Abstract by anuja a sonalker on Asymmetric Key Distribution

2.3 Digital Signatures: 
Public key systems are used for secret data sharing as well as authentication. Secret data 
can be exchanged by using the public key for encryption and its private key for 
decryption. In certain Public Key systems, the roles of the two keys can be reversed, the 
resulting process is called authentication. Since the public key being used is known to all 
but its corresponding private key is maintained private, if a message were to be signed by 
someone, only that public key corresponding to his private key would be able to verify 
the message. If the recipient were to obtain a sensible copy after using the sender’s public 
key to decrypt, it would mean that this message could only have been signed by the 
source who claims to have signed it. Thus he is validated or authenticated. This type of 
ciphertext is a digital signature as it possesses the distinct mark of the person encrypting 
it. Digital signatures may be used to sign certificates, which are documents declaring 
something which needs to be endorsed by some authority and does not contain any 
sensitive information. Digital Signatures are widely used in authentication, and certificate 
related issues. 
2.4 RSA Algorithm 
The RSA is a popular public-key cryptographic algorithm invented by Rivest, Shamir and 
Adleman [8]. It uses the pairs (e, N) and (d, N) as public and private keys respectively 
and exponentiation as the common method for encryption and decryption. N is the 
modulus and is computed to be the product of two very large primes p and q. For 

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authentication or signing certificates, each user makes his decryption key (e) public while 
the encryption key (d) is held in secrecy.
The signed certificate S = (M
d
) mod N 
And the message M = (S
e
) mod N.