Recurring Revenue Authors: Pat Romanski, Hollis Tibbetts, Elizabeth White, Liz McMillan, Dana Gardner

Related Topics: Java IoT, Industrial IoT, Microservices Expo, IoT User Interface, Recurring Revenue, Cloud Security

Java IoT: Article

Java Cryptography | Part 2

Encryption and Digital Signatures

In today's environment, information security is crucial for everyone. Security needs vary widely from protecting social security numbers to guarding corporate strategy. Information espionage can occur at all levels. A human resources employee or manager takes employee personnel files home to work on them and unfortunately loses them or they get stolen. An employee's notes to a supervisor regarding a case are intercepted and read via monitoring software by an outside hacker. The resulting damages can be costly and could be avoided by protecting assets with encryption technology.

This article demonstrates the implementation of the Cryptography header cited in the previous article and illustrates how to encrypt and digitally sign files using a hybrid combination of asymmetric public/private key encryption and symmetric encryption. A symmetric key is used to encrypt the file and the asymmetric public key encrypts the symmetric key. The asymmetric private key decrypts the symmetric key which in turn is used to decrypt the encrypted file.

Figure 1. Asymmetric Key Encryption Functions

The same pair of encryption keys can be used with digital signatures. The private key is used to sign a file and generate a digital signature. The public key is used to verify the authenticity of the signature. The encrypted symmetric key and digital signature along with additional information are stored in the Cryptography header which is affixed to the front of the encrypted file.

Figure 2. Asymmetric Key Signature Functions

The encryption technique requires the Java libraries developed by the Legion of the Bouncy Castle (www.bouncycastle.org). The Bouncy Castle jars, bcprov-jdk15on-147.jar and bcpkix-jdk15on-147.jar, contain all the methods required to encrypt, decrypt, sign and verify a digital signature. The following Java code snippet loads the BouncyCastle provider, which implements the Java Cryptography Security services such as algorithms and key generation.

import org.bouncycastle.jce.provider.*;
java.security.Security.addProvider(new BouncyCastleProvider());

Generating Public/Private Encryption Keys
A Java key store is a password protected file that contains the user's pair of asymmetric encryption keys and certificate. Each key store associates a unique alias to each pair of encryption keys it contains. The Java key store file name is generated as alias_nnnn.jks, for example, jxdoe_fc99.jks. Certificates hold the public encryption key that allows a file to be encrypted for a specific individual who holds the matching deciphering key. The following steps along with Java code snippets illustrate how to generate the pair of public/private keys and store them in a key store file, using the Bouncy Castle cryptography library.

Figure 3. Pair of Asymmetric Keys

Step 1: Create an instance of the KeyPairGenerator class specifying the RSA asymmetric algorithm and Bouncy Castle provider. Generate a 1024-bit asymmetric public and private key pair to be stored in a password protected key store file.

//-Generate the pair of Asymmetric Encryption Keys (public/private)
KeyPairGenerator tKPGen = KeyPairGenerator.getInstance("RSA", "BC");
SecureRandom tRandom = new SecureRandom();
tKPGen.initialize(1024, tRandom); //-Key size in bits
KeyPair tPair = tKPGen.generateKeyPair();
PublicKey tUserPubKey = tPair.getPublic();
PrivateKey tUserPrivKey = tPair.getPrivate();

Step 2: Extract four hex digits from the public key to create a unique alias for the filename of the certificate and key store.

KeyFactory tKeyFactory = KeyFactory.getInstance("RSA");
RSAPublicKeySpec tPubSpec =
tKeyFactory.getKeySpec(tUserPubKey, RSAPublicKeySpec.class);
String t4HexDigits = tPubSpec.getModulus().toString(16).substring(8,12);
String tUniqueAlias = "jxdoe_" + t4HexDigits;

Step 3: Create a certificate to hold the asymmetric public key that can be used to encrypt your confidential information or distributed to others for exchanging encrypted files.

JcaContentSignerBuilder tSignBldr =
new JcaContentSignerBuilder("SHA512WithRSAEncryption");
ContentSigner tSigGen = tSignBldr.build(tUserPrivKey);
X500NameBuilder tBuilder = new X500NameBuilder(BCStyle.INSTANCE);
tBuilder.addRDN(BCStyle.CN, "John X. Doe"); //-Common name
tBuilder.addRDN(BCStyle.E, "[email protected]"); //-E-mail
tBuilder.addRDN(BCStyle.L, "Detroit"); //-City/Locale
tBuilder.addRDN(BCStyle.ST, "MI"); //-State
org.bouncycastle.asn1.x500.X500Name tX500Name = tBuilder.build();
Calendar tCal = Calendar.getInstance();
tCal.set(2014, 12, 31);
java.util.Date tEnd = tCal.getTime(); //-Ending date for certificate
X509v3CertificateBuilder tV3CertGen = new JcaX509v3CertificateBuilder(
tX500Name,  //-Issuer is same as Subject
BigInteger.valueOf( System.currentTimeMillis()), //-Serial Number
new java.util.Date(), //-Date start
tEnd,     //-Date end
tX500Name,  //-Subject
tUserPubKey); //-Public RSA Key
X509CertificateHolder tCertHolder = tV3CertGen.build(tSigGen);
JcaX509CertificateConverter tConverter =
new JcaX509CertificateConverter().setProvider("BC");
X509Certificate tCert = tConverter.getCertificate(tCertHolder);

Step 4: Save the certificate to disk so that it can be used for encrypting your own personal information or distributing to others.

byte[] tBA = tCert.getEncoded();
File tFile = new File("C:\\" + tUniqueAlias + ".cer");
FileOutputStream tFOS = new FileOutputStream(tFile);

Step 5: Insert the certificate into an array of X509 certificates called a chain. Create a password protected key store file to hold the private key and certificate chain and save it to disk. The key store saves the private key and certificate chain as an entry at a unique key called the alias and is password protected as well. The same password will be used to protect the entry and key store.

KeyStore tKStore = KeyStore.getInstance("JKS", "SUN");
tKStore.load(null, null); //-Initialize KeyStore
X509Certificate[] tChain = new X509Certificate[1];
tChain[0] = tCert; //-Put certificate into a chain
String tKSFileName = "C:\\" + tUniqueAlias + ".jks";
tFOS = new FileOutputStream(tKSFileName);
tKStore.store(tFOS, "password".toCharArray()); //-Set KeyStore password

Encryption with Digital Signature
Encryption is used to protect a file from being read by unauthorized eyes by altering its original contents to an indecipherable form. Using a hybrid encryption technique, the file is encrypted with an AES (Advanced Encryption Standard) symmetric key and the key is encrypted using RSA asymmetric encryption. In addition to protecting a file, a digital signature can be added to provide authentication of the originator who sent/encrypted the file. The digital signature is a unique number that is generated using the owner's asymmetric private key and a hash algorithm on the encrypted file contents. The following steps along with Java code snippets illustrate how to encrypt and add a digital signature to a file.

Figure 4: AES Symmetric Key

Step 1: Let's assume you want to encrypt and digitally sign the file, C:\sampleFile.txt. Dynamically generate a symmetric "secret" key using the Java class, KeyGenerator. The symmetric key will be used to encrypt the file. The Java class KeyGenerator is instantiated using the symmetric algorithm, "AES", and provider, BouncyCastle("BC"). The instance of KeyGenerator is initialized with a secure random seed and the maximum key size in bits allowed by your country. The following code illustrates how to generate a symmetric key.

KeyGenerator tKeyGen = KeyGenerator.getInstance("AES", "BC");
SecureRandom tRandom2 = new SecureRandom();
tKeyGen.init(256, tRandom2); //-256 bit AES symmetric key
SecretKey tSymmetricKey = tKeyGen.generateKey();

Step 2: Generate a Cryptography header that stores cryptographic information used to later decrypt the file and verify the digital signature. Save the symmetric algorithm, mode and padding in the header. The following code illustrates the header instantiation and initialization.

CryptoHeader tHead = new CryptoHeader();
tHead.symKeyAlg(1);   //-AES
tHead.symKeyMode(5);  //-CTR Segmented Integer Counter mode
tHead.symKeyPadding(2); //-PKCS7 Padding
tHead.decryptID(tUniqueAlias); //-Owner's unique alias

Step 3: Load the owner's certificate and extract the public key. You can also load another person's certificate if you are encrypting the file for someone other than yourself. The public key will be used to encrypt the symmetric key.

InputStream tCertIS = new FileInputStream("C:\\" +tUniqueAlias+ ".cer");
CertificateFactory tFactory = CertificateFactory.getInstance("X.509","BC");
X509Certificate tCertificate =
PublicKey tPubKey = tCertificate.getPublicKey();

Step 4: Generate a Java Cipher object and initialize it using the owner's or another person's asymmetric public key extracted from the certificate and set its mode to "Cipher.WRAP_MODE". Use the Java Cipher and public key to encrypt and wrap the symmetric key. Store the wrapped encrypted key in the header and its length.

Cipher tCipherRSA = Cipher.getInstance("RSA", "BC");
tCipherRSA.init(Cipher.WRAP_MODE, (PublicKey)tPubKey);
byte[] tWrappedKey = tCipherRSA.wrap(tSymmetricKey);

Figure 5. Wrap Symmetric Key

Step 5: Generate an initialization vector if required by the symmetric mode chosen to encrypt the file. AES is a block cipher symmetric algorithm and the Counter (CTR) mode requires an initialization vector. The AES block size is 16 bytes.

int tSize = Cipher.getInstance("AES", "BC").getBlockSize();
byte[] tInitVectorBytes = new byte[tSize];
SecureRandom tRandom3 = new SecureRandom();
IvParameterSpec tIVSpec = new IvParameterSpec(tInitVectorBytes);

Figure 6. Initialization Vector

Step 6: Use the previously instantiated Cipher and set its mode to "Cipher.ENCRYPT_MODE". Use the public key to encrypt the initialization vector. Store the encrypted vector in the header along with its length.

tCipherRSA.init(Cipher.ENCRYPT_MODE, (PublicKey)tPubKey);
byte[] tInitVectorEncrypted = tCipherRSA.doFinal(tIVSpec.getIV());

Figure 7. Wrap Initialization Vector

Step 7:(Optional) If you are using an enterprise CA hierarchy and encrypting for yourself, use the CA asymmetric public key stored in the key store to wrap the symmetric key and encrypt the initialization vector and store both in the header. If encrypting for another person, use the owner's asymmetric key to wrap the symmetric key and encrypt the initialization vector and store both in the header. You can store the values in the header variables, wrappedSymKeyOther and initVectorOther as well as their lengths. This provides the ability for the CA or owner to decrypt the encrypted file.

Step 8: The private key is stored in a Java key store and is password protected. Load the key store using your password. Retrieve the asymmetric private key from the key store using the same password. The asymmetric private key will be used to generate a digital signature and stored in the header.

FileInputStream tStoreFIS=new FileInputStream("C:\\"+tUniqueAlias+".jks");
KeyStore tMyKStore = KeyStore.getInstance("JKS", "SUN");
char[] tPW = "password".toCharArray();
tMyKStore.load(tStoreFIS, tPW);
PrivateKey tPrivKey = (PrivateKey)tMyKStore.getKey(tUniqueAlias, tPW);

Figure 8. Private Key

Step 9: Generate a Java Signature object specifying the signature algorithm and provider. Initialize the signature engine with the owner's asymmetric private key. The signature engine is bound to the private key so that only the public key can validate it. Store the signature algorithm in the header so that it can be verified later.

Signature tSigEngine =
Signature.getInstance("SHA512WithRSAEncryption", "BC");
tHead.signatureAlg(12); //-SHA512WithRSAEncryption

Step 10: Generate a Java Cipher object based on the symmetric algorithm, mode, padding and provider which will be used to encrypt the target file. Initialize the Cipher object using the symmetric key and initialization vector and set its mode to "Cipher.ENCRYPT_MODE".

Cipher tCipherEncrypt = Cipher.getInstance("AES/CTR/PKCS7Padding", "BC");
tCipherEncrypt.init(Cipher.ENCRYPT_MODE, tSymmetricKey, tIVSpec);

Step 11: Load the file to be encrypted as a Java "FileInputStream". Encrypt the file to a temporary Java "FileOutputStream" using the Java Cipher, symmetric key and initialization vector and in parallel, sign the encrypted data with the signature engine. The stream is processed a buffer at a time till the end of the file is reached. The end result is an encrypted and digitally signed temporary file.

FileOutputStream tFileOS = new FileOutputStream("C:\\$$$$$$$$.tmp");
InputStream tFileIS = new FileInputStream("C:\\sampleFile.txt");
byte[] tInBuffer = new byte[4096];
byte[] tOutBuffer = new byte[4096];
int tNumOfBytesRead = tFileIS.read(tInBuffer);
while (tNumOfBytesRead == tInBuffer.length) {
//-Encrypt the input buffer data and store in the output buffer
int tNumOfBytesUpdated =
tCipherEncrypt.update(tInBuffer, 0, tInBuffer.length, tOutBuffer);
//-Sign the encrypted data in the output buffer
tSigEngine.update(tOutBuffer, 0, tNumOfBytesUpdated);
tFileOS.write(tOutBuffer, 0, tNumOfBytesUpdated);
tNumOfBytesRead = tFileIS.read(tInBuffer);
//-Process the remaining bytes in the input file.
if (tNumOfBytesRead > 0) {
tOutBuffer = tCipherEncrypt.doFinal(tInBuffer, 0, tNumOfBytesRead);
} else {
tOutBuffer = tCipherEncrypt.doFinal();
tSigEngine.update(tOutBuffer); //-Sign the remaining bytes
tFileOS.write(tOutBuffer, 0, tOutBuffer.length);
tFileOS.close(); //-Close the temporary file
tFileIS.close(); //-Close input file

Figure 9. Encrypt and Sign the File

The code can be made more efficient by allocating larger buffers and writing out the encrypted data after a threshold has been reached.

Step 12: Generate the digital signature from the signature engine after signing the file and store it in the header along with its length. Save the signature algorithm, signature certificate name and its length in the header.

byte[] tSignature = tSigEngine.sign();
tHead.verifySigCertName(tUniqueAlias + ".cer");

Step 13: Calculate the total size of the header and save in the header along with its version. Write the header into a ByteArrayOutputStream, which can be converted to a byte array. The Cryptography header class contains a method to write out the header to a ByteArrayOutputStream. Write out the byte array to a file using a Java "FileOutputStream."

ByteArrayOutputStream tHeadBAOS = new ByteArrayOutputStream();
Object tRC = tHead.writeOutHeaderV4(new DataOutputStream(tHeadBAOS));
String tEncryptedFileName = "C:\\sampleFile.txt." + tUniqueAlias + ".asg";
FileOutputStream tFileOStream = new FileOutputStream(tEncryptedFileName);
byte[] tArray = tHeadBAOS.toByteArray();
tFileOStream.write(tArray, 0, tArray.length);

Step 14: Append the temporary "encrypted" file to the output stream. The end result is an encrypted file with a digital signature. Note that the file extension is "ASG" instead of "AES" to imply that it is encrypted and digitally signed. The temporary file though encrypted should be securely deleted afterwards by overwriting it.

tInStream = new FileInputStream("C:\\$$$$$$$$.tmp");
byte[] tBuffer = new byte[4096];
int tLength = tInStream.read(tBuffer);
while (tLength > 0) {
tFileOStream.write(tBuffer, 0, tLength);
tLength = tInStream.read(tBuffer);


This article demonstrates how to encrypt and digitally sign any file using Java Cryptography methods and the Cryptography libraries from Bouncy Castle organization. The Cryptography header provides information required to decipher the file and validate who encrypted its contents. The header also provides the flexibility to expand the usage of Cryptography such as allowing multiple recipients to decrypt a file by using each of their public keys to encrypt the same symmetric key. As society adopts file encryption as a standard way of protection, more creative uses will be invented by future Cyber warriors.

The source code (LaCryptoJarSample.java) is available on the Logical Answers Inc. website under the education web page as an individual file and also within the zip file, laCrypto-4.2.0.zipx.

References and Other Technical Notes
Software requirements:

  • Computer running Windows XP or higher...
  • Java Runtime (JRE V1.7 or higher)

Recommended reading:

  • "Beginning Cryptography with Java" by David Hook.
  • "The Code Book" by Simon Singh

More Stories By James H. Wong

James H. Wong has been involved in the technology field for over 30 years and has dual MS degrees in mathematics and computer science from the University of Michigan. He worked for IBM for almost 10 years designing and implementing software. Founding Logical Answers Corp in 1992, he has provided technical consulting/programming services to clients, providing their business with a competitive edge. With his partner they offer a Java developed suite of “Secure Applications” that protect client’s data using the standard RSA (asymmetric) and AES (symmetric) encryption algorithms.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.

@ThingsExpo Stories
@ThingsExpo has been named the Top 5 Most Influential M2M Brand by Onalytica in the ‘Machine to Machine: Top 100 Influencers and Brands.' Onalytica analyzed the online debate on M2M by looking at over 85,000 tweets to provide the most influential individuals and brands that drive the discussion. According to Onalytica the "analysis showed a very engaged community with a lot of interactive tweets. The M2M discussion seems to be more fragmented and driven by some of the major brands present in the...
The Internet of Things (IoT), in all its myriad manifestations, has great potential. Much of that potential comes from the evolving data management and analytic (DMA) technologies and processes that allow us to gain insight from all of the IoT data that can be generated and gathered. This potential may never be met as those data sets are tied to specific industry verticals and single markets, with no clear way to use IoT data and sensor analytics to fulfill the hype being given the IoT today.
DevOps is being widely accepted (if not fully adopted) as essential in enterprise IT. But as Enterprise DevOps gains maturity, expands scope, and increases velocity, the need for data-driven decisions across teams becomes more acute. DevOps teams in any modern business must wrangle the ‘digital exhaust’ from the delivery toolchain, "pervasive" and "cognitive" computing, APIs and services, mobile devices and applications, the Internet of Things, and now even blockchain. In this power panel at @...
If you had a chance to enter on the ground level of the largest e-commerce market in the world – would you? China is the world’s most populated country with the second largest economy and the world’s fastest growing market. It is estimated that by 2018 the Chinese market will be reaching over $30 billion in gaming revenue alone. Admittedly for a foreign company, doing business in China can be challenging. Often changing laws, administrative regulations and the often inscrutable Chinese Interne...
Enterprise IT has been in the era of Hybrid Cloud for some time now. But it seems most conversations about Hybrid are focused on integrating AWS, Microsoft Azure, or Google ECM into existing on-premises systems. Where is all the Private Cloud? What do technology providers need to do to make their offerings more compelling? How should enterprise IT executives and buyers define their focus, needs, and roadmap, and communicate that clearly to the providers?
You have great SaaS business app ideas. You want to turn your idea quickly into a functional and engaging proof of concept. You need to be able to modify it to meet customers' needs, and you need to deliver a complete and secure SaaS application. How could you achieve all the above and yet avoid unforeseen IT requirements that add unnecessary cost and complexity? You also want your app to be responsive in any device at any time. In his session at 19th Cloud Expo, Mark Allen, General Manager of...
SYS-CON Events announced today that Streamlyzer will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Streamlyzer is a powerful analytics for video streaming service that enables video streaming providers to monitor and analyze QoE (Quality-of-Experience) from end-user devices in real time.
SYS-CON Events announced today that Pulzze Systems will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Pulzze Systems, Inc. provides infrastructure products for the Internet of Things to enable any connected device and system to carry out matched operations without programming. For more information, visit http://www.pulzzesystems.com.
One of biggest questions about Big Data is “How do we harness all that information for business use quickly and effectively?” Geographic Information Systems (GIS) or spatial technology is about more than making maps, but adding critical context and meaning to data of all types, coming from all different channels – even sensors. In his session at @ThingsExpo, William (Bill) Meehan, director of utility solutions for Esri, will take a closer look at the current state of spatial technology and ar...
Cloud based infrastructure deployment is becoming more and more appealing to customers, from Fortune 500 companies to SMEs due to its pay-as-you-go model. Enterprise storage vendors are able to reach out to these customers by integrating in cloud based deployments; this needs adaptability and interoperability of the products confirming to cloud standards such as OpenStack, CloudStack, or Azure. As compared to off the shelf commodity storage, enterprise storages by its reliability, high-availabil...
The IoT industry is now at a crossroads, between the fast-paced innovation of technologies and the pending mass adoption by global enterprises. The complexity of combining rapidly evolving technologies and the need to establish practices for market acceleration pose a strong challenge to global enterprises as well as IoT vendors. In his session at @ThingsExpo, Clark Smith, senior product manager for Numerex, will discuss how Numerex, as an experienced, established IoT provider, has embraced a ...
In past @ThingsExpo presentations, Joseph di Paolantonio has explored how various Internet of Things (IoT) and data management and analytics (DMA) solution spaces will come together as sensor analytics ecosystems. This year, in his session at @ThingsExpo, Joseph di Paolantonio from DataArchon, will be adding the numerous Transportation areas, from autonomous vehicles to “Uber for containers.” While IoT data in any one area of Transportation will have a huge impact in that area, combining sensor...
In the next forty months – just over three years – businesses will undergo extraordinary changes. The exponential growth of digitization and machine learning will see a step function change in how businesses create value, satisfy customers, and outperform their competition. In the next forty months companies will take the actions that will see them get to the next level of the game called Capitalism. Or they won’t – game over. The winners of today and tomorrow think differently, follow different...
“Media Sponsor” of SYS-CON's 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. CloudBerry Backup is a leading cross-platform cloud backup and disaster recovery solution integrated with major public cloud services, such as Amazon Web Services, Microsoft Azure and Google Cloud Platform.
Ask someone to architect an Internet of Things (IoT) solution and you are guaranteed to see a reference to the cloud. This would lead you to believe that IoT requires the cloud to exist. However, there are many IoT use cases where the cloud is not feasible or desirable. In his session at @ThingsExpo, Dave McCarthy, Director of Products at Bsquare Corporation, will discuss the strategies that exist to extend intelligence directly to IoT devices and sensors, freeing them from the constraints of ...
SYS-CON Events announced today that SoftNet Solutions will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. SoftNet Solutions specializes in Enterprise Solutions for Hadoop and Big Data. It offers customers the most open, robust, and value-conscious portfolio of solutions, services, and tools for the shortest route to success with Big Data. The unique differentiator is the ability to architect and ...
The Internet of Things will challenge the status quo of how IT and development organizations operate. Or will it? Certainly the fog layer of IoT requires special insights about data ontology, security and transactional integrity. But the developmental challenges are the same: People, Process and Platform and how we integrate our thinking to solve complicated problems. In his session at 19th Cloud Expo, Craig Sproule, CEO of Metavine, will demonstrate how to move beyond today's coding paradigm ...
Fifty billion connected devices and still no winning protocols standards. HTTP, WebSockets, MQTT, and CoAP seem to be leading in the IoT protocol race at the moment but many more protocols are getting introduced on a regular basis. Each protocol has its pros and cons depending on the nature of the communications. Does there really need to be only one protocol to rule them all? Of course not. In his session at @ThingsExpo, Chris Matthieu, co-founder and CTO of Octoblu, walk you through how Oct...
A completely new computing platform is on the horizon. They’re called Microservers by some, ARM Servers by others, and sometimes even ARM-based Servers. No matter what you call them, Microservers will have a huge impact on the data center and on server computing in general. Although few people are familiar with Microservers today, their impact will be felt very soon. This is a new category of computing platform that is available today and is predicted to have triple-digit growth rates for some ...
Everyone knows that truly innovative companies learn as they go along, pushing boundaries in response to market changes and demands. What's more of a mystery is how to balance innovation on a fresh platform built from scratch with the legacy tech stack, product suite and customers that continue to serve as the business' foundation. In his General Session at 19th Cloud Expo, Michael Chambliss, Head of Engineering at ReadyTalk, will discuss why and how ReadyTalk diverted from healthy revenue an...