Agent Skills: AWS SDK for Java 2.x - AWS KMS (Key Management Service)

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

Overview

Provides AWS KMS patterns using AWS SDK for Java 2.x. Covers key management, encryption/decryption, envelope encryption, digital signatures, and Spring Boot integration.

Instructions

1. Set Up IAM Permissions - Grant kms:* actions with least privilege
2. Create KMS Client - Instantiate KmsClient with region and credentials
3. Create Keys - Use createKey() → Verify key state is ENABLED before proceeding
4. Set Key Policies - Define key usage permissions → Test access before production
5. Encrypt Data - Use encrypt() for data <4KB; Verify ciphertext is not empty
6. Envelope Encryption - For larger data, use generateDataKey() → Verify data key generation succeeded
7. Digital Signatures - Create signing keys → Verify signatureValid=true after sign/verify
8. Key Rotation - Enable auto-rotation → Confirm rotation schedule is active

When to Use

• Creating/managing symmetric encryption keys for data protection
• Implementing envelope encryption for large data
• Generating data keys for local encryption with KMS-managed keys
• Setting up digital signatures with asymmetric keys
• Integrating encryption into Spring Boot applications

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) {
    try {
        GenerateDataKeyRequest keyRequest = GenerateDataKeyRequest.builder()
            .keyId(masterKeyId)
            .keySpec(DataKeySpec.AES_256)
            .build();

        GenerateDataKeyResponse keyResponse = kmsClient.generateDataKey(keyRequest);

        // Validate response
        if (keyResponse.plaintext() == null || keyResponse.ciphertextBlob() == null) {
            throw new IllegalStateException("Data key generation returned null");
        }

        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());

    } catch (KmsException e) {
        throw new RuntimeException("Envelope encryption failed: " + e.awsErrorDetails().errorCode(), e);
    }
}

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

        DecryptResponse keyDecryptResponse = kmsClient.decrypt(keyDecryptRequest);

        // Validate response
        if (keyDecryptResponse.plaintext() == null) {
            throw new IllegalStateException("Key decryption returned null");
        }

        byte[] decryptedData = decryptWithAES(
            encryptedEnvelope.encryptedData(),
            keyDecryptResponse.plaintext().asByteArray());

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

        return decryptedData;

    } catch (KmsException e) {
        throw new RuntimeException("Envelope decryption failed: " + e.awsErrorDetails().errorCode(), e);
    }
}

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