2
votes
1answer
90 views

Generating shared secret random permutation

There are three blind card game players. Each player does not trust any other, even prejudicing other two players may not be blind, or there may be others in the room, peeking at their cards. In ...
1
vote
1answer
94 views

Is it possible to encrypt data in such a way that it cannot be decrypted with the key used to encrypt it but can be decrypted with another key

I'm very new to cryptography and encryption so I apologize if the answer to this is well known, but I can't find anything in my research. The crux of the problem is the need to store data on an ...
2
votes
1answer
58 views

ECDSA signature verifiable 1-way transformations

Alice signs a message $m$ with her private key, yielding a signature ($r$,$s$). I want to prove to someone else that I have this signature, but I don't want them to have the knowledge of what ...
1
vote
1answer
106 views

Perl DES PCBC as protection against decryption/crypt analysis

Is error propagation in DES PCBC a good method to prevent decryption/crypt analysis by third parties? If I had a very large file encrypted with Perl's DES with the PCBC option, and then removed the ...
2
votes
1answer
99 views

Implementing AugPAKE over ECC

The AugPAKE spec says it can be implemented over elliptic curves. This sounds very promising, but they don't actually back that claim. Can this really be achieved? If so, how would one go about ...
1
vote
1answer
56 views

Can CBC encryption have separate keys for separate blocks of plain text?

Can we have separate key for separate blocks which we get while operating a plain text message using CBC encryption model? If yes, what are it's advantage? Please enlighten me.
4
votes
2answers
165 views

Use cases for “online” authenticated encryption?

What is the the point of an "online" mode for an authenticated cipher? I understand what "online" means in this context. However, I have trouble coming up with applications that would benefit from ...
0
votes
2answers
91 views

Times of nested algorithms in proofs of security

Proofs of security may be constructed such that an adversary $A$ is used to construct an adversary $A'$. The reduction/algorithm which uses $A$ has to perform a number of computations in order to ...
1
vote
1answer
73 views

Is it secure to choose d in a RSA key pair?

An RSA key pair consists of the private key $(n,d)$ and a public key $(n,e)$ such that $de \equiv 1 \bmod{\lambda(n)} $. Usually one chooses a small $e$ and computes $d$ by inverting it modulo ...
0
votes
0answers
89 views

Any field in a PKI certificate where some text info can be stored?

I want to store 5-10 lines of Text Info in a PKI Certificate. All I want is that when using common tools like openssl command line or certutil from Microsoft, this text info should be displayed as is. ...
1
vote
1answer
216 views

Why does Fortuna RNG use double SHA-256?

In the paper for Fortuna the authors say that you can use any good digest algorithm (obviously as long as its output is 256 bit) and then they recommend double SHA-256. Why? What's the benefit? What ...
1
vote
1answer
79 views

Near preimages, applicable to Bitcoin?

Bitcoin mining relies on generating a smaller hash than the so-called target (a function of the so-called difficultly), thus is vulnerable to a truncated preimage attack (you just need to obtain a ...
5
votes
1answer
203 views

Side-channel attacks against ECDH for Weierstrass normal form curves

I hear a lot about why Montgomery curves are used in ECC, and one reason is that the same algorithm can be used to do both point addition and doubling (this is not true for the Weierstrass normal ...
2
votes
2answers
120 views

Do we need symmetric cryptosystems?

One question I had to answer in my crypto exam today was: Do we need symmetric cryptosystems? As it stands, that's probably a debatable question, so I'd like to reformulate this as: Are ...
0
votes
1answer
103 views

Is substitution with random prefix codes secure? [closed]

The following paper interests me very much: D. W. Gillman, M. Mohtashemi, R. I. Rivest, On breaking a Huffman code. IEEE Trans. Inf. Th. Vol.42 (1996), pp 972-976. However, unfortunately due to my ...
0
votes
0answers
163 views

m ∈ Zn \Z*n, RSA works but not secure

If you happen happen to have a message m ∈ Zn \ Z*n, RSA works but not secure. How likely is it going to happen? |n|=1024 bits |p| = 512 bits |q| = 512 bits.
0
votes
1answer
89 views

Encryption of numeric value using playfair

I am studying in CSE and in my recent exam paper, A question was asked as: Construct a playfair cipher for Plaintext: semester5 and key:technology. Generally as we are taught yet, there is no ...
0
votes
1answer
261 views

AES CBC MAC splicing attack

I'm trying to implement AES CBC MAC splicing attack in Python, the idea is: given a message M, its tag Tm (MAC(M) = T), a new message N and its tag Tn we build a message such as: M||N = (M1, ..., Mn, ...
2
votes
1answer
207 views

Is there a time-space tradeoff attack for breaking symmetrical cryptos?

Is there any known techniques for using time-space tradeoff for speeding up symmetrical crypto breaking? Kind of like rainbow tables speed up breaking hashes by using huge precomputed tables. Is ...
3
votes
1answer
171 views

Security proof of FO(Fujisaki-Okamoto) hybrid encryption

The proof of FO hybrid encryption is hard to understand. $\:$ Especially, how does the challenger respond to the decryption queries when the challenger can only have some encryption queries? Can ...
3
votes
1answer
713 views

LFSR get output from characteristic polynomial?

Say you have a characteristic polynomial of an LFSR: $$f(X) = X^4 + X^3 + 1$$ How can I use this function f to get the output of the LFSR, given some initial state? Obviously I can create the LFSR ...
7
votes
3answers
601 views

How useful is NIST's Randomness Beacon for cryptographic use?

NIST have just launched a new service called the NSANIST Randomness Beacon. It has been met with some initial skepticism. Perhaps the cryptography community would have used it before June 2013 when ...
2
votes
0answers
175 views

Defending hybrid encryption schemes against padding oracle attacks

I intend to use a generic integrated/hybrid encryption scheme for transmitting information between a client and a server. Key encapsulation: a 128-bit symmetric key is generated and asymmetrically ...
5
votes
2answers
2k views

Is PBKDF2-HMAC-SHA1 really broken?

I just read through this article which demonstrates practical (and seemingly trivial) collisions in PBKDF2-HMAC-SHA1, and provides a few examples of collisions. Am I missing something here? Is ...
3
votes
1answer
178 views

derangements and permutations in cryptography

Given a partial key for a mono-alphabetic substitution cipher (missing 11 letters), calculate the number $N$ of possible keys, given that no plaintext letter can be mapped to itself. ...
1
vote
0answers
131 views

Challenge–response authentication which can be done in head?

Say we have door where you have to say a password to pass. If theres someone standing nearby he would hear the password and could also use it. So therefore the doorman gives you a different number ...
4
votes
1answer
708 views

Compare RFC 5246 SessionID re-use versus RFC 5077 Session Resumption?

Can you help me understand the differences, both algorithmic and practical, between RFC 5246 SessionID re-use and RFC 5077 Session Resumption? Both appear to be ways to nail up a second TLS session ...
3
votes
2answers
219 views

Asymmetric key derivation – Who derives the new pub key can't know the new private key

I'm looking for a peer reviewed protocol or algorithm that can do this, preferentially I need something based on elliptic-curves cryptography. Alice know the main public key of Bob (B-PUB-1). Alice ...
4
votes
2answers
710 views

How secure is the AES master key if Round Keys are found

If an attacker finds some round key of AES256, is it possible to find the master key? How safe is the master key if an attackers finds multiple round keys?
1
vote
0answers
40 views

Distributed authentication in low trust environment

I would like to inquire if there is any Method to achieve the following: There is a list $L$ of $n$ entities that are allowed to perform a certain action. $L$ is cryptographically signed by some ...
3
votes
0answers
105 views

Looking for a detailed example of proof by reduction

I'm looking for a very detailed example of proof by reduction. Say we have two or three protocols (that have been proven secure) and we construct a new protocol. We want to provide a proof of security ...
3
votes
3answers
325 views

Third-party security issues with Shamir's secret sharing scheme

In Shamir's secret sharing scheme, we are trusting a third party who generates the secret polynomial. How can we ensure security here when we are involving a third party?
2
votes
4answers
279 views

Construct an encryption algorithm using hash function [duplicate]

We know that Cryptographic hash function is generally a one-way function where we can't retrieve the original message. On the other hand, encryption is a two-way-function where we get the original ...
3
votes
2answers
225 views

Is a random oracle controled by the challenger?

When proving a Crypto scheme security under random oracle model, is the random oracle always controlled by the challenger? What if the Hash is only used by the adversary?
6
votes
2answers
209 views

Is it safe to reuse ECDH asymmetric keys for authentication?

Alice, Bob, and Carol each generate ECDH keypairs. Alice and Bob establish a communication channel and negotiate an AliceBob secret. The question is: Is it safe for Alice and/or Bob to reuse their ...
2
votes
1answer
93 views

Encryption mode with chained algorithms

Suppose that I want to encrypt some data using two different algorithm chained (e.g. AES and Serpent) and harnessing the benefits of CBC. I can do: ...
4
votes
1answer
259 views

Proof of storage scheme

I'm familiar with client puzzles, where the client performs some work and there is a way to prove to the server that the client has done so. Is there a way to do this, but where the client's resource ...
1
vote
1answer
64 views

How to invalidate decryption key in multi user model?

I want to develop an application that will allow a user to create a public/private key pair, and encrypt it symmetrically with a key such that once they enter their password, they will be able to ...
2
votes
1answer
836 views

Is it true that for RSA with no padding, the length of data must be equal to the length of key?

The question pertains not in terms of security but computing operational functionality, as it how the computation is done. Is it true that for RSA with no padding, the length of data must be equal to ...
1
vote
0answers
54 views

1-1 trapdoor function mapping the set of $n$-bit numbers to themselves

I am looking for a trapdoor one-to-one function $f : \{0,1\}^n \rightarrow \{0,1\}^n$ (that is, mapping the set of $n$ bit numbers 1-1 onto itself [any $n$ is OK]). I was considering the use of ...
1
vote
0answers
57 views

Client puzzle using hash

When a server is under attack, it send the client the following data: Nonce - a byte array of Y length Hash - the hash digest of the puzzle solution The client has to find X such as ...
4
votes
1answer
731 views

Is PKCS #1 v1.5 RSA encryption padding secure under these conditions?

The PKCS #1 v1.5 padding scheme for RSA has been proven to have some weakness when used with TLS for example. My question is: is it still secure under the following conditions? Alice sends a ...
2
votes
1answer
130 views

Questions about hash functions

Let $H$ be a secure hash function (e.g. SHA256), is it possibile to find $H(M1)$ given $H(M1||M2)$ if the length of $M1$ and/or $M2$ is exact the block size of the hash (that is, 64 bytes for SHA ...
1
vote
1answer
222 views

Hash function and outputs of arbitrary length

I know that Skein can output a digest of arbitrary size, with a kind of counter mode. Blocks of the resulting digest can be computed in parallel. What about Keccak ? I know that a sponge function can ...
1
vote
1answer
238 views

Rock-paper-scissors over network, how to protect from cheating server?

I'm trying to design cryptographic protocol to play Rock-Paper-Scissors with two parties, neither trusting each other, nor trusting server they use for communication, so game is 'provably fair'. So ...
0
votes
1answer
138 views

No of keys used in Triple DES Algorithm

I am studying Triple DES. I have got two basic questions. One, why are we following a sequence like encrypt(decrypt(encrypt)); what is the problem using a sequence encrypt(encrypt(encrypt))? ...
2
votes
1answer
144 views

Explanations for the complexity values for second preimage attack on GOST?

I've been reading the article "A (second) preimage attack on the GOST hash function" by F. Mendel et al (link) and I'm having some difficulty to grasp some of the values of complexities/probabilities ...
8
votes
3answers
1k views

SHA-224 Purpose

One of the new features of Java 8 is the SHA-224 message digest. What is the use case for having a 224-bit-length hash?
0
votes
1answer
133 views

Why is DDH not hard over $\mathbb{Z}^*_p$?

Why is Diffie-Hellman key exchange not hard over $\mathbb{Z}^{*}_p$?
1
vote
1answer
166 views

What is difference among eavesdropper attack, multiple message attack and CPA attack?

What is/are difference(s) among eavesdropper attack, multiple message attack and CPA attack in context of symmetric key encryption? I only know that in eavesdropper attack there is an adversary ...

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