What Is Public Key Encryption?

This section describes public key encryption, also called asymmetric encryption, which uses a pair of keys, a private key and a public key to encrypt and decrypt messages.

What Is Public Key Encryption? Public key encryption is also called asymmetric encryption, which uses a pair of keys, a private key and a public key. Text encrypted by one key can be decrypted the other key.

Public key encryption can be used to secure a two-way communication.

For example, Bob wants to communicate with Susan in a secure way. He will generate a private key and a public key. He will encrypt the message with the private key, and send the encrypted message and the public key to Susan. Susan will then decrypt the message with the public key.

If Susan wants to send a response, she will encrypt the response with the public key and send the encrypted response back to Bob. Bob will then decrypt the response with the private key.

This communication process can be illustrated with the following diagram:

Bob          Bob              Internet       Susan           Susan
           | Encryption  |                 | Decryption |
Original   | with        |    Encrypted    | with       |    Original
message  ->| private key | -> message   -> | public key | -> message

           | Decryption  |                 | Encryption |
Original   | with        |    Encrypted    | with       |    Original
response <-| private key | <- response  <- | public key | <- response

The idea of public key encryption was invented in 1975 by two Stanford mathematicians, Whitfield Diffie and Martin Hellman. Diffie and Hellman failed to give any real algorithm and demonstrated only that public key encryption was possible in theory.

But one year later, in 1976, three MIT mathematicians, Ronald L. Rivest, Adi Shamir, and Leonard M. Adleman invented a real public key algorithm. Their algorithm, called RSA algorithm, is based on factoring theory. See next section for more details.

Last update: 2013.

Table of Contents

 About This Book

 Cryptography Terminology

 Cryptography Basic Concepts

 Introduction to AES (Advanced Encryption Standard)

 Introduction to DES Algorithm

 DES Algorithm - Illustrated with Java Programs

 DES Algorithm Java Implementation

 DES Algorithm - Java Implementation in JDK JCE

 DES Encryption Operation Modes

 DES in Stream Cipher Modes

 PHP Implementation of DES - mcrypt

 Blowfish - 8-Byte Block Cipher

 Secret Key Generation and Management

 Cipher - Secret Key Encryption and Decryption

Introduction of RSA Algorithm

What Is Public Key Encryption?

 RSA Public Key Encryption Algorithm

 Illustration of RSA Algorithm: p,q=5,7

 Illustration of RSA Algorithm: p,q=7,19

 Proof of RSA Public Key Encryption

 How Secure Is RSA Algorithm?

 How to Calculate "M**e mod n"

 Efficient RSA Encryption and Decryption Operations

 Proof of RSA Encryption Operation Algorithm

 Finding Large Prime Numbers

 RSA Implementation using java.math.BigInteger Class

 Introduction of DSA (Digital Signature Algorithm)

 Java Default Implementation of DSA

 Private key and Public Key Pair Generation

 PKCS#8/X.509 Private/Public Encoding Standards

 Cipher - Public Key Encryption and Decryption

 MD5 Mesasge Digest Algorithm

 SHA1 Mesasge Digest Algorithm

 OpenSSL Introduction and Installation

 OpenSSL Generating and Managing RSA Keys

 OpenSSL Managing Certificates

 OpenSSL Generating and Signing CSR

 OpenSSL Validating Certificate Path

 "keytool" and "keystore" from JDK

 "OpenSSL" Signing CSR Generated by "keytool"

 Migrating Keys from "keystore" to "OpenSSL" Key Files

 Certificate X.509 Standard and DER/PEM Formats

 Migrating Keys from "OpenSSL" Key Files to "keystore"

 Using Certificates in IE (Internet Explorer)

 Using Certificates in Firefox

 Using Certificates in Google Chrome

 Outdated Tutorials

 References

 PDF Printing Version