Public key cryptography describes all cryptographic algorithms which have a pair of keys, one key that performs encryption and one key that performs decryption. One of these keys is made available publicly, allowing anyone to send messages that only the holder of the private key can read. You should ...
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Protocol to generate Client Certificates at the start of a SSL session automatically?
A more secure form of 'cookie' could be created for SSL communications through the following method.
The client generates and requests the server to sign a certificate.
Then the client authenticates ...
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119 views
Why does key generation take an input $1^k$, and how do I represent it in practice?
In my lecture, the lecturer said:
Let $K$ be the key generation algorithm. Given a security parameter represented in unary, $1^k$, $K(1^k)$ will output a keypair $(pk; sk)$, known as the public ...
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1answer
99 views
Crypto puzzle as proof of randomness?
I need an untrusted client to generate a random public/private keypair (in particular, an Ed25519 keypair, which can be generated really fast), but I'm only allowed to see the public key. The ...
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3answers
145 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 ...
2
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2answers
202 views
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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2answers
248 views
How do public key rings work in cryptographic applications?
I am wondering if there are any links to articles or resources available online, or explanations that you can give, that would help me to understand the concept of a public key ring, and why I might ...
2
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1answer
222 views
Low Public Exponent Attack for RSA
I'm having trouble understanding the algorithm for finding the original message $m$, when there is a small public exponent. Here is the example I'm trying to follow (you can also read it in the 'Low ...
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2answers
188 views
Why does the recommended key size between symmetric and assymetric encryption differ greatly?
In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
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1answer
111 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 ...
2
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3answers
338 views
Is it possible to pick your Ed25519 public key?
Is it possible to generate an Ed25519 keypair that has a very similar public key as another keypair (fooling a casual visual comparison) or is this as hard as solving one of SHA-512 or the discrete ...
2
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2answers
234 views
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 ...
2
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2answers
211 views
Is RSA in a ECB-like-mode safe for bulk encryption?
Let's say I would like to communicate with my friend using asymmetric/public-key encryption, e.g. RSA.
(Note: I do realize that in practice this is done through an intermediate symmetric key, but ...
2
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2answers
2k views
How does a chosen plaintext attack on RSA work?
How can one run a chosen plaintext attack on RSA?
If I can send some plaintexts and get the ciphertexts, how can I find a relation between them which helps me to crack another ciphertext?
2
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1answer
108 views
How does OAEP improve the security of RSA?
The heart of OAEP algorithm used for RSA encryption are the cryptographic hash functions $H$ and $G$.
Does everybody (so also an adversary) know these functions?
If YES: How does it help the ...
2
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3answers
190 views
The utility of elliptic curve cryptography
Suppose that the only public key cryptography schemes that we knew were Diffie Hellman, RSA and ElGamal. How much would this set civilization back? Are there important applications of elliptic curve ...
2
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1answer
283 views
Why can't I break ElGamal encryption by brute-forcing the secret exponent?
I am doing a course on cryptography on coursera and one of the topics covered was the ElGamal Encryption system.
I am using the terms as defined in Wikipedia.
Alice publishes $g$ and $g^x$. ...
2
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2answers
214 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 ...
2
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1answer
164 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 ...
2
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1answer
964 views
Secure way to transfer data over NFC?
I am currently writing a payment system to accept payment details from an NFC enabled smartphone (BlackBerry 9900) to a Windows client (C#.NET)
I am currently having two issues relating to security:
...
2
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2answers
919 views
How to distribute session keys in public key cryptography?
In public key cryptography we can also use session keys which are symmetric. How do the sender (say a server) provides this session key information to its clients?
If the sender (here server) ...
2
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1answer
117 views
A set of key pairs and one hash to secure them
I have a simple problem: I have a set of users' ECDSA key pairs, and say I want to encrypt them with a simple algorithm. I have access to one variable that uniquely identifies the user, so I hash it ...
2
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1answer
117 views
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 ...
2
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2answers
134 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 ...
2
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1answer
82 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 ...
2
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1answer
48 views
“proof of access” schemes
What is the state of the art way when implementing a scheme challenging a party to prove they have access to certain data?
What I'm looking for something along the lines of
Give them ...
2
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1answer
79 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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1answer
98 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.
2
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1answer
197 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 ...
2
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2answers
100 views
When to prefer exchanging cryptographic certificates over exchanging only public keys?
Let's think of the following case:
A group of peers want to exchange messages with each other. They use public-key cryptography to sign and encrypt messages. Anyone with any name can join the ...
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3answers
202 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 ...
2
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1answer
279 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 ...
2
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1answer
143 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 ...
2
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1answer
354 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 ...
2
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1answer
235 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 ...
2
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1answer
213 views
Can ElGamal encryption and ElGamal signatures be used together sharing the same key-pairs?
I'm working on a encryption system where each party can store exactly a single ElGamal private key in a device. This is a hardware limit. The system must be expanded to support signatures and ...
2
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2answers
148 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 ...
2
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2answers
157 views
Algorithm Design for only Mutual Information Sharing
Bob and Alice each have a bit string they want to keep private. They each want to know what the bitwise AND of their two strings would be without telling the other or anyone else listening to their ...
2
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1answer
196 views
Is this authenticated one-way communication protocol secure?
I am looking to see if this one-way communication protocol is secure. Assume Alice wants to send Bob a message (and doesn't need Bob to reply in the same session/channel - think email). Bob knows ...
2
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1answer
92 views
McEliece for streaming data
Under the assumption that there exists a real-world implementation of the McEliece scheme, could it be applied to streaming data as is? By that I mean in 'block cipher mode'? I've read that McEliece ...
2
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1answer
58 views
What happen if a asymmetric crypto-system deals with only one key
Assume there is a crypto algorithm that deals with matrices to encrypt and decrypt. Regardless of the specification of such algorithm, what if the algorithm assumes that two parties can securely agree ...
2
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2answers
151 views
Assymetric password encryption - Viable? Which algorithm?
We have an application that requires cleartext passwords for user authentication because of the authentication mechanism in use (RADIUS/CHAP), which unfortunately we cannot change. Since we don't want ...
2
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1answer
112 views
DLP based crypto systems with multiple independent generators
One example of a DLP based crypto system (or rather DDH based crypto system) where the public key parameters include two independent generators of the subgroup, is Cramer Shoup. Since the security ...
2
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1answer
131 views
Generate an insecure public / private key pair
I am looking for a way to generate an "insecure" public key pair. and by insecure I actually mean a pair that is breakable using brute-force (or other encryption) methods.
As far as I know PGP ...
2
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1answer
445 views
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 ...
2
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1answer
235 views
DGK Cryptosystem Encryption Speedup
Following @poncho's nice clarification of the RSA speedup here, let's see if I'm able to do the same in the case of the DGK cryptosystem:
We have pk = (n, g, h, u), sk = (p, q, $v_p$, $v_q$) which ...
2
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0answers
40 views
Key distribution and key exchange for simple secure FTP implementation [migrated]
I'm developing a simple secure file transfer protocol for a University project using openssl.
I have a Client (let be C) and a Server (let be S).
C will send to S messages like ...
2
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1answer
77 views
What's the probable usage of Interlock Protocol
I've recently read some articles about the Interlock Protocol, Article by Ron Rivest and Adi Shamir.
I'm wondering if it is possible to protect Key-exchange under Public-Key cryptography from the ...
2
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0answers
22 views
Encryption with Deduplication [duplicate]
Suppose I have a file server running ZFS with file deduplication enabled, and I have two users that are sharing files: Alice and Carol. If Alice uploads huge_file.tgz to her www/ directory, and Carol ...
2
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105 views
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 ...
2
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0answers
190 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, ...
