Welcome!

Machine Learning Authors: William Schmarzo, Pat Romanski, Ed Featherston, Liz McMillan, Elizabeth White

Related Topics: Java IoT, Microservices Expo, Machine Learning , 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
"Storpool does only block-level storage so we do one thing extremely well. The growth in data is what drives the move to software-defined technologies in general and software-defined storage," explained Boyan Ivanov, CEO and co-founder at StorPool, in this SYS-CON.tv interview at 16th Cloud Expo, held June 9-11, 2015, at the Javits Center in New York City.
Sometimes I write a blog just to formulate and organize a point of view, and I think it’s time that I pull together the bounty of excellent information about Machine Learning. This is a topic with which business leaders must become comfortable, especially tomorrow’s business leaders (tip for my next semester University of San Francisco business students!). Machine learning is a key capability that will help organizations drive optimization and monetization opportunities, and there have been some...
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
The question before companies today is not whether to become intelligent, it’s a question of how and how fast. The key is to adopt and deploy an intelligent application strategy while simultaneously preparing to scale that intelligence. In her session at 21st Cloud Expo, Sangeeta Chakraborty, Chief Customer Officer at Ayasdi, provided a tactical framework to become a truly intelligent enterprise, including how to identify the right applications for AI, how to build a Center of Excellence to oper...
While some developers care passionately about how data centers and clouds are architected, for most, it is only the end result that matters. To the majority of companies, technology exists to solve a business problem, and only delivers value when it is solving that problem. 2017 brings the mainstream adoption of containers for production workloads. In his session at 21st Cloud Expo, Ben McCormack, VP of Operations at Evernote, discussed how data centers of the future will be managed, how the p...
As DevOps methodologies expand their reach across the enterprise, organizations face the daunting challenge of adapting related cloud strategies to ensure optimal alignment, from managing complexity to ensuring proper governance. How can culture, automation, legacy apps and even budget be reexamined to enable this ongoing shift within the modern software factory? In her Day 2 Keynote at @DevOpsSummit at 21st Cloud Expo, Aruna Ravichandran, VP, DevOps Solutions Marketing, CA Technologies, was jo...
As Marc Andreessen says software is eating the world. Everything is rapidly moving toward being software-defined – from our phones and cars through our washing machines to the datacenter. However, there are larger challenges when implementing software defined on a larger scale - when building software defined infrastructure. In his session at 16th Cloud Expo, Boyan Ivanov, CEO of StorPool, provided some practical insights on what, how and why when implementing "software-defined" in the datacent...
Blockchain. A day doesn’t seem to go by without seeing articles and discussions about the technology. According to PwC executive Seamus Cushley, approximately $1.4B has been invested in blockchain just last year. In Gartner’s recent hype cycle for emerging technologies, blockchain is approaching the peak. It is considered by Gartner as one of the ‘Key platform-enabling technologies to track.’ While there is a lot of ‘hype vs reality’ discussions going on, there is no arguing that blockchain is b...
Blockchain is a shared, secure record of exchange that establishes trust, accountability and transparency across business networks. Supported by the Linux Foundation's open source, open-standards based Hyperledger Project, Blockchain has the potential to improve regulatory compliance, reduce cost as well as advance trade. Are you curious about how Blockchain is built for business? In her session at 21st Cloud Expo, René Bostic, Technical VP of the IBM Cloud Unit in North America, discussed the b...
You know you need the cloud, but you’re hesitant to simply dump everything at Amazon since you know that not all workloads are suitable for cloud. You know that you want the kind of ease of use and scalability that you get with public cloud, but your applications are architected in a way that makes the public cloud a non-starter. You’re looking at private cloud solutions based on hyperconverged infrastructure, but you’re concerned with the limits inherent in those technologies.
Is advanced scheduling in Kubernetes achievable?Yes, however, how do you properly accommodate every real-life scenario that a Kubernetes user might encounter? How do you leverage advanced scheduling techniques to shape and describe each scenario in easy-to-use rules and configurations? In his session at @DevOpsSummit at 21st Cloud Expo, Oleg Chunikhin, CTO at Kublr, answered these questions and demonstrated techniques for implementing advanced scheduling. For example, using spot instances and co...
The cloud era has reached the stage where it is no longer a question of whether a company should migrate, but when. Enterprises have embraced the outsourcing of where their various applications are stored and who manages them, saving significant investment along the way. Plus, the cloud has become a defining competitive edge. Companies that fail to successfully adapt risk failure. The media, of course, continues to extol the virtues of the cloud, including how easy it is to get there. Migrating...
The use of containers by developers -- and now increasingly IT operators -- has grown from infatuation to deep and abiding love. But as with any long-term affair, the honeymoon soon leads to needing to live well together ... and maybe even getting some relationship help along the way. And so it goes with container orchestration and automation solutions, which are rapidly emerging as the means to maintain the bliss between rapid container adoption and broad container use among multiple cloud host...
Imagine if you will, a retail floor so densely packed with sensors that they can pick up the movements of insects scurrying across a store aisle. Or a component of a piece of factory equipment so well-instrumented that its digital twin provides resolution down to the micrometer.
In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settle...
The need for greater agility and scalability necessitated the digital transformation in the form of following equation: monolithic to microservices to serverless architecture (FaaS). To keep up with the cut-throat competition, the organisations need to update their technology stack to make software development their differentiating factor. Thus microservices architecture emerged as a potential method to provide development teams with greater flexibility and other advantages, such as the abili...
Product connectivity goes hand and hand these days with increased use of personal data. New IoT devices are becoming more personalized than ever before. In his session at 22nd Cloud Expo | DXWorld Expo, Nicolas Fierro, CEO of MIMIR Blockchain Solutions, will discuss how in order to protect your data and privacy, IoT applications need to embrace Blockchain technology for a new level of product security never before seen - or needed.
Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
Nordstrom is transforming the way that they do business and the cloud is the key to enabling speed and hyper personalized customer experiences. In his session at 21st Cloud Expo, Ken Schow, VP of Engineering at Nordstrom, discussed some of the key learnings and common pitfalls of large enterprises moving to the cloud. This includes strategies around choosing a cloud provider(s), architecture, and lessons learned. In addition, he covered some of the best practices for structured team migration an...
In his general session at 21st Cloud Expo, Greg Dumas, Calligo’s Vice President and G.M. of US operations, discussed the new Global Data Protection Regulation and how Calligo can help business stay compliant in digitally globalized world. Greg Dumas is Calligo's Vice President and G.M. of US operations. Calligo is an established service provider that provides an innovative platform for trusted cloud solutions. Calligo’s customers are typically most concerned about GDPR compliance, application p...