Encrypting or Decrypting a Large Amount of Data

Scenario

If you want to encrypt or decrypt large volumes of data, such as pictures, videos, and database files, you can use envelope encryption, which allows you to encrypt and decrypt files without having to transfer a large amount of data over the network.

Encryption and Decryption Processes

• Large-size data encryption
  Figure 1 Encrypting a local file
  

  The process is as follows:

  1. Create a CMK in KMS.
  2. Call the create-datakey API of KMS to create a DEK. A plaintext DEK and a ciphertext DEK will be generated. The ciphertext DEK is generated when you use a CMK to encrypt the plaintext DEK.
  3. Use the plaintext DEK to encrypt a plaintext file, generating a ciphertext file.
  4. Store the ciphertext DEK and the ciphertext file together in a permanent storage device or a storage service.
• Large-size data decryption
  Figure 2 Decrypting a local file
  
  The process is as follows:

  1. Read the ciphertext DEK and the ciphertext file from the permanent storage device or storage service.
  2. Call the decrypt-datakey API of KMS and use the corresponding CMK (the one used for encrypting the DEK) to decrypt the ciphertext DEK. Then you get the plaintext DEK.

     If the CMK is deleted, the decryption will fail. Properly keep your CMKs.

  3. Use the plaintext DEK to decrypt the ciphertext file.

Encryption and Decryption APIs

You can use the following APIs to encrypt and decrypt data.

Encrypting a Local File

1. Create a CMK on the management console. For details, see .
2. Prepare basic authentication information.
   • ACCESS_KEY: access key of the HUAWEI CLOUD account
   • SECRET_ACCESS_KEY: secret access key of the HUAWEI CLOUD account
   • PROJECT_ID: project ID of a HUAWEI CLOUD site. For details, see .
   • KMS_ENDPOINT: endpoint for accessing KMS. For details, see .
3. Encrypt a local file.

   Example code is as follows.

   • CMK is the ID of the key created on the HUAWEI CLOUD management console.
   • The plaintext data file is FirstPlainFile.jpg.
   • The data file generated after encryption is SecondEncryptFile.jpg.

     import com.huaweicloud.sdk.core.auth.BasicCredentials;
     import com.huaweicloud.sdk.kms.v1.KmsClient;
     import com.huaweicloud.sdk.kms.v1.model.CreateDatakeyRequest;
     import com.huaweicloud.sdk.kms.v1.model.CreateDatakeyRequestBody;
     import com.huaweicloud.sdk.kms.v1.model.CreateDatakeyResponse;
     import com.huaweicloud.sdk.kms.v1.model.DecryptDatakeyRequest;
     import com.huaweicloud.sdk.kms.v1.model.DecryptDatakeyRequestBody;
     
     import javax.crypto.Cipher;
     import javax.crypto.spec.GCMParameterSpec;
     import javax.crypto.spec.SecretKeySpec;
     import java.io.BufferedInputStream;
     import java.io.BufferedOutputStream;
     import java.io.File;
     import java.io.FileInputStream;
     import java.io.FileOutputStream;
     import java.io.IOException;
     import java.nio.file.Files;
     import java.security.SecureRandom;
     
     /**
     * Use a DEK to encrypt and decrypt files.
     * To enable the assert syntax, add -ea to enable VM_OPTIONS.
      */
     public class FileStreamEncryptionExample {
     
         private static final String ACCESS_KEY = "<AccessKey>";
         private static final String SECRET_ACCESS_KEY = "<SecretAccessKey>";
         private static final String PROJECT_ID = "<ProjectID>";
         private static final String KMS_ENDPOINT = "<KmsEndpoint>";
     
     //Version of the KMS interface. Currently, the value is fixed to v1.0.
         private static final String KMS_INTERFACE_VERSION = "v1.0";
     
         /**
          * AES algorithm flags:
          * - AES_KEY_BIT_LENGTH: bit length of the AES256 key
           * - AES_KEY_BYTE_LENGTH: byte length of the AES256 key
          * - AES_ALG: AES256 algorithm. In this example, the Group mode is GCM and the padding mode is PKCS5Padding.
          * - AES_FLAG: AES algorithm flag
          * - GCM_TAG_LENGTH: GCM tag length
          * - GCM_IV_LENGTH: length of the GCM initial vector
          */
         private static final String AES_KEY_BIT_LENGTH = "256";
         private static final String AES_KEY_BYTE_LENGTH = "32";
         private static final String AES_ALG = "AES/GCM/PKCS5Padding";
         private static final String AES_FLAG = "AES";
         private static final int GCM_TAG_LENGTH = 16;
         private static final int GCM_IV_LENGTH = 12;
     
         public static void main(final String[] args) {
             // ID of the CMK you created on the HUAWEI CLOUD management console
             final String keyId = args[0];
     
             encryptFile(keyId);
         }
     
         /**
          * Using a DEK to encrypt and decrypt a file
          *
          * @param keyId: user CMK ID
          */
         static void encryptFile(String keyId) {
             // 1. Prepare the authentication information for accessing HUAWEI CLOUD.
             final BasicCredentials auth = new BasicCredentials().withAk(ACCESS_KEY).withSk(SECRET_ACCESS_KEY)
                     .withProjectId(PROJECT_ID);
     
             // 2. Initialize the SDK and transfer the authentication information and the address for the KMS to access the client.
             final KmsClient kmsClient = KmsClient.newBuilder().withCredential(auth).withEndpoint(KMS_ENDPOINT).build();
     
             // 3. Assemble the request message for creating a DEK.
             final CreateDatakeyRequest createDatakeyRequest = new CreateDatakeyRequest().withVersionId(KMS_INTERFACE_VERSION)
                     .withBody(new CreateDatakeyRequestBody().withKeyId(keyId).withDatakeyLength(AES_KEY_BIT_LENGTH));
     
             // 4. Create a DEK.
             final CreateDatakeyResponse createDatakeyResponse = kmsClient.createDatakey(createDatakeyRequest);
     
             // 5. Receive the created DEK information.
             // It is recommended that the ciphertext key and KeyId be stored locally so that the plaintext key can be easily obtained for data decryption.
             // The plaintext key should be used immediately after being created. Before using it, convert the hexadecimal plaintext key to a byte array.
             final String cipherText = createDatakeyResponse.getCipherText();
             final byte[] plainKey = hexToBytes(createDatakeyResponse.getPlainText());
     
             // 6. Prepare the file to be encrypted.
             // inFile: file to be encrypted
             // outEncryptFile: file generated after encryption
             
             final File inFile = new File("FirstPlainFile.jpg");
             final File outEncryptFile = new File("SecondEncryptFile.jpg");
     
             // 7. If the AES algorithm is used for encryption, you can create an initial vector.
             final byte[] iv = new byte[GCM_IV_LENGTH];
             final SecureRandom secureRandom = new SecureRandom();
             secureRandom.nextBytes(iv);
     
             // 8. Encrypt the file and store the encrypted file.
             doFileFinal(Cipher.ENCRYPT_MODE, inFile, outEncryptFile, plainKey, iv);
     
         }
     
         /**
          * Encrypting and decrypting a file
          *
          * @param cipherMode: Encryption mode. It can be Cipher.ENCRYPT_MODE or Cipher.DECRYPT_MODE.
          * @param infile: file to be encrypted or decrypted
          * @param outFile: file generated after encryption and decryption
          * @param keyPlain: plaintext key
          * @param iv: initial vector
          */
         static void doFileFinal(int cipherMode, File infile, File outFile, byte[] keyPlain, byte[] iv) {
     
             try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(infile));
                  BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(outFile))) {
                 final byte[] bytIn = new byte[(int) infile.length()];
                 final int fileLength = bis.read(bytIn);
     
                 assert fileLength > 0;
     
                 final SecretKeySpec secretKeySpec = new SecretKeySpec(keyPlain, AES_FLAG);
                 final Cipher cipher = Cipher.getInstance(AES_ALG);
                 final GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * Byte.SIZE, iv);
                 cipher.init(cipherMode, secretKeySpec, gcmParameterSpec);
                 final byte[] bytOut = cipher.doFinal(bytIn);
                 bos.write(bytOut);
             } catch (Exception e) {
                 throw new RuntimeException(e.getMessage());
             }
         }
     
     }

Decrypting a Local File

1. Prepare basic authentication information.
   • ACCESS_KEY: access key of the HUAWEI CLOUD account
   • SECRET_ACCESS_KEY: secret access key of the HUAWEI CLOUD account
   • PROJECT_ID: project ID of a HUAWEI CLOUD site. For details, see .
   • KMS_ENDPOINT: endpoint for accessing KMS. For details, see .
2. Decrypt a local file.

   Example code is as follows.

   • CMK is the ID of the key created on the HUAWEI CLOUD management console.
   • The data file generated after encryption is SecondEncryptFile.jpg.
   • The data file generated after encryption and decryption is ThirdDecryptFile.jpg.

     import com.huaweicloud.sdk.core.auth.BasicCredentials;
     import com.huaweicloud.sdk.kms.v1.KmsClient;
     import com.huaweicloud.sdk.kms.v1.model.CreateDatakeyRequest;
     import com.huaweicloud.sdk.kms.v1.model.CreateDatakeyRequestBody;
     import com.huaweicloud.sdk.kms.v1.model.CreateDatakeyResponse;
     import com.huaweicloud.sdk.kms.v1.model.DecryptDatakeyRequest;
     import com.huaweicloud.sdk.kms.v1.model.DecryptDatakeyRequestBody;
     
     import javax.crypto.Cipher;
     import javax.crypto.spec.GCMParameterSpec;
     import javax.crypto.spec.SecretKeySpec;
     import java.io.BufferedInputStream;
     import java.io.BufferedOutputStream;
     import java.io.File;
     import java.io.FileInputStream;
     import java.io.FileOutputStream;
     import java.io.IOException;
     import java.nio.file.Files;
     import java.security.SecureRandom;
     
     /**
     * Use a DEK to encrypt and decrypt files.
     * To enable the assert syntax, add -ea to enable VM_OPTIONS.
      */
     public class FileStreamEncryptionExample {
     
         private static final String ACCESS_KEY = "<AccessKey>";
         private static final String SECRET_ACCESS_KEY = "<SecretAccessKey>";
         private static final String PROJECT_ID = "<ProjectID>";
         private static final String KMS_ENDPOINT = "<KmsEndpoint>";
     
     //Version of the KMS interface. Currently, the value is fixed to v1.0.
         private static final String KMS_INTERFACE_VERSION = "v1.0";
     
         /**
          * AES algorithm flags:
          * - AES_KEY_BIT_LENGTH: bit length of the AES256 key
           * - AES_KEY_BYTE_LENGTH: byte length of the AES256 key
          * - AES_ALG: AES256 algorithm. In this example, the Group mode is GCM and the padding mode is PKCS5Padding.
          * - AES_FLAG: AES algorithm flag
          * - GCM_TAG_LENGTH: GCM tag length
          * - GCM_IV_LENGTH: length of the GCM initial vector
          */
         private static final String AES_KEY_BIT_LENGTH = "256";
         private static final String AES_KEY_BYTE_LENGTH = "32";
         private static final String AES_ALG = "AES/GCM/PKCS5Padding";
         private static final String AES_FLAG = "AES";
         private static final int GCM_TAG_LENGTH = 16;
         private static final int GCM_IV_LENGTH = 12;
     
         public static void main(final String[] args) {
             // ID of the CMK you created on the HUAWEI CLOUD management console
             final String keyId = args[0];
             // // Returned ciphertext DEK after DEK creation
             final String cipherText = args[1];
     
             decryptFile(keyId, cipherText);
         }
     
         /**
          * Using a DEK to encrypt and decrypt a file
          *
          * @param keyId: user CMK ID
          * @param cipherText: ciphertext data key
          */
         static void decryptFile(String keyId, String cipherText) {
             // 1. Prepare the authentication information for accessing HUAWEI CLOUD.
             final BasicCredentials auth = new BasicCredentials().withAk(ACCESS_KEY).withSk(SECRET_ACCESS_KEY)
                     .withProjectId(PROJECT_ID);
     
             // 2. Initialize the SDK and transfer the authentication information and the address for the KMS to access the client.
             final KmsClient kmsClient = KmsClient.newBuilder().withCredential(auth).withEndpoint(KMS_ENDPOINT).build();
     
             // 3. Prepare the file to be encrypted.
             // inFile: file to be encrypted
             // outEncryptFile: file generated after encryption
             // outDecryptFile: file generated after encryption and decryption
             final File inFile = new File("FirstPlainFile.jpg");
             final File outEncryptFile = new File("SecondEncryptFile.jpg");
             final File outDecryptFile = new File("ThirdDecryptFile.jpg");
     
             // 4. Use the same initial vector for AES encryption and decryption.
             final byte[] iv = new byte[GCM_IV_LENGTH];
             
             // 5. Assemble the request message for decrypting the DEK. cipherText is the ciphertext DEK returned after DEK creation.
             final DecryptDatakeyRequest decryptDatakeyRequest = new DecryptDatakeyRequest()
                     .withVersionId(KMS_INTERFACE_VERSION).withBody(new DecryptDatakeyRequestBody()
                             .withKeyId(keyId).withCipherText(cipherText).withDatakeyCipherLength(AES_KEY_BYTE_LENGTH));
     
             // 6. Decrypt the DEK and convert the returned hexadecimal plaintext key into a byte array.
             final byte[] decryptDataKey = hexToBytes(kmsClient.decryptDatakey(decryptDatakeyRequest).getDataKey());
     
             // 7. Decrypt the file and store the decrypted file.
     // iv at the end of the statement is the initial vector created in the encryption example.
             doFileFinal(Cipher.DECRYPT_MODE, outEncryptFile, outDecryptFile, decryptDataKey, iv);
     
             // 8. Compare the original file with the decrypted file.
             assert getFileSha256Sum(inFile).equals(getFileSha256Sum(outDecryptFile));
     
         }
     
         /**
          * Encrypting and decrypting a file
          *
          * @param cipherMode: Encryption mode. It can be Cipher.ENCRYPT_MODE or Cipher.DECRYPT_MODE.
          * @param infile: file to be encrypted or decrypted
          * @param outFile: file generated after encryption and decryption
          * @param keyPlain: plaintext key
          * @param iv: initial vector
          */
         static void doFileFinal(int cipherMode, File infile, File outFile, byte[] keyPlain, byte[] iv) {
     
             try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(infile));
                  BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(outFile))) {
                 final byte[] bytIn = new byte[(int) infile.length()];
                 final int fileLength = bis.read(bytIn);
     
                 assert fileLength > 0;
     
                 final SecretKeySpec secretKeySpec = new SecretKeySpec(keyPlain, AES_FLAG);
                 final Cipher cipher = Cipher.getInstance(AES_ALG);
                 final GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * Byte.SIZE, iv);
                 cipher.init(cipherMode, secretKeySpec, gcmParameterSpec);
                 final byte[] bytOut = cipher.doFinal(bytIn);
                 bos.write(bytOut);
             } catch (Exception e) {
                 throw new RuntimeException(e.getMessage());
             }
         }
     
         /**
     * Converting a hexadecimal string to a byte array
          *
          * @param hexString: a hexadecimal string
          * @return: byte array
          */
         static byte[] hexToBytes(String hexString) {
             final int stringLength = hexString.length();
             assert stringLength > 0;
             final byte[] result = new byte[stringLength / 2];
             int j = 0;
             for (int i = 0; i < stringLength; i += 2) {
                 result[j++] = (byte) Integer.parseInt(hexString.substring(i, i + 2), 16);
             }
             return result;
         }
     
         /**
          * Calculate the SHA256 digest of the file.
          *     
          * @param file
          * @return SHA256 digest
          */    
          static String getFileSha256Sum(File file) {
             int length;
             MessageDigest sha256;
             byte[] buffer = new byte[1024];
             try {
                 sha256 = MessageDigest.getInstance("SHA-256");
             } catch (NoSuchAlgorithmException e) {
                 throw new RuntimeException(e.getMessage());
             }
             try (FileInputStream inputStream = new FileInputStream(file)) {
                 while ((length = inputStream.read(buffer)) != -1) {
                     sha256.update(buffer, 0, length);
                 }
                 return new BigInteger(1, sha256.digest()).toString(16);
             } catch (IOException e) {
                 throw new RuntimeException(e.getMessage());
             }
         }
     }