cheng/libsodium
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Faster scalarmult_base() when using the ref10 implementation.

Browse Source 
Use the Ed25519 scalar multiplication function followed by a conversion to
Montgomery coordinates to generate X25519 public keys.

Suggested a while ago by @CodesInChaos
This commit is contained in:
Frank Denis 2015-12-17 00:49:59 +01:00
parent f430f3a936
commit 03973542c7
1 changed files with 25 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
src/libsodium/crypto_scalarmult/curve25519/ref10/x25519_ref10.c
View File

@ -10,8 +10,6 @@
#include "../scalarmult_curve25519.h"
#include "../../../crypto_core/curve25519/ref10/curve25519_ref10.h"
static const unsigned char basepoint[32] = {9};
/*
Replace (f,g) with (g,f) if b == 1;
replace (f,g) with (f,g) if b == 0.
@ -218,11 +216,35 @@ crypto_scalarmult_curve25519_ref10(unsigned char *q,
return 0;
}
static void
edwards_to_montgomery(fe montgomeryX, const fe edwardsY, const fe edwardsZ)
{
fe tempX;
fe tempZ;
fe_add(tempX, edwardsZ, edwardsY);
fe_sub(tempZ, edwardsZ, edwardsY);
fe_invert(tempZ, tempZ);
fe_mul(montgomeryX, tempX, tempZ);
}
static int
crypto_scalarmult_curve25519_ref10_base(unsigned char *q,
const unsigned char *n)
{
return crypto_scalarmult_curve25519_ref10(q,n,basepoint);
unsigned char e[32];
ge_p3 A;
fe pk;
unsigned int i;
for (i = 0;i < 32;++i) e[i] = n[i];
e[0] &= 248;
e[31] &= 127;
e[31] |= 64;
ge_scalarmult_base(&A, e);
edwards_to_montgomery(pk, A.Y, A.Z);
fe_tobytes(q, pk);
return 0;
}
struct crypto_scalarmult_curve25519_implementation