Is my PublicKey common for communications with all my peers?

[RajeshSomasundaram]

Consider I have to send different secure messages to 5 people. I give my public key to them or they take my public key from repository.I send a secure message to person1 and he decrypts the signature(encrypted document) with my public key.
Now, Is it possible for other persons to decrypt my signature(say,they eavesdrop!),because they are in posession with my public key(recieved through prior communications) ????
And, what is the role of private key of mine and that of the reciever??
Through what mechanism, do we tell that the message is intended to be recieved by a particular person??? Ask WHY? and WHY NOT? for deeper learning

 

[afe]

the answer to this qweston lies in Mathematics. Try to find through the Web book that describe mathematical background of public-key encryption, you'll probably find the mechanism there. Talking shortly, there aren't efficient algorythms to find private key out of the message and public key. It is not proven that it is impossible either. But all the world use public-key encryption and it is convinient and safe.

 

[hisrini]

Hi Rajesh,
U will sign the document with ur private key. Signing the document involves generating message digest(an hashing algoritm, one way algorithm is used for generating the message digest. this message digest is nothing but a number occupying some bits.) on the message u want to send and encrypting the message digest with ur private key. even if people have ur public key they can decrypt the signature and what can they do with the message digest.

If u want to send a message, then you will encrypt the message with the other party's public key so that he can only decrypt the message and view it.

Coming to ur private key, it is generally used for signing the messages. ie if u encrypt the message digest with ur private key, the other party can be sure that u r the person who have send it, since u r the only person having the private key.

rgds,
srini