https://github.com/aws/aws-sdk-java/tree/master/aws-java-sdk-s3
https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/CryptoMode.java
    AES/GCM (symmetric)

https://github.com/aws/aws-sdk-java/tree/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto

https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto/ContentCryptoScheme.java
    ??? RSA DSA ??? is only for key-wrapping
    AES_CBC
    AES_GCM
    AES_CTR
    https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto/AesCbc.java
    https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto/AesCtr.java
    https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto/AesGcm.java

https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto/S3CryptoScheme.java
/**
 * S3 cryptographic scheme that includes the content crypto scheme and key
 * wrapping scheme (for the content-encrypting-key).
 */
final class S3CryptoScheme {
    // http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html
    // http://docs.oracle.com/javase/7/docs/technotes/guides/security/crypto/CryptoSpec.html#Key
    static final String AES = "AES";
    static final String RSA = "RSA";
    private final S3KeyWrapScheme kwScheme;

    private final ContentCryptoScheme contentCryptoScheme;

    private S3CryptoScheme(ContentCryptoScheme contentCryptoScheme,
                           S3KeyWrapScheme kwScheme) {
        this.contentCryptoScheme = contentCryptoScheme;
        this.kwScheme = kwScheme;
    }

    ContentCryptoScheme getContentCryptoScheme() {
        return contentCryptoScheme;
    }

    S3KeyWrapScheme getKeyWrapScheme() { return kwScheme; }

    /**
     * Convenient method.
     */
    static boolean isAesGcm(String cipherAlgorithm) {
        return ContentCryptoScheme.AES_GCM.getCipherAlgorithm().equals(cipherAlgorithm);
    }

    static S3CryptoScheme from(CryptoMode mode) {
        switch (mode) {
            case EncryptionOnly:
                return new S3CryptoScheme(ContentCryptoScheme.AES_CBC,
                                          S3KeyWrapScheme.NONE);
            case AuthenticatedEncryption:
            case StrictAuthenticatedEncryption:
                return new S3CryptoScheme(ContentCryptoScheme.AES_GCM,
                                          new S3KeyWrapScheme());
            default:
                throw new IllegalStateException();
        }
    }
}

https://github.com/aws/aws-sdk-java/blob/master/aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/internal/crypto/S3KeyWrapScheme.java

class S3KeyWrapScheme {
    /**
     * Used for backward compatibility where the encryption only mode has no
     * explicit key wrapping scheme.
     */
    static final S3KeyWrapScheme NONE = new S3KeyWrapScheme() {
        String getKeyWrapAlgorithm(Key key) {
            return null;
        }
        @Override public String toString() { return "NONE"; }
    };
    public static final String AESWrap = "AESWrap"; 
    public static final String RSA_ECB_OAEPWithSHA256AndMGF1Padding = "RSA/ECB/OAEPWithSHA-256AndMGF1Padding";

    /**
     * @param kek
     *            the key encrypting key, which is either an AES key or a public
     *            key
     */
    String getKeyWrapAlgorithm(Key kek) {
        String algorithm = kek.getAlgorithm();
        if (S3CryptoScheme.AES.equals(algorithm)) {
            return AESWrap;
        }
        if (S3CryptoScheme.RSA.equals(algorithm)) {
            if (CryptoRuntime.isRsaKeyWrapAvailable())
                return RSA_ECB_OAEPWithSHA256AndMGF1Padding;
        }
        return null;
    }

    @Override public String toString() { return "S3KeyWrapScheme"; }
}


/**
 * A proxy cryptographic module used to dispatch method calls to the appropriate
 * underlying cryptographic module depending on the current configuration.
 */
public class CryptoModuleDispatcher extends S3CryptoModule<MultipartUploadContext> {
    private final CryptoMode defaultCryptoMode;
    /** Encryption only (EO) cryptographic module. */
    private final S3CryptoModuleEO eo;
    /** Authenticated encryption (AE) cryptographic module. */
    private final S3CryptoModuleAE ae;

    public CryptoModuleDispatcher(AWSKMS kms, S3Direct s3,
                                  AWSCredentialsProvider credentialsProvider,
                                  EncryptionMaterialsProvider encryptionMaterialsProvider,
                                  CryptoConfiguration cryptoConfig) {
        cryptoConfig = cryptoConfig.clone();    // make a clone
        CryptoMode cryptoMode = cryptoConfig.getCryptoMode();
        if (cryptoMode == null) {
            cryptoMode = EncryptionOnly;
            cryptoConfig.setCryptoMode(cryptoMode); // defaults to EO
        }
        cryptoConfig = cryptoConfig.readOnly(); // make read-only
        this.defaultCryptoMode = cryptoConfig.getCryptoMode();
        switch(this.defaultCryptoMode) {
            case StrictAuthenticatedEncryption:
                this.ae = new S3CryptoModuleAEStrict(kms, s3, credentialsProvider,
                        encryptionMaterialsProvider,
                        cryptoConfig);
                this.eo = null;
                break;
            case AuthenticatedEncryption:
                this.ae = new S3CryptoModuleAE(kms, s3, credentialsProvider,
                        encryptionMaterialsProvider,
                        cryptoConfig);
                this.eo = null;
                break;
            case EncryptionOnly:
                this.eo = new S3CryptoModuleEO(kms, s3, credentialsProvider,
                        encryptionMaterialsProvider,
                        cryptoConfig);
                CryptoConfiguration aeConfig = cryptoConfig.clone();
                try {
                    aeConfig.setCryptoMode(AuthenticatedEncryption);
                } catch(UnsupportedOperationException ex) {
                    // BC not available during runtime; but EO can still work.
                    // Hence ignoring.
                }
                this.ae = new S3CryptoModuleAE(kms, s3, credentialsProvider,
                    encryptionMaterialsProvider,
                    aeConfig.readOnly());
                break;
            default:
                throw new IllegalStateException();
        }
    }
    ...
}

src/main/java/com/amazonaws/services/s3/internal/crypto/S3CryptoModuleAEStrict.java

/**
 * Strict Authenticated encryption (AE) cryptographic module for the S3
 * encryption client.
 */
class S3CryptoModuleAEStrict extends S3CryptoModuleAE {
    /**
     * @param cryptoConfig a read-only copy of the crypto configuration.
     */
    S3CryptoModuleAEStrict(AWSKMS kms, S3Direct s3,
                           AWSCredentialsProvider credentialsProvider,
                           EncryptionMaterialsProvider encryptionMaterialsProvider,
                           CryptoConfiguration cryptoConfig) {
        super(kms, s3, credentialsProvider, encryptionMaterialsProvider,
                cryptoConfig);
        if (cryptoConfig.getCryptoMode() != StrictAuthenticatedEncryption)
            throw new IllegalArgumentException();
    }

    protected final boolean isStrict() {
        return true;
    }

    protected void securityCheck(ContentCryptoMaterial cekMaterial,
            S3ObjectWrapper retrieved) {
        if (!ContentCryptoScheme.AES_GCM.equals(cekMaterial.getContentCryptoScheme())) {
            throw new SecurityException("S3 object [bucket: "
                    + retrieved.getBucketName() + ", key: "
                    + retrieved.getKey()
                    + "] not encrypted using authenticated encryption");
        }
    }
}