Agile Computing Authors: William Schmarzo, Liz McMillan, Carmen Gonzalez, Jim Kaskade, Lori MacVittie

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
SYS-CON Events announced today that Niagara Networks 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. Niagara Networks offers the highest port-density systems, and the most complete Next-Generation Network Visibility systems including Network Packet Brokers, Bypass Switches, and Network TAPs.
SYS-CON Events announced today that Transparent Cloud Computing (T-Cloud) Consortium 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. The Transparent Cloud Computing Consortium (T-Cloud Consortium) will conduct research activities into changes in the computing model as a result of collaboration between "device" and "cloud" and the creation of new value and markets through organic data proces...
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...
SYS-CON Media announced today that @WebRTCSummit Blog, the largest WebRTC resource in the world, has been launched. @WebRTCSummit Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @WebRTCSummit Blog can be bookmarked ▸ Here @WebRTCSummit conference site can be bookmarked ▸ Here
Intelligent machines are here. Robots, self-driving cars, drones, bots and many IoT devices are becoming smarter with Machine Learning. In her session at @ThingsExpo, Sudha Jamthe, CEO of IoTDisruptions.com, will discuss the next wave of business disruption at the junction of IoT and AI, impacting many industries and set to change our lives, work and world as we know it.
In today's uber-connected, consumer-centric, cloud-enabled, insights-driven, multi-device, global world, the focus of solutions has shifted from the product that is sold to the person who is buying the product or service. Enterprises have rebranded their business around the consumers of their products. The buyer is the person and the focus is not on the offering. The person is connected through multiple devices, wearables, at home, on the road, and in multiple locations, sometimes simultaneously...
Established in 1998, Calsoft is a leading software product engineering Services Company specializing in Storage, Networking, Virtualization and Cloud business verticals. Calsoft provides End-to-End Product Development, Quality Assurance Sustenance, Solution Engineering and Professional Services expertise to assist customers in achieving their product development and business goals. The company's deep domain knowledge of Storage, Virtualization, Networking and Cloud verticals helps in delivering ...
SYS-CON Events announced today that Hitrons 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. Hitrons Solutions Inc. is distributor in the North American market for unique products and services of small and medium-size businesses, including cloud services and solutions, SEO marketing platforms, and mobile applications.
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.
OnProcess Technology has announced it will be a featured speaker at @ThingsExpo, taking place November 1 - 3, 2016, in Santa Clara, California. Dan Gettens, OnProcess’ Chief Analytics Officer, will discuss how Internet of Things (IoT) data can be leveraged to predict product failures, improve uptime and slash costly inventory stock. @ThingsExpo is an annual gathering of IoT and cloud developers, practitioners and thought-leaders who exchange ideas and insights on topics ranging from Big Data in...
SYS-CON Events announced today that Enzu 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. Enzu’s mission is to be the leading provider of enterprise cloud solutions worldwide. Enzu enables online businesses to use its IT infrastructure to their competitive advantage. By offering a suite of proven hosting and management services, Enzu wants companies to focus on the core of their online busine...
The explosion of new web/cloud/IoT-based applications and the data they generate are transforming our world right before our eyes. In this rush to adopt these new technologies, organizations are often ignoring fundamental questions concerning who owns the data and failing to ask for permission to conduct invasive surveillance of their customers. Organizations that are not transparent about how their systems gather data telemetry without offering shared data ownership risk product rejection, regu...
The Open Connectivity Foundation (OCF), sponsor of the IoTivity open source project, and AllSeen Alliance, which provides the AllJoyn® open source IoT framework, today announced that the two organizations’ boards have approved a merger under the OCF name and bylaws. This merger will advance interoperability between connected devices from both groups, enabling the full operating potential of IoT and representing a significant step towards a connected ecosystem.
November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Penta Security is a leading vendor for data security solutions, including its encryption solution, D’Amo. By using FPE technology, D’Amo allows for the implementation of encryption technology to sensitive data fields without modification to schema in the database environment. With businesses having their data become increasingly more complicated in their mission-critical applications (such as ERP, CRM, HRM), continued ...
SYS-CON Events announced today that Embotics, the cloud automation company, 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. Embotics is the cloud automation company for IT organizations and service providers that need to improve provisioning or enable self-service capabilities. With a relentless focus on delivering a premier user experience and unmatched customer support, Embotics is the fas...
SYS-CON Events announced today that Cloudbric, a leading website security provider, 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. Cloudbric is an elite full service website protection solution specifically designed for IT novices, entrepreneurs, and small and medium businesses. First launched in 2015, Cloudbric is based on the enterprise level Web Application Firewall by Penta Security Sys...
Smart Cities are here to stay, but for their promise to be delivered, the data they produce must not be put in new siloes. In his session at @ThingsExpo, Mathias Herberts, Co-founder and CTO of Cityzen Data, will deep dive into best practices that will ensure a successful smart city journey.
Data is the fuel that drives the machine learning algorithmic engines and ultimately provides the business value. In his session at Cloud Expo, Ed Featherston, a director and senior enterprise architect at Collaborative Consulting, will discuss the key considerations around quality, volume, timeliness, and pedigree that must be dealt with in order to properly fuel that engine.
SYS-CON Events announced today that MathFreeOn 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. MathFreeOn is Software as a Service (SaaS) used in Engineering and Math education. Write scripts and solve math problems online. MathFreeOn provides online courses for beginners or amateurs who have difficulties in writing scripts. In accordance with various mathematical topics, there are more tha...
Successful digital transformation requires new organizational competencies and capabilities. Research tells us that the biggest impediment to successful transformation is human; consequently, the biggest enabler is a properly skilled and empowered workforce. In the digital age, new individual and collective competencies are required. In his session at 19th Cloud Expo, Bob Newhouse, CEO and founder of Agilitiv, will draw together recent research and lessons learned from emerging and established ...