An asymmetric cipher is an encryption scheme using a pair of keys, one to encrypt and a second to decrypt a message. This way the encrypting key need not be kept secret to ensure a private communication. Similarly in public key authentication, the verification key can be public and the signing key ...

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Store and share data on web server

I'm developing an intranet for a company where admins are sharing a huge excel file containing all the necessary password, on the common TSE. I've managed making them encrypt it with a common password ...
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2answers
148 views

RSA: revealing the modulus factorization by choosing a bad message

I started reading the book Cryptanalysis of RSA and its variants by M. Jason Hinek and I stumbled upon a phrase that intrigued me: plaintext messages that are relatively prime to the modulus (i....
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1answer
245 views

what are the NTRU keysize and application in industry?

I'm a student currently working on a research project on the NTRU cryptosystem, I've read some papers about this cryptosystem, and in those papers they are talking about keysize, is it the size of the ...
2
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0answers
69 views

Ciphertext size of any CPA-secure public-key encryption scheme

I know that, for any CPA-secure public-key encryption scheme, the size of the ciphertext after encrypting a single bit is superlogarithmic in the security parameter. That is, for $(pk,sk) \leftarrow ...
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1answer
33 views

IND-CCA Security of a encryption scheme which is combination of two schemes

I have two public key encryption scheme $\Pi_0$ and $\Pi_1$ and one of them is IND-CCA secure, another one is IND-CPA secure. Let $\Pi$ be a public key encryption scheme, which is a combination of $\...
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1answer
68 views

Proof that a encrypted file has the same content as an (existing) original

Assume that Alice has a file F which she is going to send, in encrypted form, to Bob. Alice possesses F and the public encryption key K of Bob in form of an X509-certificate. She generates the file E ...
2
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1answer
16 views

Message expansion in NTRU: why is it $\log_p(q)$-to-$1$?

Suppose that we are working with the original version of NTRU with parameters $(N,p,q,k,d_f,d_g,d_\phi)$. In this case we are working with the original NTRU with the digital envelope and the ...
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1answer
312 views

Simple digital signature example that one could compute without a computer?

I am working on a document to explain Bitcoin to students. But I am having a hard time translating the principle described in §2 of the Bitcoin whitepaper in layman's terms. There is a great question ...
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3answers
89 views

Public key decryption mathematical analogy

To clarify, I'm talking about digital-signatures, not public key encryption. When I encrypt something with a private key, then it should be decryptable with a public key, as I've understood how ...
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26 views

Problem when programming Schnorr signature [on hold]

I have some questions about Schnorr signature implementation. I am trying to implement it in C++. I chose private signing key x and public verification key y = g^x. I have a message M, random number ...
2
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2answers
194 views

Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy ...
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2answers
81 views

Initializing PGP keys by one side

I am using a PGP method to encrypt and decrypt messages shared between users A and B. Upon the start of a message exchange is the initialization of the public and secret keys by both Users. Lets say ...
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2answers
407 views

How to measure ECC key size?

I have implemented a ECC key generation scheme successfully. Now I need to find ECC key sizes of each generating key pairs. I assumed that ECC key size is the size of the ECC private Key. So I would ...
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1answer
29 views

In NTRU digital envelope, do everyone know the hash function $H$ used?

I have a simple question about the NTRU original cryptosystem using a digital envelope. The article can be found here: http://grouper.ieee.org/groups/1363/lattPK/submissions/ntru.pdf It is said that ...
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0answers
94 views

Are Diffie-Hellman, RSA and other types of public key cryptography different? [duplicate]

Are these schemes fundamentally different? Are other schemes fundamentally different in the sense that you can do different operations with them (or the same operations, but needing different ...
6
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2answers
984 views

Do I really need to use the same private/public key pair in RSA?

So I'm making an Android application, I need my application to be only able to scan my own generated QR codes, and I want to make sure that nobody else can generate fake ones. The data isn't ...
5
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0answers
62 views

Using a single Ed25519 key for encryption and signature

The libsodium documentation contains a function crypto_sign_ed25519_pk_to_curve25519 that converts an Ed25519 key into a Curve25519 one, so it can be used for both ...
2
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0answers
38 views

How does Bluetooth pairing (SSP with numeric comparison) work?

I have a question concerning the pairing of two Bluetooth devices using Simple Secure Pairing with numeric comparison. The NIST document I am looking at states on page 14: Numeric Comparison was ...
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2answers
61 views

Why are asymmetric keys represented as base 64? [closed]

When one generates a public and private key with say a total of 4096 bits, why does the program output what I assume to be base 64 instead of base 10 or binary?
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1answer
5k views

Can I remove newlines in a public key?

Can I remove new lines from the RSA public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or ...
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1answer
73 views

Key Hierarchy and key Encryption

If i have two 56-bit DES keys, and I use these two key to encrypt a 256-bit AES key. Like this $K_{AT}$ encrypts $K_{BT}$ and $K_{BT}$ encrypts $K$ What is the effective security of key $K$? Is it $...
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2answers
61 views

Is this RSA signing and verification process secure?

I need to verify that messages in a communications program are from valid senders. Below is a highlevel outline of how I think the process would work. The connections themselves are done over TLS. The ...
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3answers
411 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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1answer
75 views

Why does Paillier have poor performance?

Can anyone explain to me why Paillier crypto system does not provide good performance? I read here (pdf) that RSA and ElGamal provide better performance than Paillier algorithm.
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2answers
1k views

GPG/PGP Verification of Revocation

How does one verify a key revocation? After revoking a key and sending the revocation to MIT's keyserver, I noticed that the key is listed as such: ...
3
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1answer
171 views

Can we develop a working asymmetric crypto message protocol without an asymmetric encryption algorithm?

Our crypto libraries have: DSA (4096, 512) DH (4096) AES (256) SHA (512) Let us say these are implemented directly in hardware so that trying to pull the pieces out is not possible, and the CPU ...
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26 views

Is there a sufficiently memory-hard asymmetric encryption available? [closed]

The Password Hashing Competition offers several memory-hard hashing algorithms that are aware of time memory trade-off and essentially try to make it hard for ASICs and FPGAs to brute-force hashes. ...
3
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0answers
40 views

In NTRU, if $N$ is not prime, prove that one can recover the private key by solving a lattice problem in dimension lower than $2N$

In the NTRU cryptosystem, it is suggested to take $N$ prime. I want to understand why. In Jeffrey Hoffstein, Jill Pipher and H. Silverman An Introduction to Mathematical Cryptography, they suggest (...
4
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0answers
45 views

How does Ring Learning with Errors work? [closed]

I read that Google want to integrate this into HTTPS because it is safe against quantum computers. However, the Wikipedia article might as well be written in Latin because it makes very little sense ...
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1answer
30 views

What are the benefits of being able to choose (most of) the public key in a PKC?

We're developing a public key cryptosystem whose ciphertexts are actually much more long than the plaintexts (which, according to this question, is more a benefit than an issue). However, we have a ...
3
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1answer
52 views

Is there a problem in a PK cryptosystem if the plaintexts are very small compared to the ciphertexts?

I'm wondering, suppose we have a public key cryptosystem $P = (pk,sk)$ such that $$pk: \{0,1\}^n \to \{0,1\}^{n^2},$$ that is, the ciphertexts are $n$ times longer than the plaintexts (here, $n$ is ...
3
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1answer
73 views

How to compromise the privacy of NaCl encrypted messages, when nonce is reused?

I want to know to how break NaCl encryption when a nonce is used more than once for a given key private key. According to PyNaCl docs: It is VITALLY important that the nonce is a nonce, i.e. it is ...
3
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3answers
109 views

DIY message level security?

This might be in danger of being too elementary a question for this community but I'm hoping for expert help: Assuming that TLS is not enough to protect messages transmitted between a client and a ...
8
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2answers
140 views

SAT-Based Public Key Cryptosystem

I am researching post quantum cryptography and I've stumbled upon this article which presents a PKC with an np-complete (SAT) trapdoor. I was wondering if someone could help me understand the way the ...
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2answers
181 views

How does SSL work on the browser

I recently bought an SSL certificate from a website and was able to make it work on my Apache server. As far as I know, it uses asymmetric keys and the private key is stored on the server while the ...
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0answers
73 views

How to calculate ϕ(n) from n?

I'm trying to fully understand all the steps of the RSA algorithm. I have clear so far that: $n$ comes from the product of two numbers: $p$ and $q$ The public key consists of the pair ($e$, $n$) ...
3
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1answer
99 views

Do equivalent RSA keys exist?

If $m^{ed} \bmod n = m$ for message $m$, public key $e$ and private key $d$, then adding any integer multiple of $n$ to $m^{ed}$ still equals $m$ modulo $n$. Supposing it exists, how do I find an ...
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0answers
10 views

Invert authentication and secrecy passages in public-key cryptography [duplicate]

I know that for assuring authentication and secrecy in a communication between A and B using Public-Key Cryptography I have to send something like this: $E(PU_b,E(PR_a,m))$ Where: $E$ is the ...
3
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2answers
137 views

If I send a signed email, how does the end user get the public key?

I am sending a signed email using Python and smtplib. I have successfully signed the email using this example: http://proj.badc.rl.ac.uk/svn/ndg-security/branches/Dependencies/m2crypto/doc/howto.smime....
13
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4answers
3k views

Which public key cryptosystems are not based on number theory?

Are there any public key cryptographic systems whose hardness assumptions don't involve number theoretic problems?
3
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1answer
130 views

RSA: special parameters construction

I have to show that the following construction of $q$ allows to factorize $N$ : $p \in \mathbb{P}$, the set of primes $q \gets p \cdot \left((p - 1)^{-1} \bmod e\right) \bmod e$ $k=1$ while $q \not \...
0
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1answer
26 views

In Paillier homomorphism, how do you deal with bit length? [closed]

I'm trying to figure out homomorphic encryption and would like to multiply two paillier encrypted numbers. Like so: [a].[b]=[a+b] To try this I got this Paillier.java and tried the following: <...
8
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1answer
127 views

Could this “symmetric RSA” scheme provide key compromise resistant communications?

This question, and fkraiem's answer to it, made me wonder about the security and practicality of using "symmetric RSA" to provide a partially compromise-resistant secure channel. Specifically, assume ...
1
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1answer
37 views

In Paillier homomorphism how do you substract?

I'm trying to learn homomorphism so the problem may also be in my code (which I will include). I want to compute $a - b$ where $a$ is bigger then $b$. In order to do this I tried to compute $\frac{a}...
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0answers
71 views

Feasible attacks on ECRSA cryptosystem

In ECRSA cryptosystem, I want to know the feasible attacks. For illustrations we have two prime $p$ and $q$ such that $p \equiv 2 \pmod 3$, $q \equiv 2 \pmod 3$ and generate key pair as follows: $$n = ...
0
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1answer
37 views

Do RSA keys contain a checksum mechanism? [duplicate]

I'm new to cryptography, and I was making an experiment a few minutes ago, but I want to have some deeper knowledge about RSA public and private keys. I have a set of keys One begins with ...
3
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1answer
95 views

Salting Hash stored on RFID tag?

In my application, I am trying to prevent counterfeit widgets from being used on our gadgets; think HP ink-cartridges. I will be doing such with UHF RFID tags embedded in the widgets. Unfortunately, ...
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0answers
33 views

Are public key and private key exchangeable? [duplicate]

If I get a key pair from RSA algorithm, can I make Private-Key public, and keep Public-Key secret without breaking the security of encryption and signature?
3
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1answer
62 views

Does encryption of data/information take place in peer to peer networks like Gnutella, Bittorrent?

Do peer to peer networks like Gnutella, Bittorrent have any encryption system to secure the users privacy or encrypt the file/data being shared? Elaborate please.
2
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1answer
78 views

Why is Diffie-Hellman used instead of just RSA in key-exchange (TLS, IKE)?

Why should a key exchange protocol (such as in TLS or IKE) use Diffie Hellman? Why not just use RSA? For example: Alice picks a random session key, signs it, encrypts it with Bob's public key, and ...