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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Why is RSA usually limited to messages up to 1 block

I'm wondering why RSA encryption usually is only used for messages that fit into one block. For larger messages hybrid encryption in combination with symmetric ciphers like AES seem to be the solution ...
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483 views

Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?

With a standard authenticated encryption scheme (or MAC), Alice and Bob share a symmetric key. When Alice sends something to Bob, Bob can check that it is authentic. At that point, Bob can deduce ...
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625 views

Do known-plaintext attacks exist for public key encryption?

In asymmetric ciphers we publish the public key for anyone, which means an attacker can encrypt any message they want and compare the ciphertext and plaintext without communicating with the owner of ...
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1answer
123 views

What's the strategy for future directions in cryptography? Bigger numbers/faster searching, or new methods, say, of factoring?

I'm taking a course in cryptography, and I would value any comments. This is not too technical a question, but more about directions or strategy in cryptography. My question is, is public key ...
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327 views

Determining the algorithm used to generate a digital signature

I have a string "abcd pqrs". This string is digitally signed with an X.509 certificate (with its private key) and it produces a signature. From the signed string, is it possible to find out what ...
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Difference between symmetric and asymmetric hash function?

The Linux kernel supports symmetric and asymmetric hash functions. E.g. sha1, sha256, ... See tcrypt.c and search for test_hash_speed and ...
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3answers
142 views

Public keys and their protocols

I'm having difficulties understanding exactly what this protocol means: $S \to D : \{N_S , S\}K_D$ $D \to S : \{N_S , N_D \}K_S$ $S \to D : \{N_D \}K_D$ "where $S$ represents the supervisor’s ...
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Why is it important that phi(n) is kept a secret, in RSA?

Why is it important that $\phi(n)$ is kept a secret, in RSA?
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1answer
158 views

What would the Internet be like without public-key cryptography?

The functioning of the Internet as we know it nowadays depends very heavily on public-key cryptography, including several key root systems that depend on its asymmetric properties. But what would it ...
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835 views

Why the following attack in common modulus RSA works?

Suppose that i share a common modulus $N$ with two users $u_1$ and $u_2$ with public, secret keys ($e_a,d_a$), ($e_b,d_b$). Why then $gcd(V,e_b)=1$ where $V=d_a*e_a-1/$W and $W=gcd(e_b,d_a*e_a-1)$ ...
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1answer
584 views

How to generate a public key from a private ECDSA key?

Having some specific ECDSA curve and a private key, how does one calculate the public key? I am having a hard time finding the algorithm and equations for it.
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447 views

How much extra information is in an RSA public key?

I'm trying to calculate the size of an RSA public key in Ruby. I've retrieved the key in PEM format, and once I've decoded the base64 part from the PEM format, I get the size in bytes. What I find is ...
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112 views

Polynomials and efficient computability

In public key crypto, the popular definitions of security (CPA, CCA1,2) depend on PPT adversaries. I'm trying to understand why adversaries should be PPT. It's clear that adversaries should be at ...
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1answer
569 views

What are the benefits of lattice based cryptography?

Previously we visited the benefits of elliptic curves for cryptography. Lattice based cryptography is starting to become quite popular in academia. The primary benefit of lattice based crypto is the ...
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1answer
348 views

using Post-quantum asymmetric ciphers instead of RSA

We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ...
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402 views

Public key cryptography - public key encrypts and cannot decrypt?

I understand the basics behind public key cryptography, in that each party has two keys - the public one encrypts, and the private one decrypts. What I cannot figure out is, How does the public key ...
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181 views

RSA Key generation Public exponent too big

I'm currently writing a paper about RSA (a self-chosen subject). I'm writing about the key-generation in RSA, and I have problem finding the public exponent e. I have chosen p = 61 and q = 53. Then ...
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202 views

Does RSA-OEAP have integrity and authenticity properties?

RSA-OAEP is IND-CCA2 secure (indistinguishable under an adaptive chosen ciphertext attack). Does it also have the INT-CTXT (integrity of ciphertext) and INT-PTXT (integrity of plaintext) properties? ...
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832 views

Get RSA PlainText without Knowing Private Key

If I have an algorithm,RSA-Crack(), that, for a given RSA public key (n,e), is able to decrypt 1% of the messages encrypted with that key (without knowledge of the corresponding private key).Can there ...
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1answer
506 views

In RSA encryption, does the value of e need to be random?

I am a novice programmer and am just finishing up an RSA encryption program that I am writing for practice. Currently I have the program generate a relatively small random value for the public key e. ...
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3answers
318 views

Safety of DSA key parameters sharing

I'm looking for a solution to use in a context where I need to be able to generate new asymmetric key pairs quickly (using a widely recognized algorithm, and EC-DSA is not applicable). It sounds like ...
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2answers
391 views

How should one implement a delegated shared trust protocol?

Consider the following (probably naive) scenario. Alice, who is very limited in her knowledge of security in general (clueless about securing a private key for example), wishes to delegate certain ...
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Ring Signature - paper/code difference in trying to solve inverse trap door function?

there is a paper on ring signatures and a python implementation of it here. The Step 4 in the paper describes $y_s = v =C_k,_v(y_1, y_2, ... y_r)$ for all $1 \leq i \leq r$ where $i \neq s$. The ...
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184 views

Breaking RSA, given a special kind of oracle that decrypts related ciphertexts for us

Let $c=E^{RSA}_{e}(w)$ be the ciphertext belonging to the plaintext $w$ if an $RSA$ system is used. Assume that the public exponent $e$ satisfies $e \le 10$. Furthermore, assume there is an oracle ...
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909 views

How does a client verify a server certificate?

As far as I know, when I request a certificate from Verisign (for example), and after they approved that me is me, they create a certificate (for me) which contains the digital signature and public ...
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899 views

What is a trapdoor permutation?

Can anyone explain to me what a trapdoor one-way permutation is? Is RSA a trapdoor one-way permutation? Context: I was reading about ring signatures. On page 560, it describes steps to ...
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implications of SSH server key compromission when authenticating users against a public key

Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission The question was stated as this : What could a hacker do while provided with the SSH ...
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262 views

How can I prove in zero knowldege that an ElGamal shuffle is correct for a special setting? [closed]

In a special ElGamal encryption scheme, every user has an ElGamal encryption key-pair using the same cyclic group $G$ and generator $g$. The system has a special function : $$ ...
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Can two different pairs of RSA key have the same modulus?

Can $n=pq$ be part of two different pairs of RSA keys? If such keys exist, say $(e_1,n)$ and $(e_2,n)$, how are they related? What will be the security concerns for the two users?
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2answers
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When is each key used when encrypting an email using OpenPGP?

When you send an email using PGP to encrypt emails, is the recipients public key used to encrypt the email, or is your private key used? Are they both used? At what points do each of the four keys ...
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198 views

How do I encrypt with the private key? [duplicate]

Possible Duplicate: RSA encryption with private key and decryption with a public key This wording is creeping everywhere (e.g. there): "I encrypt with the private key" and even sometimes, ...
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300 views

Can I save space for short messages by using encryption with private key instead of a signature?

Let's say I have a message, a Private Key and a Public Key. Normally if you want to see if the message is unaltered and is from the sender you would have the message part + signature part, which you ...
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131 views

Correct method to encrypt data so that it can be decrypted only by Alice and Bob

I need to build a system that stores encrypted transactions. Transaction involves always two parties. Payer and payee. Both must be able to download encrypted transaction from server and decrypt it ...
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1answer
321 views

What is the strength of unpadded RSA?

I would like to use unpadded RSA for homomorphic encryption in a toy P2P game, for things like fair coin flips and shuffling. How many bits of security does unpadded RSA have, in relation to its key ...
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415 views

How to avoid a chicken and egg scenario with encrypting passwords?

I am working on application that allows users to upload files containing company data and then share those files with a list of other users that have specific roles within the system. I want to ...
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737 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: ...
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427 views

What is the harm if I publish an encrypted RSA private key publicly?

What is the harm if I publish an encrypted RSA private key publicly? Or in this case, what is the harm if I publish many thousands or millions of them? Assuming that the private key is encrypted ...
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How are timestamps verified?

You put an input and the hash value comes as an output then when someone puts the input the hash function it is applied to see if it is the same hash original value is stored in some database , that ...
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544 views

How to jusify {e,n} is a valid RSA public key?

I have a two set of key {36,77} and {50,117}, How can validate if it is a valid RSA public keys? Is there any simple method?
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Additive ElGamal cryptosystem using a finite field

I'm trying to implement a modified version of the ElGamal cryptosystem as specified by Cramer et al. in "A secure and optimally efficient multi-authority election scheme", which possesses additive ...
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Why should the RSA private exponent have the same size as the modulus?

Consider the generation of an RSA key pair with a given modulus size $n$ and a known, small public exponent $e$ (typically $e = 3$ or $e = 65537$). A common method is to generate two random primes ...
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1answer
340 views

Is truncating a hashed private key with SHA-1 safe to use as the symmetric key for AES for data at rest?

I realize this is mixing the purposes between asymmetric and symmetric crypto, but I was wondering if it is safe to use a hashed, truncated private key (asymmetric) as the symmetric key for encrypting ...
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3answers
145 views

Is it possible to ensure security with zero pre-shared information?

Is it possible to secure a communications channel against both passive (sniffing) and active (injecting / MitM) attackers without either legitimate party knowing any pre-shared information? I know ...
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2answers
308 views

Encryption with private key?

we normally always encrypt by public key and decrypt with private key. If i encrypt with private key, then its still secure as normal PKI ? i mean known-plain-text will not take private key on the ...
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1answer
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Is this design of client side encryption secure?

I want to build a secure file storage web application. Users should be sure that server doesn't know how to decrypt files so encryption should take place at client side (i.e. in Javascript) and TLS ...
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4answers
4k views

How can one securely generate an asymmetric key pair from a short passphrase?

Background info: I am planning on making a filehost with which one can encrypt and upload files. To protect the data against any form of hacking, I'd like not to know the encryption key ($K$) used for ...
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158 views

Does a high exponent compensate for a low degree of certainty?

If a RSA certificate is created with a low degree of certainty, does the value of the exponent compensate for this? I'm asking because certain implementations of key generation software hide the ...
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Impacts of not using RSA exponent of 65537

This RFC says the RSA Exponent should be 65537. Why is that number recommended and what are the theoretical and practical impacts & risks of making that number higher or lower? What are the ...
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How to decrypt this RSA-like cipher

Suppose we have a RSA-type Modulus $n = pq$ with $p,q$ prime. We also pick a random public exponent $e$ with $\gcd(e,\varphi(n)) = 1$ and compute the private exponent $d$ with $de \equiv 1 ...
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608 views

What is the correct value for “certainty” in RSA key pair generation?

I'm creating an RSA key pair in Bouncy Castle and need to specify an int value for certainty. This Stack Overflow answer says it is a relative test for how prime the values are. There is another ...