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  • The encrypted text can be stored in a readable file, or transmitted over unprotected channels.
  • To make sense of the cipher text, it must be decrypted back into clear text. This is done with some other algorithm that uses another secretpassword or number, called the decryption key.

All of this only works under three conditions:

  • The encryption function cannot easily be inverted (cannot get back to clear text unless you know the decryption key).
  • The encryption and decryption must be done in some safe place so the clear text cannot be stolen.
  • The keys must be protected. In most systems, can compute one key from the other (sometimes the encryption and decryption keys are identical), socannot afford to let either key leak out.

Public key encryption: new mechanism for encryption where knowing the encryption key does not help you to find decryption key, orvice versa.

  • User provides a single password, system uses it to generate two keys (use a one-way function, so cannot derive password from either key).
  • In these systems, keys are inverses of each other: each one could just as easily encrypt with decryption key and then use encryption key to recover clear text.
  • Each user keeps one key secret, publicizes the other. Cannot derive private key from public. Public keys are made available to everyone, in aphone book for example.

Safe mail:

  • Use public key of destination user to encrypt mail.
  • Anybody can encrypt mail for this user and be certain that only the user will be able to decipher it.

It is a nice scheme because the user only has to remember one key, and all senders can use the same key. However, how doesreceiver know for sure who it is getting mail from?

Digital signatures

Positive identification: can also use public keys to certify identity:

  • To certify your identity, use your private key to encrypt a text message, e.g. "I agree to pay Mary Wallace $100 per year for the duration oflife."
  • You can give the encrypted message to anybody, and they can certify that it came from you by seeing if it decrypts with your public key.Anything that decrypts into readable text with your public key must have come from you! This can be made legally binding as a form of electronic signature.

This is really even better than signatures: harder to forge, and can change if compromised. Note that this idea was developed by anundergraduate (Loren Kohnfelder) in 1978 as part of his undergraduate thesis (at MIT).

These two forms of encryption can be combined together. To identify sender in secure mail, encrypt first with your privatekey, then with receiver's public key. The encryption/decryption functions to send from B to A are:

Encryption appears to be a great way to thwart listeners. It does not help with Trojan Horses, though.

Old federal Data Encryption Standard (DES). Is not public-key based, but has been implemented efficiently and appears to berelatively safe.

New Advanced Encryption Standard (AES), called Ryndal.

General problem: how do we know that an encryption mechanism is safe? It is extremely hard to prove. This is a hot topic forresearch: theorists are trying to find provably hard problems, and use them for proving safety of encryption.

Summary of Protection: very hard, but is increasingly important as things like electronic funds transfer become more andmore prevalent.


We would like to thank Prof. Barton Miller for sharing as well as for his valued advice

Questions & Answers

how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
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