2
votes
1answer
100 views

Differences between Work Factor and Time Complexity

I am interested to know if work factor means the same thing as time complexity. Quoting Work Factor : Uncovering keys in cryptosystems The Work Factor of a cryptosystem is related to its ...
0
votes
2answers
73 views

Would the Fiat Shamir identification scheme be more secure if I design it with an exponents higher than 2?

Let's say both Prover and Verifier would use nth power instead of 2nd when creating public keys and when verifying. I know it would slow it down but would that cause the protocol to be more secure?
0
votes
0answers
77 views

What do you think about this message encryption?

I am currently working on my diploma project, a high security NFC door lock and need to exchange very sensible data. That's why I thought of PGP encryption, which is as far as I know one of the ...
1
vote
1answer
93 views

What would a backdoor in symmetric key cipher look like? [duplicate]

Pretty much what the title says. DES was suspected of having one, but I couldn't imagine what it could possibly look like if only the NSA knew how to use it. Dual_EC_DRBG's backdoor is asymmetric, but ...
1
vote
0answers
99 views

What are the well known protocols that offer perfect forward secrecy? [closed]

As far as I know these are the well known protocols that offer PFS TLS/SSL (with DHE-RSA, DHE-DSS, ECDHE-RSA or ECDHE-ECDSA) SSH (RFC4253) OTR (Protocol Version 3 Spec) IPsec (with IKEv1 and IKEv2) ...
0
votes
1answer
114 views

Drawback of ElGamal encryption

I am trying to find out some disadvantages of ElGamal cryptography but I'm not able to figure out what's wrong with the algorithm. The only one I found is that a known-plain text attack is possible in ...
0
votes
1answer
95 views

Multiple keys for the same ciphertext [duplicate]

Say you have a plain text: How are you today? and you encrypt it so it becomes: LKD03Loel03skj1Q03 Now you have multiple people that need to know the plain text of this cipher text but ...
1
vote
1answer
142 views

ccrypt and its security

I would like to know how secure is ccrypt to encrypt files (like images, videos and other non-plain text data) using single password of 20+ chars length. It uses Rijndael with 256-bit block size and ...
0
votes
1answer
62 views

GCM implementation

I want to write GCM implementation myself (only for research purposes). So far, I have successfully written CTR implementation (for AES), but now I ran into few problems with GCM. If I'm not wrong, ...
1
vote
1answer
221 views

How does knowing the factorization of N help to obtain the secret?

Assuming $x=a^2 \pmod n$ and knowing $x$, $p$, $q$ how is it possible to obtain $a$?
2
votes
1answer
62 views

Is this JS library using openssl genrsa -rand improperly?

pem, a JS wrapper around openssl, has the following code in it: var params = ['genrsa', '-rand', '/var/log/mail:/var/log/messages', keyBitsize ]; Am ...
2
votes
0answers
70 views

Exponentiation with fully homomorphic encryption [duplicate]

I have often heard that because a fully homomorphic encryption scheme allows for both additions and multiplications on encrypted data, most other operations can be simulated. I don't understand how ...
1
vote
1answer
89 views

Standard serialization format for libsodium-based messages

Does anyone know of a standardized serialization format which can be (or already is) widely used for encrypted messages? For a variety of reasons (mostly complexity, age and poor support across a lot ...
5
votes
2answers
148 views

Are there any known weaknesses with ElGamal algorithm?

I am working on a messaging system and plan to use ElGamal asymmetric encryption to protect the message contents during storage and transmission. (This would be in addition to TLS used during ...
1
vote
1answer
77 views

Send an encrypted question and return answer without decryption

Oke bear with me for a minute. Once upon a time someone mentioned a hypothetical way where you would send an encrypted question to Google and Google would return an answer without decrypting it. As ...
3
votes
0answers
52 views

Are there any asymmetric composite order group bilinear pairings?

Are there any asymmetric composite order group bilinear pairings? Is there a drawback of asymmetric over symmetric bilinear pairings of composite order either in efficiency or in security ?
-2
votes
1answer
69 views

Hashes and Ciphers [closed]

So I'm brand new to cryptography, I'm confused on a few fundamental issues, and my normal avenues of research aren't bearing any fruit. I'm hoping someone can describe the relationship between ...
-1
votes
1answer
105 views

Vigenere ciphers : Need help for math analysis

I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that. This's my method to encrypt : ...
2
votes
3answers
454 views

decrypt numbers multiplied by a certain floating point number

A friend has about 10K numbers in a an excel sheet. He wanted to encrypt these numbers in order to share the file with a 3rd party that will help him reorganize the tables. What he did, to hide the ...
1
vote
2answers
129 views

Why can the last block contain a full block of padding in CBC Encryption?

I'm trying to understand the SSL Poodle Attack and I'm wondering why the last block of a CBC Record can be full of padding? Wouldn't that mean that the useful data was already a multiple of the key ...
10
votes
1answer
729 views

Why are the outputs of the md5sum tool and Crypto++'s MD5 different?

Could you please tell me what is the difference of coreutils' md5sum and sha*sum tools (...
1
vote
2answers
659 views

Multiple private keys for single public key

I am currently working in security in mobile ad-hoc networks. I have several clusters, and I want to send some data encrypted with its public key, from the cluster head to the cluster members. I ...
2
votes
1answer
98 views

PBKDF2 for login key, scrypt for encryption key

I need to derive two keys from a single password client side. One for in-browser login, the other for encryption. Is the following secure ? ...
3
votes
1answer
88 views

Why is C_digest defined in PKCS#11?

Digesting doesn't require any key and can be performed on the client side. Why does the PKCS#11 token interface standard have a C_digest method? For example, why should I send my data to a PKCS11 HSM ...
1
vote
1answer
93 views

What aspect of elliptic curve encryption paradigms makes them especially susceptible to quantum based attack algorithms?

This was a statement made during a talk at today's DFN-CERT conference but unfortunately it wasn't explained further. Can anyone shed light on why elliptic curves are susceptible to quantum based ...
-1
votes
2answers
220 views

How to choose an algorithm

I have some understanding of Cryptography and I would like to know if there is a tool or website to help me choose an algorithm based on my own needs (I'm being vague in purpose). I'm looking for a ...
-1
votes
3answers
52 views

Reduction of a modular exponentiation's base does not change the result

Can anyone help me to prove this property used in the RSA correctness theorem? $a^b\bmod{n}\equiv (a\bmod{n})^b\bmod{n}$ Specifically, here is what I have done: this is what i mean. i can't ...
1
vote
1answer
78 views

RSA Key composition

I'm trying to figure out how it is composed the RSA key. Follow what I know : For a RSA 2048, 2048 is the bit length of the module. The public key is composed by $(e,M)$ when $e$ is the public ...
1
vote
2answers
89 views

ECDSA Public key randomness

If I have a 256bit ECDSA public key how likely is it that the same public key will be generated by another person. Will it take on average 2^256 tries to generate same public key? If I xor the first ...
2
votes
2answers
676 views

AES GCM vs other encryption modes in embedded environment for network traffic

I'm doing a lot of research since I'm doing an internship for a company where I need to upgrade their security level. Their own protocol needs a cryptographic upgrade and I'm leaning towards AES since ...
0
votes
2answers
77 views

Solve the congruence using Pohlig-Hellman algorithm

Use the Pohlig-Hellman algorithm to compute a solution to: $3^x\equiv 2 \pmod {65537}$ My attempt: $p-1 = 65537-1 = 65536= 2^{16}$ $x= 2^0x_0+2^1x_1+2^2x_2+...+2^{15}x_{15}$ For $x_0$: ...
-5
votes
1answer
32 views

encryption of message “DATACONFANTIALITY” with key playfair using playfair cipher

actually i have solved the above mentioned problem but i want to check weather it is correct or not. my question is that how to encrypt the message DATACONFANTIALITY using the playfair cipher where ...
1
vote
1answer
49 views

In a additive group is it hard to calculate $bg$ given $ag, g, abg$

The ECDH problem defined that given $g,ag,bg$ it is difficult to calculate $abg$. But it is also difficult to calculate $bg$ given $ag,g,abg$. where $g$ is generator and a,b are elements of group.
0
votes
1answer
68 views

If you know the messages, and the results of HMAC(key, message) can you find the key?

If the attacker has 1 billion 4KB (random-noise) messages and sha256-HMACs for those messages (all using the same key), can they calculate the key that was used, before the universe dies?
2
votes
2answers
187 views

Using hash for one time pad key

Recently I've been delving into security algorithms, I already knew some of the (easy) math behind AES and RSA and how to and not to implement it. But well, i got a bit bored so i thought I'd just do ...
4
votes
2answers
135 views

Randomness re-use in LWE encryption scheme

Let me describe the scheme first, it is the scheme proposed by O. Regev when he introduced the LWE assumption. $sk = \textbf{s} \in \mathbf{Z}_q^n$ $pk = \textbf{A}\textbf{s}+\textbf{e}$ where ...
1
vote
1answer
78 views

Is the result of HMAC-sha256 distinguishable from random noise?

Is if the result of HMAC-sha256 distinguishable from random noise? If so, given: a collection of 1000 keys, and 1000 messages of random noise, 100 signed by each of only 10 of those keys Can ...
0
votes
1answer
92 views

Reducing size of hash function

If I have some data I hash with SHA256 as hash=SHA256(data) and then copy only the first 8 bytes of the hash instead of the whole 32 bytes. How easy is it to find a ...
0
votes
2answers
168 views

AES ECB experiment

Generally speaking, ECB mode shouldn't be used. ECB seems to be more of a basic building block than anything else. Because I thought it would be interesting to experiment with encryption (this method ...
0
votes
2answers
79 views

Schnorr's identication protocol

Schnorr's identification protocol is said to be a honest verifier zero knowledge protocol. Does it imply it will not work if the verifier is dishonest? I'm wondering if this is the case, it would ...
1
vote
0answers
105 views

Zero Knowledge Non Interactive Proof with random oracle

I am trying to write an assay about Non Interactive Zero-Knowledge proofs and would like to take the simple discrete logarithm problem example fallowing the Feige-Fiat-Shamir heuristics. I understand ...
0
votes
1answer
59 views

Linear Recurrence, keystreams, and periods

I am trying to understand the following problem: Consider the following linear recurrence over $Z_2$ of degree four: $z_{i+4} = (z_{i+3} + z_{i+2} + z_{i+1} + z_{i}) \bmod 2$ i >= 0. ...
0
votes
1answer
42 views

Hill Cipher the point of a known plaintext attack question

Is the point of a known plaintext attack on a Hill Cipher to get the matrix key?
0
votes
0answers
128 views

Substitution-permutation network

Can anyone in 6th grade English explain the steps in the Substitution-permutation network algorithm or just point a link that does so? (which is included in many of the top modern algorithms) ...
0
votes
1answer
205 views

Why don't PyCrypto and M2Crypto produce the same result as OpenSSL here (AES-128 ECB)

If I run the following, for openSSL: echo -n "0123456789abcdef0123456789abcdef" | openssl aes-128-ecb -nosalt -nopad | xxd and enter the key "YELLOW SUBMARINE", ...
0
votes
0answers
84 views

BGV FHE scheme parameters

In their paper presenting the BGV scheme, the authors mentioned in section 4.4 that, for the RLWE variant, the ring degree d, dimension n and noise distribution do not necessarily vary with the ...
2
votes
1answer
535 views

Is CAST5 still a secure algorithm to use?

I just installed GnuPG for Windows. The documentation says the default symmetric cipher is CAST5. In PGP also, default cipher was CAST5. Is CAST5 secure to use? Any known attacks reported on this ...
4
votes
0answers
90 views

Anonymisation resilient to key leak

Problem statement Elbonian citizens have been issued a card holding a random $B_j\in\{0,1\}^b$, $0\le j<2^n$, $b\ge n+20$ (representative example $b=64$, $n=28$). The habit has grown to use this ...
0
votes
1answer
123 views

Convert numeric message from RSA ciphertext to alphabetic

I have a set of numeric values that are supposed to represent a message encoded via textbook RSA. For example: 60889 37946 13359 61629 35960 13747 I've decrypted ...
0
votes
1answer
111 views

Figure out the encryption being used [closed]

There is a web API (for a game) that sends and receives data encrypted in hex format. I'm interested in accessing the api outside of the game client (mobile app). When sending a request with an ...

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