# All Questions

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### Why do PKI schemes need security proofs? [closed]

When it comes to designing new PKI-based key-exchange protocols, why are security proofs needed? Without them, can we show a protocol's security? Does there exist a PKI-based key-exchange protocol ...
226 views

### What is the relation between hash chaining and chosen prefix attack

I read that hash chaining can be used to prevent hash collisions, while the chosen prefix attack allows hash collisions for algorithms like MD5. How are they related? Does hash chaining prevent the ...
262 views

### How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
130 views

### Resources for basics of lattice crypto [closed]

I'm looking to fill in the gaps of my knowledge of lattices. Can anyone point me towards papers or books that introduce lattice crypto assuming a fairly solid math background? Mods: Feel free to ...
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### Signature with appendix

I see sometimes signatures schemes with appendix. This is about signatures schemes in which the message is needed in the verification algorithm, that is, the ouput of the signature algorithm is of the ...
84 views

### How to choose the appropriate public (i, m) and private (j, m) keys?

I studied some encryption and decryption and I have found some very interesting problem to solve on the internet. I hope I am writing to right site - there are so many in StackExchange otherwise I ...
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am sorry, an a beginner, so please forgive me if i make mistakes, so here is what I understood: PBKDF2: uses HMAC, so, the message is the password, and the key that crypts the message is the salt? or ...
546 views

### Reversing SHA1 (don't know the correct term)

Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))? pad(A) means its length is exactly 1 block (64 bytes for SHA-1) If yes, for which other hash functions it will work too? ...
124 views

### Size of Parameters in Polynomial Key-Splitting Algorithm

I've seen the elegant way of splitting a key among different people so that only a certain number need to be present to re-compute the key, yet nobody has enough information to re-compute the key on ...
142 views

### Weak One Way Function

Show The function $mult(a,b)$ is weak one way if the Integer Factorization Assumption is true. I am read the proof of this enunciated but I want know if I understand this in my way. The proof use the ...
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### reduces the coefficients of a modulo 3 on NTRU

i'm still don't understand about 'reduces the coefficients of a modulo 3' on NTRU tutorial $a = f*e = 3 - 7X - 10X^2 - 11X^3 + 10X^4 + 7X^5 + 6X^6 + 7X^7 + 5X^8 - 3X^9 -7X^{10} \pmod{32}.$ Note ...
161 views

### Solving congruences using PARI

I'm having trouble finding info in the docs about how to solve a system of congruences. The closest I can find is 'matsolvemod' in here: ...
206 views

### How to secure a mental poker protocol? [closed]

I would like to implement a mental poker protocol in a secure fashion. How should I go about that without (preferably) infringing on the Mental Poker Framework patent?
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### Why is Blum-Goldwasser not IND-CCA-2 secure?

Consider the Blum-Goldwasser encryption scheme as described on Wikipedia. I was told that it was not IND-CCA-2 secure. I heard there was malleabilty, probably it has to do with XOR-ing. But I do not ...
391 views

### Is AES reducible to an NP-complete problem?

Is breaking AES NP-hard? Can the security of AES be reduced to a NP-complete problem? If it is reducible, what does the reduction look like? If it is not reducible, why do we assume it is secure?
510 views

### Kryptos : K1. What is the origin of the “palimpsest” keyword?

I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4. I understand that the keyword "palimpsest" was reverse-engineered using the tableau (and brute-force computer processing), ...
466 views

### Learning cryptography using a FPGA

I have a FPGA and am curious what cryptographic applications I can use with it. I'm just a hobbyist / security researcher and not a professional cryptographer. Since I'm creating my own curriculum, ...
210 views

### What is the complexity of the Square attack against the reduced 4-rounds 128-bit Rijndael variant?

I'm looking at a square attack against a reduced version of AES-128 with only 4 rounds (with block and key size of each 128 bit). I have a set of 256 plaintext-ciphertext block pairs. What is the ...
939 views

### AES encryption for images [closed]

Why AES based encryption is not recommended for encrypting images with high redundancy in their content? for example, the encryption of an image which shows a bird in the blue sky. Most of the pixels ...
202 views

### How to plot the distribution of a ciphertext?

Is there any plot or visualizing program that can plot the distribution of a plaintext and then the distribution of the ciphertext after applying a ciphering encryption algorithm? I am interested ...
171 views

### Design criteria for AES

I hope somebody can help me understand the design criterias for AES. Therefore, I would be really thankful if somebody could explain "non-linearity" in this context. A criteria for the s-box in AES ...
277 views

### Why can't Homomorphic encryption schemes support algorithms with conditions/branching?

If it isn't already apparent from the title of my question, i should make clear that I have only a very basic understanding of homomorphic encryption. I would like to know why homomorphic encryption ...
140 views

### Zero Knowledge auth schemes with weak secret

In Zero Knowledge auth schemes the public DH factor of each peer is encrypted with a potentially weak pre-shared secret and the resulting ciphertexts are exchanged over an insecure channel. Why is no ...
263 views

### Polynomial for secure communication

Can we use a polynomial $P(x)$ to securely communicate ? For example Alice & Bob agree on a degree of a polynomial. The value $x$ & the coeficients are generated from a seed using a hash ...
436 views

### SSTP MSCHAP-V2 Authentication before SSL or after SSL Session

So with the recent news that there's a lovely new tool to crack MSChapV2 packets. So the question I have is on a SSTP Connection is the MSChapv2 handshake encrypted pre SSL setup or post. Obviously ...
134 views

### Combatting traffic shape analysis with spurious packets

I was reading a question about combatting traffic analysis, and a thought occured. If I send random junk messages periodically, would that defeat traffic analysis? The messages would contain some ...
175 views

### Do these 2 KSA shortcuts weaken RC4?

Alice securely gives Bob a secret key so they can exchange 10 different messages encrypted with RC4. (Messages will include a counter for uniqueness and a MAC for authentication.) For each message ...
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### How to take SHA-1 safely for my particular case?

Let me ask about my toy passwords generator program X5 which I want to improve. X5 uses a secret key and a public key to generate a password.Where any public key is supposed to be known to hackers in ...
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### Can you help me understand ECC Cryptography and it's algorithm?

I want to know the basic understanding of ECC algorithm for cryptography. But I am not aware of the algorithm. Can anyone provide me with a basic explanation of the algorithm?
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### How can I control the output of a hash function to output to specific data according to similarity?

I do not know if the question lies exactly in that field but I'll give it a try unless rejection. I want to study methods of applying LSH functions to feet in a specific area of digest values. ...
56 views

### How to calculate kinv from the given k value

I am implementing an ECDSA NIST test vectors verification application. The test vectors are taken from http://csrc.nist.gov/groups/STM/cavp/#09. One of the test vectors is given below: ...
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### Definition of perfect secrecy using ciphertext

This week my professor in class taught us the definition of perfect secrecy. He said that for any ciphertext the probability that it might have come from any message in the message space should be ...
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### Generating the keys for the RSA cryptosystem in probabilistic polynomial time

In general every public key cryptosystem has'' a probabilistic polynomial time algorithm $G$ such that $G(1^k)=(\textrm{public key}, \textrm{private key=trapdoor})$; $G$ is called the key generator. ...
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### How to implement a Cryptographic Pseudo Random Function

I need three pseudo random functions which all take a seed S (t-bits long). The functions should map from $d$ bits to $d$ bits $d$ bits to $1$ bit $d$ bits to $t$ bits $d$ is $10$ bits $t$ is ...
As we know that in DH key exchange, both Alice and Bob would agree on the parameter $p$ and $g$. Next, Alice would choose a secret key $A$ while Bob would choose a secret key $B$. Alice would compute ...