An asymmetric cipher is an encryption scheme using a pair of keys, one to encrypt and a second to decrypt a message. A special class of asymmetric ciphers are public-key ciphers, in which the encrypting key need not be kept secret to ensure a private communication.

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RSA: If I sign the same digest with same key twice, will the signatures be identical? [duplicate]

If I don't have public keys to verify the signature, can I use this to discover that two signing services are using the same key? Can you send a reference?
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56 views

Does authenticated encryption add any protection to a signed digital envelope?

The general scenario of hybrid encryption is to use public key cryptography for the exchange of a one time session key that can be used for the encryption of the plaintext with a symmetric encryption ...
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3 views

Why do some programming language API's not support private key passwords? [migrated]

Two questions: I've recently started building a basic Go web-server, and noticed that the API for starting a TLS web-server does not support a symmetrically encrypted private RSA key. The API is ...
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21 views

RSA Signature Forgery

We all know that x509 certificates carry a signature that represents the certificate digest encrypted by the private key of the issuer. I believe that the digest is encrypted only providing one ...
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0answers
19 views

How to write automaticaly server generated keys into a file? [closed]

There have a server program, which generate keys for client. I want to store these keys into a file. I implemented the server and client program in python.. When server run each time for a user, the ...
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1answer
56 views

Why is the public/private key length used in libsodium so much shorter than needed for RSA [duplicate]

Reading the libsodium source I see that is uses a key length of 32 bytes (256 bit) for private/public key encryption. For RSA private/public key encryption a key length of 2048 (or 4095) bit is ...
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83 views

What is the danger if a non-prime is chosen for RSA? [duplicate]

I was reading this question about generating primes for RSA keys. The answers point out that most implementations of of the algorithm use probabilistic prime-ness checking algorithms. The answer by ...
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1answer
190 views

Attack for RSA 1024 bit with Low Public Exponent

I am facing a challenge at university. Our teacher give us the challenge to try to break an RSA 1024 bit. We have public modulus N and public exponent e (0x03), we don't know the padding. We have a ...
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1answer
69 views

Eavesdropping experiment with private key

I am extremely new to cryptography, still trying to learn basics. I got stuck in the following example of an eavesdropping experiment with a private key. $$\begin{array} {|r|r r r|r|} \hline C & ...
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0answers
67 views

Is secure communication without public-key crytography feasible?

We all know about public-key cryptosystems, and we know some of these are computationally secure (for the time being, of course). Are there any algorithms out there which allow safe communication ...
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34 views

Why recently Edward curve formulas being developed that deviates from unification?

Edward curves were considered initially because it provides a unified formula for both doubling and addition, thus having inherent side-channel resistance. But a lot of work has been done recently ...
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1answer
34 views

Establish Trust By Signing Random Seed

I'm trying to get my server to establish trust with a client. Neither is on the Internet, so there are no certificate authorities. The typical way to establish trust in my domain is for a client to ...
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1answer
109 views

Proof that two parties can communicate

Suppose we have three parties, Alice, Bob, and Carol. Alice can receive messages from Bob and Carol individually, but can only send messages to both simultaneously. Additionally, Alice cannot tell if ...
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1answer
37 views

Why does rsyncrypto require a public key during decryption?

I recently came across a project called rsyncrypto that sacrifices some security so that you can have rsync-friendly files. My understanding is that it works by generating a symmetric key for each ...
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1answer
61 views

RSA private key d knowing e,n

I need to find RSA private key $(d, N)$ knowing $(e, N)$. It's "own" RSA implementation. As i know $p$ is random 70 bit number, then $q$ is $p-2^{10} < q < p+2^{10}$ $d$ is max 16 bit long with ...
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1answer
36 views

Deriving 2 shared secrets from one private key and 2 different public keys

I have a key pair, say $(d, Q)$. I send my public key $Q$ to 2 different people. I also get their public keys $Q_1$ and $Q_2$. Now I can derive 2 shared secrets, $d*Q_1$ and $d*Q_2$. The 2 other ...
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2answers
117 views

Why are RSA ciphertexts different for the same plaintext?

I am using SpongyCastle for a project in android. I have used RSA to encrypt the data and then decrypt it in another activity, the keys are stored in the shared preferences. I discovered a thing I ...
3
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1answer
105 views

RSA public key recovery from signatures

Is it possible (how) to recover public (512 bit long) RSA key from multiple signatures having corresponding plain texts. Padding is not randomized. I need it to verify any future message comming from ...
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3answers
67 views

Some doubts about GnuPG

I've reading on GPG since yesterday and I have a doubt: the whole system of double key encryption does make sense but it looks to me like either way you are compromising something in terms of ...
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39 views

PQ Key Exchange based on Elliptic Curve Isogenies

I was reading the Wikipedia article on Post Quantum Cryptography and was interested in opinions as to whether the Supersingular Elliptic Curve Isogeny Diffie-Hellman listed there would be a good Post ...
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43 views

Property of Multiplicative group of integers mod n

While practising on paper I've realized of a property of multiplicative group of integers mod $n$. First, let's define $G$ being $p$ a prime and $g$ a primitive root mod n or a generator of a ...
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1answer
55 views

Euler's Totient function for semiprime numbers

I have noticed, during the period I spent studying RSA, that Euler's Totient function can be calculated in another way than $ϕ(N) =(p-1).(q-1)$ Let me explain myself by pointing to a brief example: ...
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1answer
106 views

About Primitive roots mod n in Diffie-Hellman [duplicate]

I'm on the study of Diffie-Hellman and its related math (multiplicative group of integers $\mod n$). In some crypto papers and documents I've read that $g$ needs to be a primitive root mod $n$ ($g$ ...
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3answers
110 views

Fast PKI for embedded device

We are creating a device with a small microcontroller (20 MHz CPU 16 KiB RAM). We need some way to securely send signed files to device (only signature, no encryption necessary). An external company ...
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49 views

Non-interactive zero-knowledge proof for discrete logarithm without random oracle

Is there any non-interactive zero-knowledge proof for discrete logarithm without random oracle over the group $\mathbb Z_p$?
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50 views

Why is public key cryptography not widely used in governments? [closed]

Are there any practical limitations? Govt driving license, passport, SSN could be digitally signed making it easy for anyone to validate. They can have a qr code in them which can be easily validated ...
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3answers
212 views

Sharing a secret key between many users

I would like to know if there is any security issue in sharing a secret key (of an asymmetric cryptography) between several users. I know that this secret key is no longer "secret", so it's no longer ...
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1answer
66 views

PGP public RSA key format

I have been trying to use Go (I could post the code, but I think I posted enough already...) to generate a PGP RSA key. However every time I try to encrypt something with it, something fails. However, ...
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1answer
96 views

Finding public exponent e

I'm trying to create an algorithm to find the public exponent e given a plain (non-CRT) private key that doesn't include the public exponent, i.e. I've only got $n$ and $d$. A question has already ...
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1answer
45 views

How to calculate RSA CRT parameters from public key and private exponent

Given the public key (n, e) and private exponent (d), how to calculate CRT parameters (p, q, dP, dQ, and qInv) of this RSA key pair?
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2answers
88 views

Is it possible to have identical public keys for different ciphers?

Is it possible (and is there any research I can read) to have 2 key pairs for different ciphers, for example RSA 1024 and some yet to be released EC (or other asymmetric cipher) than uses 1024 bit ...
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1answer
54 views

Is there an asymmetric One-Time-Pad? [duplicate]

Is there something like a perfect asymmetric crypto-algo? Is there proof that there must be one or not. From a logical point of view it seems to be possible to design such algorithm if your keysize is ...
2
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1answer
76 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 ...
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1answer
105 views

Why doesn't this defeat RSA?

Apologies for the obviously ridiculous question but I need to know where I'm going wrong here. For RSA, we compute $n=pq$ for primes $p$ and $q$. We then choose an $e$ such that $gcd(e, ...
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1answer
110 views

Why cant Public Key Encryption be perfectly secure? [duplicate]

I would be very grateful for any help. I cant figure out why (probabilistic) public key encryption schemes can never provide perfect secrecy? Any Ideas? Excerpt: In contrast to the private-key ...
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1answer
63 views

where should private and public keys be stored? [closed]

I am kind of confused whether should a newly generated key pair be stored in a keystore or in just a normal plain text file? From what I read from online source, there are serveral explainations ...
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1answer
89 views

what is the public information in Elliptic curve cryptosystems [closed]

Currently my knowledge about Elliptic curve is quite limited to the textbook and I don't know how a practical Elliptic curve cryptosystem works. I read an example about key exchange using Elliptic ...
2
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1answer
169 views

ECC vs RSA: how to compare key sizes?

I know and I have understood the details of RSA, elliptic curve cryptography, (EC)DH and (EC)DSA. I keep reading everywhere that (if we don't consider non-deterministic computers) "ECC can achieve ...
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2answers
65 views

Is it hard to recover $p$ from $k \phi(p)$?

Given $k\phi(p)$, is it hard to recover $p$? Here, $p$ is a large prime, $\phi(\cdot)$ is Euler's totient function and $k$ is an unknown integer. Or what's the complexity to recover $p$ from $k ...
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111 views

Why does Diffie-Hellman need be a cyclic group?

Why is Diffie-Hellman defined on a cyclic group? Doesn't it work for any commutative operation which the inverse is hard to find? Say Alice and Bob agree in a public prime $c$ and both choose a ...
2
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1answer
59 views

Key Check Value standard pratice for asymetric cryptography?

I'm looking for a standard, or sound industry practice, for the equivalent of a Key Check Value, applied to the private key of a public key algorithm, like ECDSA. For DES or 3DES keys, practice (as ...
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1answer
99 views

What does signed fixed window method mean in ECC?

I am studying (sliding) window method in Elliptic Curve Cryptography (ECC) but I am confused by the term, signed fixed window method. By the way term is used in a research paper and not in the book ...
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23 views

Does Paillier Cryptosystem work in different message space? [duplicate]

I have a question about Paillier Cryptosystem. Assuming we have $c = Enc(m) = g^m \cdot r^N \mod N^2$ as the output of encryption algorithm, where $N=p_1p_2$ and $m \in \mathbb{Z}_q \subset ...
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31 views

What crypto scheme should I use on embedded m2m system with assymetric uplink/downlink bandwidth?

I am working on implementing info security into custom m2m radiolink communication system, which has some restrictions: MCU based endpoint can transmit to gateway with packets max 16 bytes long, and ...
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35 views

Registration and log in through public key cryptography?

I read about zero knowledge proofs. Let's say you want to create an account at a website. You choose a password $p$ and from $p$ you derive deterministically a public & private key pair $(e,d)$ ...
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Paillier Encryption: problems with double encryption

Given have two public keys $k1$ and $k2$, $E_{k1}(E_{k2}(m_1))$ and $m_2$. Is it possible to calculate $E_{k1}(E_{k2}(m_1 + m2))$? (or with multiplication instead of addition) At a first glance, I ...
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1answer
36 views

How do revocation certificates work in PGP?

I've already read how to build and upload them, but I'm wondering how revocation certificates work, what informations they hold and so on. Suppose my private key is compromised, but I have a ...
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1answer
80 views

Asymmetric cipher with multiple public keys

Asymmetric cryptography is well known. You generate a private key. Using the private key you generate a public key. Then you can sign a message with the private key and check signatures using the ...
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50 views

How to securely map an element from an smaller domain to the other element in a large domain

Problem: I have a small sized domain, say s-bit. It's clear that the probability for an adversary to guess an element is $ \frac{1}{2^s}$. I need to make the probability negligible. However, I need to ...
2
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2answers
84 views

How does a certificate authority issue a digital certificate?

I am new to cryptography and I want to know the details of how a Certificate Authority issues a digital certificate. From what I know (please correct me if I'm wrong at any parts of my explanation): ...