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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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22 views

ECDH: create Public Key from x, y coordinates [on hold]

I have the x, y coordinates of a EC public key ( i have the bytes also ). I need to convert the x,y coordinates bytes into a ECPublicKey. ...
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0answers
53 views

Hint for needed hardness assumption

Suppose we have a type-3 pairing $(q,\mathbb{G_1},\mathbb{G_2},\mathbb{G_T},g_1,g_2,e)$, that holds $SXDH$ assumption. Given $(g_1,g_1^a,g_1^b,g_1^c,g_1^m,g_1^{m'},g_1^{a\cdot m}, g_1^{b\cdot m'},...
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2answers
115 views

Append text to file without decrypting & encrypting again

Is it possible to add a line to a file which is encrypted symmetrically or asymmetrically (private key refers to readkey below, public key refers to append key then) without decrypting it? I was ...
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1answer
94 views

Why would an efficient integer factorization algorithm render RSA insecure?

I know that RSA relies on the integer factorization problem: given two primes p and q, their product p . q is easy to compute. But not feasible (i.e., polynomial-time) an algorithm is known that could ...
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0answers
41 views

Compute discrete logarithm with prime modulus

Given a cyclic group $G=<g>$ with known order which is divisible by $3$. How can we efficiently compute the discrete logarithm $x$ to base $g$ modulo $3$ of an arbitrary element $y=g^x\in G$? ...
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2answers
64 views

Does this “protocol” ensure only the users may learn the secret data?

EDIT: I have only left this as historic question asking, please see my proposed Answer below as a better protocol, since the original question was very broken. I need to build a website where one ...
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1answer
29 views

Hybrid encryption for MQTT payload?

i've written a simple code for payload encryption, i'v done it with AES-128 CBC mode ,it works fine ,the senario is very simple : the publisher send a JSON payload format that includes the encryption ...
1
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1answer
37 views

What is a 'known answer test' (KAT)?

Came across this concept on while reading up on the key-encapsulation protocol SIKE but haven't been able to find a good explanation of what a known answer test is formally. What is a known answer ...
2
votes
1answer
28 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 ...
1
vote
1answer
39 views

Limiting how many key pairs someone can generate without compromising their keys

Is there any way to assign someone a limited quota for how many cryptographic key pairs they can generate (ECC, RSA, any algorithm), and preferably non-interactively? By non-interactively I mean there ...
2
votes
3answers
185 views

Why is it impossible to find the private key from the public key?

From what I understand, based on the article A Beginner’s Guide: Private and Public Key Cryptography Deciphered, the public key is generated by performing $n$ tangent plus mirroring operations from ...
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0answers
28 views

Calculating private key from a chosen public key for Feige-Fiat-Shamir scheme

Motivation: This paper suggest calculating the private like so: *Precalculation: An arbitrator generates a random modulus $n$ (512-1024 bits) which is the product of two large primes.The arbitrator ...
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0answers
34 views

Decrypt SSL traffic with the OpenSSL command line [migrated]

I'm trying to do some manual data extraction/encryption/decryption with openssl command line. I've been reviewing RFC5246 to work out what I need to do. It is not crystal clear to me if I am going to ...
1
vote
0answers
38 views

Where shoul I store private/public keys and how should I share it?

I'm new in terms of encryption and I have to encrypt the data between two Java Spring applications, one have serves as MVC framework and other as Web Service, I'm implementing an asymmetric encryption ...
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1answer
34 views

Understanding certificates for public keys with subkey

I have a openpgp key with 3 subkeys: ...
0
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1answer
49 views

How could an offline app verify a signature from one of many private keys?

I have a situation where an offline app needs to be able to verify whether some data was created by a set of privileged users of the app. These privileged users will each have one private key of some ...
-1
votes
1answer
34 views

I am new to digital certificate 509V3 concept. can some one please clarify the below points [closed]

I am using RSA 2048 with SHA 256 primitive in certificate: How to verify the user certificate n + 1 with Root certificate n? why it is required to perform Certificate chain verification? How to ...
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1answer
43 views

Schnorr Pubkey Recovery

As per How does recovering the public key from an ECDSA signature work? , it's possible to recover public keys from ECDSA signatures. Is this possible for EC-Schnorr signatures as well? I'm looking ...
2
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0answers
51 views

Curve25519 / Ed25519 - Generate a private key from this term

I have 2 key pairs $(x_1, y_1)$, $(x_2, y_2)$. I also have $a = $random 256-bit array and $b = $256-bit of defined values from me. I know the values for $(x_1, y_1)$, $x_2$ and $b$. But I miss the ...
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1answer
64 views

Decode & Verify Base64urlUInt-encoded RS256 Public Key from Google

According to Google, to access the id_token it sends along with Access Tokens (for accessing their API), you must first validate the token using the RS256 Public Key available from this page. The ...
1
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0answers
70 views

ECC Curve25519: How to generate this kind of private key? / Strange key exchange mechanism

I'm currently reverse engineering a program that uses Curve25519 key exchange in network communication. I have only a basic understanding of ECC, so maybe this thing just seems strange to me. The ...
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2answers
65 views

Public-key generation - primes reuse

Given the following Trap-door Commitment scheme Secret key receiver: $x_B \in_u Z_q$ Public key receiver: $y_B = g^{x_B} \mod p$ Here, $p=q*k+1$ for two primes $p,q$ and $k \in Z$. And $g$ is the ...
2
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1answer
40 views

Using nested signatures to trust public key of inner signatures

I have a scenario where entity $A$ has an unauthentic copy of the public key $P_B$ of $B$ and an authentic copy of $P_C$ of $C$, trusted by both $A$ and $B$. Now $A$ wants to establish trust in $P_B$...
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1answer
17 views

How can one validate with a public key a JWT signature generated with a private key?

As I understand it, a JSON Web Token (JWT) consists of 3 parts: the header, specifying the hashing algorithm to use for the signature; the payload itself; and the signature, which is a hash of the ...
2
votes
3answers
65 views

Difficulty deciphering the RSA algorithm

$d = 27, e = 3, n = 40$ For encryption, I have the letter T converted to 084 by the ASCII table, which encrypts to $24$ by $84^...
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1answer
52 views

Differences between ECIES and DHIES

I'm studying the Integrated Encryption Scheme and I did't understand which are the main differences between ECIES and DHIES. Can someone help me ? Thank you in advance.
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0answers
13 views

In PKEET, OW-CCA definition, I can not understand their OW-CCA security model?

Specifically in "Probabilistic Public Key Encryption with Equality Test" article? In the article, OW-CCA definition author shown two decryption queries in random oracle model. On first Queries, ...
1
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1answer
46 views

Is K=1 a valid random integer in ElGamal signature?

In the ElGamal signature scheme, in addition to the public/private keypair, a random integer $K$ such that $\operatorname{gcd}(K,p-1)=1$ is chosen in the range $[1,p-1]$. This clearly excludes $K=p-1$...
3
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2answers
72 views

Encoding Public Keys

We would like to encode ECDSA Public Key specifically keys generated using the ed25519 for storage . What is the best and less error prone method , for now we think about using Hex strings or Base64 ...
4
votes
0answers
43 views

Where do the PKs come from in Bluetooth device?

I am studying the Elliptic Curve Diffie-Hellman (ECDH) on Bluetooth 4.2. There are some questions about the PK.. Where do these public and private keys come from? Who defines them? and Will it ...
0
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1answer
67 views

Is this RSA / SRA cipher modification secure?

I have modified SRA algorithm to suit my problem and I'm wondering if it is still safe to use. Main question is if RSA Encryption key that contains even number is a safe one way function? In RSA ...
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0answers
14 views

JWK vs. raw for key wrapping

Context (TLDR below) So I’m developing an application that uses a high-iteration-count PBKDF2 algorithm to derive a symmetric AES-GCM key from a user-provided (enforced to be reasonably strong) ...
4
votes
2answers
328 views

Elliptic curve and “vanity” public keys

I want to find an algorithm to get a private/public key pair where one coordinate of the public key has some specific prefix (for example: 20 leading zeroes). In the secp256k1 case (the Bitcoin curve),...
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1answer
89 views

Recovery public key from secp256k1 signature and message [closed]

Regarding this article about a signature recovery However, with the signature and the message that was signed, and the knowledge of the curve, it is possible to generate two public keys So we can ...
1
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1answer
55 views

Comparing stronger vs. weaker assumptions

If I have to argue that an assumption A is stronger than B, should I argue this way:- An adversary breaking the security of A does not translate to breaking the security of B. But, if an adversary ...
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1answer
25 views

Are there any “cumulative signatures” for decentralized networks?

Lets assume that there is a decentralized network $N$ with participants $A,B,C, D$ and that there was a message $m$ that all of $A,B,C,D$ agreed to. An outsider $X$ wants to know via signatures that $...
5
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0answers
42 views

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

Own research In my journey into trying to understand PGP, and public key singing and encryption as a whole, I came across this answer on CE. It is an answer to a question with the title: Should we ...
3
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1answer
84 views

Why ISO/IEC 9796 (signature with message recovery) instead of just encrypt the short message with private key?

I've had a look at “Practical Cryptanalysis of ISO/IEC 9796-2 and EMV Signatures” and read the very good answer https://crypto.stackexchange.com/a/17846/59673 and I understand that signature and ...
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1answer
56 views

How to define a FHE scheme whose plaintext space is infinite using boolean circuits?

There are many kinds of fully homomorphic encryption scheme by using boolean circuits. And the plaintext space $\mathcal{P} = \{ 0,1 \}$. If there is a -bit FHE scheme, we can construct a FHE scheme ...
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0answers
26 views

Proof of work using any computational puzzles

if we have a system in which any user can send arbitrary messages of his choice, and any one can receive that message. So a malicious user can send any messages which may lead to DOS attacks. Any ...
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1answer
90 views

Half of any bitcoin (crypto) public key - (public key half) is possible

I found a topic on bitcointalk Public key x and y == Double(Half of the Public key x and y) half any public key is possible how that possible , in crypto there is subtraction and multiplication ...
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1answer
38 views

Is it possible to manage an encrypted dataset for face recognition?

Im in my final year of PhD in computer vision and my supervisor has given me a task that I am not very familiar with. So I am teaching myself homomorphic encryption everyday. This question is mostly ...
0
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1answer
60 views

Calculating distance between two vectors using Paillier homomorphic encryption [closed]

I am basically trying to perform euclidean distance calculation in the encrypted domain (Paillier encryption). Using the homomorphic properties of Paillier, the squared euclidean distance formula can ...
5
votes
1answer
90 views

Ed25519 PKCS8 private key example from IETF draft seems malformed

Malformed PKCS8 Key Algorithm Identifiers for Ed25519, Ed448, X25519 and X448 for use in the Internet X.509 Public Key Infrastructure § 10.3. Examples of Ed25519 Private Key states the following: <...
0
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0answers
33 views

Can a PKE scheme whose plaintext space is infinte also be regarded as a 1-bit PKE scheme?

Let $\Pi = (G,E,D)$ be a 1-bit PKE scheme, now I consturct a PKE scheme $\Pi' = (G', E', D')$ as follow $$(pk',sk') \leftarrow G'(k): (pk,sk) \leftarrow G(k);~ u,v \leftarrow \{0,1\}^k;~ pk' \...
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1answer
121 views

ECDSA vulnerability related to recovering private key using same r

I'm considering this for bitcoin transaction as it uses ECDSA so if the signer generates two signatures suppose s1 and s2. where: I get it that any attacker who have s1 and s2 can recover its private ...
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1answer
50 views

How to distinguish between private key and public which are visible in text editors?

I would like to know how to understand which one is private key and public key while seeing them in raw text format?
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0answers
23 views

How to assert that n distinct users have generate an aggregate signature?

If We have n users, each one generate message m1 and signs it to generate (σ1). then by using aggregate signature scheme, we get the aggregate signature of all messages m from n users. Is there a ...
9
votes
1answer
832 views

After ECDH with Curve25519, is it pointless to use anything stronger than AES128?

Is the following reasoning correct: After ECDH with Curve25519, the resulting shared secret will be an EC public key with a bit strength of 128 bits. This public key would then be hashed (let's say ...
3
votes
2answers
98 views

Generating secure short activation code for offline applications

My application is as follows User has a hardware system (with an unique ID) that does not have connectivity but has a keypad for input. To make the hardware operational, the user has to go to central ...