Questions tagged [public-key]

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 private.

Filter by
Sorted by
Tagged with
1
vote
1answer
39 views

Adversary for attack on one variant of ElGamal

I came by the following question: Consider the following variant of ElGamal encryption. Let $p= 2q+ 1$, let $G$ be the group of squares modulo $p$ so $G$ is a subgroup of $Z_p^*$ of order $q$, and ...
0
votes
0answers
12 views

How would I get started in auditing and finding vulnerabilities in encryption algorithms?

I know, it sounds dumb. Very dumb in fact. But regardless, I want to actually begin doing security research on cryptographic algorithms (SHA, RSA, ECDSA, etc.). I would prefer that this question be ...
0
votes
1answer
62 views

Combine signature with encryption

I have some embedded device for which I want to sign and encrypt firmware files. Firmware updates are generated by me and may be installed by the customer. The encryption is supposed to protect the ...
0
votes
0answers
26 views

Proof by reduction for for digital signature scheme $S_2((sk_0,sk_1), m):=(S(sk_0,m), S(sk_1,m))$

Let $(Gen,S,V)$ be a secure signature scheme (existentially unforgeable under a chosen message attack) with message space${\{0,1\}}^n$. Generate two signing/verification key ...
2
votes
1answer
117 views

Any ideas on login using Digital Signature PKCS

I am curious to know about possibility to login into web application just by identifying the user based on digital signature in usb token. any reference in this direction?
0
votes
1answer
31 views

How to devise cryptographic system with data-sharing ability and password reset

I originally posted this in the security.stackexchange forums but then I was directed to this one which seems more befitting for my question. I am writing a C# .NET application. For my application the ...
0
votes
0answers
35 views

Same private key for signing and decryption

I am designing a service which identifies records with public keys. All other fields are encrypted with that public key and protected by a HMAC. For authentication, I am thinking about signing ...
3
votes
0answers
62 views

Key strength comparison: symmetric key vs RSA/DH key

I came across different reputable sources quoting different equivalent symmetric key strengths for RSA/DH keys. This NIST paper (page 67) states the following offer corresponding security strenghts (...
1
vote
1answer
50 views

Manually creating a GPG Public Key

I want to manually create a GPG public key that can be imported into GPG, i.e. I want to create a file with a Public-Key Packet, a User ID Packet and a Signature Packet (for an example see here). I ...
1
vote
2answers
130 views

Sensible amateur usage of web crypto API

I want to know if my usage of the web crypto API is sensible. I want to use it for symmetric and public-key encryption and decryption, and signatures, but as a non-expert I am scared by the warning on ...
159
votes
4answers
107k views

Why is elliptic curve cryptography not widely used, compared to RSA?

I recently ran across elliptic curve crypto-systems: An Introduction to the Theory of Elliptic Curves (Brown University) Elliptic Curve Cryptography (Wikipedia) Performance analysis of identity ...
118
votes
6answers
77k views

Should we sign-then-encrypt, or encrypt-then-sign?

We regularly want to send messages that are both (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active ...
48
votes
3answers
34k views

Definition of textbook RSA

What is the definition of textbook or "raw" RSA? What are some of the properties of textbook RSA? How does it differ from other schemes based on RSA?
0
votes
1answer
887 views

RSA encryption/decryption process is not working correctly

I'm trying to apply the RSA cryptosystem to encrypt a byte M=72, using predefined modulus n, public key exponent ...
3
votes
1answer
124 views

Is choosing $1$ as a public exponent valid in RSA?

I know it will not encrypt anything. But is $1$ valid as a public exponent in an RSA public key?
0
votes
0answers
34 views

RSA encryption/decryption values not working as expected [duplicate]

I'm faced with an issue I can't seem to understand when it comes to RSA. Below are my values for all of the parameters, unfortunately I can't seem to get the expected decrypted values from my ...
1
vote
0answers
23 views

Generating a recovery phrase for a RSA key-pair

What is an optimal way to associate a RSA key-pair with a recovery phrase/seed for access recovery purposes? I've seen a lot of cryptocurrency wallets provide this feature, however, I'm not looking to ...
1
vote
2answers
352 views

Is it fair to say that MACs use a signing algorithm?

The Wikipedia page on MAC calls the algorithm that is used to generate the MAC as a signing algorithm. Is that a fair use of that term? Can we then say that HMAC-SHA-1 uses SHA-1 as the signing ...
7
votes
2answers
399 views

Calculating RSA Public Modulus from Private Exponent and Public Exponent

If I know the private and public exponents ($d$ and $e$) of an RSA key pair, is it possible to (efficiently) calculate the public modulus $n$?
5
votes
3answers
1k views

What is the purpose of Pseudorandom Function Families (PRFs)?

I'm currently in a course in Cryptography, and was wondering why pseudorandom function families exist at all. If there existed one pseudorandom function f(x), based on its definition, could that not ...
0
votes
0answers
35 views

How does CL signature work?

I'm studying the CL signature that how can it works. However, I cannot understand how equation (42) is calculated. What is the last three factors? The value T is as follows: $$T \leftarrow(A')^{\...
0
votes
0answers
79 views

Can we defends against RSA Timing attack when we use java.math.BigInteger.modPow?

I think that Montgomery and sliding window techniques are applied within java.math.BigInteger.modPow (and more specifically ...
3
votes
2answers
75 views

How to generate Multiple Encryption Keys for use in RSA polymorphic multiplication

I am a long time scroller, first time poster in the crypto stack. I've recently been finding myself leaving the realm of mainstream/standard crypto (imo that consists of symmetric/asymmetric ...
1
vote
1answer
49 views

Creating nested messages in OpenPGP

I need to create a nested message in OpenPGP (my understanding is that the protocol itself should support it). Let's say I have Payload ("Time in Lordran is ...
4
votes
2answers
2k views

Recovering private key from Secp256k1 signatures

I've seen many answers here and many articles that says we can recover the private key from reused R signatures. But, what if the r,s signatures are different in transaction of bitcoin then is there a ...
0
votes
0answers
22 views

Could someone please explain the implementation of public-private key encryption for storing passwords?

As someone new to cryptography,I have a question about how logins work on websites. I understand mathematically how asymmetric encryption works and how https web requests work to securely send ...
0
votes
2answers
105 views

Computing PGP ed25519 and curve25519 keygrips?

There are public key algorithmic differences for how PGP computes fingerprints and keygrips. For the v4 protocol, fingerprints are not exclusively computed from public keys while keygrips are. RFC ...
0
votes
0answers
56 views

Which public-key cryptosystems are used the most?

Does anybody know if there is some kind of measure on how often public-key cryptosystems like El Gamal, RSA,... are implemented. Which ones are most common?
2
votes
1answer
286 views

Revoke a GPG key using previously generated revoke certificate after renewd (change expiration date)

I have few sub-questions Do secret keys get expired, or just the public key gets expired? Do I have to back up the master sec key each time I renew it? For an ...
0
votes
0answers
17 views

How do NTLMv2 hashed passwords work?

We have an application which embeds NTLMv2 password hashes into its configuration. In attempting to assess the security of this practice, I'm not finding much straightforward information about how an ...
1
vote
2answers
57 views

How to derive a private/public keypair from a random seed?

For RSA, my understanding is that large primes are found randomly to build a private/public keypair. If a static seed can be used in that random search process, it should be possible to derive the ...
4
votes
2answers
269 views

Key Exchange vs Key Encapsulation

From what I understand, the steps of a key exchange protocol are Alice and Bob each encrypt something using their public key and private key and send the result to each other Alice and Bob each do ...
14
votes
2answers
2k views

Can I still use insecure curves/ciphers for time relevant encryption?

Can Ciphers that are known to be insecure because their keysize is considered too small still be used in appliances that have a tight decryption timeframe? In particular I am looking at ECC2K-130. ecc-...
0
votes
1answer
43 views

What if the CSR is intercepted in transit while sending it to CA?

I was studying PKI the other day and I had a serious thinking about the following question. What is CSR? - It is a block of encoded text that is given to the CA when applying for an SSL certificate ...
0
votes
0answers
23 views

Authentication using a nonce

For an authentication problem imagine the following scenario with two devices: 1 server 1 client. The client starts a conversation with the server and sends him his public key. All public keys in ...
6
votes
2answers
302 views

Why does Encrypt-Then-Sign not yield a CCA-secure public-key encryption scheme?

In symmetric cryptography, combining an IND-CPA secure symmetric encryption scheme with a secure MAC with the encrypt-then-MAC method yields a IND-CCA secure symmetric encryption scheme. I am trying ...
3
votes
1answer
52 views

What is the exact meaning of the public key cryptosystem properties in New Directions In Cryptography by Diffie and Hellman

I'm quite new to cryptography and don't have much mathematical knowledge. I'm studying cryptography, especially public key algorithms. I have some basic knowledge of public key algorithms so I know ...
1
vote
0answers
42 views

What's happening with IEEE 1363?

IEEE 1363 (or more precisely, IEEE 1363-2000) - the IEEE Standard Specifications for Public-Key Cryptography - has been inactive for so long, that it is now with status Inactive-Reserved by IEEE, and ...
0
votes
0answers
35 views

What is the code when looking at the LPN problem?

We are given the problem in this question. We know that we have to use the algorithm $A_D$ in order to get $e_i$. Our idea is that we construct a vector $l$ of $l_i$'s by getting $n$ samples from the $...
4
votes
1answer
46 views

Can libsodium's X25519 encryption construction be generalized?

It is my understanding that libsodium's sealed_box is based on X25519, a Diffie-Hellman function: By combining the X25519 key agreement with a symmetric cipher and having a recipient derive the ...
0
votes
1answer
83 views

TLS 1.2 AES-GCM decryption problem

I'm trying to decrypt a PCAP encrypted with TLS 1.2. I have the private key and Wireshark is able to decrypt the data so what I am doing should work but there is obviously something wrong. The ...
3
votes
0answers
111 views

Solving LPN using algorithm for syndrome decoding

Given an algorithm $A_D$ which solves an instance of the decoding problem $e \in \mathbb{F}_2^n$ in time $T_D$ given a parity check matrix $H \in \mathbb{F}_2^{(n-k)\times n}$ and a syndrome $s \in \...
0
votes
0answers
46 views

How to get fixed m from different pairs of n, e and c in RSA?

In RSA cryptosystem, if I have two (or more) pairs of public key and also the corresponding ciphertexts, can I get the fixed message from them? I cannot think up any good idea for now.
6
votes
1answer
133 views

Why is recipient hashed in this Sign/Encrypt/Sign proposal?

Own research In my journey into trying to understand PGP, and public key signing and encryption as a whole, I came across this answer on CE. It is an answer to a question with the title: Should we ...
115
votes
7answers
68k views

How big an RSA key is considered secure today?

I think 1024 bit RSA keys were considered secure ~5 years ago, but I assume that's not true anymore. Can 2048 or 4096 keys still be relied upon, or have we gained too much computing power in the ...
0
votes
0answers
19 views

Can we use HMQV in an asynchronous setting?

Following the HMQV paper, to perform a key-exchange, Alice ($\hat{A}$) and Bob ($\hat{B}$) perform the following: $\hat{A}$ generates the long-term key pair ($sk_A= a$, $pk_A =g^a$) and the ephemeral ...
6
votes
2answers
545 views

Does Cramer-Shoup allow re-randomization?

Is it possible to re-randomize a ciphertext with the Cramer-Shoup System? I have some Cramer-Shoup ciphertexts and i want to re-randomize them, so they look different and are unlinkable to there ...
28
votes
2answers
28k views

Why is asymmetric cryptography bad for huge data?

I've been told that asymmetric cryptography requires that the message to be encrypted be smaller than its key length. Why is this? I know about hybrid encryption, which uses symmetric encryption to ...
0
votes
0answers
31 views

Encrypt encryted message vs DS

In digital signature The encrypted message is signed by the sender private key and verify using sender public key. The encrypted message is encrypted with another public private key pair which the ...
1
vote
1answer
47 views

Interchangeability of hash outputs

I'm looking at tweetnacl, its crypto_sign_keypair, crypto_sign, and crypto_sign_open ...

1
2 3 4 5
35