0
votes
0answers
8 views

What is the difference between openssl pkeyutl -sign and openssl rsautl -sign [migrated]

What is the difference between openssl pkeyutl -sign -pkeyopt digest:sha256 and openssl rsautl -sign ? Do they do the same ...
1
vote
1answer
46 views

Can CFB mode of block cipher be used as a commutative encryption?

Can CFB mode of block cipher be used as a commutative encryption? Is it possible to use CFB mode of AES block cipher to create commutative encryption? With CTR it is possible but not secure.
0
votes
0answers
29 views

How do I decrypt a file I didn't encrypt? [closed]

I backed up a game save from my android device using ADB and backed up the save data, not the app. It is encrypted even though I didn't encrypt. I would like to know how to decrypt it, as I tried ...
0
votes
0answers
58 views

Analyzing complexity of HMAC-SHA-256?

I'm new to cryptography, please don't mind me if I'm asking anything wrong. How can I analyse the complexity of HMAC-SHA-256 if the size of my key is 128 bits and my message contains 128 bits ...
1
vote
1answer
57 views

Converting a pre-image resistant hash to second pre-image resistant

I am looking for some standard conversion from any hash function $f$, which has pre-image resistance, to another hash function with second preimage resistance. Is there such a standard conversion?
1
vote
1answer
39 views

Why should $a,b < N$ for Montgomery Reduction?

In Montgomery reduction, when calculating $a \times b \mod N$, it is required that $a \lt N$ and $b \lt N$. I think $0 \le T \lt N \times R$ is enough for the Montgomery Reduction. Rationale: Let ...
2
votes
2answers
91 views

Question about the key in RC4

I am planning to develop a more secure version of the RC4 algorithm. Since I´m not an encryption expert, I´ld like you to help me find answers to the following questions: Does the value of the key ...
0
votes
0answers
12 views

AES GCM 128, c#: very 12 byte tag instead of 16 [closed]

I'm using Security.Cryptography.dll and I'm wondering if there is a way to decrypt and check tag which is shorter(12 bytes)? I have situation where only 12 of 16 bytes of tag are sent in network ...
-2
votes
1answer
41 views

Shuffleless PRNG function with non-repeating values?

I need a simple PRNG function of type: Integer = PRNG(n, maxval) as I would like to count from 0 to maxval, not in a linear manner, but in a pseudorandom manner where I still use every value, but ...
-1
votes
1answer
42 views

i cant understand the meaning and the difference between linearity equation and affine and non linearity?

i cant understand the meaning and the difference between linearity and affine and non linearity equations and what is the meaning of the free term in affine form and how it make the equation non ...
0
votes
0answers
13 views

Adapt existing GOST code in C to hash a file [migrated]

I am trying to hand-code the GOST hash function using C. I came across the following code by Markku-Juhani Saarinen (from link). ...
0
votes
0answers
15 views

Understanding JCE Cipher Algorithm Strings [migrated]

I am new to cryptographic ciphers and I am trying to understand the strings that JCE uses to specify cryptographic algorithms. For example, using the documentation at: ...
1
vote
0answers
22 views

Chance to find HMAC key/salt when having knowledge of the hashed data?

I'm not sure how to word this... I'm working with a HMAC (I think of it being a "salted hash"). I know the entire string being hashed, I do NOT know the salt. I also know the first 8 characters of the ...
0
votes
0answers
18 views

Can anyone help me identify the hash function used for these? [closed]

I have a bunch of XML files that contain hashes of images, but I don't recognise the hashes. I know what files they correspond to, but for the life of me I can't identify these (I have a suspicion ...
5
votes
1answer
49 views

Keys in HMAC and NMAC

I'm quite new to this topic and have several questions concerning HMAC and NMAC: Why does NMAC need two keys? How can it be attacked if we just used some sort of initialization vector instead of the ...
0
votes
0answers
24 views

Secure storage of sensitive data [closed]

I don't like using a throwaway but somewhat need to. I'm seeking advice regarding a cryptographic implementation. I have a server that needs to be able to process, manage and hand data back to a user ...
0
votes
0answers
23 views

How can I send a file from a server to specific client? [closed]

I am trying to create a server/client in python using sockets for sending encrypted files in between clients. The server acts as the intermediate for this purpose. At first the client1 encrypts data ...
3
votes
4answers
296 views

Are specially designed fonts sometimes used in cryptography?

As a font designer, I was thinking that it would be very easy to design a special font that could either jumble characters of a language (or of a code) or simply (with the features offered by the OTF ...
0
votes
0answers
22 views

Why doesn't COMODO use their root cert for the SSL certs they sell? [migrated]

I noticed that OS X ships with a COMODO Root Certificate, but that the certs they sell to websites stem from the AddTrust External CA Root. Why is this?
0
votes
0answers
23 views

How to find the crypt algorithm from a table of crypt vs results? I guess this is MD5 [closed]

Im new on Crypt things, I want to know how to find the "salt" or the algorithm used to convert this strings. I read long time ago about this but for get it even how this process was named. I guess ...
0
votes
0answers
8 views

Does we need IV if we're generating a new Symmetric key for every message? [duplicate]

We need to encrypt individual messages, for every message we: Generate a new AES key Encrypt the message with the key (AES/CBC/PKCS5Padding) Encrypt the symmetric key with with a public key ...
3
votes
1answer
46 views

Implementing forward secrecy in OpenPGP with public key authentication

I am trying to consider the feasibility of implementing an encrypted file sharing system, which both provides forward secrecy but also allows public key verification. I am stuck on the marriage ...
0
votes
0answers
5 views

Length of output of AES 128 encryption in python [migrated]

When I am trying to convert to hex the output of my AES 128 encryption code using pycrypto. I am using hexlify .the output is 64 bits for a 32 bits input. The output is always double the size for any ...
2
votes
1answer
41 views

Favor hash size or field size when systems are disparate?

I'm working on an implementation of Krawczyk's Hashed MQV (HMQV). I'm using Crypto++, which is a C++ library. C++ has some features where classes that represent the crypto objects can be combined ...
5
votes
1answer
469 views

Can hash functions improve a lousy PRNG?

If I have a poor PRNG, could a cryptographically secure hash function make a better output? Say the PRNG can produce as much numbers as you wish, reasonably random, but not good enough to be used in ...
0
votes
0answers
34 views

XOR + HMAC security analysis? [closed]

I'm new to cryptography don't mind me if I'm asking anything invalid.I'm working on security in Device to Device communication based on LTE-A. Can anyone please explain about analyzing some of the ...
0
votes
0answers
32 views

Database of Cryptographic Hardness Assumptions [closed]

I'm looking for a specific website that lists all of (or many) of the hardness assumptions used in cryptography. The website lists the problems along with a short explanation and references. ...
0
votes
0answers
66 views

Can I get the private key through the public key in RSA? [closed]

I want to obtain private key in RSA to decrypt a msg. Decrypt -> M = C^d (mod n) I know that: Crypted msg (C) = 0x293D9E806D9F9040E52F71B4026FD5AA95D965E7319728F220ADB44794CEA3D6 Public key ...
4
votes
0answers
55 views

Better lower bound on min-entropy

In “Randomness Condensers for Efficiently Samplable, Seed-Dependent Sources” by Dodis, Ristenpart, and Vadhan (PDF), I have seen the statement that: any tuple of distributions $(X,Z)$ is $ε$-close ...
2
votes
1answer
61 views

Hash functions to generate one time pad

Newbie question... may be... Stream cypher, will XOR message bits with one time pad bits Suppose I have a pseudo random number generator, like a Mersenne twister or sort of. I could use the ...
5
votes
1answer
95 views

Can Alice send Bob a secure message with only DSA and no key exchange?

Suppose Bob has a DSA key pair, and Alice has Bob's public key. Is there any secure way that Alice can send Bob a message only he can read if Bob can not send any reply? I think the answer is no, ...
1
vote
0answers
24 views

Improve security of transposition ciphers

As we know, breaking a Transposition Cipher is quite trivial and can be easily done by either exploiting single letter frequencies (not $d$-gram frequencies though, given that $2 < d < L$), or ...
2
votes
1answer
32 views

Finding keys of modified DES encryption

This is a question I had in my exam today, and I'll be glad if someone can help me to find the answer. A student built an encryption algorithm (something between DES and 3DES), in which the ...
3
votes
1answer
89 views

Why don't use random padding in RSA?

Consider the following scenario: Sender S sends a message to receiver R. He uses a hybrid encryption scheme with RSA as key-encapsulation algorithm and AES-256-CTR (4byte-counter) and SHA256-HMAC. ...
3
votes
2answers
88 views

Why should one prefer Salsa20 over ChaCha?

We are all aware of Google's approach to introduce ChaCha/Poly1305 as TLS cipher suite. The rationale seems clear: ChaCha is newer and seems to provide better security (and maybe speed?) gained from ...
1
vote
1answer
73 views

Simulation based proofs: Simple examples

I am aware that,(in theory) in order to proof that a scheme is secure using simulation based proof we replace an adversary in real world with a simulator in ideal world. Then we try to show that their ...
3
votes
0answers
81 views

Has anyone heard of matrix-based “Roman Doll” encryption techniques?

I've been told that prime-number factoring is based on a "roman-doll" sequence of matrices, where a seed matrix of height Y and width X exists consisting of all zeros except for a single 1 at row Y ...
0
votes
1answer
29 views

What values constitute failing for ENT tests?

The dieharder tests give a clear PASSED, WEAK, etc and I'm wondering what those thresholds ...
1
vote
1answer
35 views

ElGamal and Paillier key sizes for short messages

I am using ElGamal and Paillier schemes to encrypt a large number of short messages: typical 4-byte integers. I do this for the homomorphic properties of these schemes. However, the way the ...
3
votes
1answer
75 views

64bit nonce in AES-CTR, why not 128?

I'm just a bit confused about the nonce/IV in AES-CTR ... it seems the suggested way to go is have a 64bit random nonce, and use the last 64bits as the counter, "starting at 0". I'm just wondering ...
3
votes
2answers
76 views

Determine AES key given encrypted and unencrypted files

Given an encrypted file, the original unencrypted (cleartext) file, and knowledge of which AES encryption algorithm was used, is it possible to determine the key that was used to encrypt the data in a ...
3
votes
1answer
480 views

Why does “2xAES-256” provide “99.99%” security strength whereas “1xAES-128” provides “40%”? [closed]

I recently was "directed" to FlipsCloud, a company selling security solutions (as far as I can tell). In particular I've investigated their page and found a page on their "encryption features". This ...
0
votes
0answers
24 views

Identification schemes: Okamoto

I am reading Cryptography theory and practice by Stinson. The book is talking about the proof of security of Schnorr and Okamoto schemes. It claims that if an impersonater can find (in the case of the ...
0
votes
1answer
35 views

Collision Probability of MD5 over different attacks

I am researching on collision probability of MD5 on various attacks against it. Can someone help me with finding what is the least probability that there will be collision in specific attack on MD5 ? ...
0
votes
1answer
38 views

Cryptography in wireless medium

.i'm new to this Area. Que. how do i implement asymmetric key algorithm into wireless medium using ns 2.35 ? e.g. node A is a sender and B is a receiver now A is sending a pkt using Bs public ...
1
vote
0answers
41 views

Why does encryption in STS protocol protect against identity attacks?

The basic STS protocol contains encryption of the signature as shown in Wikipedia. https://en.wikipedia.org/wiki/Station-to-Station_protocol If we would like to defend against MITM attack, this ...
2
votes
0answers
30 views

Blowfish Weak keys

I've read about the weak key issue with Blowfish, but can't seem to find anything that explains the practical effect of weak keys on Blowfish with the full 16 rounds. Is there any actual attack upon ...
-3
votes
2answers
80 views

What needs to be proved for a cryptosystem to be secure?

For example showing that it is easy to produce ciphertext from plaintext but is difficult/impossible to get plain text from ciphertext. I am asking in general but am more interested in asymmetric ...
4
votes
1answer
83 views

Deterministic ECDSA signatures?

ECDSA signatures depend on parameter k that is chosen by the signer. As a result, there are many signatures for the same private key d and message m. What I want to achieve is a deterministic ...
0
votes
1answer
80 views

How many bits to flip in an RSA public key to do signature forgery?

Scenario: Alice wants to verify a signature from Bob. Alice knows Bob's RSA public key (e, n). However, Alice is getting the data, the signature of the data and the public key from an attacker Eve. ...

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