# All Questions

1answer
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### Does adding a salt to the message before HMAC processing add any security?

An HMAC function is designed to verify message integrity, i.e., that the message has not been tampered with. It is generally (always?) implemented by using a hashing function ...
2answers
126 views

### What curve and key length to use in ECDSA with BouncyCastle

I'm developing a client/server system in Java which is not interacting with third party software, so I don't have to worry about compatibility. At a certain point, I need the client and server to ...
1answer
118 views

### Skein state size advantages

Skein is defined for three different internal state sizes: 256 bits, 512 bits, and 1024 bits – with Skein-512 as the “primary proposal”. Is there any advantage – other than potential memory or speed ...
1answer
87 views

### Is either brainpoolP320r1 or brainpoolP320t1 a SafeCurve?

Not all elliptic curves are safe to use for cryptography, especially from an ECC safety perspective. The site http://safecurves.cr.yp.to/index.html shows that two tested Brainpool curves, ...
2answers
170 views

### Password-based encrypted key storage?

RFC 5959 specifies the encrypted storage of private keys based on PBKDF2-HMAC-SHA-256 and AES encryption (in ECB mode). Is there a particular reason AES is used, instead of simply XORing the key ...
1answer
77 views

### How does Web Cryptography API produce secure PRNG?

How does Web Cryptography API (eg window.crypto.getRandomValues) produce secure PRNG? Specifications: https://dvcs.w3.org/hg/webcrypto-api/raw-file/tip/spec/Overview.html#RandomSource-interface ...
1answer
74 views

The paper Expressive, Efficient, and Revocable Data Access Control for Multi-Authority Cloud Storage contains the following simplification: $$e(C_i,\text{GPK}_{uid})\cdot e(D_i, ... 1answer 241 views ### Adi Shamir's secret database of all primes I was going through these presentation slides (PDF) on Crypto 2013. It summarizes the paper, Factoring RSA keys from certiﬁed smart cards: Coppersmith in the wild. In the last slide, it was ... 2answers 256 views ### Is SipHash cryptographically secure? I'm evaluating different hash algorithms for use in my application. One of the kind of algorithms I am looking at are cryptographically secure ones to protect against DOS attacks. SipHash seems ... 6answers 2k views ### Where can I begin to study the math behind modern cryptography? I've been studying crypto for almost a year now, implementing algorithms, reading books, studying code, etc. The deeper I go in, the more I realize there is; I feel like I've just barely scratched the ... 1answer 192 views ### What should I be aware of when implementing algorithms myself? I plan to build my own crypto library. The project will be primarily for me to learn (and if useful for no other purpose, that is fine). In the past I have implemented a few hashes, and AES quite a ... 2answers 95 views ### The modulus of RSA public key I am studying the RSA cryptosystem. The public key consists of (n, e), the modulus (product of two large primes), and the encryption exponent. I want to separate the modulus n and exponent e. A ... 1answer 120 views ### Getting 88bytes cipher output from 48bytes input in AES The other day I saw this Hybrid Cryptographic Algorithm in the Google and felt curious about it. I am trying to understand this Hybrid Algorithm. And hopefully its not so hard to understand whats ... 0answers 38 views ### Malicious KGC attack in the identity-based authenticated key exchange protocol There are two users A and B who are in different domain. Let's assume that A\in KGC_1 and B\in KGC_2. If they want to establish secure session, then they must run an identity-based ... 0answers 38 views ### Comparing n-multiple amount of merkle trees? I would like to know what best steps are there in finding differences between a high order amount of merkle tree's or if a better associative structure should be used. I ask this questions because ... 1answer 69 views ### Generate Finite Field power of g consider the field \mathbb{F}_{2^4}, defined by using polynomial representation with the irreducible polynomial f(x) = x^4 + x + 1. Given element g = (0010) as a generator for the field, How ... 0answers 87 views ### Convergent encryption has dictionary attack, but why hash function doesn't? Convergent encryption (CE), E_k(d), is a way to encrypt the data d, with the characteristic that the encryption key k is k=h(d), where h(\cdot) is a cryptographic hash function. Consider a ... 1answer 96 views ### Hamiltonicity proof of knowledge I'm learning the POK notion and definitions and as a self exercise I wante to prove the statement that the Hamiltonicity protocol is a POK system with knowledge error 1/2. So the question will be ... 0answers 43 views ### Type 2 to Type 1 pairing transformation - why not considered? How come that in various articles about pairings I never saw anybody mention that there is a possibility to turn Type 2 pairing into Type 1 by setting e' : G_2 \times G_2 \rightarrow \mu, (P,Q) ... 3answers 109 views ### Encrypting text file line by line with stable encryption I want to store files in a secure manner (i.e. no one should be able to decrypt the contents of the file without the secret key) but I also want a diff tool to be able to show me which lines changed ... 1answer 66 views ### Cryptool - DES (ECB and CBC ) - double encyption So, I uploaded a text file in Cryptool and encrypted it with DES-ECB with the key FF FF FF FF FF FF FF FF. I encrypted the cipher text again, with DES-CBC using ... 1answer 71 views ### Use ElGamal to solve Diffie-Hellman problem Say we are able to decrypt a Elgamal ciphertext c using only the public key. Apparantly it is now possible to solve the Diffie-Hellman problem (given g^a, g^b calculate g^{ab}). How? I know how ... 0answers 38 views ### In symmetric searchable encryption are the algorithms public? If a user (other than the data owner) possesses the secret key in symmetric searchable encryption scheme are they able to run the trapdoor algorithm, or is this not publicly available? 1answer 111 views ### Is SHA256 good enough to shrink a key? I have a key that is the combination of two shorter keys generated by PBKDF2, which together are long more or less 64 bytes. Now I need to shrink it down to 32 bytes and I'm not sure what to use to do ... 0answers 34 views ### Feasible way to check n-dimensional equidistribution of PRNGs I am currently gathering some test methods and test suites for random number generator qualities, and am a bit stuck at finding something feasible to test for n-dimensional equidistribution. As input ... 3answers 127 views ### Algorithm for computing square roots in GF(2^n) Short question: is there an algorithm for efficiently computing square roots in \mathbb{F}_{2^n}? 0answers 76 views ### Public and Private key encryption in simple math Can anybody show me (or point me to resource) how to generate public key and private key with simple math? Steps which can be reproduced in a simple calculator – so the message, keys all can be ... 1answer 82 views ### Can a homomorphic encryption scheme be made CCA2 Secure? Is it possible to modify a homomorphic encryption scheme so that it can be CCA2 secure? From the definition of a homomorphic scheme, it seems that it is malleable, which would result in lack of CCA2 ... 1answer 95 views ### Pseudorandom permutations on domains of arbitrary (i.e. not a power of 2) size The Feistel cipher algorithm produces a pseudorandom permutation with domain size equal to 2^{2m} (for some m \in \mathbb{Z}^+). That is, a one-to-one function \pi of the set \{0, 1, 2, \dots, ... 1answer 568 views ### Are there any specific requirements for the function F in a Feistel cipher? In a Feistel cipher (as shown below), it seems that the security of the cipher would be entirely dependent upon the function F. What requirements on F are necessary for a secure Feistel cipher? Is ... 1answer 96 views ### Math to replace s-boxes - Good or bad idea? The following was going through my brain for the past week. If my thoughts are generally known to the cryptographic community would someone provide a link or two. Even if I’m making a classic newbie ... 1answer 63 views ### Is a keyed PRF a MAC? I remember I read that a MAC can be considered as a PRF. Can a variable-length input keyed-PRF be considered as a MAC? 1answer 36 views ### Problem with Python Implementation of Key Exchange part OTR Protocol Being new to software development and crypto in general, I thought I would write a simple p2p encrypted chat app using the otr protocol detailed here: https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html ... 1answer 161 views ### Does collision resistance imply (or not) second-preimage resistance? I've seen contradictory results. Sometimes hash functions are collision-resistant but not necessarily second-preimage resistant. I've seen this kind of things in papers from Bart Preneel: “Security ... 1answer 132 views ### Elliptic Curve Crypto, is a distributed signing method possible using Shamir's Secret Sharing? Note: A distributed signature scheme exists for RSA: Practical Threshold Signatures, Victor Shoup. Is it possible to adapt such scheme for ECC? A centralized signing machine is vulnerable to ... 1answer 139 views ### Determine LFSR phase quickly? I know it's possible with work backwards from the output bits of an LFSR to determine its feedback polynomial in a O(n) fashion. I'm also curious if, given an LFSR state and polynomial, is it ... 1answer 86 views ### Indistinguishable encryptions in the presence of an eavesdropper equivalence I'm trying to prove that definition 5 and definition 6 in this document are equivalent. This is what I've done at the moment: Asume that the scheme has Indistinguishable encryptions in the presence of ... 0answers 125 views ### Can I get a public key from PGP signature? [migrated] I have a PGP signature of a known message. However, I am not sure who signed it. Can I get the public key - or, at least, the fingerprint/other way of searching for it on a public keyserver - just ... 1answer 110 views ### Attacks on AES-128 (ECB) based on some knowledge of plaintext I'm working with a third party protocol which employs AES-128 in ECB mode of operation to encrypt a packet composed of 16-byte blocks (it encrypts each block independently). I'm trying to determine if ... 1answer 251 views ### RSA 896 vs 1024 vs 2048 in Javascript? I am currently working on a secure messaging website and I had been using RSA 2048 for encryption, decryption and signing of messages but I found it to be EXTREMELY LAGGY so i've moved to 1024. I did ... 0answers 30 views ### Does OpenTSA support PKCS11 to talk to HSMs? We are planning to implement the time-stamping service (RFC 3161) using OpenTSA wanted to know: Does OpenTSA support PKCS-11 (Cryptoki) to talk to HSMs? BTW: I did not find documentation or much ... 2answers 388 views ### Exactly two of the four roots must be greater than N/2 Theorem: Let y be a quadratic residue in \mathbb{Z}_N* where N=pq. There are exactly four integers x_1, x_2, x_3, x_4 where 0 < x_1 < x_2 < \frac{N}{2} < x_3 < x_4 < N ... 0answers 73 views ### Types of cryptography We have cryptography based on hard problems from number theory, like DDH. When we speak about symmetric cryptography with AES, a mode of encryption (CBC, ...), what is the type of problem ? What is ... 2answers 122 views ### Pi Message Encryption [duplicate] I created a simple yet efficient message encrypting page that will encrypt messages using Pi. Though not being an expert in this area, I am nowhere near sure how secure this is and how easy it would ... 1answer 70 views ### Quantum key distribution simulation I'm looking for a simulation of the Quantum Key Distribution protocol. Does anyone here have one that they could recommend? 1answer 109 views ### Combining Random Hashes - avoiding collisions and ensuring randomness I have a series of integers which I want to convert to random integer (64 bit). The idea here is to produce random numbers very quickly. The issues that good quality random numbers are required with a ... 2answers 259 views ### Is there a standard way to use a nonce with HMAC? Many protocols use HMAC on messages that include a nonce, but they don't seem to do it in a consistent way. For example, in OAuth the nonce is in the middle of an URL-encoded key-value string, like ... 2answers 83 views ### Associative standard cryptographic hash function I am looking for a standard hash function which satisfies the following property: A hash function H(a,b) = F(h(a),h(b)) with h (within F) any standard cryptographic hash function and F an ... 1answer 51 views ### How to find out the method used to encrypt [closed] How to find out the method used to encrypt the string 123456 which results in the value: 6g9SkDLIKa8l2VhafFnHvg==? 1answer 149 views ### How to calculate inverse affine transform in AES from forward affine transform? In AES the forward affine tranformation matrix is defined as:$$ \begin{bmatrix} 1& 0& 0& 0& 1& 1& 1& 1 \\ 1& 1& 0& 0& 0& 1& 1& 1 \\ 1& ...

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