In this paper the term "simultaneously hardcore" is defined to be: "We say that a block of bits of x are simultaneously hard-core for a one-way function f(x), if given f(x) they cannot be distinguished from a random string of the same length." Could somebody give me an example of something th...

I stumbled across a question while studying about MAC, I was thinking if the attacker knows the key and the MAC and he wants to change the message to send to the victim, Then how many blocks can he change with whatever he wants?? I think that he is unable to change the last plaintext block as t...

I'm trying to design an extension to Shamir's Secret Sharing that would allow the participant to specify a password instead of remembering/storing a large integer or binary data. So far, I have two ideas, both based on some PBKDF: Run the password through a strong PBKDF to make $k_i$ then publi...

Given a message $M$ and a 256 bit key $K$, perform HMAC($K$, $M$) with a 256 bit hash function resulting in: $a$ = 9a58e0eef2effc968d27cd61c47394867ceae43c7a877d59938f8400fe1a0204 Now take every second hexadecimal symbol resulting in a 128 bit hash: $b$ = a80e2fc6d7d14346ca4ca7d93f40ea24 Assu...

Disclaimer: I was looking for a place to ask this question on SE and this site seems to be the most fitting. If this question doesn't belong here, feel free to redirect me. Just out of boredom and curiosity, I've started to develop my own secret notation alphabet (for manual use, no computers in...