10
votes
1answer
430 views

Status of Algebraic Eraser key exchange?

Algebraic Eraser™ is a relatively new asymmetric key agreement protocol (also designated the Colored Burau Key Agreement Protocol), based on a simultaneous conjugacy search problem in a braid ...
4
votes
1answer
86 views

Why are obfuscators generally defined to be probabilistic algorithms, rather than deterministic ones?

One possible explanation is, randomness is not going to hurt you, so might as well use it. Also, if we are hoping to prove impossibility, it only makes the result stronger. One other explanation is ...
2
votes
1answer
78 views

Preserving Confidentiality and Integrity in a Public channel

Let's say I've got two people that are trying to talk in a public channel $A$ and $B$ and they want to preserve their confidentiality and integrity. Which cryptographic algorithm would they want to ...
1
vote
1answer
73 views

How to split up $GF(2^{128})$ into smaller fields?

I've heard that it's possible to split up $GF(2^{128})$ into copies of several smaller fields like $GF(4)$ so as to make the math easier in some cases. How do you do that? I know how it works for ...
4
votes
1answer
170 views

Understanding ransomware – What makes plain-text-attacks or brute-forcing so hard?

Say I have four files. Two are completely unencrypted, while the other two are the exact same files other than that they have been encrypted with (apparently) the same public key (via a ransomware ...
2
votes
1answer
116 views

State of the art techniques for Anonymous Authentication?

What are the state of the art techniques for Anonymous Authentication? What are the most popular ones? The problem domain I am considering is with respect to different users accessing cloud content; ...
2
votes
1answer
125 views

Are there any successful preimage attacks?

Are there any successful preimage attacks on any serious cryptographic hash algorithm or at least on serious-looking non-cryptographic hashes (like MurmurHash)?
5
votes
0answers
45 views

An MPC protocol from Elgamal is a good solution a homomorphic multiplication?

I want to compute a multiplication between many secret values and then distribute the result to everyone involved. For this, I thought about an MPC protocol built from Threshold Homomorphic Elgamal. ...
0
votes
0answers
57 views

Solving ADFGVX decoding with only ciphertext

Hi I'm new to the world of crypto and I'm trying to decode a message. I know it is encrypted using the ADFGVX cipher. I also have a ciphertext, but I have no other information given to me. My question ...
0
votes
1answer
39 views

Lagrange Coefficients & Polynomial in KP-ABE

My question is how these concepts relate in ABE. I am assuming that the attributes are used to share the master secret key and only a user with the right attributes for a particular access tree is ...
1
vote
1answer
82 views

Perfect Secrecy in Symmetric Key Systems

For symmetric key systems does perfect secrecy imply that all ciphers in the cipher space are equiprobable? I would think not, but I am finding it hard to come up with a counter example.
0
votes
0answers
123 views

Complexity using RSA

You encrypt a message using the RSA encryption system as $t^e \pmod n$ , where $t, e < n$ and $t$ is the numerical equivalent of the message. The message is written in a $27$-letter alphabet and is ...
4
votes
0answers
88 views

How can I implement decryption for NTRU homomorphic encryption scheme?

I have come across this paper On-the-fly multiparty computation via on-the-cloud Multikey from Fully Homomorphic Encryption by Lopez-Alt et al., where authors describe a NTRU-based homomorphic ...
3
votes
0answers
109 views

How does CTR-ESSIV work?

I'm using Wikipedia and Handbook of Applied Cryptography as references. I know that ESSIV generates an initialization vector (IV) by combining a hashed key with the sector number. However, I only see ...
2
votes
0answers
46 views

Example of Projective Coordinates

Given the affine form of coordinates $(x,y)$ such as $(5,3)$, if I want to convert $(5,3)$ to projective coordinates $(x,y,z)$, should the form of point be $(5,3,1)$? It is triplet not a point, right? ...
8
votes
1answer
110 views

A general definition for cryptocurrencies

I am trying to find the definitions to several terms related to digital currencies. Unfortunately, I am always ending up on Bitcoin-oriented pages and websites which only take Bitcoin itself into ...
1
vote
1answer
88 views

Cycling hashing in PBKDF's and their limitations in strength?

I hope this question isn't too similar to one that's already been asked. I also want to point out I know part the answer already, AFAIK: I just want some expert input on this. Let's model a hash that ...
10
votes
1answer
18k views

AES CBC mode or AES CTR mode recommended?

What are the benefits and disadvantages of CBC vs. CTR mode? Which one is more secure?
3
votes
0answers
183 views

Why does HMAC use two different keys?

Suppose $H$ is a hash function; why is $H(k||H(k||m))$ not secure? See this HMAC definition. In there, indeed two keys are used and the mac algorithm is $H(k_1 ||H(k_2 ||m))$ . Why don't we use $H(k||...
0
votes
1answer
77 views

Stern identification scheme to signature scheme

I'm trying to understand the comment in the page 103 of the book Postquantum Cryptography. about convert the identification Stern procedure for signing. Can you write an example of signature of this ...
1
vote
0answers
21 views

If you use an AES key just once, do you need to use IV, and/or pad the message? [duplicate]

I am developing an application that is going to use AES encryption. Since it is going to use a different key for every message encrypted... Would it be secure to use a constant IV? (i.e null bytes) ...
-1
votes
1answer
49 views

Understanding the cryptography used in a file [closed]

I use a software that stores a raw binary file with information, and exports it to a text file. I have access to the data in the original binary file. You can find a sample of the contents of the raw ...
3
votes
3answers
1k views

What are the differences between proofs based on simulation and proofs based on games?

what are the main pros and cons of proving the "security" of a crypto scheme under simulation proofs instead of game based proofs?
1
vote
0answers
48 views

Symmetric encryption vulnerable when encrypting and decrypting are the same?

To my understanding, symmetric encryption is where encrypting and decrypting data can occur with the same key. It's possible for symmetric encryption that the encrypting and decrypting algorithms are ...
5
votes
1answer
141 views

Encryption scheme like RSA where encryption is the inverse of decryption

In RSA, it is basically equivalent to use the private key $d$ to encrypt as it is to use the public key $e$ to encrypt. They are exactly inverses: $e=d^{-1}$. I need to know, are there other public ...
2
votes
0answers
122 views

Formal proof of theorem concerning the Random Oracle Model

Reading a book on cryptography by Douglas R. Stinson I've met the following theorem, which is stated without proof (see here). Thereby, $\mathcal{F^{X,Y}}$ denotes the set of all functions from $\...
2
votes
1answer
76 views

Does the time to evaluate a hash function depend on the function input size?

Suppose we have a (variable-input size) hash function modeled as a random oracle. Can it be consistent to say that the time to evaluate this function depends on the input size ?
6
votes
2answers
229 views

Scrypt not “old enough” to be safe?

I just check all the questions with scrypt tag about that and usually it's said that scrypt is nice in theory and theoretically better than bcrypt and PKDF2, but it's too young to be "completely safe"....
2
votes
0answers
114 views

Convert projective to affine coordinates in ECC? [closed]

I am working with my project. I use projective coordinates but when I convert to affine coordinates, I can't get it. Can anyone help me? Projective Coordinates $(X,Y,Z)$ to Affine Coordinates $(X,Y)$:...
1
vote
1answer
75 views

Non-numeric Diffie-Hellman?

It may seem that this is a programming question, but I just need advice on the cryptography side of the question. I want to implement the Diffie-Hellman key exchange algorithm on iOS (since no free ...
4
votes
1answer
104 views

Could we share a secret key using the Birthday problem?

I stumbled upon this code on-line, it seems obvious to me that generating all 2^40 keys in trivial time can always be achieved as can hashing each and everyone of them, using the SHARED Salt that "Eve"...
4
votes
1answer
104 views

Contrasting Key Rotation Requirements : Asymmetric vs. Symmetric Ciphers

I'm trying to contrast key rotation requirements for asymmetric and symmetric ciphers. In the case of symmetric ciphers, we have the results such as the so called "CBC Theorem" (stated on pg. 24 of ...
5
votes
1answer
1k views

Should the secret key of Shamir's secret-sharing algorithm be interpreted byte by byte?

Should the secret message of Shamir's secret-sharing algorithm be interpreted and processed byte by byte? Interpreting it byte by byte makes it easier to process, but in case one of the shareholders ...
6
votes
1answer
119 views

Elligator-2 against curves over Fq, q mod 4 = 3

It appears that the conditions for applicability of Elligator-2 against many of the SaveCurves curves, where $q \mod 4 = 3$ will inevitably poke a hole in the bit-string set over $(0, 1, .. (q-1)/2)$. ...
1
vote
1answer
45 views

XOR or add in one time pads? [duplicate]

Is there any difference in adding the plain text and key vs using xor instead(apart from the performance improvements)?
3
votes
1answer
526 views

Should AES.decrypt(ct, wrong_key) return blank or wrong result?

I am trying to use AES as cipher for an application I am building. I am using a JavaScript library (https://code.google.com/p/crypto-js/) to perform encryption and decryption with AES. When I ...
0
votes
0answers
199 views

Strength of TripleDES (DESede) in Java (Sun JCE)?

I'm introducing Jasypt to a spring-boot project. The default algorithm for storing passwords with it is PBEWithMD5AndDES. Since I've got some reservations on using that cipher, I'm looking into ...
1
vote
1answer
123 views

SHA256 for large files

I have a hardware engine for SHA256 which can process 64K of data, but the input data size I am getting is around 1MB. What should I do to process 1MB size. What should be my input after 1st 64KB ...
4
votes
1answer
162 views

Determining if Server/Client's TLS configuration is Vulnerable to SLOTH

In the context of SSL/TLS protocol and SLOTH vulnerability. I want to find out if certain websites(webservers) or applications that use TLS are vulnerable. I need some guidance for this. My idea is ...
3
votes
1answer
163 views

Unable to understand hash function representations

I have some hash function representations, which I find it hard to understand. I have searched a lot but didn't found anything helpful. Please help me understand the hash function representations ...
5
votes
0answers
34 views

OTR AKE protocol implementations security

While looking at the different versions of OTR protocol I discovered a strange thing: there is no trace of the patch for the weaknesses that were noted in “Finite-State Security Analysis of OTR ...
0
votes
0answers
34 views

How to calculate unicity distance of Fleissner grille?

I need to calculate unicity distance of Fleissners grille of $M \times M$ size. All I know is that plaint text redundancy equals $2$. The alphabet is not specified. Is it possible to calculate its ...
0
votes
0answers
108 views

splitting the plaintext and ciphertext into blocks

Say I was to use RSA with a given value of n. I choose to split the plaintext and ciphertext written in a 27 letter alphabet into blocks with k and m characters resp. How would I find the largest ...
0
votes
0answers
80 views

Semaev summation polynomials

I am little confused how this attack works. We have the points $P, Q$ such that $Q = nP$. We let $u_{1} $and $u_{2}$ such that $R(x,y)=u_{1}P+u_{2}Q$. Then if we find the solution $x_1,...,x_n$ of the ...
4
votes
2answers
129 views

Name and security of these non-invertible functions?

I would like to learn more about a specific set of non invertible functions: The function should accept 2 inputs: one hidden and the other visible. The output and the function should also be visible....
2
votes
2answers
88 views

BOOLEAN FUNCTIONS: generate a function $f: \{0, 1\}^n \rightarrow \{0, 1\}$ from a $n \times n$ S-Box

I want to calculate the hamming weight of a S-Box using this formula: $\text{hw}(f) = \sum_{x=0}^{2^n-1} f(x)$. Where $f: \{0, 1\}^n \rightarrow \{0, 1\}$ My problem is that I don't know how to get ...
1
vote
4answers
147 views

Is it safe to use XOR to encrypt data key using master key

I am implementing a hierarchical key system with a randomly generated master key and many randomly generated data keys that should be encrypted using the master key. I am wondering what the best way ...
0
votes
0answers
29 views

Uniformly distributed sub-sequences of a main PRG sequence

Let $ g_s $ be a pseudo-random generator that generates uniform distributions of numbers ($s$ : seed) of a fixed bit-size. One wants to compare the pseudo-randomness of certain subsets of elements ...
0
votes
0answers
87 views

Proof that this is not a secure pseudorandom function

$p$ is a large prime number. Consider the following function $F:\mathbb Z^*_p \times \mathbb D\rightarrow\mathbb Z^*_p$ where $\mathbb D=2,....,p-1$. $F_k(x)=x^k \bmod p$ Proof that it's not ...
1
vote
1answer
50 views

Is this a secure keyed hashing construction?

I need a PRF for use with PBKDF2, however, the only thing I have is the AES block cipher primitive. I'm attempting to derive a keyed hash function from the block cipher. The design is based on the ...

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