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Choosing a suitable prime for accumulators

I am trying to work out accumulators and generate $S = \{ e_1,e_2 \ldots, e_n \} $ from this (Section 3.4 - Choosing a Suitable Prime). For each element of $e_i$ compute its representation $x_i$.(This ...
0
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0answers
27 views

Need for DHKE in TLS [duplicate]

Why does TLS as used in https need DHKE? Since the server presents a certificate with a public key, can that not be used for session key establishment? The client (browser) can generate a session key, ...
0
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0answers
7 views

What will be the key size for rsa, ecdhe and ecdsa from the cipher suite given? [migrated]

From the cipher suites tls_rsa_with_aes_128_cbc_sha256 and tls_ecdhe_ecdsa_with_aes_128_cbc_sha256 how do I know what will be ...
1
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0answers
28 views

Changing a bit in IV of MD5

It is obvious that changing even one bit in data or IV (initialization vector) will change the hash value a lot. I want to know if, for example, changing a single bit within the $IV$ in MD5 can be ...
0
votes
1answer
23 views

Multi signature encryption (multiple people can decrypt)

I understand that multi sig transactions exist so that X of N need to sign to release a transaction. If only 1 of N is required I guess any of the recipients can spend. This made me wonder, is it ...
2
votes
2answers
118 views

Identify AES Mode

Let's say I have an API that accepts Plaintext and IV as input parameter and returns the ciphertext. I know that API is using AES 128 encryption but now I need to identify which encryption mode (ECB, ...
1
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0answers
39 views

Hashing of variable-length chunked data leading to leakage of secret key from side channel?

Hypothetically, secret data could be hashed in some schemes in one way or another. Could chunking of the data lead to exposure of secret component through side channel? Say converting a randomized ...
0
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0answers
27 views

Re-encrypt modified file section with AES-CTR

I am trying to encrypt a file using AES/CTR/NoPadding. The goal is to re-encrypt the new/changed blocks and leave the old ones unchanged then generate a new MAC. My thinking is that when the file ...
0
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0answers
21 views

Hard ADVGX Decryption [closed]

Decrypt the ADVGX code, without a keyword or matrix. FGGAADXXFAXFGGAGAGAAFDXXXAFGFGGGFXGXXAGGFXGDAGFX Important Hint:
1
vote
1answer
55 views

SHA3-512 similar message digest

How is it possible to find a similar message-digest for SHA3-512 for the first 80 bits or so? There was a Q/A on this site where the answer stated that 80 bits that $2^{42}$ computations are required. ...
2
votes
1answer
38 views

Random salt and PBKDF2 key

Suppose I wrote a function $$(salt,IV ) = \text{keyIVGenerator}(passwd)$$ which generates a random salt of size 32-bytes and a random Initialisation Vector (IV) of size 16-bytes. Then, use a Key ...
-4
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0answers
33 views

The following is question. I missed a class and thus am unable to solve it. Someone help me please [closed]

The DHKE (Diffie-Hellman key exchange ) is done in the GF(2^5). The irreducible polynomial is P(x)=x^5+x^2+1. The α value is x^2. If the private keys of a=3 and b=12 what is the session key Kab?
0
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0answers
29 views

Does anyone know the encryption of this data? [closed]

I'm analyzing a game packet and I would like to know if anyone knows the encryption used here, because I don't know if it was the company itself that built this algorithm or it's some algorithm that I ...
1
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0answers
30 views

Can XEX or XTS modes be used with only one tweak? (part 2)

This question is similar to Can XEX or XTS modes be used with only one tweak? except I am interested to know if one can instead use $X = E_{k}(0) \otimes \alpha^j \\ C = E_{k}(P \oplus X) \oplus X$ in ...
2
votes
1answer
30 views

What is the most efficient 1-out-of-N Oblivious Transfer construction described in current literature?

I have been studying Oblivious Transfer for my bachelor's thesis and have been surprised at the number of variations of OT. From what I've read so far, the constructions proposed by Naor and Pinkas in ...
1
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0answers
51 views

How to increase Poly1305 performance?

I was analysing the Chacha20 algorithm and the Poly1305 MAC generation from RFC 7539. It seems that the Chacha20 is quite faster compared to AES on CPUs without hardware support like AES-NI. But ...
0
votes
0answers
20 views

Can zk-SNARKs prove satisfiability for NP-hard languages?

In general, I think of zk-SNARK circuits representing a language in NP, meaning it is "computationally easy" to verify. However I was reading about a recent zk-SNARK (Sonic) which has as ...
0
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0answers
17 views

Threshold schemes

I am looking for a reference that lists all major $(n,k)$ secret sharing schemes. Can anyone help me get such a reference?
1
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1answer
42 views

finding second pseudo preimage faster than brute force

As far as I know finding second preimage of a hash function is almost as hard as finding preimage. But I want to know that is there any way to finding second pseudo preimage faster than brute force? I ...
3
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3answers
117 views

Designing a secure UDP-based communication protocol

SUMMARY UPDATE: I have changed the title of this question from "Using an encrypted packet counter as a counter value in AES-CTR" to "Designing a secure UDP-based communication protocol&...
-1
votes
1answer
35 views

Can I derive IV, if I know Encrypted Txt, Key and Encryption Method?

I want to know is there any way to derive the initialization vector, if I know all the other details. AES SHA 256bits CBC pkcs5padding Input: Hello Key: 123 Output: xORGCDL88sa8cUrK8JNSCQ== Now, how ...
2
votes
1answer
27 views

Exchanging key material between HSMs of different manufacturers

In the future we may be setting up a system to secure a large number of symmetric (device) keys (a few million) by using HSMs. So, the keys themselves will be stored outside the HSM, but they will be ...
2
votes
1answer
63 views

How does randomized hashing defeat collision attack?

SEC#1 recommends randomized hashing when using SHA-1 with ECDSA; SPHINCS+ uses randomized hashing in WOTS+ to defeat collision attack so as to reduce signature size. How does a randomized hashing ...
1
vote
1answer
47 views

Is it possible to use an S-box similar to the one used in DES in AES? How would this work?

I'm reviewing some questions given to me by a professor and am stumped on this one. My initial guess is that yes, this is possible, but I do not know how to explain it, specifically for a function $\{...
0
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0answers
18 views

xor DECODING without a key [closed]

How do I find the binary key that decodes FA41086EF9153F into a readable word in English. So Far, I have tried several keys of different lengths and nothing makes sense .. any one has any hints?
1
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1answer
42 views

can we know the sign of a ciphertext (homomorphic)

Is it possible to know the sign (positive or negative) of an homomorphic ciphertext particularly under paillier scheme ?
1
vote
1answer
57 views

AES attack 4 rounds

I have currently a problem which I am unable to solve. I want to implement an attack on AES after 3 rounds without the mix columns on the 3rd. The goal is from the last round to guess the value of ...
0
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0answers
29 views

How to estimate the maximum computational cost bound for Key Derivation Functions (KDFs) before it becomes useless security-wise?

From my understanding of Key Derivation Functions (KDFs), e.g. scrypt, Argon2, etc, we can tune their parameters such that it eventually becomes harder for an attacker to brute force a password-to-key ...
1
vote
1answer
59 views

Using a nonce as a salt for key derivation

I'm currently playing a bit with PyNaCl (python binding to libsodium) and I want to use the secretbox for symmetric encryption between two parties, which means they both must know the (in my case ...
1
vote
1answer
55 views

Zero-knowledge proof for multiplication in the exponent

We have $c_1=g_1^x$, $c_2=g_2^y$ and $c_3=g_3^{x/y}$, where $g_1,g_2,g_3$ are generator of a group of order $n$ and we don't know the DL between them. Is there any sigma protocol or zkp that can prove ...
6
votes
2answers
791 views

Need help understanding math behind Rijndael S-Box

in Rijndael SubBytes() step all bytes of input block are substituted based on a lookup table S-Box. S-Box is initialized by taking all elements of $GF(2^8)$, ...
1
vote
0answers
22 views

Black-box secret sharing schemes

My question is about black box secret sharing schemes (BBSSS). Do these schemes have any advantages over the better known secret sharing schemes like Shamir’s?
2
votes
1answer
55 views

Why shouldn't cryptocurrency hash algorythms, resist side channel attack?

2015's Argon2 publication suggests that cryptocurrency hashing like password hashing on backend servers should not be subject to side-channel attack: Argon2d is optimized for settings where the ...
0
votes
1answer
22 views

Is establishing a secret key possible given this characteristic primitive?

I am wondering if there are any readily available solutions for the following problem: I have a ring-topology network with several devices connected to it, some malicious, some legitimate. I want to ...
-3
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0answers
57 views

Why are the MD5 Hash values the same? [closed]

Why or why not are the MD5 Hash values the same?
0
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2answers
61 views

AES confused about how ShiftRows() step works

Advanced Encryption Standard has a ShiftRows() operation that cyclically shifts last three rows of 16 byte block as shown here. This process is explained here in ...
0
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0answers
25 views

Hash Function with Same Output for Similar Data

I have some code that creates a 3D mesh. The way I process the mesh I end up with a lot of vertices that are extremely close to each other but not identical. I want to create a hash from those ...
-1
votes
0answers
36 views

How to find the secret of a hashing algorithm? [closed]

I'm trying to do a CTF challenge where you have to find the secret of a hashing algorithm used to hash strings. You are given two strings and their corresponding hashes. There is also a hint to use a ...
3
votes
1answer
64 views

How does the Concat KDF work?

I am writing an application using JSON Web Encryption with ECDH using the X25519 Curve. The RFC says that ECHD-ES derived secret is run through a Concat KDF. Given ...
0
votes
1answer
39 views

AES 128-bit encryption - not getting expected results

I am trying to implement AES encryption on my own (128 bit key and ECB mode for now) and I can't seem to get expected results. From what I understand about AES algorithm is that it divides message in ...
0
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0answers
19 views

Probability of finding a valid block when cryptocurrency mining

Today I learned that for BTC, the probability of a hash being valid is approximately 1/(D*2^32), whereas D denotes to the difficulty. I was wondering if this is ...
0
votes
1answer
26 views

PRF and deterministic polytime function implie PRG

I'm struggling while trying to resolve this exercise. I already read all questions about PRG and PRF here and some proofs around the internet but none of them helped me. let's consider a function $C$ ...
0
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0answers
31 views

What is a quantifier in game-based definitions?

I'd like to know what are quantifiers in game-based security definitions (in cryptography) Some relevant examples and sources are also much appreciated. Edit: for example, in a formal definition, we ...
0
votes
0answers
17 views

Pipelining of the extender in SHA256

I am currently working on a project in which we are working on implementing a fast version of SHA256 using VHDL. Currently our solution consists of multiple cores computing SHA256 iteratively in ...
1
vote
1answer
151 views

Security of RSA cryptosystem variant

A variant of RSA cryptosystem is given as following: $$N=p*q$$ $$ed=1 \space \space mod \space \space (p^r-1)(q^r-1)$$ $$c= m^e \space \space mod \space \space N $$ $$m= c^d \space \space mod \space \...
1
vote
1answer
20 views

Is it necessary to prove EUF-CMA security of blind signature based on one-more type assumption?

One more type means one-more DL, one-more DHP, etc. I find many papers do the EUF-CMA security proof in this way. Is it necessary? What is the difference between proof based on one-more type ...
3
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0answers
52 views

Is AES-GCM-SIV with fixed IV deterministic authenticated encryption?

Is there any functional or strong security difference beyond speed between AES-GCM-SIV with implicit fixed public IV and no additional data AES-CTR (or AES-OFB) with 128-bit IV computed per HMAC-SHA-...
0
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0answers
28 views

Block cipher exercise CTR, CBC and ECB [closed]

I'm trying to figure out this exercise about CTR, CBC and ECB given Encryption Matrix [29->0, 11->1, 26->2, 1->3, 21->4, 4->5, 15->6, 31->7, 27->8, 28->9, 2->10, 14-&...
0
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0answers
24 views

What tools to use to figure our what the hash/encryption algorithm is? [closed]

So, here goes. One of our programmers has created his own "hashing" algorithm to assign to a UID to store into the cookies. Data he has used to derive the hash: ...
0
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0answers
32 views

Text cipher option that can decrypt the same ciphertext to two DIFFERENT and DESIRED outputs given DIFFERENT keys (and/or alphabet)

I have a pen pal that I discuss with. In our latest discussion it was proposed to write a short message that is ciphered and have the other one find what it is, given some clues. I would like to ask ...

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