Welcome!

Microservices Expo Authors: Pat Romanski, Liz McMillan, Elizabeth White, Dana Gardner, Christopher Keene

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.


@MicroservicesExpo Stories
DevOps at Cloud Expo, taking place Nov 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long dev...
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
Using new techniques of information modeling, indexing, and processing, new cloud-based systems can support cloud-based workloads previously not possible for high-throughput insurance, banking, and case-based applications. In his session at 18th Cloud Expo, John Newton, CTO, Founder and Chairman of Alfresco, described how to scale cloud-based content management repositories to store, manage, and retrieve billions of documents and related information with fast and linear scalability. He addres...
Akana has announced the availability of version 8 of its API Management solution. The Akana Platform provides an end-to-end API Management solution for designing, implementing, securing, managing, monitoring, and publishing APIs. It is available as a SaaS platform, on-premises, and as a hybrid deployment. Version 8 introduces a lot of new functionality, all aimed at offering customers the richest API Management capabilities in a way that is easier than ever for API and app developers to use.
The burgeoning trends around DevOps are translating into new types of IT infrastructure that both developers and operators can take advantage of. The next BriefingsDirect Voice of the Customer thought leadership discussion focuses on the burgeoning trends around DevOps and how that’s translating into new types of IT infrastructure that both developers and operators can take advantage of.
With so much going on in this space you could be forgiven for thinking you were always working with yesterday’s technologies. So much change, so quickly. What do you do if you have to build a solution from the ground up that is expected to live in the field for at least 5-10 years? This is the challenge we faced when we looked to refresh our existing 10-year-old custom hardware stack to measure the fullness of trash cans and compactors.
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...
The emerging Internet of Everything creates tremendous new opportunities for customer engagement and business model innovation. However, enterprises must overcome a number of critical challenges to bring these new solutions to market. In his session at @ThingsExpo, Michael Martin, CTO/CIO at nfrastructure, outlined these key challenges and recommended approaches for overcoming them to achieve speed and agility in the design, development and implementation of Internet of Everything solutions wi...
Internet of @ThingsExpo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 19th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - comp...
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.
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.
Thomas Bitman of Gartner wrote a blog post last year about why OpenStack projects fail. In that article, he outlined three particular metrics which together cause 60% of OpenStack projects to fall short of expectations: Wrong people (31% of failures): a successful cloud needs commitment both from the operations team as well as from "anchor" tenants. Wrong processes (19% of failures): a successful cloud automates across silos in the software development lifecycle, not just within silos.
There's a lot of things we do to improve the performance of web and mobile applications. We use caching. We use compression. We offload security (SSL and TLS) to a proxy with greater compute capacity. We apply image optimization and minification to content. We do all that because performance is king. Failure to perform can be, for many businesses, equivalent to an outage with increased abandonment rates and angry customers taking to the Internet to express their extreme displeasure.
The 19th International Cloud Expo has announced that its Call for Papers is open. Cloud Expo, to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, Big Data, Internet of Things, DevOps, Digital Transformation, Microservices and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportuni...
Right off the bat, Newman advises that we should "think of microservices as a specific approach for SOA in the same way that XP or Scrum are specific approaches for Agile Software development". These analogies are very interesting because my expectation was that microservices is a pattern. So I might infer that microservices is a set of process techniques as opposed to an architectural approach. Yet in the book, Newman clearly includes some elements of concept model and architecture as well as p...
SYS-CON Events announced today that eCube Systems, a leading provider of middleware modernization, integration, and management solutions, will exhibit at @DevOpsSummit at 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. eCube Systems offers a family of middleware evolution products and services that maximize return on technology investment by leveraging existing technical equity to meet evolving business needs. ...
A company’s collection of online systems is like a delicate ecosystem – all components must integrate with and complement each other, and one single malfunction in any of them can bring the entire system to a screeching halt. That’s why, when monitoring and analyzing the health of your online systems, you need a broad arsenal of different tools for your different needs. In addition to a wide-angle lens that provides a snapshot of the overall health of your system, you must also have precise, ...
The following fictional case study is a composite of actual horror stories I’ve heard over the years. Unfortunately, this scenario often occurs when in-house integration teams take on the complexities of DevOps and ALM integration with an enterprise service bus (ESB) or custom integration. It is written from the perspective of an enterprise architect tasked with leading an organization’s effort to adopt Agile to become more competitive. The company has turned to Scaled Agile Framework (SAFe) as ...
As the world moves toward more DevOps and Microservices, application deployment to the cloud ought to become a lot simpler. The Microservices architecture, which is the basis of many new age distributed systems such as OpenStack, NetFlix and so on, is at the heart of Cloud Foundry - a complete developer-oriented Platform as a Service (PaaS) that is IaaS agnostic and supports vCloud, OpenStack and AWS. Serverless computing is revolutionizing computing. In his session at 19th Cloud Expo, Raghav...
Cloud Expo 2016 New York at the Javits Center New York was characterized by increased attendance and a new focus on operations. These were both encouraging signs for all involved in Cloud Computing and all that it touches. As Conference Chair, I work with the Cloud Expo team to structure three keynotes, numerous general sessions, and more than 150 breakout sessions along 10 tracks. Our job is to balance the state of enterprise IT today with the trends that will be commonplace tomorrow. Mobile...