AWS SDK for Java 2.x – AWS KMS (Key Management Service)

Overview

This skill provides comprehensive patterns for AWS Key Management Service (KMS) using AWS SDK for Java 2.x. Focus on implementing secure encryption solutions with proper key management, envelope encryption, and Spring Boot integration patterns.

Instructions

Follow these steps to work with AWS KMS:

1. Set Up IAM Permissions – Grant kms:* actions as needed with least privilege
2. Create KMS Client – Instantiate KmsClient with proper region and credentials
3. Create or Import Keys – Use createKey() or import existing key material
4. Set Key Policies – Define who can use/manage each key
5. Encrypt Data – Use encrypt() for small data (<4KB) directly
6. Use Envelope Encryption – For larger data, generate and encrypt data keys
7. Implement Digital Signatures – Create signing keys and verify signatures
8. Rotate Keys – Enable automatic key rotation for compliance

When to Use

Use this skill when:

• Creating and managing symmetric encryption keys for data protection
• Implementing client-side encryption and envelope encryption patterns
• Generating data keys for local data encryption with KMS-managed keys
• Setting up digital signatures and verification with asymmetric keys
• Integrating encryption capabilities into Spring Boot applications
• Implementing secure key lifecycle management
• Setting up key rotation policies and access controls

Dependencies

Maven

<dependency>
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>kms</artifactId>
</dependency>

Gradle

implementation 'software.amazon.awssdk:kms:2.x.x'

Client Setup

Basic Synchronous Client

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.kms.KmsClient;

KmsClient kmsClient = KmsClient.builder()
    .region(Region.US_EAST_1)
    .build();

Basic Asynchronous Client

import software.amazon.awssdk.services.kms.KmsAsyncClient;

KmsAsyncClient kmsAsyncClient = KmsAsyncClient.builder()
    .region(Region.US_EAST_1)
    .build();

Advanced Client Configuration

KmsClient kmsClient = KmsClient.builder()
    .region(Region.of(System.getenv("AWS_REGION")))
    .credentialsProvider(DefaultCredentialsProvider.create())
    .overrideConfiguration(c -> c.retryPolicy(RetryPolicy.builder()
        .numRetries(3)
        .build()))
    .build();

Basic Key Management

Create Encryption Key

public String createEncryptionKey(KmsClient kmsClient, String description) {
    CreateKeyRequest request = CreateKeyRequest.builder()
        .description(description)
        .keyUsage(KeyUsageType.ENCRYPT_DECRYPT)
        .build();

    CreateKeyResponse response = kmsClient.createKey(request);
    return response.keyMetadata().keyId();
}

Describe Key

public KeyMetadata getKeyMetadata(KmsClient kmsClient, String keyId) {
    DescribeKeyRequest request = DescribeKeyRequest.builder()
        .keyId(keyId)
        .build();

    return kmsClient.describeKey(request).keyMetadata();
}

Enable/Disable Key

public void toggleKeyState(KmsClient kmsClient, String keyId, boolean enable) {
    if (enable) {
        kmsClient.enableKey(EnableKeyRequest.builder().keyId(keyId).build());
    } else {
        kmsClient.disableKey(DisableKeyRequest.builder().keyId(keyId).build());
    }
}

Basic Encryption and Decryption

Encrypt Data

public String encryptData(KmsClient kmsClient, String keyId, String plaintext) {
    SdkBytes plaintextBytes = SdkBytes.fromString(plaintext, StandardCharsets.UTF_8);

    EncryptRequest request = EncryptRequest.builder()
        .keyId(keyId)
        .plaintext(plaintextBytes)
        .build();

    EncryptResponse response = kmsClient.encrypt(request);
    return Base64.getEncoder().encodeToString(
        response.ciphertextBlob().asByteArray());
}

Decrypt Data

public String decryptData(KmsClient kmsClient, String ciphertextBase64) {
    byte[] ciphertext = Base64.getDecoder().decode(ciphertextBase64);
    SdkBytes ciphertextBytes = SdkBytes.fromByteArray(ciphertext);

    DecryptRequest request = DecryptRequest.builder()
        .ciphertextBlob(ciphertextBytes)
        .build();

    DecryptResponse response = kmsClient.decrypt(request);
    return response.plaintext().asString(StandardCharsets.UTF_8);
}

Envelope Encryption Pattern

Generate and Use Data Key

public DataKeyResult encryptWithEnvelope(KmsClient kmsClient, String masterKeyId, byte[] data) {
    // Generate data key
    GenerateDataKeyRequest keyRequest = GenerateDataKeyRequest.builder()
        .keyId(masterKeyId)
        .keySpec(DataKeySpec.AES_256)
        .build();

    GenerateDataKeyResponse keyResponse = kmsClient.generateDataKey(keyRequest);

    // Encrypt data with data key
    byte[] encryptedData = encryptWithAES(data,
        keyResponse.plaintext().asByteArray());

    // Clear plaintext key from memory
    Arrays.fill(keyResponse.plaintext().asByteArray(), (byte) 0);

    return new DataKeyResult(
        encryptedData,
        keyResponse.ciphertextBlob().asByteArray());
}

public byte[] decryptWithEnvelope(KmsClient kmsClient,
                                  DataKeyResult encryptedEnvelope) {
    // Decrypt data key
    DecryptRequest keyDecryptRequest = DecryptRequest.builder()
        .ciphertextBlob(SdkBytes.fromByteArray(
            encryptedEnvelope.encryptedKey()))
        .build();

    DecryptResponse keyDecryptResponse = kmsClient.decrypt(keyDecryptRequest);

    // Decrypt data with decrypted key
    byte[] decryptedData = decryptWithAES(
        encryptedEnvelope.encryptedData(),
        keyDecryptResponse.plaintext().asByteArray());

    // Clear plaintext key from memory
    Arrays.fill(keyDecryptResponse.plaintext().asByteArray(), (byte) 0);

    return decryptedData;
}

Digital Signatures

Create Signing Key and Sign Data

public String createAndSignData(KmsClient kmsClient, String description, String message) {
    // Create signing key
    CreateKeyRequest keyRequest = CreateKeyRequest.builder()
        .description(description)
        .keySpec(KeySpec.RSA_2048)
        .keyUsage(KeyUsageType.SIGN_VERIFY)
        .build();

    CreateKeyResponse keyResponse = kmsClient.createKey(keyRequest);
    String keyId = keyResponse.keyMetadata().keyId();

    // Sign data
    SignRequest signRequest = SignRequest.builder()
        .keyId(keyId)
        .message(SdkBytes.fromString(message, StandardCharsets.UTF_8))
        .signingAlgorithm(SigningAlgorithmSpec.RSASSA_PSS_SHA_256)
        .build();

    SignResponse signResponse = kmsClient.sign(signRequest);
    return Base64.getEncoder().encodeToString(
        signResponse.signature().asByteArray());
}

Verify Signature

public boolean verifySignature(KmsClient kmsClient,
                             String keyId,
                             String message,
                             String signatureBase64) {
    byte[] signature = Base64.getDecoder().decode(signatureBase64);

    VerifyRequest verifyRequest = VerifyRequest.builder()
        .keyId(keyId)
        .message(SdkBytes.fromString(message, StandardCharsets.UTF_8))
        .signature(SdkBytes.fromByteArray(signature))
        .signingAlgorithm(SigningAlgorithmSpec.RSASSA_PSS_SHA_256)
        .build();

    VerifyResponse verifyResponse = kmsClient.verify(verifyRequest);
    return verifyResponse.signatureValid();
}

Spring Boot Integration

Configuration Class

@Configuration
public class KmsConfiguration {

    @Bean
    public KmsClient kmsClient() {
        return KmsClient.builder()
            .region(Region.US_EAST_1)
            .build();
    }

    @Bean
    public KmsAsyncClient kmsAsyncClient() {
        return KmsAsyncClient.builder()
            .region(Region.US_EAST_1)
            .build();
    }
}

Encryption Service

@Service
@RequiredArgsConstructor
public class KmsEncryptionService {

    private final KmsClient kmsClient;

    @Value("${kms.encryption-key-id}")
    private String keyId;

    public String encrypt(String plaintext) {
        try {
            EncryptRequest request = EncryptRequest.builder()
                .keyId(keyId)
                .plaintext(SdkBytes.fromString(plaintext, StandardCharsets.UTF_8))
                .build();

            EncryptResponse response = kmsClient.encrypt(request);
            return Base64.getEncoder().encodeToString(
                response.ciphertextBlob().asByteArray());

        } catch (KmsException e) {
            throw new RuntimeException("Encryption failed", e);
        }
    }

    public String decrypt(String ciphertextBase64) {
        try {
            byte[] ciphertext = Base64.getDecoder().decode(ciphertextBase64);

            DecryptRequest request = DecryptRequest.builder()
                .ciphertextBlob(SdkBytes.fromByteArray(ciphertext))
                .build();

            DecryptResponse response = kmsClient.decrypt(request);
            return response.plaintext().asString(StandardCharsets.UTF_8);

        } catch (KmsException e) {
            throw new RuntimeException("Decryption failed", e);
        }
    }
}

Examples

Basic Encryption Example

public class BasicEncryptionExample {
    public static void main(String[] args) {
        KmsClient kmsClient = KmsClient.builder()
            .region(Region.US_EAST_1)
            .build();

        // Create key
        String keyId = createEncryptionKey(kmsClient, "Example encryption key");
        System.out.println("Created key: " + keyId);

        // Encrypt and decrypt
        String plaintext = "Hello, World!";
        String encrypted = encryptData(kmsClient, keyId, plaintext);
        String decrypted = decryptData(kmsClient, encrypted);

        System.out.println("Original: " + plaintext);
        System.out.println("Decrypted: " + decrypted);
    }
}

Envelope Encryption Example

public class EnvelopeEncryptionExample {
    public static void main(String[] args) {
        KmsClient kmsClient = KmsClient.builder()
            .region(Region.US_EAST_1)
            .build();

        String masterKeyId = "alias/your-master-key";
        String largeData = "This is a large amount of data that needs encryption...";
        byte[] data = largeData.getBytes(StandardCharsets.UTF_8);

        // Encrypt using envelope pattern
        DataKeyResult encryptedEnvelope = encryptWithEnvelope(
            kmsClient, masterKeyId, data);

        // Decrypt
        byte[] decryptedData = decryptWithEnvelope(
            kmsClient, encryptedEnvelope);

        String result = new String(decryptedData, StandardCharsets.UTF_8);
        System.out.println("Decrypted: " + result);
    }
}

Best Practices

Security

• Always use envelope encryption for large data – Encrypt data locally and only encrypt the data key with KMS
• Use encryption context – Add contextual information to track and audit usage
• Never log sensitive data – Avoid logging plaintext or encryption keys
• Implement proper key lifecycle – Enable automatic rotation and set deletion policies
• Use separate keys for different purposes – Don’t reuse keys across multiple applications

Performance

• Cache encrypted data keys – Reduce KMS API calls by caching data keys
• Use async operations – Leverage async clients for non-blocking I/O
• Reuse client instances – Don’t create new clients for each operation
• Implement connection pooling – Configure proper connection pooling settings

Error Handling

• Implement retry logic – Handle throttling exceptions with exponential backoff
• Check key states – Verify key is enabled before performing operations
• Use circuit breakers – Prevent cascading failures during KMS outages
• Log errors comprehensively – Include KMS error codes and context

References

For detailed implementation patterns, advanced techniques, and comprehensive examples:

• @references/technical-guide.md – Complete technical implementation patterns
• @references/spring-boot-integration.md – Spring Boot integration patterns
• @references/testing.md – Testing strategies and examples
• @references/best-practices.md – Security and operational best practices

Related Skills

• @aws-sdk-java-v2-core – Core AWS SDK patterns and configuration
• @aws-sdk-java-v2-dynamodb – DynamoDB integration patterns
• @aws-sdk-java-v2-secrets-manager – Secrets management patterns
• @spring-boot-dependency-injection – Spring dependency injection patterns

External References

• AWS KMS Developer Guide
• AWS SDK for Java 2.x Documentation
• KMS Best Practices

Constraints and Warnings

• Data Size Limit: Direct encryption limited to 4KB; use envelope encryption for larger data
• Key Usage Limits: KMS has quotas on API calls per second
• Key Material: Imported key material cannot be managed by AWS for rotation
• Key Deletion: Key deletion requires 7-30 day waiting period
• Regional Boundaries: KMS keys cannot be used across regions
• Cost Considerations: KMS charges per API call and for key storage
• Asymmetric Keys: Not all regions support asymmetric key types
• Key Policies: Changes to key policies require careful IAM review
• Envelope Encryption: Proper implementation required for data key security
• Logging: Enable CloudTrail to audit all KMS API usage