asymmetric cryptography Flashcards
positives of asymmetric encryption
can be used to send secret keys
dont need secure key exchange
dont need trust between sender and reciever
negatives of asymmetric encryption
slow encryption speed
security issues with encryption long plaintexts
what does the diffie-hellman key exchange do
allows you to share a secret key without prior knowledge of the person
how does the diffie-hellman key exchange work
both the sender and receiver have a prime number p and generator g(system wide)
they then both choose their own secret number between 1 and p -1
both calculate g ^ chosen number and send them to eachother
once recieved they then do that key ^ of their chosen number
not the generator has been put to the power of both numbers which means that they both now have the same value
why does the diffie hellman key exchange work
due to the discreet log problem
makes it mathematically hard to figure out what the first number the g was put to the power to is
how does an asymmetric encryption system work
public key is available to everyone and is used to encrypt whilst the private key is used to decrypt
what are three examples of asymmetric encryption systems
el gamal
rsa
rabin
how is rsa deterministic
if you use the same plaintext then youll get the same cipher
how do we make rsa not deterministic
using rsa-oaep; rsa with optional asymmetric encryption padding
how do we encrypt with rsa
using the public key (n,e)
cipher = m^e mod n
how do we decrypt with rsa
using the private key d and n from the public key
plaintext = c^d mod n
how do we encrypt with rsa-oeap
generate a random value r
a = hash1(r) XOR message
b = hash2(a) XOR r
ciphertext = (a||b)^e mod n ; concatenate a and b then encrypt with public key
how do we decrypt with rsa-oeap
firstly using the secret key to decrypt gets (a||b) by performing c^d mod n
using the hash to get r; hash2(a) XOR b = r
using the hash to get m; hash1(r) XOR a
how do we sign with rsa signatures
apply the decryption algorithm using the secret key
a = hash(m)
signature = a^d mod n
how do we verify rsa signatures
apply the encryption algorithm with the public key
a = (sig)^e mod n
verify hash(m) = a
