# All Questions

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### Cryptography — with a semi-priveleged user in the middle — to prevent request-tampering with another server

I'm working on a chat server for a mobile app I am writing. I would like to use a different application server for non-chat related operations and another application for chat operations. I would ...
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### Why does computing g^a * g^{-a} with the PBC library result in zero?

My example code is as follows: /* * Example 1 * 1) Calculate g^a * 2) calculate g^{-a} * 3) multiply g^a * g^{-a} * */ Note: here ...
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### Cryptography Implementation in software

I am trying to implement a password manager in C and I had a question about the proper steps in implementing the crypto. I looked at some implementations, google talks on crypto and what the standards ...
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### Cryptographic library quality [closed]

I've been working on a project that will require secure communication over the internet, so I've been thinking of TLS 1.2. After looking around I chose Botan but then I thought about using a more ...
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### Is anyone aware of Du atallah multiplicative secret sharing scheme for dot products for > 2 party scenario?

I am working on Du Atallah's multiplicative secret sharing scheme for more than 2 party scenario. Is anyone aware of its multiparty version (more than 2 parties). The paper for 2 party can be found ...
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### What is a 'secret key factory'? What precisely is it doing? [closed]

I have found a Java implementation of AES CBC mode that runs in Netbeans. The lines below appear to create the key from password and salt: ...
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### Sequence of Encrypting RSA like Chaum Blinding scheme

I'd be a noob in cryptography but reading up a little on RSA, I do get some understanding and I want to specifically resolve this issue. UPDATED Lets say we have the following values in place: ...
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For example: I have 3 plaintexts ($a$, $b$, $c$) and 4 keys ($K_1$, $K_2$, $K_3$, $K_4$), making a table map to the cipher text, key as row and plaintext as column $\begin{matrix} \ \ \ \ \ \ \ \ \ \ ... 0answers 81 views ### El Gamal encryption scheme and symmetric encryption scheme Consider the El Gamal encryption scheme, a symmetric encryption scheme (KG,E,D), and the following hybrid encryption scheme having an encryption algorithm that, on input a public key (G,q,g,h), where ... 0answers 76 views ### How we transfer 128bits cipher to a 4x4 matrix for AES input? Why the input cipher for AES encryption, can write in 4x4 matrix with 8 bits entires, and can said is 128bits? if each cell is 8bits in binary, how we said this matrix is represent 128bits? 0answers 43 views ### Index of coincidence for completely random text over k alphabets I'm confused about /Friedman's method 2 (using a table with column of k size of key, and n/k rows, n is the total size for cipher text) m = ... 0answers 77 views ### Is this a correct understanding of Universal Hash Functions? I'm studying universal hash functions and have been reading several papers but now i'm focusing on Wegman and Carters original paper from 1979 (Universal classes of hash functions) and the H1 class. ... 0answers 54 views ### Reliability of a single-pass deniable authentication protocol? I look for one-pass deniable authentication protocol with a short message payload for my project and find a solution: ... 0answers 113 views ### Hill cipher key space Key space is the set of all possible keys that can be used to generate a key. We using the number of valid key to describe it. I've given a hill cipher of block size$k$over alphabet of size$p$, ... 0answers 67 views ### Is there a malleable pubkey digital signature scheme? I'm trying to find a special kind of Digital Signature Scheme. The scheme should allow me to transform a signature$s=\text{sign}(sk,m)$(for a private key$sk$and a message$m$) into a signature ... 0answers 64 views ### Definition of a Statistical Test In Professor Boneh's online Cryptography course at Coursera, I am a little puzzled by his definition of a statistical test where he writes: A(x) = iff |#0(x) - #1(x)| <= 10.√n Now, if – as ... 0answers 51 views ### Is timestamping possible without publishing? The Wikipedia article Trusted Timestamping states that we can timestamp data by publishing it's hash. Publishing can be done either independently or via a third-party publisher, as explained by ... 0answers 148 views ### For a one-time pad, which MAC method is information-theoretically secure? In the the main post about MAC methods it mentions a few methods: Authenticate And Encrypt: The sender computes a MAC of the plaintext, encrypts the plaintext, and then appends the MAC to the ... 0answers 38 views ### Delinearization in whitebox techniques I'm reading through Chow et al.'s paper and Link et al.'s paper. There's a part I don't understand about Delinearization. They convert some steps of AES/DES into a Matrix, then divide the matrix in ... 0answers 73 views ### How to compare different signature scheme's performance? I am interested in comparing the computational performance of two signature schemes. However, I am unsure how to do that. My candidates are RSA and Shamir's ID Based Signature scheme. To get a fair ... 0answers 55 views ### Expand 1-n Oblivious Transfer to retreave only an item I, for which permissions exist To my understanding in a 1-n Oblivious Transfer the Sender has some Values$X_1...X_N$and the receiver wants to retreave some$X_I$, with$1 \le I \le N$. Can one now somehow guarantee, that the ... 0answers 69 views ### Is Encryption without knowing the input directly possible at all? I know the question is rather unusual, but let me clarify what I'm searching for: There is one person, lets call her$Alice$.$Alice$has$n$plaintexts$t_1..t_n$and$n$public keys$pk_1..pk_n$of ... 0answers 117 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 ... 0answers 118 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 ... 0answers 38 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 ... 0answers 51 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 ... 0answers 46 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 ... 0answers 73 views ### RSA timing attack Given an RSA implementation that uses Montgomery multiplications and CIOS exp algo, but NOT CRT. Given a decryption1 oracle that takes chosen cipher text and responds the plain text and the time it ... 1answer 55 views ### What is the idea behind hashing the QueryString in OAuth? In OAuth 1.0a and 2.0 using MAC Authorization, I need to generate a hash of all the QueryString Parameters, which requires normalization (alphabetical ordering) of them. I'm trying to understand what ... 0answers 37 views ### McEliece information set decoding attack vulnerability Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ... 0answers 77 views ### Public-key based on roots of polynomial In general it's hard to calculate the roots of a given polynomial P(x). But the other way back calculating the coefficients is much easier (Vieta's formulas). If this is a one-way function, is it ... 0answers 71 views ### Does a dynamic accumulator exist yet? [closed] I’m looking for a one-way accumulator which can safely add new members (deletion is not necessary) and does not rely on a trusted party in any way. I’ve been looking for one, I need it for this ... 0answers 128 views ### Is this a secure (and correct) sign-then-encrypt technique for transferring messages? After reading some information on the way iMessage works I have been working on writing some code to try my hand at securely transferring messages in a similar manner and I wanted to confirm that the ... 0answers 70 views ### Problem implementing MixBytes functionality in Groestl Disclaimer: School work. I am trying to implement Groestl through Java, and have got stuck on the MixBytes section which can be found here section 3.4.5 page 11. As per the description of matrix ... 0answers 88 views ### Trying to calculate the strength of a Bitcoin brain wallet created with a custom diceware password I want to create a brain wallet using a custom diceware since I don't like the original one. Instead of 7776 words it has 46656 because I use 6 dice for each word instead of 5, and also it only has ... 1answer 90 views ### Is there need for message authentication if a public key is transmitted and then used to encrypt a symmetric key? First I'd like to note that I'm really a beginner at cryptography, and while this interests me and while I have researched it in the past few months, there is still a lot of things that simply aren't ... 0answers 136 views ### AES encryption takes more time to decrypt than encrypt Please let me know if this is not the right place to ask this question. I will remove it. I am trying to find how much time an AES encryption and decryption takes for a given amount of data and key. ... 2answers 76 views ### counter to indicate hotp count I was trying to figure out how HOTP kept from wrapping over, when I saw this explanation of how it works, by Thomas Pornin [source]: The intended scenario is the following: the client has a ... 0answers 364 views ### Which eliptic curves in OpenSSL 1.0.1f meet all / most of the SafeCurves requirements? [closed] I am using nginx compiled with OpenSSL 1.0.1f (most current release available). Nginx allows administrators to set a configuration parameter called ssl_ecdh_curve, ... 0answers 26 views ### Is there a flaw in whole disk encryption vs volume or folder encryption? [duplicate] My company just implemented whole disk encryption on all laptops (Symantec) and the concept seems flawed. Please correct me if I'm wrong, but if I have known file in plain text and that same file in ... 0answers 142 views ### Rainbow tables and blowfish I'm thinking of implementing rainbow tables for a specific blowfish problem, but I have trouble thinking of the proper way to apply the original paper (and its application to hash functions) to ... 0answers 75 views ### Parallel-resistant proof-of-work scheme without hidden knowledge Follow-up to: Parallel-resistant proof-of-work scheme? Is there a proof-of-work scheme that: can only be solved serially; given the solution, can be verified in minimal time; deterministically ... 1answer 57 views ### Using a hash with a constant key to create easily verifiable codes I'll keep my question short. If I keep handing out different codes generated by this function, will it be trivial to figure out the secret key? ... 0answers 77 views ### Does “use of SHA-256 in cryptography” imply use of SHA-256 both in HMAC and DH key exchange, assuming these are the only uses of hash in system? [closed] I am beginner to Cryptography. And recently I came across the requirement like "use of SHA-256 in cryptography". Does "use of SHA-256 in cryptography" imply use of SHA-256 both in HMAC and DH key ... 0answers 90 views ### Weil pairing implementation - low level programming language I'm just started to studying elliptic curve cryptosystems. My one month-goal is to write a simple signature system based on the Weil-pairing. Some parts of it can be written without deeper ... 0answers 77 views ### Which hardware-accelerated AES-GCM implementations support encryption in-place? [closed] By encrypt in place I mean the following. Suppose I have an input plaintext of length L and I have also allocated an extra E bytes at the start and/or end of the buffer, with E << L. So the ... 0answers 82 views ### Is MITM possible after key exchange phase done successfully in RSA? Is MITM attack theoretically possible after public/private key pair exchange is done successfully. Say Alice and Bob have genuine public keys of each other. Is MITM possible further during ... 0answers 43 views ### Random numbers for Master Key and Key_block Exploration through RFCs concludes that random numbers used in the creation of Master Key and Key Block(Key material for Encryption Key and Mac Secret) are from ServerHello.random and ... 2answers 98 views ### Tweakable encryption algorithms vs Key wrapping I have read many articles about Key wrapping and tweakable cipher modes. However, I don't understand the main difference between them? What you recommend for Key storage and Key Archive. 0answers 64 views ### Why don't we use H(m||k) as a MAC? [duplicate] HMAC seems a bit complicated. Why can't we use$H(m||k)$as a MAC? Unlike$H(k||m)\$, length extension attacks won't work. Is there some other obvious attack?

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