1
vote
1answer
31 views

Question about discrete log - why can one attacker not solve for g but two colluders can?

I'm reading about the broadcast encryption described in Fiat and Naor's paper, I screen grabbed the relevant part below. My question is essentially: If there's a secret: $g^{abc}$ $mod$ $A$ (where ...
2
votes
1answer
61 views

Encoding a message to a point of curve y^2=x^3+7 and Bitcoin Core

Where should I look at in Bitcoin Core source code to figure out how the signature process trasform a message in a curve point? To sign a transaction (message) in Bitcoin system, you need to encode ...
4
votes
2answers
159 views

Non-interactive proof that an element is in a subgroup

I am just reading the DAA paper (http://eprint.iacr.org/2004/205.pdf, Appendix A). A party $\mathcal{I}$ generates two group elements $g' \in \mathrm{QR}_n$ and $h = g'^r \bmod n$ with $r \in_R \left| ...
1
vote
3answers
152 views

Sage Vs C++(with NTL) for implementing cryptosystems

Is Sage a better alternative to C++(with NTL), for programming that involves math objects like polynomial rings in cryptosystems? I hear that Sage is an open source alternative to Magma. I have used ...
2
votes
1answer
56 views

Algorithm for n-of-m keys with partial results

Is there any known and proven algorithm which allows n-of-m keys en/decryption, but doesn't require the keys to be in one location? That is, it allows the plaintext (or ciphertext) to be encrypted (or ...
0
votes
2answers
100 views

Why does Diffie-Hellman need be a cyclic group?

Why is Diffie-Hellman defined on a cyclic group? Doesn't it work for any commutative operation which the inverse is hard to find? Say Alice and Bob agree in a public prime $c$ and both choose a ...
0
votes
0answers
13 views

PyCrypto export/import of signature [migrated]

created a client-server application with sockets and I am trying to transfer the signature from client to server. I convert it from tuple to string and then back to tuple. But signing stops working. ...
1
vote
1answer
117 views

Is encryption time greater than decryption time?

Is encryption time always greater than decryption time for all encryption techniques (AES / DES / RSA / DNA), or is there a mistake somewhere in my implementation?
8
votes
2answers
105 views

Information-theoretic bound on leakage by timing measurement

I'm looking for an information-theoretic bound on leakage by timing measurement. I'm assuming that an attacker wants to leak out of a black box a secret key of $k$ bits that is secretly injected ...
1
vote
1answer
43 views

Malicious party security model: When one party is corrupted at a time

Consider we have three parties,namely client $A$, client $B$ and a server. Client $B$ and the server can be malicious, but we do not allow the adversary to simultaneously corrupt the server and ...
0
votes
1answer
86 views

Affine transformation in AES: Matrix representation

I know that the affine transformation of the AES can be represented both as a polynomial evaluation over $\operatorname{GF}(2^8)$ and as a matrix-vector multiplication (see, e.g., p.212 C.4 of The ...
1
vote
0answers
29 views

Proper way to generate symmetric keys

I'm trying to educate my self in key management, how to store them, how to generate them, how to use them properly. I've been trying to find how you would generate a key for symmetric encryption (say ...
0
votes
2answers
21 views

Why does spiped use both nonces and ephemeral keys?

Colin Percival's spiped utility uses a pre-shared key and Diffie-Hellman with ephemeral keys to provide forward secrecy. The protocol is summarized in the ...
1
vote
1answer
59 views

Special case of format-preserving encryption

Is there encryption algorithm with the following properties? We always have plaintext in natural language, and the produced ciphertext is also in natural language.
1
vote
1answer
59 views

Secure symmetric encryption algorithm for any-size base62 data

I am searching for a secure algorithm to encrypt base62 (or any other base) data for ids in urls. It should feature: No blocksize etc, limiting the length of the message to a factor of n If you ...
2
votes
1answer
157 views

Will non-ECC algorithms like RSA eventually become too inefficient?

The strength of symmetric and asymmetric encryption schemes scales with the key length, but there is a difference between symmetric algorithms like AES and asymmetric algorithms like RSA. For ...
1
vote
1answer
37 views

Given an encrypted file, what are possible ways to find its encryption algorithm?

Given an encrypted file, what are possible ways to find its encryption algorithm? Heuristic ways are okay as well.
9
votes
3answers
2k views

Why is the P-521 elliptic curve not in Suite B if AES-256 is?

In the NSA's document, "The Case for Elliptic Curve Cryptography", we have ...
0
votes
1answer
126 views

Problem with testing MD5 collisions

I am trying to test MD5 collisions presented in “Collisions for Hash Functions MD4, MD5, HAVA” (PDF) by Xiaoyun Wang, Dengguo Feng, Xuejia Lai, Hongbo Yu; 2004. I wrote a PHP script to test it, but ...
0
votes
1answer
84 views

How many characters per block in an El Gamal ECC cryptosystem?

While I look for how many characters that can be encrypted using the The elliptic curve ElGamal cryptosystem. of each block found for these lines. But I can not understand Actually in our case we ...
-1
votes
0answers
25 views

Disabling CBC ciphers does not stop Chrome from negotiating to use CBC ciphers [migrated]

I am getting an message about 'obsolete cryptography' from Chrome. Your connection to (site) is encrypted with obsolete cryptography. The connection is encrypted using AES_256_CBC... Per ...
1
vote
1answer
33 views

What is a good way to handle longer strings using FPE?

While experimenting with this FPE based on FE1 http://botan.randombit.net/manual/fpe.html (well actually a port of it in C#) I found when the string length gets too long (number of characters N) ...
3
votes
1answer
369 views

AES file encryption with PBKDF2. Safe parameters?

I'm developing an application that will use public key authentication to contact some webservice. So the user has his keypair on his computer, and I want that file to be encrypted using AES with a key ...
0
votes
0answers
32 views

Can I place a private key on a sim card? [migrated]

After google searching about this idea and yielding very little in results I've come to resort to stack exchange: Is it possible to place a private key on a sim card? Is it possible for a smart ...
0
votes
1answer
31 views

DSA: Authentication and assurance of authorized parties

When dealing with Asymmetric cryptographic algorithms, usually the sender of the critical data asks the listener for a Public Key for encrypting the data and sending them. This is while the private ...
2
votes
2answers
65 views

How to calculate if probability is negligible or not

If i have probability $Q = 2C(A\times B)$ where $A$ and $B$ are unknown probabilities and $C$ is a non-negligible probability, what can i speculate about probability $Q$ and how can i calculate bounds ...
11
votes
1answer
9k views

Calculating RSA private exponent when given public exponent and the modulus factors using extended euclid

When given $p = 5, q = 11, N = 55$ and $e = 17$, I'm trying to compute the RSA private key $d$. I can calculate $\varphi(N) = 40$, but my lecturer then says to use the extended Euclidean algorithm to ...
0
votes
1answer
58 views

anonymous signature implementation and usage?

This is one of the question asked in my class. Implement a anonymous digital signature. So it means hiding signers information. i could not find any article in anonymous digital signing. Also another ...
0
votes
0answers
43 views

How to map a handful of numbers in a large range to a much smaller range deterministically without collissions

I want to map a set of long integers (say around 100 different values) that can span the entire 64 bit integer range to a much smaller range such as from 0 to 25000 deterministically with almost zero ...
-1
votes
0answers
15 views

SSL-connection between client and server: how can one make this connection secure?

Suppose a browser C is setting up a SSL-connection with a server S. Then after C has initiated the connection with S by sending a "hello"-message and nonce, S sends back a nonce and a certificate ...
0
votes
0answers
26 views

Does “identity-based dynamic threshold signature” exist and could such scheme contain a “Signature Combination” algorithm?

I came across [1] and I'm very puzzled by this paper. They use a building block which they call "identity-based dynamic threshold (IBDT) signature", citing paper [2]. First of all [2] does use this ...
1
vote
2answers
75 views

What does ⊕ mean in cryptography?

Can someone please help me with the question below? Explain why 0 ⊕ x ≠ 1 ⊕ x, whatever the value of the bit x. Hence, explain why flipping a bit in the plaintext produces a predictable ...
1
vote
1answer
47 views

Differential Privacy and appropriate noise distribution

In differential privacy solutions and more specifically for queries that they do entail counting the proposed solutions define the laplace distribution that is best calibrated for low error. Other ...
1
vote
1answer
55 views

What is the “Walsh Function” about?

I'm currently dealing on the so called “Walsh Function” (WF) that is written like: $$f^W(a)=\sum_{x\in{F^n_2}}(-1)^{f(x)+(a,x)}$$ What I know is that this function is used to approximate an arbitrary ...
33
votes
7answers
25k views

Taking advantage of one-time pad key reuse?

Suppose Alice wants to send encryptions (under a one-time pad) of $m_1$ and $m_2$ to Bob over a public channel. Alice and Bob have a shared key $k$; however, both messages are the same length as the ...
-2
votes
1answer
62 views

How difficult is homomorphic encryption? [closed]

I want to learn more about homomorphic encryption and eventually make a career from it. Currently, I'm thinking to have my bachelor degree in this field. What background should I have for this ? How ...
0
votes
1answer
43 views

Encrypt file name

I'm looking to encrypt (rename) mutiple files name based on a passphrase. Currently the passphrase would be numeric but I can change that to something else if required. I would like to be able to ...
0
votes
2answers
159 views

Cryptosystems used to generate public key certificate

Where can we find the cryptosystems used to generate public key certificate? Are the cryptosystems under the signature algorithm and signature hash algorithm? Do I need to analyze the packets ...
0
votes
1answer
109 views

security proof in pairing based cryptography

Let : $G_{0}$ and $G_{1}$ be two multiplicative cyclic groups of prime order $p$. $g$ is a generator of $G_{0}$ and $e$ is a bilinear map, $e : G0 × G0 → G1.$ $𝐶_{1} = 𝑔^{𝛽𝑠_{1}} $, $ 𝐶_{2} = ...
5
votes
2answers
471 views

Why use randomness in digital signature algorithms?

I understand why randomness has to be employed in encryption, because deterministic ciphers are not IND-CPA. I don't understand why digital signature schemes that employ randomness, like RSA-PSS, are ...
0
votes
1answer
24 views

How openssl padding for AES cfb IV?

From a few documents I have read and a few questions about padding here, I think if I passed a encrypted text fewer than BLOCK SIZE, openssl would pad it per PKCS7. And use that padded encrypted text ...
-1
votes
0answers
23 views

RSA : Is finding Public key given Private key as hard as finding Private key given Public key? [duplicate]

The question is quite straightforward : In RSA, is finding Public key given Private key is as hard as finding Private key given Public key? If no, can you explain why?
7
votes
1answer
124 views

Factoring two RSA moduli $N_i=p_i\cdot q_i$ knowing that $p_2=p_1+2$?

It is given two RSA moduli $N_1$ and $N_2$, known to be of the form $N_i=p_i\cdot q_i$, with $p_i$ and $q_i$ unknown primes, and such that $p_2=p_1+2$. Can we make use of that relation to factor the ...
2
votes
1answer
96 views

Is the reduction from left-or-right IND-CPA to real-or-random IND-CPA tight?

A modern trend in cryptography consists of defining security as rigorously as possible, and then designing schemes which are secure according to those definitions. Proving security comes in the form ...
2
votes
1answer
81 views

What does signed fixed window method mean in ECC?

I am studying (sliding) window method in Elliptic Curve Cryptography (ECC) but I am confused by the term, signed fixed window method. By the way term is used in a research paper and not in the book ...
0
votes
0answers
63 views

How do I prove IND-CPA security of RSA-OAEP?

How do I prove that RSA-OAEP is IND-CPA secure? It would be very good to show how to prove it formally, but an informal proof would also be enough. Because of the random number in RSA-OAEP, RSA gets ...
55
votes
8answers
14k views

How much would it cost in U.S. dollars to brute force a 256 bit key in a year?

I am often told that any key can be broken and that it is only a matter of time and resources for any key to be broken. I know that this it technically true. However, I think that there is probably a ...
1
vote
2answers
263 views

Is ECB mode safe to use with RSA encryption? [duplicate]

Firstly, bear with me, I'm relatively new to cryptography. In a recent static analysis scan of our application, one of the findings complained that we are using ECB: A mode of operation of a block ...
1
vote
1answer
248 views

How to verify a shared secret using only AES?

I have two devices that need to verify that they both are in possesion of the same secret key. One of the devices is a very limited embedded device that only has AES128 available, no SHA or other hash ...
2
votes
1answer
131 views

Are well designed crypographic codes unbreakable? (NOT ciphers)

Codes are not to be confused with ciphers. It is known that all known ciphers are theoretically breakable except the one-time pad and this isn't what the question is about. Some cryptographic codes ...

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