Latest Crypto related questions

Score: 0
Mani Varma Indukuri avatar
Can I copy digital signature for malicious purpose?
gb flag

I am reading Cryptography. I have multiple questions to ask.

  1. I signed my QR code with my private key so that people can verify it's mine. QR code has data which is public. I have this QR code on my document. Problem is, can an attacker copy this signature of this QR code on the document, and create a fake document with same QR code signed by me ? I assume signature just a sequence of characters after ...
Score: 5
fgrieu avatar
Can an arbitrary physical image be a key?
ng flag

Assume an arbitrary secret physical image¹, such as a privately made chemical Polaroid™ similar to this cables

Is there a feasible and secure way that this physical image could be used as cryptographic key, functionally equivalent to an AES key or RSA private key, without "accompanying² other digital data" beyond the physical image? We'll assume a scanner digitizes the physical image at each use, and all t ...

Score: 0
gandalf0215 avatar
Is there a way to combine the Fuzzy extractor (or SS+ Ext) with state-of-art deep learning model?
gf flag

I recently reviewed biometric authentication with deep learning model, and I found, in cryptography, the fuzzy extractor,FE (or secure sketch,SS, plus strong extractor) have solve this problem good enough based on error-correcting codes, is there any research from this point to combine them? For deep learning model, it is natural to give a good representing for the input biometric object(e.g. face image ...

Score: 0
J.Doe avatar
Doubt regarding converting hex to byte in SHA-256 input
br flag

Hash functions such as SHA-256 takes a binary string as input. Now given a hex string when we convert it to a normal text string the computed SHA-256 value would be the same. Herein lies my problem

Let us consider a simple string in hexadecimals 2E; its SHA-256 value is cdb4ee2aea69cc6a83331bbe96dc2caa9a299d21329efb0336fc02a82e1839a8.

When converted into byte form should we write 46 or 046. In eit ...

Score: -1
J.Doe avatar
How to pad in the SHA256 Algorithm (an example using Bitcoin Header)?
br flag

For any bitcoin block we combine various Header fields to create a string which is an input to a 2 pass SHA algorithm. The resultant hash must match with the Hash in the Block header for the Block to be valid.

To test this logic as well as SHA algorithm, I used the header of Block number 695877 (https://blockchain.info/rawblock/695877?format=json) to create the Input string 04008020546c35998681264442 ...

Score: 0
mattjoe avatar
Saving highly sensitive data in US cloud - what encryption would you use?
jp flag

We have a cloud-based application running on AWS servers and are looking for a way to store highly sensitive user data there without giving AWS the possibility of exposing our data to the US government (cloud act). Therefore, we don't want to use AWS-owned services for encryption / decryption like KMS or HSM. We want to stay in full control of the keys that encrypt / decrypt data - all the time.

 ...

Score: 1
DaWNFoRCe avatar
Formal Verification for Multiparty Computation and Homomorphic Encryption?
cn flag

I've recently found some work on the use of Formal Verification Software, like ProVerif for enclaves. I wonder is if its feasible to have something similar for MPC and Homomorphic Encryption and their applications?

I always thought there were limitations adopting simulation based proofs and Universal Composability, in general, in Formal Verification, but as of late I'm thinking there must be mor ...

Score: 1
DaWNFoRCe avatar
Is it possible to Publicly Query Privately Held Data with proof of Correctness?
cn flag

We can secretly query inputs from a public DBs using what we call in the literature PIR. We can secretly query inputs from a privately held DB by means of Private Set Intersection (PSI). We can also secretly read/write from a private DB, using ORAM. We can even secretly query a private distributed state, by combining ORAM and MPC.

I wonder, however, what happens for the one use case not annotated ...

Score: 3
DannyNiu avatar
How are the instantiations of RSAES-OAEP and SHA*WithRSAEncryption different in practice?
vu flag

For the spare-time project I had been working on, I'm evaluating the PKCS#1 padded RSA schemes for implementation.

For PKCS#1 v1.5, encryption doesn't seem to require a hash function, and the signature doesn't need additional mask-generating function (MGF) beyond a digest algorithm for hashing the message.

For PKCS#1 v2.x, both encryption and signature are instantiated with a MGF, a hash function, a ...

Score: 0
painter Qiao avatar
what does "product of two cyclic groups" mean
dk flag

enter image description here

I am reading "Elliptic curve cryptosystems" and the link is here(https://www.ams.org/journals/mcom/1987-48-177/S0025-5718-1987-0866109-5/S0025-5718-1987-0866109-5.pdf). I don't understand the meaning of "product of two cyclic groups" in it. Can anyone explain it to me? It's better to have a simple example.

Score: 1
caveman avatar
How is Argon2's Blake2b different than normal Blake2b?
in flag

This post says that Argon2's Blake2b is a reduced one, which is also agreed by Argon2's specs as it states that it uses only a 2 round Blake2b.

But, on the other hand, page 15 of Argon2's specs states that it modifies Blake2b to add 32-bit multiplications in order to increase latency (I guess they mean by needing to wait for extra CPU cycles?).

My questions are:

  1. If Argon2 wants to make Blake2b harde ...
Score: 1
Understanding this notation for the probability distribution of order preserving encryption
ru flag

I'm reading this PDF: https://link.springer.com/content/pdf/10.1007/978-3-642-01001-9_13.pdf about order preserving encryption functions and there's this on page 9 (or 232):

enter image description here

It's describing the formula for the probability distribution. So I guess it's saying that the probability distribution of some variable.

What is the dollar sign, the <- and how do I interpret this Pr?

Score: 2
caveman avatar
Efficient way to pick an array index by using a, say, 64 bit random number?
in flag

Say, I have uint64_t rand = <some random number>, and char array[20] = .... My goal is to pick an element in array based on the content of rand.

  1. One slow way is to use the remainder: size_t i = rand % 20 then pick the element by array[i].
  2. Another way, which I guess is faster, is i = rand/UINT64_MAX * 20. Or, to avoid needing floating operations, its inverse counter part 20/(UINT64_MAX/ra ...
Score: 2
fgrieu avatar
Early field use of digital signature
ng flag

What are documented early field uses of digital signature?

The oldest I found is reported by Charles H. Bennett, Gilles Brassard, Seth Breidbart, Stephen Wiesner's Quantum Cryptography, or Unforgeable Subway Tokens (in proceedings of Crypto 1982). They cite Gina B. Kolata's New Codes Coming into Use (in Popular Science, May 1980) as the source of the following. The relevant portion of both article ...

Score: 1
Proof that someone has access to a private key whose public key is part of a known group
np flag

I'm a crypto newbie and hoping to get pointed in the right direction. I've seen some related questions like this but none that satisfy my requirements.

Let's say Jane's Forum is a large community, and every member of Jane's Forum has a public/private keypair. The public key is associated with their profile and visible to anyone.

Bob's Backpack Shop is willing to send a free backpack to every memb ...

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