# Tagged Questions

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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### Re-sending captured encrypted data

Let’s assume Bob is some algorithmic stock trading machine. Bob takes commands from Alice, who sends messages to Bob. For example: Alice could be sending a message to Bob to stop trading. But if ...
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### 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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### 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 is 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 ...
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### Determine if a public key point y is negative or positive, odd or even?

Take an elliptic curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point? Examples: Private key 1 -> (x,...
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### Is reverse NTRU still secure?

I'm currently prototyping something with the NTRU encryption scheme but I wish to use it in "reverse" -- distribute private keys so anyone can decrypt, but keep the public keys secret and thus only ...
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### Digital signatures using a partially public key

I'm thinking to sign a message using a key that is made up of a publicly shared key and a privately shared key. The operation for mixing the two keys could be concatenation, if it suffices. To ...
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### How is a public/private key pair generated from a Diffe-Hellman key exchange?

I very well understand the DH key exchange. But what is the public key and private key at the end of the exchange. For example: Alice and Bob agree to use a modulus $p = 23$ and base $g = 5$ (which ...
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### Using related pair of cryptographic keys to open/seal plaintext

I am using curve25519xsalsa20poly1305/fn.seal from sodiumoxide crate written in Rust language which is a wrapper over libsodium ...
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### Adding two RSA private key

We've constructed a new private RSA key from two known private RSA keys $Priv_1$ and $Priv_2$ as follows: $$p = next\underline{}prime\left(\frac{Priv_1(p) + Priv_2(p)}{2}\right)$$ and q = next\...
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### What are the practical limitations of Asymmetric encryption vs Symmetric encryption? [duplicate]

I hear it commonly said that the advantages of Symmetric encryption are speed and no limit to the amount of data that can be symmetrically encrypted. I also hear it commonly said that the advantages ...
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### Security of a signature scheme based on both factoring and discrete logarithms

I have seen this paper: A New Signature Scheme Based on Multiple Hard Number Theoretic Problems by Ismail and Tahat: In this paper, we propose a new signature scheme based on two hard number ...
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### How to deliver an encrypted message to multiple recipients without revealing keys

Let's say I have generated a private and a public key. I create a message and encrypt it with the public key. I deliver this encrypted message and a private key to multiple recipients. Why would I do ...
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### Is it safe to reuse a symmetric key when using asymmetric encryption?

I've written a C# Library that I hope will be used for security purposes in a commercial application. The application will communicate through the internet and not on an internal network. I am using ...
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### What is stopping someone from saving encrypted info, and decoding it later?

When I send encrypted data to a website, using public key encryption, what is stopping someone who is listening from storing my encrypted data, and decryption it in a few years after they have ...
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### Envelope Encryption with asymmetric keys vs KMS

In Envelope encryption a symmetric secret key is used to sign the data and then another key is used to encrypt the secret to produce an encrypted secret key. The encrypted messages is packaged with ...
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### Knowing pre-encryption data, can we find the private key CryptoWall used?

I'm just repurposing a question already asked about Cryptolocker for CryptoWall: "If we know exact contents of some of the files prior to them being encrypted, would it be feasible to use those ...
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### How feasible would it be to generate 300 million public key pairs in 8 hours?

Assume there is a hypothetical situation where one would need to generate hundreds of millions of public key pairs of reasonable strength in a limited time. What would be required in terms of ...