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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 ...
Kevin Burke's user avatar
20 votes
2 answers

Difference between X25519 vs. Ed25519

I am reading 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, ...
ams's user avatar
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23 votes
1 answer

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, ...
Jonas's user avatar
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11 votes
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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 ...
Perseids's user avatar
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10 votes
3 answers

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 I see that a base point for Curve25519 is ...
sribin's user avatar
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4 votes
2 answers

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 ...
ustulation's user avatar
2 votes
1 answer

Ed25519 to X25519 transportation

Using montgomeryX = (edwardsY + 1)*inverse(1 - edwardsY) mod p it is possible to transport an Edwards curve point (Ed25519 ...
FooBar's user avatar
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1 vote
1 answer

Proof of possession. x25519 + ed25519

There are Client and Server. Client have previously send public keys for x25519 and ed25519 to the server. And now need to prove that it has private keys for them. I have found similar solutions in ...
Alexander Smirnov's user avatar