# All Questions

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### what is the difference between one way function and hard core predicate?

Does anyone know what the difference between a one way function is and a hard core predicate? Are they related to each other or different?
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### Difference between SHA1 and SHA1HMAC? [duplicate]

Can anyone let me know the difference between SHA1 and SHA1HMAC algo?
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### Alter plaintext in block cipher AES in CBC mode

How can I alter the plaintext before decryption by changing the IV? I know what the value of the plaintext should be. I also know the value of the IV (initial vector). The IV and the AES block are ...
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### Is it interesting to design stream ciphers parametrized by a CSPRNG?

Would it be interesting to have new stream ciphers whose design is parametrized by a CSPRNG? I.e. to instantiate the stream cipher, you just have to select and plug in any CSPRNG of your choice.
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### Which parameters of the ATV-FHE scheme should be kept private?

I try to implement the ATV-FHE scheme as it is described in section 2 of this paper. I also read this paper that says how parameters should be chosen. Are there some parameters that must be kept ...
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### Are private and public key sizes of Elliptic curve related?

I'm new to elliptic curve cryptography. I just want to know in the case where I take a random number (private key) and find its associated public key, does the size of the public key depends upon ...
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### A (current or soon-to-be) NIST-recommended alternative to ECC?

So this comes from the professional rumor-mill, and I'm wondering if anyone might either debunk or shed light on this. My understanding is ECC is generally now preferred over RSA simply due to how ...
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### Three party coin flipping protocol with only 2 active participants

Is there a coin flipping protocol where: Alice, Bob and Carol don't trust each other, and The coin is flipped only by Alice and Bob, and The result must be trusted by all three participants.
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### Why do cryptographic hashes need to be fixed length?

Why do cryptographic hashes need to have a fixed length output? I know that the shallow answer is that an output that varies by key size or file size can leak information somehow, leading to ...
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### Why is SSL/TLS so complicated?

I'm new to SSL/TLS and I'm staring as a new security researcher. It appears to me that SSL/TLS protocol is needlessly complex for arriving at a shared secret. The complexity results in so many bugs ...
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### In FHE over integers is each bit of the cyphertext encrypted under the new key?

In the paper Fully Homomorphic Encryption over the Integers, a method is shown for doing homomorphic encryption using only integers. The basic idea is that a bit m is encoded as a large integer c. ...
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### What communications security protocols exist that aren't based on PKC?

Lets say that you have two devices that need to communicate in a secure manner. These devices can share secrets before communication takes place (This sharing of secrets occurs over another secure ...
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### How to decrypt RSA cipher text? [closed]

How can I decrypt an RSA cipher text in which I am only provided with a public key and the cipher text. The person who encrypted it made a mistake in taking the exponent.
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### How to compare two CSPRNGs? [duplicate]

Let's say I am given to CSPRNGs: RNG1 and RNG2. I want to select the best one of the two for cryptography. How should I do it? Any of the two RNGs can be initialized with a secret key during tests and ...
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### Is there a single-use signature scheme, where a second use of the private key discloses it to the world?

With ECDSA (and possibly DSA too) I'm aware that if the same value for $k$ is used with the same private key $D_A$ to sign two different messages, then anyone possessing the two messages $m_0$ and ...
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### How to calculate LOW(b) and HIGH(b) in spritz cryptography

I try to implement spritz cryptography like this paper . But I don't know how to calculate LOW(b) and HIGH(b). In paper page 7. ...
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### How many bits of an exponent are leaked when doing a powmod?

How many bits of the exponent $x$ are leaked when you calculate and reveal $g^x \pmod p$ for some generator $g$ of $\mathbb Z^∗_p$? The low bit of $x$ is obviously leaked: the low bit equals ...
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### RSA time function

I am doing a paper on textbook RSA (highschool-level). I am explaining and proving the significance of the public key exponent in time and security. So far, I have encrypted a constant message with a ...
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### PublicKey Unknown Encoding

I have a public key: ...
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### Best practises to generate IV for AES-CTR in this scenario

I'm building a cloud storage application that will store files on my servers. I want these files to be encrypted with AES in CTR mode and the key will be always the same. I'm wondering what would be ...
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### How does the size of the prime affect Elliptic Curve Bit Security?

I am using the MIRACL Library to implement an Elliptic Curve Diffie Hellman based Key Exchange according to ECDH-Scheme-Wikipedia. Referring to the Miracl Docs they suggest a few curves. Each curve ...
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### Is there a library-less implementation of DSA available to read? [closed]

Is there a pedagogical library-less implementation of DSA available to read? (Not ECDSA.) Obviously BigInteger and hash functions may be from libraries, but I want to read the implementation of all ...
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### Intermediate values for testing Blowfish

I am trying to implement the Blowfish algorithm in VHDL. To debug my code, I need the intermediate values of s-box and P vectors after each iteration. Where can I find this data set? p.s :- I know ...
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### What is scale-invariance notion of a fully homomorphic encryption scheme?

I read this paper https://eprint.iacr.org/2012/078.pdf and I didn't understand what does the author mean with scale-invariance perspective. The perspective in which we view the ciphertext is ...
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### With EC secp256k1 is there a way of transforming a function of the private key to a function of the public key?

A key pair has a private key $D_A$ and a public key $Q_A$. $D_A$ is an integer less than the curve's $n$. Is there any (boolean) function of the private key $f(D_A)$ which can be transformed into a ...
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### With ECDSA is there a way for the verifier to calculate any properties of $k$?

With ECDSA, given $(r,s)$ and $m$, is there a way for a verifier to calculate any (boolean) properties of $k$, without knowing $k$ or the private key $D_A$? (I understand that $k$ should be random, ...
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### Why does the modulus of Diffie–Hellman need to be a prime?

I read a lot about Diffie-Hellman, but there is one thing I dont understand: why does the modulus p need to be a prime? What if it would not be a prime?
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### Which method to generate one time password?

I'm looking for a concrete algorithm to generate one time passwords. The situation is as follows: Alice and Bob exchanged a passphrase over a secure channel in the beginning. They want to ...
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### Why is only one oracle + challenge-response phase sufficient for IND-CPA security?

The CRYPTUTOR wiki from UIUC uses the following definition of the IND-CPA game: We (privately) choose a key K according to the key generation algorithm: K $\gets \mathsf{KeyGen}$. We ...
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### Salary Negotiation Problem

Imagine Alice is applying for a new job. Alice has an idea of the minimum salary that she is willing to accept—let's call this value A. Bob, the hiring manager for ...
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### Is it possible to correct the exponent of an RSA public key if it has been altered?

Is it possible to change the exponent of an RSA public key?
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### Is there a standard notation for a message concatenated with its signature?

I'm wondering what's the standard (or canonical) notation for "a message along with its signature", i.e. $$\mathit{Message}~\Vert~\sigma_k(\mathit{Message}) \text.$$ Here the duplicated ...
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### Is there an algorithm to hide text in another text, while preserving the meaning of the latter?

Is there a way to hide a text message $A$ inside another text $B$ using a cryptographic cipher/algorithm, while preserving the sense/meaning of $B$ and without anybody being able to notice there is a ...
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### Can you explain “k out of n” from the VCS paper by Naor and Shamir

I am new to visual cryptography. I’ve just read the paper “Visual Cryptography” by Moni Naor and Adi Shamir and I'm stuck on the chapter about the “$k$ out of $n$” construction. I am aware that, on ...
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### How to compare performances of lattice-based and pairing-based IBE schemes

I try to compare the performances (cost of Enc, Dec, ... size of keys, ciphertexts, ...) of IBE schemes using lattices (LWE hardness assumption) or pairing (Diffie-Hellman hardness assumption). I've ...
677 views

### Is it usual for a signed message to contain the public key of the signer?

In protocols/systems which use ECDSA, is it common for the message to contain the public key of the message signer? If not, how do recipients know that the message has been signed by the correct ...
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### What is the correct name for bytes which are to be signed?

I have some bytes, and I sign them with my private key using ECDSA. The resultant (71) bytes are the signature. But what is the name of the bytes I have signed? (If this were encryption, they would ...
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### Forcing participants to be honest in Secure Multiparty Communication

Alice and Bob engage to compute a secure function f(a,b) where a and b must be present in a ...
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### Usefulness of ability to calculate $m^{p+q}$ with RSA

I noticed that with only an RSA public key, it is possible/tractable to calculate $m^{p+q} \pmod n$ for any $m$ without knowing $p$ or $q$. Namely, $m^{p+q} \equiv m^{n+1} \pmod n$. (This follows ...
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### Is it possible to recover an RSA modulus from its signatures?

Let's say that you have some small number of RSA signatures of known data: you know some pairs $(m_k, c_k)$ such that ${c_k}^e \equiv m_k \pmod n$. If you know $e$, because probably it's one of \$\{3, ...
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### Understanding SSL vulnerability within Apple's GOTOFAIL

Currently learning and reading about the fascinating SSL Key Exchange and came upon the Apple GOTOFAIL incident back in 2014. I'm going through the code during that time and came across this section. ...