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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ECC public key encryption and authentication - ECIES with ECDSA vs ECDH with AES

I'm currently working on a project where I want to establish a secure and authenticated communication channel between to entities, using Elliptic Curve Cryptography. Now I'm not really sure how to ...
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110 views

Asymmetric Cryptography Confusion - 'Sign' a file to guarantee its source

What I want to do is use asymmetric crypto to guarantee that a file comes from a source. I have software that runs on lots of wireless devices, and each of those has a license file with an encrypted ...
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3k views

Is it true for Java that the transformation mode and padding is ignored when using RSA?

Consider GregS's comment to this question (more specific to bouncycastle's provider implementation): http://stackoverflow.com/questions/11717646/bouncycastle-rsa-key-size-and-padding The mode, ...
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137 views

Why is $-1$ an illegal message in the Goldwasser-Micali Encryption Scheme

I'm not sure why in the Goldwasser-Micali encryption scheme with a Blum integer $N$, the message $-1$ is always a illegal message. Can you give me some direction for starting? What is illegal ...
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710 views

How difficult is it to brute force d in RSA: d = (1/e) mod φ in a CPT attack?

Given that RSA key generation works by computing: n = pq φ = (p-1)(q-1) d = (1/e) mod φ If I was an attacker who wanted to brute force d, could I brute force d given just the public key, the ...
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131 views

Self authenticating tamper resistant first meetings

I'm not sure what the precise words I am looking for are so I apologize if there is a better way to phrase this. What I am thinking of is ways to transfer an identity in a way that it is tamper ...
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498 views

Ed25519 choice of private key implementation

This answer to another question describes the different values chosen as private key and public key by various Ed25516 implementations. What are the advantages / disadvantages of each? (Table ...
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652 views

Can you identify the public key used to encrypt something?

If I encrypt a string with a public key, does the encrypted ciphertext reveal the public key I used to encrypt it? Basically, I don't want anyone to know who the ciphertext is addressed to. I'm ...
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2k views

Secure encrypt-then-sign with RSA

I understand that when you want to encrypt and sign data with RSA the generally recommended approach is sign-then-encrypt. However, I have encrypted data that I need to sign, to prove the author of ...
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3answers
245 views

Algorithm to securely exchange identities

Say four people each have a public/private key pair that they can use to encrypt or sign messages. They have an anonymous way to post messages such that the others can see them. Malicious entities can ...
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639 views

How are the primes used to generate RSA keys?

I am confused about how keys in RSA asymmetric encryption are generated and what the implications for open communications are. Textbooks say the one-way function is merely two primes (with some ...
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1k views

Digital Signature Algorithm signature creation

I was studying DSS from "Cryptography and Network Security" by William Stallings. What puzzled me was the DSS approach figure described in the text. It says it uses Public and Private Keys for ...
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90 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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36 views

Is there a way to turn a PGP key into its semi-prime counterpart?

From my understanding of PGP keys they use the RSA algorithms to encrypt/decrypt messages. So, I know that the RSA algorithms use a semi-prime number to encrypt/decrypt messages. So, what I was ...
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36 views

How does this solution guarantee authentication of B and privacy?

The exercise is: What could be changed on the second message " Kya(Kxb(Ra,Ks)) " to guarantee B's authenthicity and also privacy? My teacher's solution was "add a destination" , so it would be ...
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56 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 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 a ...
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174 views

RSA 1024 bit forge a new matching signature from a chosen message

I have an RSA signature scheme with 1024-bit key where I know the following: Public modulus $N$ Public exponent $e=3$ A lot of signatures Summary: To compute a signature, an MD5 hash is ...
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135 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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126 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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Multiple private keys for single public key

I am currently working in security in mobile ad-hoc networks. I have several clusters, and I want to send some data encrypted with its public key, from the cluster head to the cluster members. I ...
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252 views

Smart Card - Entropy during on-board public key generation

I know that some (advanced) smart cards or tokens allow generating key pair directly on the device, but I wonder how the card can gather entropy during the process. Any idea ?
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697 views

Why does FIPS 186-4 require specific sizes for keys?

In FIPS 186-4, page 32, about FFC crypto it is required that the length of $p$ will be exactly 1024 bit and the length of $q$ will be exactly 160 bit. Why is the requirement not stated in terms of ...
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198 views

Which public key encryption scheme is re-randomizable? How can I re-randomize an encryption scheme?

Which public key encryption scheme is re-randomizable? Is there any library for re-randomizable encryption scheme? If not, how can I re-randomize a given public key encryption scheme? I cannot find ...
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254 views

How to protect against ephemeral key reuse in some signature schemes?

Given that some signature schemes (for instance Elgamal) use an ephemeral key that cannot be reused ever. How do people usually protect against this? I'll elaborate more: if you reuse the ephemeral ...
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704 views

Elliptic Curve Encryption Ciphertext Size

I'd like to know how much bigger is the ciphertext when encrypting a message using ECC encrytpion? ECIES (or ElGamal)
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241 views

Can keys from Bitcoin's Hierarchical Deterministic Wallets be correlated (reducing privacy)?

I'm trying to understand if the feature "Hierarchical Deterministic Wallets" in Bitcoin allows for complete privacy of all derived keys, and if any of those keys can be associated with each other ...
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265 views

How vulnerable is RSA when using it to encode ~1000s of datasets with 500bytes each? How easy can the private key passphrase be hacked?

I know that this is not the best use case for RSA, but for a customer of mine I have to encode user data on the server in a way so that it can be decoded/downloaded by the customer through a "secure" ...
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3k 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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250 views

Are asymptotic lower bounds relevant to cryptography?

An asymptotic lower bound such as exponential-hardness is generally thought to imply that a problem is "inherently difficult". Encryption that is "inherently difficult" to break is thought to be ...
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57 views

How to verify a sever's ECDSA fingerprint during SSH

I have read somewhere that Servers which have SSH access for users in the public can have their public key posted publicly (e.g., on a website), so that people who access such a server using SSH can ...
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130 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....
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138 views

How to determine if padding has been used while encrypting a message with RSA?

I am trying to decrypt a RSA encrypted text file. I have a 2048 bit public key. Analyzing the public key with openssl reveals the exponent used is 3. ...
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230 views

public key cryptography and authentication for cross-platform network application

I'm developing network based application for control and telemetry on Linux based embedded system. I'm using ZMQ network library and Google Protocol Buffers serialization library for communication ...
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106 views

Implementing forward secrecy in OpenPGP with public key authentication

I am trying to consider the feasibility of implementing an encrypted file sharing system, which both provides forward secrecy but also allows public key verification. I am stuck on the marriage ...
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722 views

RSA key pair generation and FIPS 140-2, 186-4

I need to securely generate RSA key pair and I need to have access to private exponent in order to process it further. What's the difference in FIPS 140-2 and FIPS 186-4 in connection with RSA key ...
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110 views

Managing data access through asymmetric cryptography

I want to manage authorization, as 3rd-party permissions, through asymmetric cryptography. I'm concerned about how it is possible to share access of encrypted data with N entities, be able to revoke ...
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231 views

Asymmetric algorithm for one time signing of small cleartext

I want to generate a key pair such that the private key can be used once to sign a small message (1024 bytes) at some indeterminate point in the future and the public key can be used to verify that ...
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272 views

Is it possible to perform a rudimentary asymmetric key encryption algorithm by hand?

I have at least three, distinct motivations for having a simple way to use asymmetric key encryption by hand or without modern computers. First, I was recently demonstrating to a 12-year-old how ...
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295 views

Asymmetric key derivation – Who derives the new pub key can't know the new private key

I'm looking for a peer reviewed protocol or algorithm that can do this, preferentially I need something based on elliptic-curves cryptography. Alice know the main public key of Bob (B-PUB-1). Alice ...
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345 views

Can minimum encrypted message length be used to identify public key algorithm or derived some of its features?

Encrypting a very small message using public key cryptography always result in larger encrypted messages. Is it possible to deduce the algorithm used, key length, etc just by looking at the minimum ...
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397 views

Should new applications still use RSA? Is it worth going down the ECDH route for protocols?

I am currently designing an application for communication between two and more users. At the moment I am trying to figure out what methods to use for the asymmetric cryptology. With the recent "...
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Cloneability of AES-128

I would like to implement an anti-counterfeiting scheme for tools my company manufactures. This would ideally be done via RFID/NFC tags. However, the environment in which these tags operate would ...
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27 views

X509 converted to Encrypted and Signing keys

We have proprietary tool which takes a p12 file and generates a .key file. Inside the key file, I see two PEM formatted sections: Encrypting Certificate and Signing Certificate. When I open them on my ...
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162 views

end-to-end encrypted chat app with symmetric + public key encryption, TLS and cert pinning

A big drawback of end-to-end encrypted messaging services is that, as soon as you lose your device, you lose all your messages. Your private key is gone after all. I was wondering though, wouldn't it ...
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285 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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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 \...
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How did G.H. Hardy's work contribute to today's public-key cryptography?

I know that Hardy's work in number theory was used by Clifford Cocks in 1973 to develop the basis for public-key cryptography. What specifically was this work, and how is it used today in ...
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Security implications of public nonce

I'm planning to use the crypto_box() functions of Nacl (or, alternatively, the crypto_box_easy() functions of libsodium) to ...
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Relations between RSA and DLOG, factoring and DLOG

Definition: (The generalized Diffie-Hellman problem) Let $n=pq$ for two large primes $p,q$. Given $x, x^a, x^b,n$, find $x^{ab}\pmod{n}$. (1) Is there a known reduction from the GDH problem to ...
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Basic attacks on McEliece; finding S and P

Take a McEliece cryptosystem with public generator matrix $G' = S G P$ where $G$ is a generator of a secret code with known fast decoding (not necessarily a Goppa code over $\mathbb{F}_2$), $S$ is ...