1
vote
2answers
36 views

Combined message separation

I have two ciphertexts, I suppose that its RC4 with reused key. I have XORed both ciphertexts and obtained message containing combined cleartexts. I suppose that the underlaying messages are written ...
0
votes
1answer
61 views

Converting a number to a member of a multiplicative cyclic group

I am currently trying to make an implementation of the ElGamal encryption for educational purposes. As I understand it, when using the encryption with multiplicative cyclic groups, one generates a ...
0
votes
1answer
83 views

how to represent message as an integer between $1$ and $n-1$ [closed]

I am trying to implement simple El-Gamal cryptosystem. And I can't understand how to represent message as an integer between $1$ and $n-1$. The only thing that comes to my mind is: if $n$ bit length ...
1
vote
1answer
73 views

ElGamal and Schnorr groups

As I gather, a normal practice for choosing a cyclic group for ElGamal key generation is to find a safe prime $p$ and use a multiplicative cyclic group with modulus $p$ and order $q = (p-1)/2$. ...
0
votes
0answers
21 views

Data anonymization and search with wild-cards

Broadcast encryption technique proposed by Water et al. http://www.slideserve.com/nairi/revocation-systems-with-very-small-private-keys takes a leap from earlier schemes as it provides smaller user ...
6
votes
1answer
1k views

Knowing pre-encryption data, can we find the private key CryptoLocker used?

One of our users seems to have been hit by CryptoLocker. As a result, he has a hard drive full of encrypted files. The ransom-ware claims to have used public key encryption on the files. If we know ...
0
votes
1answer
121 views

How much work is required to detect multiple collisions for a hash function?

Assume an ideal hash function of output size n bits, detecting one collision requires approximately 2^(n/2) evaluations of the ...
2
votes
0answers
61 views

Is it possible to perform one-way Diffie-Hellman MITM?

Here's something that is bugging me recently: suppose that me and my friend establish an OTR session and - as a result of that - DH key exchange is performed. My friend verifies my key, but I cannot ...
0
votes
1answer
58 views

Should the nonce passed to GCM be authenticated?

This answer recommends authenticating the IV with HMAC when using AES and then HMAC. Since AES-GCM provides authentication too, should the external nonce passed to GCM be authenticated separately ...
0
votes
1answer
99 views

Fairness in cryptography [closed]

Two users A and B decided to share a file of same size and transfer data bit by bit. And at the end of exchange, A will have B's data and B will have A's data. Assuming, A starts to transfer the ...
1
vote
3answers
199 views

RSA Key generation: How is multiplicative inverse computed?

As per Wikipedia, RSA keygen goes like this: Choose two distinct prime numbers p and q. Compute $n = pq$. Compute $\varphi(n) = (p − 1)(q − 1)$. Choose an integer e such that $1 < e < ...
0
votes
1answer
26 views

Security issues for integrating AAA and OTP services [closed]

What are the main security issues for integrating AAA and OTP services. In our organization with about 1000 clients, we want to integrate the services. What are the main security issues about the ...
0
votes
1answer
51 views

display an image encrypted with ECB [closed]

On wikipedia there is an example of a picture encrypted with ECB: http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Electronic_codebook_.28ECB.29 I just wanted to know how an encrypted ...
0
votes
1answer
50 views

Why the data length is shifted 3-bit in MD4 Java implementation? [closed]

In RFC 1320, It is stated that "A 64-bit representation of b (the length of the message before the padding bits were added) is appended to the result of the previous step. In the unlikely event that b ...
2
votes
2answers
1k views

Is python a secure programming language for cryptography?

I know Python is a powerful programming language but is it secure for cryptography? I mean is it possible to reverse engineer the program (written in python) and discover the algorithm of cryptography ...
0
votes
0answers
67 views

chameleon signature vs regular signatures

I am trying to understand the practical usage of sanitizable signatures particularly on Chameleon Hashing and Signatures. Chameleon hash, or trapdoor function allow parties with the knowledge of the ...
0
votes
1answer
116 views

Is RC4 +XOR secure for small data?

I need to encrypt transmission between my device (with AVR processor) and base. I create packet data - it will be encrypted into string: ...
0
votes
1answer
61 views

wireless network security protocol

In network security, encryption and integrity done by the same algorithm that is AES-CCM in that MIC generated by CBC-MAC and encryption done by CTR mode. So suppose I want to do encryption with any ...
2
votes
1answer
110 views

BEAST attack confusion

I understand that BEAST is a CPA using javascript injected onto the browser's webpage. Apparently the thing that BEAST exploits is the fact that the IVs are predictable. What I'm confused about is why ...
-1
votes
1answer
96 views

HMAC-Ripemd-160 in TrueCrypt

I'm wondering if it is still secure. I know TrueCrypt closed its doors but I continue using it because the cryptoaudit didn't find any huge bugs or security issues in TrueCrypt. But I have a bad ...
0
votes
1answer
173 views

Find private exponent in RSA

The other answers for this confuse me, I know the principle of d in terms of the equation it has to satisfy. However I'm not sure how I would go about finding the private exponent without trial and ...
0
votes
2answers
96 views

Automated testing of cipher security for import/export compliance [closed]

What do we know about systems that automatically test and grade cipher security. The application in mind would be for checking for compliance with import/export regulations. I imagine a system that ...
40
votes
5answers
12k views

How big an RSA key is considered secure today?

I think 1024 bit RSA keys were considered secure ~5 years ago, but I assume that's not true anymore. Can 2048 or 4096 keys still be relied upon, or have we gained too much computing power in the ...
1
vote
1answer
153 views

Is there a kind of OS entropy pool on Windows systems? [closed]

I am wondering if Windows provides an equivalent of /dev/urandom from linux ? Or any kind of system entropy pool ?
4
votes
3answers
176 views

Hash which can be used to verify one of multiple inputs?

Is there a hash function H1 which, when given inputs a, b, etc., produces output ...
0
votes
0answers
25 views

Hiding and Binding key in Groth-Sahai NIZK proof system

In context of Groth-Sahai NIZK proof system, I have a couple of doubts on Hiding and Binding keys. In case of hiding keys (highlighted in red), how is it ensured that $\tau(A) \subseteq \langle ...
5
votes
0answers
294 views

Why is EdDSA collision-resilient with SHA-512?

In the Bernstein et al. paper about EdDSA, the authors claim EdDSA is resilient against collisions (i.e. it can still be secure even if the hash function used isn't collision-resistant), drawing on a ...
2
votes
1answer
70 views

Committing Bilinear equation in Groth-Sahai framework

Groth-Sahai framework enables us to commit to QE, MSME, PP equations. Now, is the equation below committable in GS framework? A bilinear map $e: G_1 \times G_2 \rightarrow G_T$. $g_1 \in G_1$ and ...
0
votes
0answers
119 views

Two questions on EMSA-PKCS1-v1_5

If I implement EMSA-PKCS1-v1_5 in the following two non-standard ways, what kind of things could go wrong? The padding structure will be referred as (00|01|PS|00|DER(Digest Algo)|Digest), where | is ...
1
vote
0answers
65 views

chacha20-poly1305 padding and length encoding

The AEAD construction for chacha20-poly1305 described in the IETF proposal [1] encodes message lengths into the text that is to be hashed. The newer proposal [2] goes further and pads associated data ...
0
votes
1answer
52 views

Why should I use X.509 Authentication over PKC based Authentication?

So I have two examples and I don't understand why one would be chosen over the other. Example 1. A sends EPUb[r1] to B (asks B to prove knowledge of ...
0
votes
0answers
38 views

Problems in the results of NIST PNRG suite

I am a beginner in the field of cryptography.I have problems interpreting the NIST (sts-2.1.2) suite results. After running the statistics with 100 samples (each sample of 1000000 byte length) a new ...
0
votes
2answers
106 views

RSA signing security

I'm curious about the security of RSA signing with the same public private key pair when the same message is sent multiple times. It's my understanding that once you generate the hash of the message ...
1
vote
0answers
77 views

Exploration of Blum Micali Security By Seed Size

I'm new to cryptography and am most intrigued by mathematically based pseudo random number generators. With reference to the Blum Micali algorithm: $X_{i+1} = G^{X_i} \bmod P$ can security be ...
0
votes
0answers
238 views

Public key encryption and big files with NaCL

I am trying to encrypt big files using NaCL (actually PyNaCL) - see http://nacl.cr.yp.to/box.html After reading some docs, I came up with this prototype : Bob wants to send a big file to Sarah. They ...
0
votes
3answers
101 views

Updating the secret key used for HMAC

I am designing a distributed system, composed by a set of physically distributed embedded devices (8 bit cores with less than 1 KB of RAM). The devices need to be able to authenticate the originator ...
1
vote
1answer
58 views

Verifying identity using a sha-1 hash

I was reading http://blog.zorinaq.com/?e=74 which is about a Windows kernel developer. The developer proves that he is an actual developer by posting the SHA1 hash of a particular revision of a file. ...
1
vote
0answers
72 views

Performing HMAC with random key before MAC comparison

In Laravel (a PHP framework) I can see that they calculate a HMAC with a random key over the final HMAC before comparison. This additional HMAC calculation is of course performed for both the ...
2
votes
2answers
112 views

What if OT breaks in Yao's garbled circuit?

Two semi-honest parties are computing F with Yao's garbled circuit. Sender garbles it with his inputs baked in then sends it to the receiver. At this point the receiver must use OT to get his keys. ...
0
votes
1answer
174 views

How to implement HMAC SHA-256

I am trying to figure out how the HMAC SHA-256 hashing algorithm works. I know that we have to use the following: H (K ^ opad)|| H ((K ^ ipad)|| text)). The ...
1
vote
1answer
155 views

open source whitebox-crypto implementation

I am trying to code a simple WBC situation to help my understanding about white-box cryptography. Details: I have 2 programs, a "server" and a "client", the server utilises caesar cipher (key = 2) ...
4
votes
0answers
95 views

What are the current limitations (and capabilities) of Functional Encryption used for access control?

I'm trying to make my way in Functional Encryption used for access control. I read a lot of papers such as "How to Run Turing Machines on Encrypted Data", "Functional Encryption: New Perspectives and ...
0
votes
4answers
146 views

Comparison among algorithm based on key length

Some months ago I found in some paper that we cannot compare symmetric algorithm with asymmetric algorithm based on the key length and more important we cannot compare asymmetric algorithm using only ...
3
votes
0answers
56 views

Pollard's Rho - Restricting the random function to the exponents

Pollard's Rho is usually constructed using a function $f:G \rightarrow G$ which behaves 'random enough' in order to detect a collision with Floyd's cycle detection trick. It is easy enough to observe, ...
6
votes
2answers
152 views

Abstracting primitives and modes of operation

I am developing a symmetric crypto library and have reached a roadblock. Looking at block ciphers, it is quite obvious that all block ciphers are trivially abstractable as a simple primitive ...
-2
votes
1answer
91 views

I have a keyword and cipher text but cannot decode it please help! [closed]

coded text: ij gj hnev xudmyx hn igim umif obaxidyw kxzq si the key is JULIET, but i cannot figure out how it is used. Any help would be awesome!
0
votes
1answer
128 views

Help converting sha256 to 32-bit stream

I need some help with hash value calculation. I am a bit confused by this statement that I found on w3 website on calculation of a DigestValue for xmldsig ( ...
0
votes
0answers
84 views

Is ASCON cipher broken?

http://eprint.iacr.org/2015/030 present several attacks of ASCON but does not have a conclusion section. I'm having troubles estimating what are the consequences on the use of ASCON. What's your ...
1
vote
2answers
171 views

What cryptanalysis is possible against two independent keystreams XORed against plaintext?

If a wise person was unsure about which commercial cryptography standards are truly secure from the fascist powers that be, it would seem the obvious option for companies and individuals is to now use ...
2
votes
2answers
91 views

Formal security of recycled random blinding in a Paillier scheme

This question is a follow-up/variant on a previous question. Supposing that we are trying to generate a large number of (indistinguishable) ciphertexts of a given plaintext and want to avoid the ...

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