Author Deven Puri
Roll no 03329023





problem 1  Suppose A's Diffie-Hellmann parameters (P, g) are (24691, 106) respectively and his public key is 12375, write a program to compute A's private key.

sol: c program is in file hellman.c .If inputs are (p,g) 24691 106  and public key 12375 
output is 22392.
logic is keep computing powers of g mod p,if Xth power of g mod p is 12375 then X is your answer.



problem 3
What effect does a transmission error in C1 (first bit of cipher text) have on the decrypted cipher text at the reciever?. Assume CBC mode
sol : in CBC mode encryption and decryption is done in blocks of 64 bits .A 1 bit transmission error will corrupt two blocks 

What is the effect in the cipher text block due to an error in P1 of plain text?. Assume CBC mode.
What is the error at the reciever?
sol: Obviously crypography does not deal with error in plain text.The decrypted text will be same as encrypted plain text.

If a bit error occurs in the i th transmitted byte in CFB mode, how far does the error propagate?. 
sol: the decryption of the ith byte and next eight transmitted bytes will be affected   




problem 2
program  SignDigest(in file SignDigest.java) 
run "Signdigest cgic.html >output"
output file contains the figures