# Questions tagged [secp256k1]

This tag should be used for anything related to the secp256k1 algorithm used for Bitcoin's public key cryptography.

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### On an Elliptic Curve is that possible that from $P$ we can tell if $a$ is quadratic residue modulo $N$?

Imagine that, On an Elliptic Curve cryptography scheme where $P=a\times G$, Bob shares his public key $P$ with Eve (the devil who wants to know secrets he is not supposed to). Bob has also revealed a ...
58 views

### The better algorithm for Modular Exponentiation on secp256k1/r1

I know Modular Exponentiation ($r = b^e \bmod m$) is important for RSA, and I can find some algorithm that if e is expressed in binary form (for exp: )--in such way for a n-bit long e, one can expect ~...
9 views

### How to calculate a valid signature? [migrated]

I am trying to create a signature that is valid on https://etherscan.io/verifySig, but it shows always that my signature is invalid: I created a random private and public key: ...
54 views

### Chinese remainder theorem in ECDSA for parameters in secp256k1?

It is known that it is possible to apply the Chinese remainder theorem and attack RSA under precise conditions. https://tls.mbed.org/public/WSchindler-...
36 views

### Is it safe to implement elliptic curve Diffie Hellman with secp256k1

I need to implement X3DH Key Agreement Protocol according to Signal specification, in the document they suggest using either X25519 or X448 curves. I assume those curves have been chosen for this ...
89 views

### How to calculate the order of secp256k1?

The elliptic curve secp256k1 is defined as $y^2 = x^3 + 7$. The prime for the field is set to: ...
111 views

### ECC Point Addition on Jacob coordinate -- Not Commutative?

I have a python script that does the ECC point addition (code paste below), it simply performs the P =Q1+Q2 on Jacob coordination. However, when doing some regression tests, I found that if I exchange ...
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### Is it acceptable to use a HMAC-SHA256 hash as a secp256k1 private key?

Say I want to generate a deterministic private key related to some data, for instance to a domain name. The easiest way I can think of is: take a secret material which will work as "generator&...