# All Questions

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### Does encrypting with MGF1/SHA-512/1024-bit seed equal to a 1024-bit key block cipher?

Suppose: Alice uses SHA-512 with MGF1(as in PKCS#1 V2) and a 1024-bit random seed to generate a mask, XORs the mask with a message(M), gets a cipher text (CT), and sends the CT to her old friend ...
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### Best/average/worst-case complexity for cryptography

I understand that the complexity of a problem can be measured by it's best-case, average-case, or worst-case complexity. Am I correct in thinking that, for cryptographic purposes, each of these is of ...
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### Difference left-or-right CPA security, IND-CPA security

I am trying to understand the notion of left-or-right-CPA (LOR-CPA) security for private-key encryption schemes introduced in my lecture. If I understood it correctly so far, the only difference to ...
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### Does SIV mode work for asymmetric crypto?

In ECIES and similar schemes, is it possible to use a hash of the plaintext as the IV?
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### How does TLS differ from SSH from a strictly cryptographic perspective?

How does TLS differ from SSH from a strictly cryptographic perspective? I know that there are many non-cryptographic differences between them, but I would like to know the cryptographic ones.
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### Ciphers providing Deniable encryption?

I stumbled on the concept of Deniable encryption on Wikipedia, with the following scenario: Deniable encryption allows the sender of an encrypted message to deny sending that message. This ...
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### SIV - Synthetic IV - S2V Construction? Benefits over a MAC or Hash?

Looking at the SIV construction in rfc-5297 - https://tools.ietf.org/html/rfc5297 With regards to the generation of the SIV, using S2V construction, I am struggling to find the benefits of the chosen ...
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### Active s-box of 8x8 MDS for AES

one way to enhance the security of AES by increasing the number of active s-boxes .larger MDS matrices are used to increase the number of active s-boxes. using 4x4 MDS matrix generate 25 active s-box ...
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### How does Blom's scheme work?

How does Blom's scheme work? Is the polynomial expression of it a normal one? A few additional questions: How big does the prime modulus need to be? Can it be bigger than the size of the derived ...
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### How easily could this method of cryptography be cracked? [closed]

Background A couple of years back, in my naivety, I dreamt up a method to encrypt information. The result can be seen on my website, I evidentially thought it was pretty neat and I decided to mix it ...
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### Are there any historic examples of breaking the one-time pad because of a careless key re-use? i.e simple attack on a multiple-time pad?

It doesn't have be using a truly random key, (it could be the Enigma) but the attack must be based on XORing two parts of ciphertext.
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### Implementing hmac+bcrypt in bash script

I was recently reading Mozilla's Secure Coding guidelines and found their password storage method interesting. They combine an hmac hash of the password with bcrypt which allows for added security ...
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### How does the speed of fast stream ciphers compare to non-cryptographic PRNGs?

Modern stream ciphers are so fast that I am wondering if they are good choices for non-cryptographic applications. Specifically, I am wondering how much slower optimized ChaCha8 or ...
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### Is RSA safe anymore? [duplicate]

Some people may have heard of Shor's algorithm. It allows for integer factorization on a quantum computer. This wasn't a problem a little while ago since we didn't have any quantum computers. Google ...
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### Is there any difference between NIST and SECP curves in-terms of their algorithms and implementation?

I'm implementing ECDSA for NIST P-256 curve. I just want to know the same implementation will work for SECP curves also?. If it doesn't, then please suggest me references of algorithms or sample ...
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### Is it okay to bail out early when length mismatch is detected?

Is it okay to bail out early when length mismatch is detected? Specifically, when verifying authenticated encryption, is it okay to bail out early if the wrong amount of ciphertext or the wrong ...
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### NIST SP800-108 KDF modes comparison

According to NIST SP800-108, there are three modes that can build KDF from PRF: counter mode, feedback mode and double-pipeline iteration mode. Assume that the same PRF and input distribution are ...
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### How to conver roots of Weber polynomial to hilbert class polynomial over modulo prime?

Using any non square root discriminant $D$, we can able to find the Weber class polynomial. How can I convert the roots of a Weber polynomial to a Hilbert class polynomial over modulo prime?
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### Considerations on using a single long-term key for file encryption

I'm thinking about designing my own container file format that allows me to store a file in it along with, say, a thumbnail or other metadata. Some of these files are confidential and therefore must ...
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### Negative lookup table concept

Interested in password cracking, I thought of a concept for lookup tables that can tell if a hash can be created using a dictionary in about O(log n) time. A simple overview of the idea is a follows: ...
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### Encryption of both data and code [duplicate]

Suppose we have 3 parties: Alice possesses invaluable data $x_1, x_2, ...$; Bob can compute some extremely useful function $f$; Carol owns a world's largest data center which have enough resources to ...
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### gnupg master key with certificate and authentication capabilities

After researching about GPG and Smartcards I came to a dilemma. The usual setup I've seen more widely is a master key (with SC capabilities) and 3 subkeys (with S, E, A each): ...
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### What will browser show when a user access website and website present certificate of some other domain with same top level domain [closed]

For example, User tries to access a.example.com and server presents abc.example.com with a.example.com not in SANs list. Will it be just a warning or an error?
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### Usage of 3DES for single block

I have a device, HASP, which has functionality to encrypt 8 byte data using 3DES in ECB mode, with three different keys, I am interested how secure is this? I know it might not be most secure, but how ...
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### Why does Rabin cryptosystem split the message into key blocks?

Why does Rabin cryptosystem split the message into key blocks and not into plain text blocks like in Merkle Damgard Construction? Is it because it acts in a way similar to IV? Probably not, it ...
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### Creating a message authentication scheme

I have such situation. I have a device like dongle. But it has certain limitations. For example, it can only have implemented encryption and decryption functionality. The availability of ciphers ...
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### Can anyone tell whether this RHO step of SHA3 is correct?

In rho step of SHA3, I have done right circular rotation whether its correct ?? I am doing in Verilog so I am using concatenation operator for rotation. For x=0 and y=1 that is A[0][1] rotation will ...
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### Can anyone breifly explain the 'theta step' of compression box in SHA3?

Can you tell me the 'theta' step of compression box. D[X] = C[X-1] ^ ROT(C[X+1, 1]) In this step all the indices should be taken modulo 5. ...
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### Importance of timing attack resistance with AES

I've implemented AES in my library with several variations: a straight C version, a version using x86 SSSE3, and a version using x86 AES-NI. The SSSE3 and AES-NI implementations are constant-time, ...
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### Length Extension Attack on SHA1 [duplicate]

I am trying to understand how to perform a length extension attack on a SHA1 hash function that is used as a MAC (where the key is prepended to the hash output). If I am given the message, ...
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### How to measure performance for ABE Schemes

I have these 3 Schemes: 1) J. Bethencourt, A. Sahai, and B. Waters, "Ciphertext-policy attribute-based encryption" 2) F. Guo, Y. Mu, W. Susilo, D. Wong, and V. Varadharajan, "Cp-abe with ...
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### To understand Feistel permutations in md5

Recently I am trying to understand the md5 algorithm.In this algorithm 4 Feistel permutations FF,GG,HH and KK are used.I have faced a problem to understand the FF. The FF is defined as ...
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### Simulation of a custom build network security algorithm with ElGamal Cryptosystem using Elliptic Curve

I am trying to build an algorithm to encrypt and decrypt text using ElGamal Cryptosystem using Elliptic Curve. My algorithm generation is done. But at simulation part I stuck. My algorithm steps are ...
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### RSA : Double-Encryption and order of Encryption

I'm studying cryptography and we're looking at RSA. We're required to do a double encryption from Alice to Bob and then Bob back to Alice. We've been told the order of encryption is important and it ...
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### Is there any zero-knowledge technique to verify proof of knowledge of shared secret key?

Generally, to verify knowledge/key generated between two interacting parties in an authentication protocol uses Hash, MAC, Digital Signatures or encryption (based on random challenge). But I would ...
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### Difference between single-pass and two-pass MACs

I am having trouble understanding where the count of "passes" come in. What constitutes a pass in the context of message authentication codes? How are single-pass MACs achieved?
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I know it's generally bad to store password in the clouds, and that I should be using salted-hashed password only. I'm making an application that will authenticate a user (with salted-hash), and then ...
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### Ways to identify mystery ciphers with no information but the code itself? [duplicate]

I recently offered to solve a cipher that was sent to my friend because he couldn't. I'm really having issues with the identification, I've tried a simple Caesar shift, and it came back with nothing. ...
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### Do most TLS 1.2 implementations express curves in a canonical form when performing EC arithmetic?

Sorry if this is a silly question, but does anyone know if the cryptographic libraries which implement TLS 1.2 for Firefox, Chrome, etc. express a given curve in a canonical form (i.e. one of ...
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### How are the attributes of a user authenticated in attribute-based encryption?

It seems that the papers I am reading do not talk much about this point. That is how the attributes of a user are authenticated in ABE system. To my understanding, there is an attribute authority ...
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### How is the root certificate transmitted to pc?

i understand that the purpose of root certificates and CA's is to ensure that the communication parties are who they say they are. But how is the root certificate acquired? Is it not possible that ...
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### Gaussian distribution in lattices

In many lattice based cryptosystems, Gaussian distribution is used. Can you explain why only Gaussian distribution is preferred?
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### Multi Authority Attribute Based Encryption Library

Anyone aware of a library that has MA-ABE implemented in any language preferably python? P/S - I hope this is the right place to ask this. Apologies if not, then a redirect will be appreciated
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### Have ciphertext and key but need to figure out encryption method

So I have a block cipher (I think) that I need to break. I have the ciphertext and the key, but not the method of encryption, and was wondering if anyone could help me figure that out? The key is a 9 ...
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### AES Twofish Serpent [duplicate]

AES-Twofish-Serpent how to create this combo encryption? I am using Linux Mint and i want to encrypt few big folders in one folder, but to be hiden.
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### What are the pre-requisites I need to be able to code Salsa20 in C#?

I've taken a basic course in Cryptography and we've learnt various algorithms and their usage. I've implemented RC4 and Triple DES in C# with ASP.NET. For a project that I am a part of, I need to ...
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### How do you apply bilinear mapping to attribute based encryption?

I'm new to both bilinear mapping and ABE. I have a vague idea of how bilinear mapping works now, but I don't understand how it applies to ABE. Can someone give me an example?
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### Permuted Hash Table

Suppose we have a hash table, $HT$, consisting of $100$ bins.The hash table uses a hash function $H$ that is public. We all know that given value $a$ we can compute the address in the hash by ...