Welcome!

IoT User Interface Authors: Elizabeth White, John Basso, Craig Lowell, Pat Romanski, XebiaLabs Blog

Related Topics: Java IoT, Microservices Expo, IoT User Interface, Agile Computing, Recurring Revenue, Cloud Security, SDN Journal

Java IoT: Article

Java Cryptography | Part 3

Decryption and verifying signatures

After you have secured your private electronic information using encryption and learned how to encrypt and digitally sign files for others, how do you extract the information and determine who encrypted the file? Asymmetric public/private key encryption allows you to decipher the information and verify the accompanying digital signature if it exists.

This article illustrates how to decrypt and verify the digital signature on files encrypted 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.

Figure1: Asymmetric Key Encryption Functions

The same pair of 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.

Figure 2: Asymmetric Key Signature Functions

The decryption 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, contains 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());

Decryption for Files or Java Objects
Once a file has been encrypted and/or signed using the DocuArmor application, it can be deciphered by the owner of the matching asymmetric private key. The process involves reading the header, extracting the symmetric key and deciphering the appended encrypted data. The following steps along with the Java code snippets illustrate the process used to decrypt an encrypted file.

Step 1: Assume you want to decrypt the encrypted file, C:\sampleFile.txt.jxdoe_nnnn.asg and the String variable, tUniqueAlias = "jxdoe_nnnn", holds the alias associated to the encrypted file. Read the header from the encrypted file and determine decrypted output name.

File tSrcFile = new File("C:\\sampleFile.txt." + tUniqueAlias + ".aes");
String tDecryptFile = tSrcFile.getName();
tDecryptFile = tDecryptFile.substring(0, tDecryptFile.lastIndexOf('.'));
tDecryptFile = tDecryptFile.substring(0, tDecryptFile.lastIndexOf('.'));
OutputStream tFileOStream = new FileOutputStream(tDecryptFile);
DataInputStream tDInStream =
new DataInputStream(new FileInputStream(tSrcFile));
Object tRC = CryptoHeader.readHeader(tDInStream);
CryptoHeader tHead = (CryptoHeader)tRC;

Step 2: 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 decrypt the symmetric key.

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

Figure 3: Private Key

Step 3: Generate a Java Cipher object using the asymmetric private key and set its mode to "Cipher.UNWRAP_MODE".

Cipher tCipherRSA = Cipher.getInstance("RSA", "BC");
tCipherRSA.init(Cipher.UNWRAP_MODE, (PrivateKey)tPrivKey);

Step 4: Use the Java Cipher and asymmetric private key to unwrap the symmetric key. It's located in the header at the instance variable, wrappedSymKey or wrappedSymKeyOther, along with symmetric algorithm at symKeyAlgDesc. The symmetric key will be used to decrypt the file.

String tAlg = tHead.symKeyAlgDesc();
Key tSymmetricKey =
tCipherRSA.unwrap(tHead.wrappedSymKey(),tAlg, Cipher.SECRET_KEY);

Figure 4: Unwrap Symmetric Key

Step 5: Re-initialize the same Cipher to Cipher.DECRYPT_MODE. Use the Cipher and the asymmetric private key to decrypt the initialization vector stored within the header at the instance variable initVector or initVectorOther.

tCipher.init(Cipher.DECRYPT_MODE, (PrivateKey)tPrivKey);
byte[] tInitVector = tCipher.doFinal(tHead.initVector());
IvParameterSpec tIvParmSpec = new IvParameterSpec(tInitVector);

Figure 5: Unwrap Initialization Vector

Step 6: Generate a Java Cipher object using the symmetric key and initialization vector and set its mode to "Cipher.DECRYPT_MODE". The string representing the symmetric algorithm, mode and padding can be extracted from the Cryptography header using the "transformation" method.

tCipherDecrypt = Cipher.getInstance("AES/CTR/PKCS7Padding", "BC");
or tCipherDecrypt = Cipher.getInstance(tHead.transformation(), "BC");
tCipherDecrypt.init(Cipher.DECRYPT_MODE, tSymmetricKey, tIvParmSpec);

Step 7: Use the Java Cipher to decrypt the rest of the file to a Java FileOutputStream. The DataInputStream points to the start of the encrypted data after reading the header. The end result is a decrypted file.

byte[] tInBuffer = new byte[4096];
byte[] tOutBuffer = new byte[4096];
int tNumOfBytesRead = tDInStream.read(tInBuffer);
while (tNumOfBytesRead == tInBuffer.length) {
//-Encrypt the input buffer data and store in the output buffer
int tNumOfBytesUpdated =
tCipherDecrypt.update(tInBuffer, 0, tInBuffer.length, tOutBuffer);
tFileOStream.write(tOutBuffer, 0, tNumOfBytesUpdated);
tNumOfBytesRead = tDInStream.read(tInBuffer);
}
//-Process the remaining bytes in the input file.
if (tNumOfBytesRead > 0) {
tOutBuffer = tCipherDecrypt.doFinal(tInBuffer, 0, tNumOfBytesRead);
} else {
tOutBuffer = tCipherDecrypt.doFinal();
}
tFileOStream.write(tOutBuffer, 0, tOutBuffer.length);
tFileOStream.close();

Figure 6: Decipher the Encrypted File

Step 7a: If the encrypted file contains a Java object, use the Java Cipher to decrypt the rest of the file to a Java ByteArrayOutputStream instead of a FileOutputStream. The end result can be converted to an instance of its original Java class.

ByteArrayInputStream tBAIS = new ByteArrayInputStream(tBAOS.toByteArray());  
ObjectInput tOIS = new ObjectInputStream(tBAIS);
Object tObject = tOIS.readObject();  //-Original Java object
tBAOS.close();
tBAIS.close();
tOIS.close();

Alternatively, the same technique can be used to decrypt the encrypted file using the symmetric key that was wrapped with the CA or owner's asymmetric public key. If the file was encrypted for another user, the owner can decrypt it using the additionally wrapped symmetric key. If the file was encrypted for oneself, the CA can decrypt it using the additionally wrapped symmetric key in the enterprise version.

Signature Verification
When a file has been digitally signed with a user's asymmetric private key, the signature is stored in the Cryptography header. The signature can be validated with the user's matching asymmetric public key stored in a certificate. The process involves reading the header, extracting the digital signature and validating it against the rest of the signed file and the asymmetric public key. The following steps describe the process used to verify a digital signature.

Step 1: Assume you want to verify the signature on the encrypted and digitally signed file, "C:\sampleFile.txt.jxdoe_nnnn.asg" and the String variable, tUniqueAlias = "jxdoe_nnnn", holds the alias associated to the file. Read the header from the signed file. After the header is read, keep in mind that the DataInputStream now points to the beginning of the encrypted data.

File tSrcFile = new File("C:\\sampleFile.txt." + tUniqueAlias + ".asg");
DataInputStream tDInStream =
new DataInputStream(new FileInputStream(tSrcFile));
Object tRC = CryptoHeader.readHeader(tDInStream);
CryptoHeader tHead = (CryptoHeader)tRC;
byte[] tCurrSignature = tHead.signature();

Step 2: Retrieve the certificate whose name is stored in the header and contains the asymmetric public key needed for verification. Retrieve the asymmetric public key from the certificate associated with the digital signature.

String tCertName = "C:\\" + tHead.verifySigCertName();
InputStream tInStream = new FileInputStream(tCertName);
CertificateFactory tFactory = CertificateFactory.getInstance("X.509","BC");
X509Certificate tCert =
(X509Certificate)tFactory.generateCertificate(tInStream);
tInStream.close();
PublicKey tPubKey = tCert.getPublicKey();

Figure 7: Extract Public Key

Step 3: Instantiate a Java signature engine and initialize it with the signature algorithm stored in the header and the asymmetric public key. The default value is "SHA512WithRSAEncryption".

Signature tSgnVerifyEngine = null;
String tSigAlg = tHead.signatureAlgDesc();
tSgnVerifyEngine = Signature.getInstance(tSigAlg,"BC");
tSgnVerifyEngine.initVerify(tPubKey);

Step 4: Use the Java signature engine to process the rest of the signed file and calculate a hash number that will be compared with the signature stored in the header.

int tBlockSize = 4096;
byte[] tBuffer = new byte[tBlockSize];
int tLength = tDInStream.read(tBuffer);
while (tLength == tBlockSize) {
tSgnVerifyEngine.update(tBuffer, 0, tBlockSize);
tLength = tDInStream.read(tBuffer);
}

if (tLength > 0) {
tSgnVerifyEngine.update(tBuffer, 0, tLength);
}

Step 5: After the file has been processed, use the Java signature engine to verify its result with the digital signature. A Boolean result is returned on whether the signature was valid.

Boolean tResult = tSgnVerifyEngine.verify(tCurrSignature);

Summary
The article demonstrates how to decrypt and verify the digit signature of and encrypted file using Java Cryptography methods and the Cryptography libraries from Bouncy Castle organization. Using the information provided within the Cryptography header, the user can validate who encrypted its contents and/or decipher the encrypted file. 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.


@CloudExpo Stories
Machine Learning helps make complex systems more efficient. By applying advanced Machine Learning techniques such as Cognitive Fingerprinting, wind project operators can utilize these tools to learn from collected data, detect regular patterns, and optimize their own operations. In his session at 18th Cloud Expo, Stuart Gillen, Director of Business Development at SparkCognition, discussed how research has demonstrated the value of Machine Learning in delivering next generation analytics to imp...
With over 720 million Internet users and 40–50% CAGR, the Chinese Cloud Computing market has been booming. When talking about cloud computing, what are the Chinese users of cloud thinking about? What is the most powerful force that can push them to make the buying decision? How to tap into them? In his session at 18th Cloud Expo, Yu Hao, CEO and co-founder of SpeedyCloud, answered these questions and discussed the results of SpeedyCloud’s survey.
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. In his session at @ThingsExpo, Craig Sproule, CEO of Metavine, demonstrated how to move beyond today's coding paradigm and shared the must-have mindsets for removing complexity from the develo...
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...
Basho Technologies has announced the latest release of Basho Riak TS, version 1.3. Riak TS is an enterprise-grade NoSQL database optimized for Internet of Things (IoT). The open source version enables developers to download the software for free and use it in production as well as make contributions to the code and develop applications around Riak TS. Enhancements to Riak TS make it quick, easy and cost-effective to spin up an instance to test new ideas and build IoT applications. In addition to...
Identity is in everything and customers are looking to their providers to ensure the security of their identities, transactions and data. With the increased reliance on cloud-based services, service providers must build security and trust into their offerings, adding value to customers and improving the user experience. Making identity, security and privacy easy for customers provides a unique advantage over the competition.
CenturyLink has announced that application server solutions from GENBAND are now available as part of CenturyLink’s Networx contracts. The General Services Administration (GSA)’s Networx program includes the largest telecommunications contract vehicles ever awarded by the federal government. CenturyLink recently secured an extension through spring 2020 of its offerings available to federal government agencies via GSA’s Networx Universal and Enterprise contracts. GENBAND’s EXPERiUS™ Application...
SYS-CON Events announced today that Isomorphic Software will exhibit at DevOps Summit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Isomorphic Software provides the SmartClient HTML5/AJAX platform, the most advanced technology for building rich, cutting-edge enterprise web applications for desktop and mobile. SmartClient combines the productivity and performance of traditional desktop software with the simp...
"We've discovered that after shows 80% if leads that people get, 80% of the conversations end up on the show floor, meaning people forget about it, people forget who they talk to, people forget that there are actual business opportunities to be had here so we try to help out and keep the conversations going," explained Jeff Mesnik, Founder and President of ContentMX, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
"When you think about the data center today, there's constant evolution, The evolution of the data center and the needs of the consumer of technology change, and they change constantly," stated Matt Kalmenson, VP of Sales, Service and Cloud Providers at Veeam Software, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
Redis is not only the fastest database, but it is the most popular among the new wave of databases running in containers. Redis speeds up just about every data interaction between your users or operational systems. In his session at 19th Cloud Expo, Dave Nielsen, Developer Advocate, Redis Labs, will share the functions and data structures used to solve everyday use cases that are driving Redis' popularity.
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with the 19th International Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world and ThingsExpo Silicon Valley Call for Papers is now open.
You think you know what’s in your data. But do you? Most organizations are now aware of the business intelligence represented by their data. Data science stands to take this to a level you never thought of – literally. The techniques of data science, when used with the capabilities of Big Data technologies, can make connections you had not yet imagined, helping you discover new insights and ask new questions of your data. In his session at @ThingsExpo, Sarbjit Sarkaria, data science team lead ...
"My role is working with customers, helping them go through this digital transformation. I spend a lot of time talking to banks, big industries, manufacturers working through how they are integrating and transforming their IT platforms and moving them forward," explained William Morrish, General Manager Product Sales at Interoute, in this SYS-CON.tv interview at 18th Cloud Expo, held June 7-9, 2016, at the Javits Center in New York City, NY.
To leverage Continuous Delivery, enterprises must consider impacts that span functional silos, as well as applications that touch older, slower moving components. Managing the many dependencies can cause slowdowns. See how to achieve continuous delivery in the enterprise.
Up until last year, enterprises that were looking into cloud services usually undertook a long-term pilot with one of the large cloud providers, running test and dev workloads in the cloud. With cloud’s transition to mainstream adoption in 2015, and with enterprises migrating more and more workloads into the cloud and in between public and private environments, the single-provider approach must be revisited. In his session at 18th Cloud Expo, Yoav Mor, multi-cloud solution evangelist at Cloudy...
Aspose.Total for .NET is the most complete package of all file format APIs for .NET as offered by Aspose. It empowers developers to create, edit, render, print and convert between a wide range of popular document formats within any .NET, C#, ASP.NET and VB.NET applications. Aspose compiles all .NET APIs on a daily basis to ensure that it contains the most up to date versions of each of Aspose .NET APIs. If a new .NET API or a new version of existing APIs is released during the subscription peri...
Security, data privacy, reliability, and regulatory compliance are critical factors when evaluating whether to move business applications from in-house, client-hosted environments to a cloud platform. Quality assurance plays a vital role in ensuring that the appropriate level of risk assessment, verification, and validation takes place to ensure business continuity during the migration to a new cloud platform.
SYS-CON Events announced today that 910Telecom 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. Housed in the classic Denver Gas & Electric Building, 910 15th St., 910Telecom is a carrier-neutral telecom hotel located in the heart of Denver. Adjacent to CenturyLink, AT&T, and Denver Main, 910Telecom offers connectivity to all major carriers, Internet service providers, Internet backbones and ...
Ovum, a leading technology analyst firm, has published an in-depth report, Ovum Decision Matrix: Selecting a DevOps Release Management Solution, 2016–17. The report focuses on the automation aspects of DevOps, Release Management and compares solutions from the leading vendors.