# All Questions

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### Reduction to cdp,dl or cdh?

Assuming a randomize encoding scheme that takes as input a secret key $\mathsf{sk} \in \mathbb{Z}_p$ for a large prime number $p$. Then the algorithm outputs $g^{\mathsf{sk}x}, x \in \mathbb{Z}_p^*$. ...
164 views

### Factorize RSA knowing several N and E

I did a CRT challenge yesterday and theres one problem I was unable to solve, probably due to my lack of understanding advanced crypto math. Its about RSA. There are ten given pairs of N and E ...
98 views

### PGP public RSA key format

I have been trying to use Go (I could post the code, but I think I posted enough already...) to generate a PGP RSA key. However every time I try to encrypt something with it, something fails. However, ...
33 views

### Ephemeral key is held constant in ElGamal

Is there a known algorithm to recover the sender's messages in ElGamal $\mathbb{F}_p^*$ if the ephemeral key is held constant in two or more transmissions, assuming the messages are always distinct? ...
190 views

### Do Gap-CDH groups exist?

A Gap-CDH group is such that, given group elements $g, a = g^x, b = g^y$, it is hard to compute $g^{xy}$, but, given a group element $c$, easy to verify if $c = g^{xy}$. While such groups have been ...
323 views

### Is it possible to break enigma code with a todays laptop [on hold]

I have a 500 characters enigma encoded text. Random rotors were used (not the ones from wikipedia). I know of this flaw. I can guess some words that sould be in the text, but this probably doesn't ...
2k views

### Can you explain Bleichenbacher's CCA attack on PKCS#1 v1.5?

I've studied that the Bleichenbacher's CCA attack on PKCS#1 v1.5. is a base to many versions of attacks in the area. I'm trying to understand that attack, but every explanation I saw starts with the ...
157 views

### Fast attack on approximate GCD problem?

This question is about the approximate GCD problem which is defined as follows: Given any number of the approximate multiples $a_i = p \cdot q_i + r_i$ of $p$, where $p$, $q_i$ and $r_i$ are integers, ...
26 views

### CPA-security of a pseudorandom permutation encryption scheme

Let $F$ be a pseudorandom permutation, and define a fixed-length encryption scheme $(Gen, Enc, Dec)$ as follows: on input $m \in$ $\{0,1\}^{n/2}$ and key $k \in \{0,1\}^n$, algorithm Enc ...
152 views

### Can a 1 byte difference in AES 128 bit keys make huge difference in output?

If we take some randomly generated key of AES-128 and we change any random 1 byte of that 16 byte key, will this make huge difference in the AES cipher text generated over same input string? Does ...
178 views

### Regular MACs vs Carter-Wegman MAC

Carter-Wegman MAC variants (VMAC, UMAC etc) are known to be very fast and efficient when compared to MAC algorithms that are based on block ciphers and compression functions (like HMAC, CMAC etc). ...
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### How can I generate a good password from a SHA512 hash?

I have to change local administrator passwords on machines. I don't want to store password in a database. I have to generate a password that I can find later to connect to the machine again. So I ...