2
votes
1answer
46 views

Inversion Free Direct Conversion between Twisted Edwards (X,Y,Z) and Montgomery (X,Z)

The Wikipedia page for Montgomery curves shows how to convert points on a twisted Edwards curve to and from points on an equivalent Montgomery curve. However, their description and the original ...
2
votes
1answer
38 views

On composition of encryption schemes

If we composed (as in function composition) multiple CPA-secure encryption schemes would the result also be CPA-secure?
2
votes
1answer
60 views

How do we guarantee plaintext is coprime in RSA?

The specifications for RSA state: $P^{\phi(N)} \equiv 1 ~mod~N$ if and only if $P$ and $N$ are coprime. Here $P$ is the plaintext and $N$ is the product of two suitable primes $x_1, x_2$. My question ...
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 ...
2
votes
1answer
58 views

Optimal bandwidth cost for Oblivious RAM

Goldreich and Ostrovsky show that any ORAM algorithm must have bandwidth cost $\Omega(logN)$, where $N$ is the total number of blocks outsourced. This is in Theorem C of this paper. But they didn't ...
2
votes
1answer
129 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 ...
2
votes
1answer
32 views

Why must the sender and receiver be synchronised in synchronous stream ciphers?

I would like to know why the sender and receiver must be synchronized in synchronous stream ciphers as said in Synchronous stream cipher. Why is there no synchronization between the sender and ...
2
votes
1answer
36 views

Use of Lamport's Signature as a primitive

Is Lamport's One Time Signature used as a primitive to construct any other cryptographic protocols?
2
votes
1answer
23 views

Is this transposition cipher information-theoretically secure for 1 message?

Given: $m = \{0,1\}^{n}$; a plaintext message of length $n$ encoded in binary $k = randomshuffle([0, 1, ..., 2n-1])$; A secret key consisting out of unique numbers between 0 and $2n-1$ in a true ...
2
votes
1answer
60 views

Retrieve value of private key after encryption with the public key

Is there a way to find an RSA private key after it is encrypted with the corresponding public key? Does there exist an algorithm to recover the private key in this special case?
2
votes
1answer
62 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 ...
2
votes
1answer
106 views

How multiplicative property of RSA can be exploited

It is known that RSA has the multiplicative property $E(m_1) \cdot E(m_2) = E(m_1 \cdot m_2)$ because $m_1^e \cdot m_2^e = (m_1 \cdot m_2)^e \pmod n$ But how can this property be used to break ...
2
votes
1answer
107 views

Encrypt entire payload or only confidential parts of payload?

In cases where a large complex data structure contains elements that are a mix of confidential and not-so-confidential data, what would be the pros & cons of: encrypting the entire structure ...
2
votes
1answer
111 views

New to cryptology, studying Message Authentication Codes

I understand the basic operational theory behind MAC, but I'm getting tripped up on some of the finer details. Also the differences between MAC, HMAC and MIC are getting lost on me, including the ...
2
votes
1answer
111 views

What use is the signature without the message under RSA?

Using RSA for signing & verification, is there a way to take a valid signature for an unknown message, and for someone else to generate a valid signature using a different key against the valid ...
2
votes
1answer
98 views

Can Poly1305-AES be used with AES-256?

I'm reading through Bernstein's The Poly1305-AES message-authentication code. The MAC is predicated on 16-byte block ciphers like AES and produces 16-byte authentication tags. However, Bernstein does ...
2
votes
1answer
90 views

Stacked LFSR - why not used?

New to cryptographic, weak in math. I have designed a PRG which consist of 33 LFSR's, each 32 bits wide. I use one of the LFSR's as "selector", using the 5 LSB from this register to select one of ...
2
votes
1answer
58 views

Is it secure to transmit a short plaintext with its MAC?

I have a short (32-bit) message that needs to be authenticated. Due to the constraints of my platform, I would like to use Speck32/64 (32-bit block, 64-bit key) with a Matyas-Meyer-Oseas one-way ...
2
votes
1answer
39 views

Discrete log accumulator without pairings

Here $g$ is some fixed generator of a discrete log group. I don't want the group to be bilinear for efficiency and BDH-skepticism reasons. Is anyone aware of a discrete log accumulator? What I mean ...
2
votes
2answers
224 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 ...
2
votes
1answer
201 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 ...
2
votes
1answer
208 views

How to accurately calculate Unicity Distance for English?

The Unicity Distance for the DES cipher is around $8.6$ characters, and can be calculated using the $U=H(k)/D$ formula, where $D = R - r$, and where $R = 8$ is the number of bits in a byte (ASCII is 7 ...
2
votes
2answers
76 views

Is there any advantage on encrypting the CMAC together with the message?

I'm reading a protocol specification where the procedure is to generate a CMAC, take the first 4 bytes of it, append this authentication tag to the message and then encrypt the message + CMAC together ...
2
votes
2answers
144 views

Why are some $x$ coordinates unsuitable for an ECDSA generator point?

For Bitcoin's ECDSA curve (secp256k1, where $a=0$, $b=7$), why can't the generator point's first coordinate be $x=0$? That is, the point on the curve would be $(0,y)$ where $y$ satisfies $y^2 = 0^3 + ...
2
votes
2answers
88 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 ...
2
votes
2answers
117 views

Can I simulate iterated AES-ECB with other block cipher modes?

I am trying to write some code using the Web Crypto API (http://www.w3.org/TR/WebCryptoAPI/#algorithm-overview) which provides only some of the block cipher modes for AES, intentionally excluding ...
2
votes
2answers
357 views

Chosen plaintext vs Chosen ciphertext

What is the difference between chosen plaintext and chosen ciphertext attack? In both of these adversary has access to paintext-ciphertext pairs.Then where lies the difference?
2
votes
1answer
125 views

How to use ElGamal to encrypt zero?

ElGamal encryption algorithm is as follows: To encrypt a value $m$, it chooses a random value $r$, and calculates $c_1=g^r$ $mod$ $q$ $c_2=m*h^r$ $mod$ $q$ where $g$ is the group generator, $x$ is ...
2
votes
1answer
88 views

OpenSSL des-ede3 not producing same output as test vector implies it should be

I'm encrypting one of the standard TDEA/3DES/DES-EDE test vectors with openssl: ...
2
votes
1answer
178 views

How to customize a standard encryption algorithm?

I want to modify and customize AES encryption algorithm and develop a variant of it. What factors should I consider so that it does not become weaker? What skill sets would be required to undertake ...
2
votes
1answer
162 views

Is it safe to AES-CBC and AES-CMAC both using the same key?

There is a very similar question (Using a derived key for CMAC) but it doesn't quite answer this one (at least for me it does not). I have a situation where I need to transfer some data. My data has ...
2
votes
1answer
93 views

Roots in modulo field

I have a point $(X,Y)$ on an elliptical curve $E(a,b)$ where $a=-3$ and $B$ is a large number that is in hexadecimal from -51BD. To compress this point oficially in a program, we know that every $X$ ...
2
votes
1answer
118 views

Private Information Retrieval--Is it still theoretical?

Are there any real world products in which private information retrieval techniques are used?(a data hosting server oblivious of which data item was fetched from it?)If not what are the major barriers ...
2
votes
1answer
136 views

Modes of encryption for hard drives?

What are the currently recommended modes of encryption for large disks? Basic requirements would seem to be that you can update an encrypted sector independently of others, which rules out most ...
2
votes
1answer
80 views

Do data-dependent rotations have any advantage over fixed rotations?

There are many ARX ciphers, however most use fixed rotations. I know data-dependent compared to fixed rotations are: patented harder to implement constant time more expensive in hardware harder to ...
2
votes
1answer
96 views

How many of primitive point on the elliptic curve?

In elliptic curves for cryptography, I know $nG=O$, where $G$ is a base point represented by $G=(x_g,y_g)\ on\ E(F_P)$, where $n$ is Order of point $G$. For example, $P(0,6)$ is a primitive point on ...
2
votes
2answers
108 views

What is primary security in ECC?

I read the following paragraph in a book about Elliptic Curve Cryptography, but didn't understand it: The primary security in ECC is the parameter $n$; where $n$ is Order of point $G$, that is $n$ ...
2
votes
1answer
88 views

Encryption in which ciphertext is bigger than plaintext?

Is there an encryption which would produce a ciphertext longer than the plaintext? (please ignore block-chaining IV stuff, which would result in a data being generated from the plaintext). The point ...
2
votes
1answer
115 views

How secure is a lagged fibonacci sequence for encrypting brief messages?

Say I start with a 26-letter keyword and convert the letters into 26 integers (A=0, B=1...Z=25) nr[0] to nr[25]. Then I create a stream, nr[26] onwards, with a lagged fibonacci sequence where nr[n]= ...
2
votes
1answer
110 views

Encrypted read-only message queue

I'm creating a prototype for a messaging queue with some custom logic (can't re-use any existing solution). One requirement is to have all messages encrypted. There are three classes of nodes ...
2
votes
1answer
70 views

Can adding nonces make challenge response authentications weaker?

In a custom protocol we want to replace an aged tiger32 based challenge response authentication. I suggested that we use something existing, so threw HMAC into the room. As per wikipedia it works as: ...
2
votes
1answer
171 views

what are DP and DQ in Encryption by RSA in c#

I want to know about these tags in RSA Encryption by private Key. when I use this code: ...
2
votes
1answer
223 views

Calculate the RSA private exponent from the CRT parameters

I am trying to make the RSA structure of Openssl manually, knowing the public key ($n$, $e$) and the CRT parameters $p$, $q$, $d_P$, $d_Q$, and $u = q^{-1} \mod p$. That is, I want to get the $d$ ...
2
votes
1answer
156 views

Using modulus in one time pad?

I would like to know what is the real purpose of using a modulus in the equivalent of a Vernam cipher: Data $d$, large number $M$. Assume the key length is $\lambda$ bits. Then $M$ could be ...
2
votes
1answer
169 views

Hashing passwords

The common way to store passwords in web applications is this form: $$hash(password||salt)$$ Does it make sense to store them in the following form instead:? ...
2
votes
1answer
107 views

What's causing the poor randomness in this program: the LCG, or the program logic itself?

(Crypto Gods, I should begin by stressing that I haven't lost my mind: I'm not doing this in real life, I'm just trying to understand the theory behind what's happening. With your help, hopefully I ...
2
votes
2answers
154 views

Maximum password length in PBKDF2

Haven't found any clear cut answer in Google so its up to you guys: DK = PBKDF2(PRF, Password, Salt, c, dkLen) Here, what is the upper limit of password length? ...
2
votes
2answers
155 views

Diffie–Hellman Ephemerality Nomenclature

Below is a short excerpt of available DH cipher suites available on a machine. I understand EDH is ephemeral DH, and that ECDH is for Elliptic-Curve DH which is computationally faster. ECDHE is both ...
2
votes
1answer
55 views

Constant data as input to hash

I want to use hash function on some data, and part of this data, might be constant for a certain period. The output of the hash function is used as authentication data (MAC). I want to know if there ...

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