File syn_x25519.h¶

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X25519 Diffie-Hellman key exchange — RFC 7748, pure C99. More...

#include <stdint.h>

Public Functions¶

Type	Name
void	syn_x25519 (uint8_t shared_out, const uint8_t scalar, const uint8_t point) X25519 scalar multiplication.
void	syn_x25519_pubkey (uint8_t public_out, const uint8_t private_key) Derive a public key from a private key.

Public Static Functions¶

Type	Name
void	syn_x25519_clamp (uint8_t key) Clamp a 32-byte private key per RFC 7748.

Detailed Description¶

Elliptic-curve Diffie-Hellman on Curve25519 using the Montgomery ladder. Provides shared-secret computation and public-key derivation.

This is the most computationally expensive WireGuard operation (~1–2 seconds on Cortex-M4 @ 64 MHz) but only runs during handshake, not on every packet.

** **

uint8_t my_priv[32], my_pub[32], shared[32];

// Generate keypair (private key = 32 random bytes, then clamp):
fill_random(my_priv, 32);
syn_x25519_clamp(my_priv);
syn_x25519_pubkey(my_pub, my_priv);

// Compute shared secret with peer's public key:
syn_x25519(shared, my_priv, peer_pub);

Public Functions Documentation¶

function syn_x25519¶

X25519 scalar multiplication.

void syn_x25519 (
    uint8_t shared_out,
    const uint8_t scalar,
    const uint8_t point
)

Computes shared = scalar * point on Curve25519.

Parameters:

shared_out Output: 32-byte shared secret.
scalar 32-byte private scalar (should be clamped).
point 32-byte public point (peer's public key).

function syn_x25519_pubkey¶

Derive a public key from a private key.

void syn_x25519_pubkey (
    uint8_t public_out,
    const uint8_t private_key
)

Computes public = scalar * basepoint (the Curve25519 generator, u=9).

Parameters:

public_out Output: 32-byte public key.
private_key 32-byte private key (should be clamped).

Public Static Functions Documentation¶

function syn_x25519_clamp¶

Clamp a 32-byte private key per RFC 7748.

static inline void syn_x25519_clamp (
    uint8_t key
)

Sets bits to ensure the scalar is a multiple of the cofactor (8) and has the high bit set for constant-time operation.

Parameters:

key 32-byte key to clamp (modified in place).

The documentation for this class was generated from the following file src/syntropic/crypto/syn_x25519.h