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Microsoft JDBC Driver for SQL Server. The Azure Key Vault feature in Microsoft JDBC Driver for SQL Server depends on Azure SDK for JAVA and Azure Active Directory Library For Java.
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/*
 * Microsoft JDBC Driver for SQL Server
 * 
 * Copyright(c) Microsoft Corporation All rights reserved.
 * 
 * This program is made available under the terms of the MIT License. See the LICENSE file in the project root for more information.
 */

package com.microsoft.sqlserver.jdbc;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;
import java.security.Signature;
import java.security.SignatureException;
import java.security.cert.X509Certificate;
import java.text.MessageFormat;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;

/**
 * 
 * This class holds information about the certificate
 *
 */
class CertificateDetails {
    X509Certificate certificate;
    Key privateKey;

    CertificateDetails(X509Certificate certificate,
            Key privateKey) {
        this.certificate = certificate;
        this.privateKey = privateKey;
    }
}

class KeyStoreProviderCommon {

    static final String rsaEncryptionAlgorithmWithOAEP = "RSA_OAEP";
    static byte[] version = new byte[] {0x01};

    static void validateEncryptionAlgorithm(String encryptionAlgorithm,
            boolean isEncrypt) throws SQLServerException {
        String errString = isEncrypt ? "R_NullKeyEncryptionAlgorithm" : "R_NullKeyEncryptionAlgorithmInternal";
        if (null == encryptionAlgorithm) {

            throw new SQLServerException(null, SQLServerException.getErrString(errString), null, 0, false);

        }

        errString = isEncrypt ? "R_InvalidKeyEncryptionAlgorithm" : "R_InvalidKeyEncryptionAlgorithmInternal";
        if (!rsaEncryptionAlgorithmWithOAEP.equalsIgnoreCase(encryptionAlgorithm.trim())) {

            MessageFormat form = new MessageFormat(SQLServerException.getErrString(errString));
            Object[] msgArgs = {encryptionAlgorithm, rsaEncryptionAlgorithmWithOAEP};
            throw new SQLServerException(form.format(msgArgs), null);

        }
    }

    static void validateNonEmptyMasterKeyPath(String masterKeyPath) throws SQLServerException {
        if (null == masterKeyPath || masterKeyPath.trim().length() == 0) {
            throw new SQLServerException(null, SQLServerException.getErrString("R_InvalidMasterKeyDetails"), null, 0, false);
        }
    }

    static byte[] decryptColumnEncryptionKey(String masterKeyPath,
            String encryptionAlgorithm,
            byte[] encryptedColumnEncryptionKey,
            CertificateDetails certificateDetails) throws SQLServerException {
        if (null == encryptedColumnEncryptionKey) {

            throw new SQLServerException(null, SQLServerException.getErrString("R_NullEncryptedColumnEncryptionKey"), null, 0, false);

        }
        else if (0 == encryptedColumnEncryptionKey.length) {

            throw new SQLServerException(null, SQLServerException.getErrString("R_EmptyEncryptedColumnEncryptionKey"), null, 0, false);

        }

        validateEncryptionAlgorithm(encryptionAlgorithm, false);

        int currentIndex = version.length;
        int keyPathLength = convertTwoBytesToShort(encryptedColumnEncryptionKey, currentIndex);
        // We just read 2 bytes
        currentIndex += 2;

        // Get ciphertext length
        int cipherTextLength = convertTwoBytesToShort(encryptedColumnEncryptionKey, currentIndex);
        currentIndex += 2;

        currentIndex += keyPathLength;

        int signatureLength = encryptedColumnEncryptionKey.length - currentIndex - cipherTextLength;

        // Get ciphertext
        byte[] cipherText = new byte[cipherTextLength];
        System.arraycopy(encryptedColumnEncryptionKey, currentIndex, cipherText, 0, cipherTextLength);
        currentIndex += cipherTextLength;

        byte[] signature = new byte[signatureLength];
        System.arraycopy(encryptedColumnEncryptionKey, currentIndex, signature, 0, signatureLength);

        byte[] hash = new byte[encryptedColumnEncryptionKey.length - signature.length];

        System.arraycopy(encryptedColumnEncryptionKey, 0, hash, 0, encryptedColumnEncryptionKey.length - signature.length);

        if (!verifyRSASignature(hash, signature, certificateDetails.certificate, masterKeyPath)) {
            MessageFormat form = new MessageFormat(SQLServerException.getErrString("R_InvalidCertificateSignature"));
            Object[] msgArgs = {masterKeyPath};
            throw new SQLServerException(form.format(msgArgs), null);
        }

        byte[] plainCEK = decryptRSAOAEP(cipherText, certificateDetails);

        return plainCEK;
    }

    private static byte[] decryptRSAOAEP(byte[] cipherText,
            CertificateDetails certificateDetails) throws SQLServerException {
        byte[] plainCEK = null;
        try {
            Cipher rsa = Cipher.getInstance("RSA/ECB/OAEPWithSHA-1AndMGF1Padding");
            rsa.init(Cipher.DECRYPT_MODE, certificateDetails.privateKey);
            rsa.update(cipherText);
            plainCEK = rsa.doFinal();
        }
        catch (InvalidKeyException | NoSuchAlgorithmException | NoSuchPaddingException | IllegalBlockSizeException | BadPaddingException e) {
            MessageFormat form = new MessageFormat(SQLServerException.getErrString("R_CEKDecryptionFailed"));
            Object[] msgArgs = {e.getMessage()};
            throw new SQLServerException(form.format(msgArgs), e);
        }

        return plainCEK;

    }

    private static boolean verifyRSASignature(byte[] hash,
            byte[] signature,
            X509Certificate certificate,
            String masterKeyPath) throws SQLServerException {
        Signature signVerify;
        boolean verificationSucess = false;
        try {
            signVerify = Signature.getInstance("SHA256withRSA");
            signVerify.initVerify(certificate.getPublicKey());
            signVerify.update(hash);
            verificationSucess = signVerify.verify(signature);
        }
        catch (InvalidKeyException | NoSuchAlgorithmException | SignatureException e) {
            MessageFormat form = new MessageFormat(SQLServerException.getErrString("R_InvalidCertificateSignature"));
            Object[] msgArgs = {masterKeyPath};
            throw new SQLServerException(form.format(msgArgs), e);
        }

        return verificationSucess;

    }

    private static short convertTwoBytesToShort(byte[] input,
            int index) throws SQLServerException {

        short shortVal;
        if (index + 1 >= input.length) {
            throw new SQLServerException(null, SQLServerException.getErrString("R_ByteToShortConversion"), null, 0, false);
        }
        ByteBuffer byteBuffer = ByteBuffer.allocate(2);
        byteBuffer.order(ByteOrder.LITTLE_ENDIAN);
        byteBuffer.put(input[index]);
        byteBuffer.put(input[index + 1]);
        shortVal = byteBuffer.getShort(0);
        return shortVal;

    }
}