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# Questions tagged [x25519]

Curve25519 is an elliptic curve offering 128 bits of security (256 bits key size) and designed for use with the elliptic curve Diffie–Hellman (ECDH) key agreement scheme.

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### Summarize the mathematical problem at the heart of breaking a Curve25519 public key

It's pretty easy to generate a Curve25519 private key: generate 32 random bytes of data and then do: e[0] &= 248 e[31] &= 127 e[31] |= 64 You can then ...
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### Difference between X25519 vs. Ed25519

I am reading https://en.wikipedia.org/wiki/Curve25519 and it states Also in 2018, RFC 8446 was published as the new Transport Layer Security v1.3 standard. It requires mandatory support for X25519, ...
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### Distinguishing x25519 public keys from random?

I recently read a piece of protocol that avoided sending ephemeral x25519 keys in the clear as an effort to foil deep-packet inspection. I understand that x25519 public keys are effectively 255 bits, ...
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### curve25519 weak points for contributory behaviour

The Diffie-Hellman on curve25519 is usually calculated using the base point $(9,…)$ which induces a cyclic subgroup of $G:=\{\infty\}\cup(E(F_{p^2})\cap(F_p\times F_p))$ with index 8, i.e. there is a ...
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### Curve 25519 (X25519, Ed25519) Convert coordinates between Montgomery curve and twisted Edwards curve

I have some misunderstanding about EdDSA conversion coordinates between Montgomery curve and twisted Edwards curve. In https://www.rfc-editor.org/rfc/rfc7748 I see that a base point for Curve25519 is ...
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### Is using different public keys for different peers safer than reusing the public key, beyond forward secrecy?

In X25519 (ECDH over Curve25519) Peer A and B exchange their Public Keys ...
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