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859 views

Python implementation of a blind signature scheme which doesn't involve RSA

RSA seems a bit creepy after the Snowden revelations and i'm looking for a simple python based blind signature library to fiddle around with. So far i've been unable to find anything. What am i ...
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769 views

Two questions on EMSA-PKCS1-v1_5

If I implement EMSA-PKCS1-v1_5 in the following two non-standard ways, what kind of things could go wrong? The padding structure will be referred as (00|01|PS|00|DER(Digest Algo)|Digest), where | is ...
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361 views

Is ASCON cipher broken?

http://eprint.iacr.org/2015/030 present several attacks of ASCON but does not have a conclusion section. I'm having troubles estimating what are the consequences on the use of ASCON. What's your ...
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200 views

processing time for multiplication and exponentiation in pairing base cryptography

I'm using the Boneh-Boyen-Shacham signature scheme and want to estimate complexity in my scheme. As reported in "Scott M., Efficient Implementation of Cryptographic pairings", if we set parameters ...
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395 views

Polynomial Inversion over Galois Field

Hello guys I am looking to calculate the Inverse of a given polynomial in Galois field I have found the little Fermat's algorithm and the Itoh-Tsujii I am getting a bit confused with both algorithm ...
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136 views

transforming RC2 keys to have effective minimum length in implementations with fixed effective lengths

mcrypt's implementation of RC2 has a fixed effective length of 1024 bits, however, it is possible to simulate keys with effective lengths between 1-1024 by doing something like this: http://php.net/...
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75 views

Designing hash function in space-efficient identity based encryption

Let $n$ be an RSA-prime and we know prime factorization of $n(=pq)$. The hash function is the current context maps from a given user identity(id) to a positive integer less than $n$, whose jacobi ...
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543 views

Brute Force AES Calculations

I have an encryption service in which the user decides the length and the type of key, so I would like to build a tool that educates the user on the brute force times for the key they created if using ...
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182 views

NRPAD and FPAD padding schemes (Korean Seed?)

I've got an API spec that specifies NRPAD and FPAD as possible padding schemes. I see these being used together with the Korean SEED algorithm. The SEED specification however is void of any padding ...
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0answers
257 views

Low exponent attack against RSA

According to this: http://www.cims.nyu.edu/~regev/teaching/lattices_fall_2004/ln/rsa.pdf One can calculate the message m, if there was no padding scheme involved. My question: is it possible to find ...
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303 views

Montgomery Multiplication in FPGA explanation

I'm trying to implement an RSA module in a FPGA. I choose to use Montgomery multiplication. I've found a document where the Montgomery Multiplication is pretty clear. I don't understand only a step. ...
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508 views

fuzzy commitment implemenation to make secure biometric template

I want implement some ideas from an article that is about making secure biometric templates using fuzzy commitment and fuzzy vault. I need to implement just the fuzzy commitment (fuzzy commitment is a ...
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0answers
79 views

What are the consequences of not checking the server mac in a TLS connection?

The context for this question (it's quite involved) can be found in this document: https://docs.google.com/file/d/0B15itpMWb2ztWTJrYTgzX204OVU However, I want to make it clear that you don't have to ...
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96 views

Looking for crypto with derived keys?

I am looking for cryptographic algorithm or combination of them. Basically I need an algorithm, which can generate private key and for this key can be computed multiple keys based on some seed. So a ...
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61 views

Locally Dedcodable Codes and Private Information Retrieval

Does anyone know about Locally Decodable Codes (LDCs)? It seems the private information retrieval schemes that based on LDCs are computationally efficent (answer a query without processing the whole ...
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110 views

Question Error Correcting Codes

Let $C$ be a code over the finite field $GF(2)$ with generator matrix $G$ and parity matrix $H$. Let $e+C=C'$ be a coset of code $C$. Let $S$ be a non-singular matrix and $H'=H\times S$. Finally, let $...
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53 views

Correlated or biased coin protocols?

There are a number of papers in the literature describing secure/fair coin flipping protocols. Unfortunately in my case, I am looking for coins that are epsilon-biased or epsilon-correlated. I am ...
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436 views

Example of CL PKC

I am trying to solve the example of algorithms of Certificateless Signature by manually and solving the mathematics of Algorithms but not succeed while doing mathematical calculations. Please ...
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347 views

How to safely sign a 6 characters String?

I have to decide, whether a document, which I am given, was correctly signed by a private key. my Ideas is to sign the document id using RSA with the private key and to print the following onto the ...
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1answer
85 views

Retrieve message from rsa ciphertext based on some conditions

Assume: $x = m^{e-1}\bmod n$ $y = m^{d-1}\bmod n$ Here $m$ is a message, $e$ is the public exponent, $d$ is the private key and $n$ is the modulus of an RSA key pair. Now if I know $e=65537$, $x$, $...
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1answer
121 views

ECC public key encryption without symmetric cipher

Imagine the following scenario. A process is running in background and permanently encrypting some data. An adversary has full control of the process, e.g. it can dump the process memory any time and ...
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1answer
106 views

RSA: Decrypting message with public key and private key

I am trying to decrypt a message which its ciphertext in Hex A3 BB 05 00. The original plain text is 8 bits and it is encrypted by a 32 bits RSA key. I have successfully found the public key is $(e=...
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1answer
99 views

Needham–Schroeder fix by adding opponent's identity to the first message

Recap: Needham–Schroeder is as follows: $A \rightarrow B : \{A, N_a\}_{pk_B}$ $B \rightarrow A : \{N_a, N_b\}_{pk_A}$ $A \rightarrow B : \{N_b\}_{pk_B}$ Then, there is a MITM attack by Lowe ...
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1answer
369 views

Certificate public key keyexchange, Which key exchange is used in browsers?

I have a question regarding the keyexchange happening in web browsers. If you check the certificate here on crypto.stackexchange you can go under details and see that the public key is type RSA (2048 ...
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1answer
82 views

How do i manage encryption keys with a cloud provider?

I would like to provision services from a Software as a Service (SaaS) provider. This is multitenant environment (multiple companies will be using a single instance of the application, with a single ...
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1answer
47 views

What are the approaches to private computations?

I'm talking about the ability to safely run a virtual machine on a physical device that is not trusted. It is necessary that the owner can not access the data that the virtual machine operates on. I ...
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1answer
189 views

Negative exponents in Shoup's threshold RSA?

I'm trying to implement threshold RSA operations, starting with decryption based on Peeters, R., Nikova, S., & Preneel, B. (2008). Practical RSA Threshold Decryption for Things That Think. ...
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1answer
96 views

How to establish if a string contains a message

If you have a string S, then the string can be composed of four things: cleartext 'random' data encrypted data compressed or otherwise non-encrypted, but modified, cleartext If you want to see if ...
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1answer
145 views

Cryptography system that limits the length of the encypted message

I have two devices which communicate via sms. This communication should now be encrypted. The devices can only send messages with the lenght of 160 characters. So i am looking for an encryption ...
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1answer
139 views

Elliptic Curve - X Coordinate

I am currently working on a Koblitz curve. I have found the curve has two matching groups based on the base curve point and N-1 point. My question is as follows: Is there an algorithm to determine how ...
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1answer
1k views

How is public key cryptography used for digital signature?

In public key cryptography, there are two different keys used for the encryption and decryption of data . I am wondering how it is used for digital signature
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1answer
1k views

Passing data securely through QR codes?

We have to implement a way to securely transfer data from a POS to a mobile app using QR codes. The mobile app gets the payment parameters (amount, description, purchase_id, store_id) to create the ...
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2answers
234 views

Private Information Retrieval and Writing at the same time possible?

Are there any (possibly multiserver) private information retrieval (PIR) schemes that support private reads and writes (so called PIR Writing) at the same time, while having sublinear (in the database ...
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1answer
56 views

The security of adding random noise many time pad

In may application, I have a series of real number $\{v_1, v_2, \ldots, v_N\}, v_i\in\mathbb{R}$. To protect them, I add a random noise $r\in\mathbb{R}$ to each themselves like one-time-pad encryption ...
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5answers
378 views

Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
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0answers
16 views

Work with keys instead of pem files/certificats?

Unlike certificates, keys do not expire and can be modified to access more services after their creation. So it is more efficient to use keys? What are the pros and cons ?
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1answer
42 views

Alternatives to XTEA as encryption algorithms for stenography

I recently implemented an algorithm written in Python that was using the XTEA encryption method. Are there any more reliable algorithms than the XTEA , regarding to memory usage and PSNR ratio ,other ...
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0answers
28 views

Create CSR manually

Google cloud has HSM key management service. It enables creating RSA keypair and has missing CSR creation functionality. How to create CSR manually programmatically in the form that it could be signed ...
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31 views

Difference between Scalable Bloom Filters and Secure Bloom Filters

I am trying to find a library for "Secure Bloom Filters" but all the python libraries ([bloom-filter][1], ...
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0answers
31 views

Finding Collisions on CBC-MAC with known IV and key

Given a message $m$ which is encrypted using a known IV and known key in CBC mode which gives MAC $t$ which is 20 bytes. How can we create a message $m'$ which produces the same MAC $t$? Using the ...
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1answer
132 views

Asymmetric encryption that preserves the plaintext size

I'm looking for an asymmetric encryption algorithm that preserves the size of the thong in clear text. The encrypted file must not be longer than the plaintext file and must not contain any special ...
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1answer
79 views

Which is more secure, AES CTR or OTP with generate key?

My idea of the OTP is to generate from 50 letters (5 words, each 10 letters) a new pad of 2000 random letters, then attach user email to the pad end (to make it unique). The keywords and the pad will ...
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1answer
53 views

How to calculate base value in modular exponentiation

If you have $a^b \bmod n = c$, and $b,n,$ and $c$ values are given, is it possible to find a value for $a$ within a given range? So is it possible to find $a$ in $a^{2051} \bmod 3149=636$ knowing a ...
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1answer
49 views

Deterministic procedure for mapping an arbitrary value into a 𝑝,𝑞 pair for public key cryptography

I want public key cryptosystem to used for re-encryption as describe in Can Paillier ,RSA or any other schemes be used for universal re-encryption like elGamal? Now i have little solution for ...
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2answers
923 views

How to find the key of XOR encryption in Java?

I am trying to find the key of an XOR-encrypted string in Java. It is very probable that the key is eight characters long. I have the encrypted string. I do not understand how to go backwards and ...
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1answer
42 views

Rijndaelcipher mix column query

I quote a wikipedi para that says The operation consists in the modular multiplication of two four-term polynomials whose coefficients are elements of ${\displaystyle \operatorname {GF} (2^{8})} $. ...
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1answer
348 views

What is the difference between Forgery and Chosen-Message Attacks?

I did some researches about forgery attack and chosen-message attack. For me, forgery attacks are more focused on the verifiability whereas chosen-message attacks are similar to brute-force attacks. ...
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1answer
103 views

Original papers for hashing functions

I would like to learn how hashing functions are discovered / created. In part of this process I think it would be helpful to see the original works or papers of any authors of cryptographic or non-...
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1answer
55 views

Verification of the NI-ZK Proof

I'm currently learning about ZKP and Non-interactive zero knowledge (NI-ZK) but I'm confused in the process of NI-ZK verification. I have taken the following example to learn about NI-ZK from this ...
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1answer
84 views

Zero Knowledge Interactive Proof vs zero knowledge proof

What is the difference between Zero Knowledge Interactive Proof and zero knowledge proof? Nathan Aw

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