# All Questions

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### Montgomery and Galois fields

I'm a little bit confused about the design of a RSA module in VHDL. My question isn't directly related to hardware design. I've read a lot of publications and I bought also a book. In one publications ...
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### 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 ...
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### Supress password prompt in GPG [migrated]

Using GnuPG one can symmetrically encrypt a file using: gpg -c --cipher-algo TWOFISH --digest-algo SHA512 secret.txt and decrypt using: ...
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### 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 ...
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### Equality of commitments to group elements and exponents in Groth-Sahai proofs

In Groth-Sahai NIZK proof system, is it possible to show the equality of commitments to group elements and exponents without opening them? Assume, the group involved here is $\mathbb{Z_p}$, i.e. the ...
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### 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 ...
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### 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. ...
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### 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. ...
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### 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 ...
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### 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, ...
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### 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 ...
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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!
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### 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 ( ...
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### Clarifying parts of the programming code in Timing Attack on AES

I am trying to understand the code of Bernstein in this paper, specifically, the code of Appendix: server.c. I need some help for understanding the following lines: ­ ...
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### 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 ...
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### How does bitmessage encryption work?

I have been reading around protocol specification and there is either too much technical detail or too bad articles on various sites. I need you to explain in simple words how encryption in ...
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### How does multi platform encrypted cloud storage work?

I'm really interested in end-to-end encrypted cloud storage and couldn't find out how following scenario could work: A user of a cloud provider which provides zero-knowledge-authentication (like for ...
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### RSA public key exponent generation confusion

Quote from Wiki: $e$ having a short bit-length and small Hamming weight results in more efficient encryption — most commonly $2^{16} + 1 = 65537$. However, much smaller values of $e$ (such as $3$) ...
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### Can AES in CCM or GCM counter mode interoperate with AES in “plain” counter mode (CTR)?

I am exploring the use of Windows CNG to replace some OpenSSL-based code that takes advantage of AES in counter mode. From the outside, everything should look the same after the switch. The section ...
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### 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 ...
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### Nonces being used in SSL and MAC to prevent replay attacks

I'm a bit confused in the way nonces are used in these processes to prevent replay attacks. Heres How I think it works during SSL: Nonces are exchanged during stage one of the handshake protocol. ...
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### Unbreakable code and mathematical impossibility

Is an unbreakable code mathematically possible , considering a code with finite number of characters but has infinite combinations , using brute force is it not compulsory that the correct code be ...
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### 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) ...
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### Is RSA with SHA1 broken?

I am using CryptSignMessage to sign a string/file. Is using RSASha1 insecure? I know Sha1 is broken as a hashing algorithm, but does that also mean that using it for signing with RSA is broken?
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### Confused with the role of AES round keys

AES works when each plaintext block is arranged in a 4x4 array of bytes called states. State goes through 10 rounds of encryption consisting of 4 operations: bytesub, shiftrow, mix columns and add ...
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### PKI Infrastructure

I've got a very simple but for me a difficult question. I analyzed the public key cryptography and understand the process. But I didn't understand why is only the receiver able to decrypt to message. ...
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### TimeStamp in Cache-time attacks on AES [closed]

I have recently read about AES cache timing attacks. More specifically, I read Daniel Bernstein paper Cache-timing attacks on AES. I have a question about the code in Appendix A: ...
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### What kind of attack does the current brokenness of SHA-1 allow?

I understand that the following is becoming feasible, or already is: Find any 2 data (d1 and d2), for which SHA1(d1) = SHA1(d2) However, it is not entirely clear ...
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### 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 ...
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### 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 ...
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### 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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### 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 ...
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### How bad would it be to reuse the random blinding factor in a scheme like Paillier?

A secure and somewhat fast way to "re-encrypt" (refresh? anonymise?) a Paillier ciphertext, $c$, is to multiply it by an exponentiated random value: $c \gets c \cdot r^n \mod n^2$ (with \$r \in ...
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### Key Recovery Smart-Vercauteren SWHE

In the article (https://eprint.iacr.org/2009/571.pdf, pag 8) of Smart and Vercauteren, it is mentioned that the recovery of the private key is an instance of the small principal ideal problem. But I ...
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### white-box cryptography and its applications [closed]

I am a programmer who is doing research into whitebox cryptography. What I hope to do is to use WBC for an DRM application however as some of us may know, WBC is theoretically impossible therefore I ...
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### Programming language for modular arithmetic over large numbers [closed]

I'am trying to implement algorithms on integer factorization.This involves dealing with integers of 200-500 digits and doing modular arithmetic over them.Which programming language has inbuilt support ...
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### 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 ...
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### If the ciphertext of Goldwasser-Micali has been falsified, what is the plaintext after decryption?

Alice encrypts 0 using Goldwasser-Micali encryption scheme and sends the ciphertext to Bob. If some bits are flipped during the transmission, what can Bob get after decrytpion. Can Bob get 1 with a ...
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### Simplifying the zero-knowledge proof example? [duplicate]

There is this http://en.wikipedia.org/wiki/Zero-knowledge_proof#Abstract_example. Now I'm curious about this. Why is it not possible for Victor to stand at the entrance and watch Peggy take one path ...
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### Has the POODLE SSL vulnerability ever actually been used? [migrated]

Is there any evidence that the the POODLE SSL or TLS has actually been proven to be a risk for file transfer like SecureFTP etc...? ...or is it just a theoretical exposure?