3
votes
1answer
254 views

Weaker alternative to Ed25519?

For me, the main advantages of Ed25519 are that it avoids patents (by computing in one dimension) and that it is fast. However, the 128bit security of Ed25519 is sometimes too strong to comply with ...
0
votes
0answers
25 views

Security for multiple functions for a functional encryption scheme

Assuming a functional encryption scheme $F$ in which an untrusted server is able to learn the sum, the multiplication and the sum of the inverses of an $n$ dimensional vector $x \in \mathbb{F}_N^*$ ...
0
votes
1answer
37 views

Value of S and r in Fiat-Shamir Protocol

In the book Cryptography and Network Security by Forouzan,in chapter 14, Fiat-Shamir protocol, its mentioned that two large prime numbers p and q are chosen and kept secret. However n=p*q is made ...
2
votes
1answer
74 views

RFID Protocol Cryptanalysis

Assume we have the following scheme for RFID: TAG & READER both have initially k keys. Every session the TAG computes $k_i$=F($k_{i-1})$ where F is a function which computes XOR of previous key ...
1
vote
1answer
40 views

Errata for NIST SP 800-63

I'm looking through the latest version of NIST SP 800-63, and there is a table (Table A.1) in the Appendix that supposed give the "entropy" of a password for a 94 character alphabet for various ...
1
vote
1answer
72 views

Benefit of using random key in Shamir's Secret Sharing

I am implementing Shamir's Secret Sharing, and I find that in (t,n)-threshold scheme, the shares are just using 1,2,3...,n as the key to form the shares ...
0
votes
1answer
72 views

SSL / TLS digital signature exchange

If server is sending its digital signature, in which message / where does the digitally signature is provided to the client. Is it after the server_hello message because there the public key of the ...
1
vote
1answer
36 views

Meaning of Signature hash algorithm field in certificate

I'd like to understand what is the meaning of this field, especially considering that when calling a crypto library to sign data the digest method is specified by the caller. For example, this simple ...
0
votes
1answer
41 views

Rationale of “r” AES key use in OTR version 3 AKE protocol?

I just tried to review & understand AKE (Authenticated Key Exchange) protocol as defined in OTR secure messaging protocol version 3 here , and aiming to achieve Perfect Forward Secrecy I am a ...
-1
votes
0answers
62 views

What are the difference between cryptographic primitives and encryption primitives?

For example, from reading I found that the cryptographic primitives of both AES and DES are Confusion and Diffusion. However the encryption primitive for DES was Substitution and Permutation while ...
-3
votes
0answers
83 views

Decryption using Key and vector. [closed]

Decrypt the enclosed text using not so advanced encryption technique. Key is “abcdefgh” and vector is “abcdefgh”. ÷ó*ÁÛýÁ n9†“Ü,YÓ©?†]žÀ
-4
votes
0answers
117 views

How to decrypt the text using the key and vector? [closed]

Decrypt the enclosed text using not so advanced encryption technique. Key is “abcdefgh” and vector is “abcdefgh”. ÷ó*ÁÛýÁ n9†“Ü,YÓ©?†]žÀ
-3
votes
0answers
56 views

Question about feistel network [on hold]

What’s the output of two round Feistel network, 1) when input is 1^32||0^32 (L0 is 32 bit 1, R0 is 32 bit 0)? 2) when input is input is ^064(L0 is 32 bit 0, R0 is 32 bit 0)? This is all I have...I ...
-4
votes
0answers
42 views

Why is plain ElGamal not secure?

Why is plain ElGamal not secure? What is the proof behind it?
-4
votes
0answers
37 views

What’s the output of two round Feistel network [closed]

What’s the output of two round Feistel network, 1) when input is 132||032 (L0 is 32 bit 1, R0 is 32 bit 0)? 2) when input is input is 064(L0 is 32 bit 0, R0 is 32 bit 0)?
1
vote
1answer
80 views

How does the Blowfish algorithm key initialization work

I'm having some trouble understanding the Blowfish encryption algorithm. From the Wikipedia article... The secret key is then, byte by byte, cycling the key if necessary, XORed with all the ...
1
vote
0answers
53 views

Standards/RFCs for non-Diffie-Hellman perfect forward secrecy?

Some time has passed since PFS introduction and we now have secure&proven asymmetric ciphers that can generate strong keys very efficiently (elliptic RSA variants and/or QD-Mceliece can generate ...
2
votes
1answer
51 views

Secure ElGamal with OAEP

Is it possible to make ElGamal IND-CCA2 using OAEP or OAEP+? The reason I ask is that I recently answered this question and it came to my mind that OAEP or OAEP+ might be possible solutions. Note ...
0
votes
0answers
25 views

AES-XTS: find key from ciphertext and plaintext [duplicate]

Let's say I have a plaintext, the corresponding ciphertext encrypted using AES-XTS, and the initialization vectors. Is there any way - not brute force, of course - to compute the key? Even if there's ...
0
votes
0answers
28 views

Information Theoretically Secure Mediated Digital Signatures [closed]

Suppose Alice wants to sign a message $m$ and send it to Bob, through Charlie. Is there a way to do it such that it is information theoretically secure?
0
votes
1answer
53 views

Prove there is PRG that is not necessarily one-to-one

We assume that there is at least one PRG .Now prove there is a PRG like $G:\{0,1\}^{n} \rightarrow \{0,1\}^{l(n)} $ such that it is not necessarily one-to-one.
1
vote
1answer
34 views

CTR_DRBG versus OFB_DRBG

As far as I know, in the development of ANSI X9.82, there was consideration of OFB_DRBG, a pseudorandom number generator based on block ciphers like CTR_DRBG, but it appears to have been rejected of ...
2
votes
0answers
57 views

Looking for C++/Python Open Source code library for cryptanalysis of classical ciphers

I've done a significant amount of coding over the years working on classical ciphers (e.g., Chaocipher, D'Agapeyeff). My main programming languages today are C++ and Python, although there was a time ...
0
votes
0answers
37 views

Is the key schedule of Serpent a circle?

The creation of the prekeys for Serpent works by XORing some previous values with a counter and a fixed value. Every word is 32 bits big and 4 words form a round key (after applying a S-Box, but this ...
0
votes
0answers
67 views

Russia: need to disclose encryption keys to FSB [closed]

Is it true that in Russia you as a citizen have an obligation to send copy of any and all of your encryption keys to FSB even without waiting for a demand? I don't even know where else to ask this ...
3
votes
0answers
60 views

How to recover $e$ from $f_A(e) = Ae \mod q$ when knowing trapdoor

I have a silly question, but I don't know a solution, so I need to question. Assume, with a algorithm $TrapGen(1^\lambda)$, it generates $A\in\mathbb{Z}_q^{n\times m}$ with a basis $B ...
0
votes
0answers
44 views

GPG: What public key do I have to publish? [migrated]

I just created a master key and two subkeys. The first subkey is used for encryption, the second one for signing. Now i am wondering what public key do I have to publish on my website. Does is ...
0
votes
1answer
52 views

AES Mix Columns and Shift Rows

Why we use Mix Columns and Shift Rows in AES? FOr example, if i want implement an AES algorithm without Mix Columns and Shift Rows what is the difference in the ciphertext?
1
vote
3answers
68 views

Why do we get the following equation in case of a One Time Pad?

If m: message, M: message space, k: key, K: keyspace, c: cipher, C: cipher space and $E_k$: encryption function, such that $E_k(m) = c,\ m,m^* \in M,\ k\in K,\ c\in C.$ My first question is, is the ...
-6
votes
2answers
77 views

OTP - Reusing key IS SECURE! PROVED! [duplicate]

EDIT: This is not a duplicate, in this I have explained WHY this should be secure and not if it is secure, so please stop down-vote if you haven't read everything. I have questioned before about my ...
1
vote
1answer
45 views

Zero knowledge proof relation + number is binary

I want to develop a ZKPK for the following problem: $$Y=g_0^{r_Y} \prod_{i=1}^n g_i^{s_i}$$ and $$Z=h_0^{r_Z} \prod_{i=1}^n h_i^{s_i}$$ I want to proof knowledge of $r_Y,r_Z$ and $s_i$ which I have ...
1
vote
1answer
38 views

Using similar passwords and salts for PBKDF2

I'm trying to generate a bunch of pseudo-random keys for AES using PBKDF2, where the AES ciphers will be used in CTR mode as pseudo-random number generators. My goal is to create a 2-dimensional ...
0
votes
0answers
77 views

Axolotl ratchet crypto protocol in plain English [on hold]

I have been trying to read and understand https://github.com/trevp/axolotl/wiki but there's too much technical wording which I can't understand. From what other developers tell me it's the safest ...
0
votes
0answers
30 views

Would a pictographic, phoneme-based, hand cipher be difficult to crack with computer crypt-analysis?

What I'm talking about is a hand cipher which uses phonemes instead of individual characters and pictograms instead of the usual shuffling/substitution methods (e.g Caesar, Solitare, Vignere). The ...
1
vote
2answers
82 views

What do these notations mean in the definition of Perfect Secrecy, if we read those in English?

If m: message, M: message space, k: key, K: keyspace, c: cipher, C: cipher space and $E_k$: encryption function, such that $E_k(m) = c,\ m,m^* \in M,\ k\in K,\ c\in C.$ Then, what do the following ...
0
votes
0answers
63 views
0
votes
1answer
48 views

Is $f\colon x\mapsto g(x+1)$ necessarily a pseudorandom function?

Let $l\in\mathbb N$ and suppose $$g\colon\;\{0,1\}^l\to\{0,1\}^l$$ is a pseudorandom function. Is $f$, defined as below, necessarily a pseudorandom function as well? $$f(x)=g((x+1)\bmod2^l)$$
1
vote
0answers
28 views

Generate hash value using public key along with message

I was trying to understand one way signature chaining on message by saxena and soh. As the message is passed from one user to other, every user can combine their signature to create one single ...
-4
votes
1answer
48 views

Encryption & Decryption of Video using RSA [closed]

I need code in java for Encrypt & Decrypt any file using RSA Algorithm. I have code which takes a text file read data from it and then encrypt it. but I need program to encrypt mp3, mp4 any file.
0
votes
0answers
29 views

Using a Secure RNG in Probabilistic Fair Exchange

I am attempting to implement probabilistic fair exchange described in Probabilistic Non-Repudiation without Trusted Third Party. A secures a message using AES with 512 bit keys (in my ...
1
vote
1answer
55 views

(Simple) Tool for analysing performance (speed in particular) of cryptographic hash function?

I am doing some research for which I intend to insert some (external) function in different cryptographic hash functions and I would like to analyse how the insertion of this extra code in the hash ...
-1
votes
1answer
52 views

OTP - Reuse key BUT add IV, is it secure enough?

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! I have already asked a similar question and now I can continue to this question about adding a "extra key" = IV. My last question ...
-2
votes
1answer
80 views

OTP - Why not reuse key? EDITED! [duplicate]

EDIT: REUSING KEY IS SECURE! OTP - Reusing key IS SECURE! PROVED! This might sound really dumb but why is it bad/insecure too use the same key twice on One-time-pad? Question: Why and how does using ...
0
votes
1answer
58 views

What is the proper way to generate a fixed length key from a variable length password?

The password is entered by the user and the key is processed locally. Neither the password nor the key will be stored, only used and forgotten (but hopefully not by the user). Is SHA256 by itself ...
0
votes
1answer
64 views

How much of Probability do I need to know to study Cryptography?

I have just started MSc in Computer Security. I didn't study probability before. Now, I have some short time to complete my MSc semester. What are the minimum topics from 'Probability' do I need to ...
-4
votes
0answers
44 views

Can anyone crack this enigma code? [closed]

I wanted to test the knowledge of these forums. Anyway here you go CCMF Hint:All the rings are so Awesome
0
votes
0answers
32 views

What is “Asymptotically tight time complexity”? Is this code's time complexity asymptotically tight? [closed]

What is the time complexity of this code O(xnk)? Is the time complexity asymptotically tight? ...
0
votes
0answers
18 views

Substitution Permutation Network (SPN) - Decryption In Mathematica

I am working with a Substitution Permutation Function, SPN, in Mathematica. I have an encryption function for an SPN. By changing the parameters that go into the spn function, and not the function ...
0
votes
1answer
60 views

How to encrypt a vector $e\in Z^{m}$ using LWE

I have a vector $e \in Z^{m}$, now I want to encrypt it by using LWE (Learning With Errors). Because in LWE, we have to encrypt of a bit $\{0,1\}$. How can I encrypt a vector $e \in Z^{m}$? Thank you ...
0
votes
0answers
21 views

Why the Symmetric Key algorithm requires small key compared to Asymmetric algorithm? [duplicate]

According to a book I am studying: The key lengths for symmetric and asymmetric algorithms are dramatically different. For instance, an 80-bit symmetric key provides roughly the same security as a ...

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