetPublicKey(ctx, &kmspb.GetPublicKeyRequest{
		Name: name,
	})
	if err != nil {
		return fmt.Errorf("failed to get public key: %w", err)
	}

	// Parse the public key. Note, this example assumes the public key is in the
	// RSA format.
	block, _ := pem.Decode([]byte(response.Pem))
	publicKey, err := x509.ParsePKIXPublicKey(block.Bytes)
	if err != nil {
		return fmt.Errorf("failed to parse public key: %w", err)
	}
	rsaKey, ok := publicKey.(*rsa.PublicKey)
	if !ok {
		return fmt.Errorf("public key is not rsa")
	}

	// Convert the message into bytes. Cryptographic plaintexts and
	// ciphertexts are always byte arrays.
	plaintext := []byte(message)

	// Encrypt data using the RSA public key.
	ciphertext, err := rsa.EncryptOAEP(sha256.New(), rand.Reader, rsaKey, plaintext, nil)
	if err != nil {
		return fmt.Errorf("rsa.EncryptOAEP: %w", err)
	}
	fmt.Fprintf(w, "Encrypted ciphertext: %s", ciphertext)
	return nil
}

Java

To learn how to install and use the client library for Cloud KMS, see Cloud KMS client libraries.

To authenticate to Cloud KMS, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

import com.google.cloud.kms.v1.CryptoKeyVersionName;
import com.google.cloud.kms.v1.KeyManagementServiceClient;
import com.google.cloud.kms.v1.PublicKey;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.StringReader;
import java.nio.charset.StandardCharsets;
import java.security.GeneralSecurityException;
import java.security.KeyFactory;
import java.security.spec.MGF1ParameterSpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.Base64;
import java.util.stream.Collectors;
import javax.crypto.Cipher;
import javax.crypto.spec.OAEPParameterSpec;
import javax.crypto.spec.PSource;

public class EncryptAsymmetric {

  public void encryptAsymmetric() throws IOException, GeneralSecurityException {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "your-project-id";
    String locationId = "us-east1";
    String keyRingId = "my-key-ring";
    String keyId = "my-key";
    String keyVersionId = "123";
    String plaintext = "Plaintext to encrypt";
    encryptAsymmetric(projectId, locationId, keyRingId, keyId, keyVersionId, plaintext);
  }

  // Encrypt data that was encrypted using the public key component of the given
  // key version.
  public void encryptAsymmetric(
      String projectId,
      String locationId,
      String keyRingId,
      String keyId,
      String keyVersionId,
      String plaintext)
      throws IOException, GeneralSecurityException {
    // Initialize client that will be used to send requests. This client only
    // needs to be created once, and can be reused for multiple requests. After
    // completing all of your requests, call the "close" method on the client to
    // safely clean up any remaining background resources.
    try (KeyManagementServiceClient client = KeyManagementServiceClient.create()) {
      // Build the key version name from the project, location, key ring, key,
      // and key version.
      CryptoKeyVersionName keyVersionName =
          CryptoKeyVersionName.of(projectId, locationId, keyRingId, keyId, keyVersionId);

      // Get the public key.
      PublicKey publicKey = client.getPublicKey(keyVersionName);

      // Convert the public PEM key to a DER key (see helper below).
      byte[] derKey = convertPemToDer(publicKey.getPem());
      X509EncodedKeySpec keySpec = new X509EncodedKeySpec(derKey);
      java.security.PublicKey rsaKey = KeyFactory.getInstance("RSA").generatePublic(keySpec);

      // Encrypt plaintext for the 'RSA_DECRYPT_OAEP_2048_SHA256' key.
      // For other key algorithms:
      // https://docs.oracle.com/javase/7/docs/api/javax/crypto/Cipher.html
      Cipher cipher = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");
      OAEPParameterSpec oaepParams =
          new OAEPParameterSpec(
              "SHA-256", "MGF1", MGF1ParameterSpec.SHA256, PSource.PSpecified.DEFAULT);
      cipher.init(Cipher.ENCRYPT_MODE, rsaKey, oaepParams);
      byte[] ciphertext = cipher.doFinal(plaintext.getBytes(StandardCharsets.UTF_8));
      System.out.printf("Ciphertext: %s%n", ciphertext);
    }
  }

  // Converts a base64-encoded PEM certificate like the one returned from Cloud
  // KMS into a DER formatted certificate for use with the Java APIs.
  private byte[] convertPemToDer(String pem) {
    BufferedReader bufferedReader = new BufferedReader(new StringReader(pem));
    String encoded =
        bufferedReader
            .lines()
            .filter(line -> !line.startsWith("-----BEGIN") && !line.startsWith("-----END"))
            .collect(Collectors.joining());
    return Base64.getDecoder().decode(encoded);
  }
}

Node.js

To learn how to install and use the client library for Cloud KMS, see Cloud KMS client libraries.

To authenticate to Cloud KMS, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

//
// TODO(developer): Uncomment these variables before running the sample.
//
// const projectId = 'my-project';
// const locationId = 'us-east1';
// const keyRingId = 'my-key-ring';
// const keyId = 'my-key';
// const versionId = '123';
// const plaintextBuffer = Buffer.from('...');

// Imports the Cloud KMS library
const {KeyManagementServiceClient} = require('@google-cloud/kms');

// Instantiates a client
const client = new KeyManagementServiceClient();

// Build the key version name
const versionName = client.cryptoKeyVersionPath(
  projectId,
  locationId,
  keyRingId,
  keyId,
  versionId
);

async function encryptAsymmetric() {
  // Get public key from Cloud KMS
  const [publicKey] = await client.getPublicKey({
    name: versionName,
  });

  // Optional, but recommended: perform integrity verification on publicKey.
  // For more details on ensuring E2E in-transit integrity to and from Cloud KMS visit:
  // https://cloud.google.com/kms/docs/data-integrity-guidelines
  const crc32c = require('fast-crc32c');
  if (publicKey.name !== versionName) {
    throw new Error('GetPublicKey: request corrupted in-transit');
  }
  if (crc32c.calculate(publicKey.pem) !== Number(publicKey.pemCrc32c.value)) {
    throw new Error('GetPublicKey: response corrupted in-transit');
  }

  // Import and setup crypto
  const crypto = require('crypto');

  // Encrypt plaintext locally using the public key. This example uses a key
  // that was configured with sha256 hash with OAEP padding. Update these
  // values to match the Cloud KMS key.
  //
  // NOTE: In Node < 12, this function does not properly consume the OAEP
  // padding and thus produces invalid ciphertext. If you are using Node to do
  // public key encryption, please use version 12+.
  const ciphertextBuffer = crypto.publicEncrypt(
    {
      key: publicKey.pem,
      oaepHash: 'sha256',
      padding: crypto.constants.RSA_PKCS1_OAEP_PADDING,
    },
    plaintextBuffer
  );

  console.log(`Ciphertext: ${ciphertextBuffer.toString('base64')}`);
  return ciphertextBuffer;
}

return encryptAsymmetric();

PHP

To learn how to install and use the client library for Cloud KMS, see Cloud KMS client libraries.

To authenticate to Cloud KMS, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

function encrypt_asymmetric(
    string $projectId = 'my-project',
    string $locationId = 'us-east1',
    string $keyRingId = 'my-key-ring',
    string $keyId = 'my-key',
    string $versionId = '123',
    string $plaintext = '...'
): void {
    // PHP has limited support for asymmetric encryption operations.
    // Specifically, openssl_public_encrypt() does not allow customizing
    // algorithms or padding. Thus, it is not currently possible to use PHP
    // core for asymmetric operations on RSA keys.
    //
    // Third party libraries like phpseclib may provide the required
    // functionality. Google does not endorse this external library.
}

Python

To learn how to install and use the client library for Cloud KMS, see Cloud KMS client libraries.

To authenticate to Cloud KMS, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

# Import base64 for printing the ciphertext.
import base64

# Import cryptographic helpers from the cryptography package.
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import padding

# Import the client library.
from google.cloud import kms


def encrypt_asymmetric(
    project_id: str,
    location_id: str,
    key_ring_id: str,
    key_id: str,
    version_id: str,
    plaintext: str,
) -> bytes:
    """
    Encrypt plaintext using the public key portion of an asymmetric key.

    Args:
        project_id (string): Google Cloud project ID (e.g. 'my-project').
        location_id (string): Cloud KMS location (e.g. 'us-east1').
        key_ring_id (string): ID of the Cloud KMS key ring (e.g. 'my-key-ring').
        key_id (string): ID of the key to use (e.g. 'my-key').
        version_id (string): ID of the key version to use (e.g. '1').
        plaintext (string): message to encrypt

    Returns:
        bytes: Encrypted ciphertext.

    """

    # Convert the plaintext to bytes.
    plaintext_bytes = plaintext.encode("utf-8")

    # Create the client.
    client = kms.KeyManagementServiceClient()

    # Build the key version name.
    key_version_name = client.crypto_key_version_path(
        project_id, location_id, key_ring_id, key_id, version_id
    )

    # Get the public key.
    public_key = client.get_public_key(request={"name": key_version_name})

    # Extract and parse the public key as a PEM-encoded RSA key.
    pem = public_key.pem.encode("utf-8")
    rsa_key = serialization.load_pem_public_key(pem, default_backend())

    # Construct the padding. Note that the padding differs based on key choice.
    sha256 = hashes.SHA256()
    mgf = padding.MGF1(algorithm=sha256)
    pad = padding.OAEP(mgf=mgf, algorithm=sha256, label=None)

    # Encrypt the data using the public key.
    ciphertext = rsa_key.encrypt(plaintext_bytes, pad)
    print(f"Ciphertext: {base64.b64encode(ciphertext)!r}")
    return ciphertext

Ruby

To learn how to install and use the client library for Cloud KMS, see Cloud KMS client libraries.

To authenticate to Cloud KMS, set up Application Default Credentials. For more information, see Set up authentication for a local development environment.

# Ruby has limited support for asymmetric encryption operations. Specifically,
# public_encrypt() does not allow customizing the MGF hash algorithm. Thus, it
# is not currently possible to use Ruby core for asymmetric encryption
# operations on RSA keys from Cloud KMS.
#
# Third party libraries may provide the required functionality. Google does
# not endorse these external libraries.

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