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Digital Signature in Application.

Posted on 2004-08-25
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Last Modified: 2010-04-11
Hi Fellow,
I need some urgent assistance from your side regarding digital signature,
I am a bit confuse about this concept, i had covered the theory on the Digital Sign.
Now i need some real facts about digital signature , public and private key,
My First Confusion is:
Who will generate Public and private key in the application, i means if i will add a new user in the application then who and how the Public and the private key of that user will be generated.
Second :
What will be the length of the Public and the private key( in digits) i know the key will be generated of 512,1024 bits ,but what will be the human readable lenght on the Keys, whether the keys will be in Numeric form or in Alpha Numeric for or in Hexa Decimal form,
Third confusion is:
Can we change the public ,private key of the user , then how will be encrypt/decrypt the documents.
Will the change in the keys will change the digtal signature.

forth confusion
core difference between electronic and digital signature.
Please while answering all the above queries, keep one thing in mind that i am fully aware of SHA, RSa, DES, IDEA.
please do not send any link just send me the description of the Above Questions.
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Question by:softsolvers
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Accepted Solution

by:
ErikPhilips earned 250 total points
ID: 11897599
Answer 1: It up to you.  I have personally written software that does Private/Public key encryptions.  You can buy somethnig from someone else or build it yourself.  It really depends on your application.  If you application needs to be compatible with another application (say PGP emai) then you need to find a source that can provide you with either an implementation of the algorythm or the source.

Answer 2:  All keys in all systems are simply numbers.  However you want to display these numbers is up to you.  You could display them as Binary or Decimal or Hexadecimal, it doesn't matter because numerically they are all the same.  I dont know what "human readable length" means, so I may not have completely understood what you were looking for.

Answer 3: Most of the time when you need to change a public or private key using Public Key/Private key encryption you have to change both.  Most secure systems do this that I'm aware of.  Secondly when you change either key, the information needs to be re-encrypted.
(The reason you should recreate both public and private keys is because if you don't it becomes easier to get the private key from the public keys available with 2 encoded messages, not nessesarily possible, just theoretically easier)

Answer 4:  
I'm not aware of any difference between "eletronic" and "digital" when prefixing the word "signature".

0
 

Author Comment

by:softsolvers
ID: 11899358
Thanks ErikPhilips,
From Human readable length i means what will be the length of the Public and teh Private Key,
Is Public key is some thing like 395448548 ???
What is the minimum length we can assign to the Public key and the private key,
and the last one what algo we need to use to generate own public key,
What i feel right now we will take 2 prime no. and then use it to generate primary key ???is it so?????
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Expert Comment

by:ErikPhilips
ID: 11899437
oh, those keys are going to be HUGE.  Length is really up to you, but realize that the smaller it is, the more likely it is to break it and fake messages.  Thats the whole point of how the current Public Key/Private key system works.  Anyone could really find the key mathematically, it would just take TOO long with a large enough keys.  Some people feel safe with 1024 other feel safe with 4096.

http://triade.studentenweb.org/

Click on Gint on the left.

Download PrimeGenerator and RSA.zip.  Thats the basics of ONE type of Public Key/Private Key system.

1024 bit public key looks like: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=dFWx


4096 would look like:
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DyL+oARoLMKVI9mAOXi6LSE2eNonLATBEv5oyPfhmd7NBw2IVat2A5PqqNT3u6pI
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1SoUtY1S8Nf0g4BkyvCQ7EWNsUa0kFlv/YCkMt9LLtjBEXtLRObPdO9fKvyBsn7v
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01D49Vlf3HZSTz09jdvOmeFXklnN/biudE/F/Ha8g8VHMGHOfMlm/xX5u/2RXscB
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iCZE+04VlDEK
=g1X4
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