All Questions

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Can $r$ and $s$ from an ECDSA signature be negative numbers?

I have an ECDSA implementation in Mathematica over secp256k1 and $r$ and $s$ are always positive numbers. But if you encode them as bytes, the most significant byte can be over ...
9 views

Calculate entropy of key derived from PBKF2 function

I am using PBKF2 to derive a encryption key from a password. suppose entropy of my password is y and my PBKF2 function has x number of iterations. So how to calculate the entropy of finale key derived ...
16 views

Is SSL broken? If so, what can I do about it?

But recently, with the scandals about the filtrations, I read that the NSA (and of course others, but I'm not particularly worried about NSA) is able to break SSL and track your data. It is true? ...
18 views

Guessing encryption algorithm based on key and ciphertext

Is it possible to tell which encryption algorithm was used, assuming I have a key and a encrypted text? To not complicate the situation let assume we are speaking about symmetric algorithms only. ...
16 views

How to perform authentication without central server in P2P?

How you be sure that the man who you're talking with is the one who you think he is? I.e. how to perform authentication in P2P network without central trust server or Certificate Authority? I'm just ...
35 views

How to use HKDF to combine two keys

I have heard that to combine two keys HKDF is better than using XOR function. But if you look at the HKDF RFC I could not figure out how to use it for concatenating two keys. What I can see is HKDF ...
34 views

How to understand unforgeability, strong unforgeability and existential unforgeability?

The definitions of unforgeability, strong unforgeability and existential unforgeability always confuse me, who can give me a plain explanation of the three definitions and the differences between ...
24 views

Pollard’s Rho Method

I can't get my head around Pollard’s Rho Method for solving discrate log problem I have read in a book: The basic idea is to pseudorandomly generate group elements of the form α^i · β^j ...
49 views

Outsourcing arbitrary computations

Consider the following scheme. Alice wants Bob to make some computations for her, but she doesn't want to reveal the data on which he's going to do it. So, she encrypts the data, sends them to Bob, he ...
41 views

How is password character validation in 3D secure is implemented?

We have a website which stores hashed passwords in the database. During logins we hash the password entered by user and compare two hashes. This is quite standard so far. Our client which is in ...
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131 views

RSA exhibits symmetrical properties

This question is broken into two sections really: Symmetry in RSA I have been analyzing raw RSA and I have noticed some interesting symmetrical properties of the algorithm. Assume that $M$ is a ...
93 views

Calculation of time to crack SHA-256 hash

A problem is given: 1 million users are authenticated with 9-digit PIN codes (e.g. 343534643). The PIN values are stored as hash values in a database. The hash is SHA-256, and is computed as: ...
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Attacks against El Gamal private key [duplicate]

El Gamal encryption involves picking (p,g,b) which is our public key. We compute b=a^x mod p. Here, x is the private key which we don't know. What are some efficient and strong algorithms today used ...
131 views

Would it be possible to create a game where one would need to decrypt a simple encryption?

This might sound pretty weird, but I was thinking of a game a person could play alone with a pen and paper. I got this idea where the person would write a random four letter string on a paper, and ...
41 views

Can someone Decrypt this for me? I cant figure it out [on hold]

my friend gave me this message and said it was for me, he made it using a code encryption thingy he made. I know for a fact that it IS a message and I really need to know what it says. I thought that ...
106 views

Attacks against El Gamal private key

El Gamal encryption involves picking $(p,g,b)$ which is our public key. We compute $b=a^x$ $mod$ $p$. Here, $x$ is the private key which we don't know. What are some efficient and strong algorithms ...
37 views

Authentication mechanism for low memory, low computing power device

I am looking for an authentication mechanism that works best with low memory, low computing power devices. I came across a paper "A Practical Zero-Knowledge Protocol Fitted to Security Microprocessor ...
78 views

What exactly is inside a private key?

May sound stupid to many, but I would like to have some pointers on what exactly is contained inside a private key. I have decent understanding of public/private keys/certificates (have created them ...
66 views

What does pseudo pre-image of a hash function mean?

So finding a pre-image means given the hash value, one tries to find a message that gives this value using the function's standard IV. What about pseudo-preimage?
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Anyone knows *08FA77CAB469297F05D? [on hold]

I need decrypt this text, but i don't know the crypto. Help me. More few pass: 6387DC55D6497DD2F01 08FA77CAB469297F05D 7BA8FAFA952B2000D22