3,477 reputation
1519
bio website
location United States
age
visits member for 2 years, 9 months
seen 14 mins ago

Jul
24
comment Is there a generic attack on encrypted CRC32 when used as a MAC?
@Antikithira : $\:$ Do the outputs distinguish between invalid padding and invalid CRC? $\hspace{1.3 in}$
Jul
24
comment Different padding rules for Merkle-Damgard and Keccak/sponge function
... by their length and probably also by what they start with. $\;$
Jul
23
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
Let us continue this discussion in chat.
Jul
23
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
@Joshua : $\;\;\;$ Should your comment have "the MAC becomes" instead of "MAC is"? $\:$ I can't figure out how to parse what you wrote. $\;\;\;\;\;\;\;$
Jul
23
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
@otus : $\:$ I just edited in an example. $\;\;\;\;$
Jul
23
revised Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
gave an example
Jul
23
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
It's a "just do it" construction that I'll describe later. $\;$
Jul
23
answered Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
Jul
23
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
If the plaintext message had been modified, then a secure MAC would be overwhelmingly likely to catch that. $\:$ However, there exist encryption schemes such that one can easily modify a single ciphertext so that whether or not that modifies the plaintext depends in a predictable-and-useful way on what the plaintext message was. $\;\;\;\;$
Jul
23
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
... where "it" is ...? $\;$
Jul
23
comment Secure way to store fixed size string of digits
Should the data about the user otherwise stay private? $\:$ What is the size of your strings of digits? $\hspace{.5 in}$
Jul
23
comment Is there a generic attack on encrypted CRC32 when used as a MAC?
@Antikithira : $\:$ Also, is the CRC computers over Headers too or just Data? $\hspace{1.62 in}$
Jul
23
comment Secure way to store fixed size string of digits
Are you assuming the user exists and testing whether they have a given identifier, or testing whether there exists a user with a given identifier? $\;$
Jul
23
comment Secure way to store fixed size string of digits
"and the system should return zero to one results", indicating whether such a user exists or whether a given user has that identifier? $\;$
Jul
23
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
If the decryptor can't reject, then we "care if the ciphertext has been altered" because it might be easy to modify a single ciphertext so that whether or not it is detected that "any bits of the message have been changed by the attacker" depends in a predictable-and-useful way on what the message was. $\hspace{.68 in}$
Jul
23
comment Lowest number challenge scheme
An adversary can just give the output of the Socialist Millionaire protocol. $\;$
Jul
23
comment RSA with modulus n=p²q
More generally, one could also use moduli of the form $\; p^{\hspace{.03 in}j} \hspace{-0.02 in}\cdot q^{\hspace{.02 in}k} \;$ for coprime $j$ and $k$. $\hspace{1.21 in}$ Also, one could make the operations actual permutations by computing gcd(N,x) $\hspace{1.39 in}$ and sending x to gcd*((x/gcd)^e mod N/gcd). $\;$
Jul
23
comment Is there a generic attack on encrypted CRC32 when used as a MAC?
What padding do they use? $\:$ How many possible plaintexts are there? $\;\;\;\;$
Jul
23
comment Lowest number challenge scheme
@owlstead : $\:$ "If you always run both of them," you'd be revealing whether or not $\:a=b\;$. $\hspace{.98 in}$
Jul
22
comment Why is MAC using nonce+message+hash(nonce+message+identifier) not the standard?
I mean that it might be easy to modify a single ciphertext so that whether or not the decryptor rejects depends in a predictable-and-useful way on what the message was. $\:$ (That is not beyond "what MAC-then-encrypt in general allows".) $\;\;\;\;$