NAME

#include <monocypher.h>

void
crypto_x25519_inverse(uint8_t blind_salt[32], const uint8_t private_key[32], const uint8_t curve_point[32]);

DESCRIPTION

The crypto_x25519_inverse() function performs scalar multiplication of the multiplicative inverse of a scalar for X25519. This is a highly advanced, specialized feature; unless you are implementing a protocol that requires this specifically, you likely have no reason to be using these functions and are probably looking for crypto_x25519() instead. Expect elliptic curve jargon on this page.

This function is used, for example, with exponential blinding in oblivious pseudo-random functions (OPRFs). The arguments are:

blind_salt

The output point.

private_key

The private key (scalar) to use. First, the value is clamped, then the clamped value's multiplicative inverse (modulo the curve order) is determined. The clamped value's multiplicative inverse then has its cofactor cleared, and that final value is then used for scalar multiplication.

curve_point

The curve point on X25519 to multiply with the multiplicative inverse (modulo the curve order) of private_key.

SEE ALSO

crypto_x25519(), intro()

HISTORY

The crypto_x25519_inverse() function first appeared in Monocypher 3.1.0.