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Last Post by jbennet

thnx ervy1 .... jbnnet i'm not exctly lookin for some1 doin btech ... i'm lookin for some1 good in cryptography ... digital signatures in particular


look at an A2 computing textbook for AQA theres a massive chapter on digital sitgnitures and encryption.


wowowow ... dude b a bit specific ... "A2 computing text book for AQA "" ??? gimme some author publisher books name and something like tht


From my textbook:

E-mail may be more easily intercepted and altered than paper mail without the knowledge of
either the sender or the recipient.
In symmetric encryption, the same key is used to encrypt and decrypt a message. In
asymmetric encryption, one key is used to encrypt a message and another key is used to
decrypt the message.

Symmetric encryption is NOT used for encrypting e-mail messages as if you send the key with the message, anyone can decrypt the message and so the key would need to be sent by means other than email e.g post, otherwise anyone could intercept the key and use it do decrypt the message;

In asymmetric encryption, one key is made publicly available (the public key) and the
other key is kept secret by its owner (the private key).


Jack and Jill want to communicate with each other confidentially, and they each have a
private and a public key.

If jack wanted to encrypt a message to send to Jill, which only Jill can read he would need Jills public key. Jill would use her private ket to to decrypt the message sent by Jack.

A digital signature authenticates the message, that is, it verifies that the message came
from the given sender and that it has not been tampered with. A Digital signature is produced by:

a)hasheing the message data into a message digest;

b)encrypting the message digest with the senders private key

If If Jack digitally signs the message sent to Jill, Jill can verify Jack’s digital signature as follows:

a) Jills software decrypts the signature using Jack’s public key contained in digital certificate sent with the message

b) to verify Jacks public key she decrypt digital certificate a using Certificate Authoritys public key

c)Jill’s software then hashes the mesage into a message digest;

d)If the recalculated message digest is the same as the original message digest (decrypted signature) then Jill knows that the signed data has not been changed


OMG dude ... i kno wat ios cryptography and how it is done ... the problem is in implementation ... how do u convert the message into integers, ... how do u store it, how do u make the digests, how do u handle the converted message using RSA's or DSA's or Elgamal .... the practical stuff thts wat i'm lookin for ....

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