3
votes
1answer
118 views

Is email an example of public-key cryptography?

It seems like email is at least analogous to public-key cryptography, the public portion of the key being your email address, and the private portion of the key being the password to the email ...
1
vote
1answer
278 views

How can I find the multiplicative inverse in the first transformation of the SubBytes() transformation in AES?

In FIPS-197 §5.1.1 , it says the first transformation in the SubBytes() transformation is: Take the multiplicative inverse in the finite field $\text{GF}(2^8)$ described in Sec. 4.2; the ...
2
votes
1answer
235 views

Is it possible to perform a rudimentary asymmetric key encryption algorithm by hand?

I have at least three, distinct motivations for having a simple way to use asymmetric key encryption by hand or without modern computers. First, I was recently demonstrating to a 12-year-old how ...
-1
votes
1answer
202 views

Pseudo Random Generator with fixed Hamming Weight [closed]

I'm searching for way to generate secure pseudo random sequence with a fixed Hamming weight using a seed. I found below code but I need a seed to generate a sequence ... (and need know if is possible ...
1
vote
1answer
166 views

Public and private key lengths

I am generating RSA Public and Private keys with node.js instead of reading them from pem/crt files as I can hide them inside a private object using this module https://www.npmjs.org/package/private ...
3
votes
2answers
122 views

Could scrypt salts contribute to entropy if passwords & salts are only stored in human memory?

I'm unsure of how exactly the salt is manipulated by scrypt and its potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a ...
6
votes
1answer
985 views

Description of signatures with message recovery (as in ISO/IEC 9796-2 and EMV Signatures)

I'd like to get an overview of how the signatures with message recovery work, especially in case EMV and other smart card systems. Is there a nice overview available without being required to read the ...
2
votes
1answer
241 views

Where do I truncate the bits in SHA 256 hash algorithm?

I'm implementing SHA-256 in PHP using strings. Where do you truncate in the algorithm? There are a lot of places where there's binary addition happening so the number of bits in $W(i)$ keep ...
-1
votes
1answer
220 views

How to calculate bit strength of Integer Factorization Cryptography (IFC) such as RSA using Python

I would like to know how to calculate the bit-strength of Integer Factorization Cryptography (IFC) such as RSA by using Python. I gathered it is based off the complexity of factorizing the modulus ...
2
votes
1answer
76 views

Is HMAC padding the same as bcrypt?

I have been watching Christof Paar on his YouTube lectures also I used bcrypt to store two passwords with salts and I find that I have a few questions. I am interested in what bcrypt does to the ...
3
votes
2answers
122 views

Ballot box with multiple parties. All can read it, or none can read it

I am trying to create a decentralized moderation system for the game Diplomacy, a game for seven players. In each round of a face-to-face game, each player writes their moves on paper then puts it in ...
2
votes
2answers
287 views

Password-based encrypted key storage?

RFC 5959 specifies the encrypted storage of private keys based on PBKDF2-HMAC-SHA-256 and AES encryption (in ECB mode). Is there a particular reason AES is used, instead of simply XORing the key ...
2
votes
1answer
159 views

User-specified PBKDF2 password, salt, and iterations limits

For a decentralized login where a user is left to select the password, salt, and iterations, what minimums for each should be enforced? In other words, because none are ever stored by the ...
1
vote
1answer
122 views

Protocol composition [closed]

I have been trying to wrap my head around different definitions of protocol security (stand alone, sequential composition, parallel composition, universal composition) and how the proofs of any of ...
2
votes
1answer
186 views

Is either brainpoolP320r1 or brainpoolP320t1 a SafeCurve?

Not all elliptic curves are safe to use for cryptography, especially from an ECC safety perspective. The site http://safecurves.cr.yp.to/index.html shows that two tested Brainpool curves, ...
4
votes
1answer
264 views

Parallelized Pollard's Rho algorithm for ECDLP + Jacobian coordinates

My implementation of the parallelized Pollard's Rho algorithm is using Jacobian coordinates to avoid the costly inversion operation when performing point addition. I am wondering if there are any ...
7
votes
2answers
387 views

Fast hashing into elliptic curve

Is there a fast algorithm for mapping $n$-bit numbers $s$ (for fixed $n$) into a cyclic subgroup of an elliptic curve (over a finite field) in which the Discrete Logarithm Problem is hard? By fast, I ...
1
vote
1answer
66 views

Fiat–Shamir: why do r and s have to be smaller than n?

I have a question regarding the Fiat–Shamir identification protocol. In this source (pdf) for example it says on pages 9 and 10 that the random commitment $r$ and the private key $s$ have to be ...
4
votes
2answers
126 views

Does knowing multiple hash of the same content make it more likely to generate original plain text?

Say I'm trying to brute force the original plain text of an SHA256 hash, does knowing the RIPEMD160 hash of the same text help? In other words, does providing access to hash values of the same text ...
1
vote
1answer
120 views

LFSR and Markov chain question [closed]

This may seem an elementary question about LFSRs, and their link to Markov chains. LFSRs show Markov chain behaviour in that there can be a transition matrix defined over the LFSR, this follows from ...
1
vote
1answer
79 views

Modes of Operations Exercise

I am currently stuck at an exercise for my Cryptography Class in University which is: Alice wants to send a message $M = (M_1,M_2) =$ "Pay Bob \$100 from bank accout $12345$" to her bank (encrypted). ...
1
vote
2answers
237 views

Signing a document: which algorithm to use?

What I want to do is to digitally sign a document. I am new to cryptography and was wondering what issues to take into account. The only criteria is that a textual document signed should produce a ...
1
vote
0answers
132 views

Mutual authentication with Public Key and session Key

I am trying to understand two protocols for mutual authentication and if they are secure or not. $K$ is the session key, and it's calculated $k=H(TimeStamp)$. Are the following both cases secure? ...
3
votes
2answers
238 views

Using PBKDF2 twice with different argument order

I'm pretty sure this is a really bad approach (in theory), but one of my clients is doing this and I was wondering… How bad it is to perform pbkdf-2 in this way (with 2000 iterations)? ...
4
votes
1answer
127 views

Length-preserving all-or-nothing transform

Is there any known way to construct a length-preserving all-or-nothing transform? In other words, a secure all-or-nothing transform where the length of the output is the same as the length of the ...
9
votes
5answers
421 views

Choose a random number that is different from a bunch of other secret numbers

I'm looking for an algorithm where n participants each have a different secret number between $[0..x]$ (and where $x$ is known) and where the participants then select randomly another, non-secret, ...
1
vote
1answer
252 views

SHA1 collision event probability after n iterations

There are String1 and String2 - some variables-strings. The probability of collision for different ...
6
votes
1answer
377 views

Is HMAC needed for a SHA-3 based MAC?

HMAC does nested hashing in order to prevent Length Extension Attacks. Given that you use the SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that ...
1
vote
2answers
127 views

SHA1 multipart calculation

Is it possible to combine SHA1 digest values to get the SHA1 of the concatenated parts ? I know the "S1" SHA1 of "part 1" and the "S2" SHA1 of the "part 2" and I would like to know the SHA1 of the ...
1
vote
1answer
141 views

Non-commutitive and nonassociative algebraic structures in cryptography

Are there any cryptographic algorithms or primitives that have been developed and studied that make use of non-commutative or non-associative algebraic structures such as quaternion integers or ...
1
vote
0answers
76 views

RSA: Common modulus attack problem [duplicate]

I understand in theory how the common modulus attack works (as described here: how to use common modulus attack?) Though, I did not understand completely how it worked with a negative $s_i$. Since ...
1
vote
2answers
80 views

Key cracking: Prefer many small texts over one large text?

If an attackers sets out to crack the symmetric key of e.g. AES-CTR, would they prefer to have access to many small cryptotexts or one large cryptotext? I.e. is it more interesting for the attacker to ...
3
votes
1answer
478 views

AES VS PRNG+HASH+XOR

I was thinking of doing symmetric encryption using just hashing and simple XOR encryption. It would work as: Alice and Bob share a symmetric key Alice manages to send an (authenticated) IV to Bob ...
2
votes
1answer
72 views

TLS - sharing 1792 bits of unidirectional keys

I've just watched a video on the TLS protocol and learnt that it uses unidirectional keys (meaning keys for both sides, from browser to server and from server to browser). Given that the server uses ...
3
votes
2answers
136 views

Basic attacks on McEliece; finding S and P

Take a McEliece cryptosystem with public generator matrix $G' = S G P$ where $G$ is a generator of a secret code with known fast decoding (not necessarily a Goppa code over $\mathbb{F}_2$), $S$ is ...
8
votes
2answers
614 views

Trial divisions before Miller-Rabin checks?

I'm trying to understand prime number generation (more correctly, the primality checking) as described in Handbook of Applied Cryptography. The context is circa pages 145 - 150, and specifically ...
3
votes
1answer
753 views

How to calculate inverse affine transform in AES from forward affine transform?

In AES the forward affine tranformation matrix is defined as: $$ \begin{bmatrix} 1& 0& 0& 0& 1& 1& 1& 1 \\ 1& 1& 0& 0& 0& 1& 1& 1 \\ 1& ...
7
votes
1answer
363 views

curve25519 weak points for contributory behaviour

The Diffie-Hellman on curve25519 is usually calculated using the base point $(9,…)$ which induces a cyclic subgroup of $G:=\{\infty\}\cup(E(F_{p^2})\cap(F_p\times F_p))$ with index 8, i.e. there is a ...
1
vote
1answer
164 views

Functions that are only second-preimage resistant?

Are there functions that satisfy the second-preimage resistance property without satisfying the others (preimage and collision resistance) ? I'm looking about such functions that compress data (exit ...
3
votes
2answers
195 views

What are good combinations of public key algorithms or primitives for long term security?

There has been talk in literature about doing multiple encryption with different block ciphers or stream ciphers several times before, and the benefits and risks of such efforts. There may be hidden ...
2
votes
1answer
170 views

Strategy for random CTR initial counter values

Alice has a secret key which she uses to encrypt messages in CTR mode. CTR mode is critically vulnerable to counter reuse, and Alice has a problem: she has terrible memory and no pen to write anything ...
0
votes
2answers
719 views

RSA decrypting of a huge file by parts [closed]

I need to decrypt a huge file that I own previously encoded by myself with a RSA public key (it's possible for this step using a symmetric algorithm key). Problem is that I can't load it in my ...
1
vote
1answer
102 views

Algorithm accepting every passphrase to fool unlegit user [closed]

I'm looking for specific names and literature on crypto algorithms that accept every passphrase input by the user, in order to 'decrypt' - even with false passphrase - and present the unlegit user ...
3
votes
1answer
856 views

Why does AES-GCM need a hash/MAC in TLS?

"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256" is just one example for a cipher suite, as far as I'm concerned it means this: It uses the TLS protocol, exchanges keys with Elliptic Curve Diffie Hellman ...
0
votes
0answers
70 views

What are the consequences of not checking the server mac in a TLS connection?

The context for this question (it's quite involved) can be found in this document: https://docs.google.com/file/d/0B15itpMWb2ztWTJrYTgzX204OVU However, I want to make it clear that you don't have to ...
-2
votes
2answers
155 views

Python KDF - Master Key and Derivatives

The encrypted file can be opened by following combinations (either any 2 DK, or 1 MK): DK1 + DK2 DK1 + DK3 DK2 + DK3 DK1 + DK2 + DK3 MK Any heads-up with Python ...
2
votes
2answers
182 views

Is a collision attack possible on MD5 if message is known partially

Is it possible to find $m'$ such that $\operatorname{MD5}(m'||m_1)=\operatorname{MD5}(m_1||m_2)$ if I know $m_2$ and $\operatorname{MD5}(m_1||m_2)$? Is this a collision or a preimage attack? Also in ...
1
vote
1answer
158 views

Brute force RSA cracking

Suppose one had a complete list of primes up to $2^{n+1}-1$. Then wouldn't one be able to crack an $n$-bit RSA public key in time $O(\pi(2^{n+1}-1))$, making RSA insecure? Thanks, René
4
votes
2answers
137 views

Use of less than secure random numbers for 'a' during an SRP proof of password

With Secure Remote Password protocol SRP6a random numbers are used for s, a and b. Where ...
8
votes
1answer
370 views

Compact digital signature for noisy data

The question asks for a signature scheme, with a public verification procedure, that is tolerant to minor alterations of the signed data during its transmission [possibly in analog form over some ...

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