| Cryptography |
 |
The moment you hear the word Cryptography, we get images of the unforgetable 'Roja', Arvind Swamy playing Cryptologist. Well get to know all about(almost) Cryptography.
Cryptography, to most people, is concerned with keeping communications private. Indeed, the protection of sensitive communications has been the emphasis of cryptography throughout much of its history. As we will see, however, this is only one part of today’s cryptography.
Encryption is the transformation of data into some unreadable form. Its purpose is to ensure privacy by keeping the information hidden from anyone for whom it is not intended, even those who can see the encrypted data. Decryption is the reverse of encryption ; it is the transformation of encrypted data back into some intelligible form.
Encryption and decryption require the use of some secret information, usually referred to as a key. Depending on the encryption mechanism used, the same key might be used for both encryption and decryption, while for other mechanisms, the keys used for encryption and decryption might be different.
But today’s cryptography is more than secret writing, more than encryption and decryption. Authentication is as fundamental a part of our lives as privacy. We use authentication though out our everyday life, for instance when we sign our name to some document. As we move to a world where our decisions and agreements are communicated electronically, we need to replicate these procedures.
Cryptography provides mechanisms for such procedures. A digital signature binds a document to the possessor of a particular key, while a digital timestamp binds a document to its creation at a particular time. These cryptographic mechanisms can be used to control access to a shared disk drive, a high security installation or to a pay-per-view TV channel.
But the field of cryptography contains even more when we include some of the things cryptography enables us to do. With just a few basic tools it is possible to build elaborate schemes and protocols which allow us to pay using electronic money, to prove we know certain information without revealing the information itself, and to share a secret quantity in such a way that no fewer than three from a pool of five people (for instance) can reconstruct the secret.
While modern cryptography is growing increasingly diverse, cryptography is fundamentally based on problems that are difficult to solve. A problem may be difficult because its solution requires some secret knowledge, such as decrypting an encrypted message or signing some digital document, or the problem may be hard because it is intrinsically difficult to complete, such as finding a message which produces a given hash value.
So as the field of cryptography has advanced, the dividing lines for what is and what is not cryptography have become blurred. Cryptography today might be summed up as the study of techniques and applications that depend on the existence of difficult problems. A cryptanalyst attempts to compromise cryptographic mechanisms, and cryptology (from the Greek êñõðôüò ëüãïò, meaning hidden word) is the discipline of cryptography and cryptanalysis combined.
Brief History
The concept of securing messages through cryptography has a long history. Indeed, Julius Caesar is credited with creating one of the earliest cryptographic systems to send military messages to his generals. (When Julius Caesar sent messages to his trusted acquaintances, he didn't trust the messengers. So he replaced every A by a D, every B by a E, and so on through the alphabet. Only someone who knew the shift by 3 rule could decipher his messages.)
Throughout history, however, there has been one central problem limiting widespread use of cryptography. That problem is key management. In cryptographic systems, the term key refers to a numerical value used by an algorithm to alter information, making that information secure and visible only to individuals who have the corresponding key to recover the information. Consequently, the term key management refers to the secure administration of keys to provide them to users where and when they are required.
Historically, encryption systems used what is known as symmetric cryptography. Symmetric cryptography uses the same key for both encryption and decryption. Using symmetric cryptography, it is safe to send encrypted messages without fear of interception (because an interceptor is unlikely to be able to decipher the message); however, there always remains the difficult problem of how to securely transfer the key to the recipients of a message so that they can decrypt the message.
A major advance in cryptography occurred with the invention of public-key cryptography. The primary feature of public-key cryptography is that it removes the need to use the same key for encryption and decryption. With public-key cryptography, keys come in pairs of matched “public” and private keys. The public portion of the key pair can be distributed in a public manner without compromising the private portion, which must be kept secret by its owner. An operation (for example, encryption) done with the public key can only be undone with the corresponding private key.
Prior to the invention of public-key cryptography, it was essentially impossible to provide key management for large-scale networks. With symmetric cryptography, as the number of users increases on a network, the number of keys required to provide secure communications among those users increases rapidly. For example, a network of 100 users would require almost 5000 keys if it used only symmetric cryptography. Doubling such a network to 200 users increases the number of keys to almost 20,000. Thus, when only using symmetric cryptography, key management quickly becomes unwieldy even for relatively small-scale networks.
The invention of public-key cryptography was of central importance to the field of cryptography and provided answers to many key management problems for large-scale networks. For all its benefits, however, public-key cryptography did not provide a comprehensive solution to the key management problem.
Find out more about Cryptography
|
