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1 vote

Sending encrypted message without public key from recipient (elgamal)

If Bob was using an ephemeral key pair when encrypting for Alice, then Bob would need to send his permanent public key as the message in order for Alice to receive it. There is no way Alice could ...
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1 vote

Isn't an asymmetric cipher (like RSA) algorithm sufficient for all basic needs, when speed is irrelevant?

For the same key sizes, symmetric encryption protocols are safer than asymmetric protocols. Informally, the cryptanalysis algorithms used to decipher RSA try to identify the prime values used to ...
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2 votes

Isn't an asymmetric cipher (like RSA) algorithm sufficient for all basic needs, when speed is irrelevant?

Beware that beside RSA, we don't know many "asymmetric block ciphers" per the question's definition (essentially trapdoor permutations), thus building over this won't allow substitution with ...
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0 votes

How to use symmetric encryption on 1on1 and group chat messenger?

Here are some resources which might help you understand your problem. This kind of use-case lends itself to the use of public key cryptography. Secure messaging protocols of this form already exist - ...
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2 votes

Is this AES GCM + asymmetric schema secure?

NaCL provides a set of crypto_box methods which do this all in one go. Libsodium provides an even easier set of crypto_box_easy ...
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1 vote
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Classical vs Quantum-Safe Algorithms and Protocols / Application Approach

Various proposals are being explored for X509 V3 certificates in a Post Quantum Cryptography (PQC) world. Is this understanding, correct? In my view, there are essentially two way to have both ...
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0 votes

Sharing RSA private keys using key exchange algorithms like Diffie–Hellman Algorithm?

This is going in the wrong direction, so I'll answer by showing two alternatives: Share e.g. a strong machine generated password for this with enough randomness to pass as a secret key. The reason to ...
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4 votes
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Questions on "A CERTIFIED DIGITAL SIGNATURE" Pg. 19

Yes, that is correct. No, the value $f^{16}(x)$ should be thought of as computed and published prior to any signatures being generated. Only if the signer has the foresight to compute and publish $f^n(...
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1 vote
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Public-key/asymmetric encryption where you can only leak the decrypted message by leaking your password

I think I found a solution to make this possible! The key concept is called Deniable Authentication, and the purpose is to know who's sending a message, but not being able to prove it to others. A ...
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0 votes

Public-key/asymmetric encryption where you can only leak the decrypted message by leaking your password

I believe what you are looking for is impossible. However, I will suggest you another way to tackle this issue that might be helpful which is based on plausible deniability. First, I'll try to explain ...
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1 vote
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How does the KeyGen of Merkle's improvement of Lamport's OTS work?

You only need to store the hash values for the 1s. The checksum bits at the end (which encode the number of 0s) ensure that messages cannot be crafted in such a way to flip 1s down to 0s as doing so ...
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0 votes

Best way to encrypt sensitive data on server with HSM and symmetric keys

Since this a more of a theoretical SE, I will make a more generic theoretical approach along with some specific details. You have to define a threat model at first. To define it, there are a bunch of ...
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3 votes

Public-key/asymmetric encryption where you can only leak the decrypted message by leaking your password

Your idea of an encryption method including a nonce, and in a way that Alice cannot recover the nonce is practical; however it doesn't solve your problem. One possibility would be a variant of El ...
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2 votes

ElGamal-based BBS proxy re-encryption implementation?

There's a Python implementation in the Charm Crypto library: https://github.com/JHUISI/charm/blob/dev/charm/schemes/prenc/pre_bbs98.py
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3 votes
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Lamport Diffie One-time Signature

I am going through the Lamport Diffie One-time signature. As a side note; this work is an early effort that culminated in what is known as "Stateful Hash Based Signature Methods"; modern ...
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1 vote

Do you know protocols, where it is necessary to obtain several "independent" points on the same elliptic curve?

Your question is essentially: Is it useful to be able to sample a tuple $(Q_1, Q_2, \dots, Q_n) \in E(F)^n$ such that no relation is known among the points, but the tuple is not sampled from the ...
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1 vote
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Can Bob and Alice do an authenticated Diffie–Hellman key exchange if Bob only knows the hashsum of Alice's key?

Correct, Bob can be sure there is no man-in-the-middle attack when initiating communication with Alice, as long as he has been reliably informed of the hash of Alice's public key and the hash is ...
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2 votes

Do you know protocols, where it is necessary to obtain several "independent" points on the same elliptic curve?

There is a "hash-to-point" function used in several schemes, where it is necessary to generate an EC point where the discrete log w.r.t. any other EC point is unknown. In particular: A ...
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8 votes
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Do you know protocols, where it is necessary to obtain several "independent" points on the same elliptic curve?

Do you know protocols where it is necessary to obtain several "independent" points on the same elliptic curve? One obvious place where this occurs if you are implementing a Pedersen ...
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0 votes
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RSA Algorithm: What are the maximal possible locks that your friend can have so that he/she can secretly share that to you?

CAUTION: There's is something so wrong in the question that it's reasonable to dismiss it, see second section. But first let's try to answer it as if we didn't notice. In one of several slightly ...
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3 votes
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Is it theoretically possible to delegate public key generation?

If I understand your scheme correctly, then Alice needs a separate secure channel to communicate $i$ to Bob. Monero solves this problem by creating a one-time destination public key every time funds ...
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