Chapter 4 and 5: Public Key Cryptography/ Hash functions Flashcards
There are two keys describe the public key and private key to the sender and recipient
sender uses recipients public key to encrypt
Recipient uses private key to decrypt
Public key cryptography is based on….
trap door one way function, one way meaning it is easy to compute in one direction but hard in the other direction
what is a digital signature
sign by encrypting with your private key, any one can verify the signature by decrypting with public key.but ONLY YOU could have signed it.
the general knapsack is …
NP-complete
general knapsack is ..
hard to solve
super increasing knapsack
is easy to solve, each weight greater than the sum of all previous weights
what are the weakness of knapsack
Trap door, one way, lattice reduction
Trapdoor with knapsack is
convert SIK into general knapsack using modular arithmetic
one way knapsack is
general knapsack easy to encrypt, hard to solve.
knapsack is secure or insecure
insecure
RSA
2 large prime numbers, N=pq is the modulus.
RSA public key is
(N,e)
RSA private key is
d
what breaks the RSA
factoring the modulus breaks the RSA
what is Diffie Hellman (g^a and g^b)
Not used for encrypting or signing
it is based on discrete log problem
in diffie hellman what can trudy find to get k
trudy can find a or by then she gets the key k , if trudy can solve discrete log problem she can find a or b
what must you be aware of in MIM
Man in the middle, attack on diffie hellman
digital signature provides what
provides integrity and on repudiation
No non-repudiation with ..
Symmetric keys
what does the certificate contain
it contains the name of the user and users public key and other info. it is signed by the issuer a CA certificate authority
the signature on a certificate is verified using what
CA’s public key.
what is PKI
Public key infrastructure: the stuff needed to securely use public key crypto
what are the three PKI trust models
Monopoly model, oligarchy model, anarchy model
what are the plus’s in symmetric key
sped, no public key infrastructure (PKI) needed
what are the plus’s in public key
signatures (non-repudiation)
no shared secret (but, private keys…)
what are the 5 things a crypto hash function must have?
Compression- output length is small efficiencry- easy to compute for any x one-way wak collision resistance strong collision resistance
what are the popular crypto hashes
MD5 and SHA-1
what is MD5
128 bit output
MD5 collisions are easy to find
invented by Rivest
what is SHA-1
160 but output
a U.S government standard inner workings similar to MD5
what is HMAC
a hashed MAC
where are hash’s used
authentication message integrity message fingerprint data corruption detection digital signature efficiency
Spam reduction work for the sender is
2 to the N hashes
spam reduction work for the recipient is
always 1 hash
spam reduction chose n that is
work acceptable for normal email user
work is too high for spammers
where do we use random numbers
generate keys
symmetric keys
RSA: prime numbers
Diffie Hellman: secret values
what is entropy
is a measure of randomness
where are random numbers being used to gnerate keys
Symmetric keys
RSA: prime numbers
Diffie Hellman: Secret values
cards that are shuffled what factor
52! > 2^225 possible shuffles
Randomness two features
can get quality random bits by such methods
BUT quantity of bits is very limited
what is watermark’s two features
visibility and robustness
describe visibility in water mark
Invisible- watermark is not obvious
visible such as TOP SECRET
what are the two features in robustness
robust and fragile
describe robust
robust is readable even if attacked example add robust invisible mark to digital music, if pirated music appears on internet can trace back to original soure of leak
describe fragile
fragile is damaged if attacked example add fragile invisible mark to audio file, if watermark is unreadable, recipient knows that audio has been tampered integrity
