What Is Cryptography?

In this section we will give you a brief description of what cryptography is, the basic terminology, etc. and explain how iSafeguard™ works.

Basic Terminology

Cryptography is the science of mathematical manipulation of data for the purpose of securing the data so that the information is hidden from any one for whom it is not intended, even those who can see the manipulated data.

Data in its original form is known as plaintext or cleartext. The manipulated data is known as ciphertext. The process for producing ciphertext from plaintext is called encryption or encipher. The process for producing plaintext from ciphertext is called decryption or decipher.

Now that you know the basic terminology let's look at an example.

Shared Secret Cryptography

Let's assume that you have a very important message you want to send to your best friend, Bob, "Hello, Bob, how are you doing?" You want to send it securely; even people who intercept the message won't be able to read it. So you figured out an algorithm to encrypt the message. Here are the algorithm details: you replace letter "A" with letter "D", letter "B" with letter "E" and so on, the whole encryption table looks like this:

After encrypting, your message reads like this "Khoor, Ere, krz duh brx grlqj?" You tell Bob the secret and Bob can read the message. Of course you must find a way to tell Bob the secret securely; otherwise anyone who knows the secret can read your message. This is a very simple encryption and decryption algorithm (known as Caesar Cipher). You can imagine how important it is to keep the secret.

Since the same key is used for encryption and decryption in shared secret cryptography it is also known as symmetric cryptography and the key is called symmetric key.

Public Key Cryptography

In contrast, public key cryptography doesn't count on this shared secret to communicate securely. You create an encryption key and a decryption key. When a message is encrypted using your encryption key, it can only be decrypted using your decryption key. You make your encryption key public (thus public key), list it in the directory, email it to other people, whatever. But you must keep your decryption key private (thus private key). The decryption key (or private key) should never leave your hand.

If someone, say, Bob, wants to send you a secret message he can use your encryption key to encrypt his message, only you, with your decryption key, can decrypt the message. There is no shared secret between you and Bob to allow you to communicate securely. This is the key advantage of public key cryptography.

Since you now understand that an encryption key is a public key, a decryption key is a private key, we will use the terms public key and private key when we mean encryption key and decryption key from now on. The public key and private key are related - they are a pair, called key pair. When we say a key pair we mean a public key and the related private key.

Since different keys are used for encryption and decryption in public key cryptography it is also known as asymmetric cryptography.

Note: Since a private key is always stored with the corresponding public key we sometimes use private key and key pair interchangeably if that does not cause confusion.

Modern Cryptographic Algorithms

The above discussion about shared secret cryptography and public key cryptography is overly simplified - but it does give you the ideas. In modern cryptography much more complex systems are used.

The following lists some of the algorithms commonly used in industry and government:

• RC4 - symmetric algorithm
• RC2 - symmetric algorithm
• DES - symmetric algorithm
• 3DES - symmetric algorithm
• AES - symmetric algorithm
• MD5 - hash algorithm
• SHA1 - hash algorithm
• RSA - public key algorithm

Public key system has great advantage over shared secret key system because it solves the key distribution problem - a key issue in shared secret cryptography. However public key algorithm such as RSA is very slow while shared secret algorithms are much faster. Therefore in real cryptosystems they are used together.

Encryption: How iSafeguard™ Works

iSafeguard™ is a hybrid cryptosystem. It takes advantages of both shared secret and public key algorithms. Here is how it works.

When encrypting a random symmetric key is generated to encrypt the message. Then the intended recipients' public keys are used to encrypt the random symmetric key. Finally the encrypted random symmetric key and the encrypted message are sent to the recipients.

When decrypting one of the recipients' private key is used to decrypt the random symmetric key. And then the random symmetric key is used to decrypt the message.

iSafeguard™ supports three symmetric algorithms RC2, RC4, 3DES, two hash algorithms MD5 and SHA1, and one public key algorithm RSA.