Welcome!

Recurring Revenue Authors: Liz McMillan, Yeshim Deniz, Carmen Gonzalez, Elizabeth White, Pat Romanski

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.


@ThingsExpo Stories
SYS-CON Events announced today that Evatronix will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Evatronix SA offers comprehensive solutions in the design and implementation of electronic systems, in CAD / CAM deployment, and also is a designer and manufacturer of advanced 3D scanners for professional applications.
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...
"Evatronix provides design services to companies that need to integrate the IoT technology in their products but they don't necessarily have the expertise, knowledge and design team to do so," explained Adam Morawiec, VP of Business Development at Evatronix, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, discussed how they built...
No hype cycles or predictions of a gazillion things here. IoT is here. You get it. You know your business and have great ideas for a business transformation strategy. What comes next? Time to make it happen. In his session at @ThingsExpo, Jay Mason, an Associate Partner of Analytics, IoT & Cybersecurity at M&S Consulting, presented a step-by-step plan to develop your technology implementation strategy. He also discussed the evaluation of communication standards and IoT messaging protocols, data...
With tough new regulations coming to Europe on data privacy in May 2018, Calligo will explain why in reality the effect is global and transforms how you consider critical data. EU GDPR fundamentally rewrites the rules for cloud, Big Data and IoT. In his session at 21st Cloud Expo, Adam Ryan, Vice President and General Manager EMEA at Calligo, examined the regulations and provided insight on how it affects technology, challenges the established rules and will usher in new levels of diligence arou...
Smart cities have the potential to change our lives at so many levels for citizens: less pollution, reduced parking obstacles, better health, education and more energy savings. Real-time data streaming and the Internet of Things (IoT) possess the power to turn this vision into a reality. However, most organizations today are building their data infrastructure to focus solely on addressing immediate business needs vs. a platform capable of quickly adapting emerging technologies to address future ...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, led attendees through the exciting evolution of the cloud. He looked at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering m...
In his session at 21st Cloud Expo, Raju Shreewastava, founder of Big Data Trunk, provided a fun and simple way to introduce Machine Leaning to anyone and everyone. He solved a machine learning problem and demonstrated an easy way to be able to do machine learning without even coding. Raju Shreewastava is the founder of Big Data Trunk (www.BigDataTrunk.com), a Big Data Training and consulting firm with offices in the United States. He previously led the data warehouse/business intelligence and B...
The 22nd International Cloud Expo | 1st DXWorld Expo has announced that its Call for Papers is open. Cloud Expo | DXWorld Expo, to be held June 5-7, 2018, at the Javits Center in New York, NY, brings together Cloud Computing, Digital Transformation, Big Data, Internet of Things, DevOps, Machine Learning 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 busin...
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...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo 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 ...
22nd International Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, and co-located with the 1st DXWorld Expo 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 ...
DevOps at Cloud Expo – being held June 5-7, 2018, at the Javits Center in New York, NY – announces that its Call for Papers is open. Born out of proven success in agile development, cloud computing, and process automation, DevOps is a macro trend you cannot afford to miss. From showcase success stories from early adopters and web-scale businesses, DevOps is expanding to organizations of all sizes, including the world's largest enterprises – and delivering real results. Among the proven benefits,...
@DevOpsSummit at Cloud Expo, taking place June 5-7, 2018, at the Javits Center in New York City, NY, is co-located with 22nd Cloud Expo | 1st DXWorld 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...
Cloud Expo | DXWorld Expo have announced the conference tracks for Cloud Expo 2018. Cloud Expo will be held June 5-7, 2018, at the Javits Center in New York City, and November 6-8, 2018, at the Santa Clara Convention Center, Santa Clara, CA. Digital Transformation (DX) is a major focus with the introduction of DX Expo within the program. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive ov...
SYS-CON Events announced today that T-Mobile exhibited at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on qua...
SYS-CON Events announced today that Cedexis will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Cedexis is the leader in data-driven enterprise global traffic management. Whether optimizing traffic through datacenters, clouds, CDNs, or any combination, Cedexis solutions drive quality and cost-effectiveness. For more information, please visit https://www.cedexis.com.
SYS-CON Events announced today that Google Cloud has been named “Keynote Sponsor” of SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Companies come to Google Cloud to transform their businesses. Google Cloud’s comprehensive portfolio – from infrastructure to apps to devices – helps enterprises innovate faster, scale smarter, stay secure, and do more with data than ever before.