diff options
| author | Jason A. Donenfeld <Jason@zx2c4.com> | 2018-02-25 21:16:05 +0100 |
|---|---|---|
| committer | Jason A. Donenfeld <Jason@zx2c4.com> | 2018-03-09 13:47:23 +0100 |
| commit | 75fc8d9bcf6d917d2cefc456cf7b0c64ab63c243 (patch) | |
| tree | 840961255d8f40510843839a4c7f21830c6f7a5b | |
| parent | 186be2742c948351c27bc068102252e10a28959b (diff) | |
curve25519: use cmov instead of xor for cswap
Also add cselect optimization.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
| -rw-r--r-- | src/crypto/curve25519-x86_64.h | 51 |
1 files changed, 39 insertions, 12 deletions
diff --git a/src/crypto/curve25519-x86_64.h b/src/crypto/curve25519-x86_64.h index 49120bd..ba857ca 100644 --- a/src/crypto/curve25519-x86_64.h +++ b/src/crypto/curve25519-x86_64.h @@ -1657,16 +1657,43 @@ static __always_inline void fred_eltfp25519_1w(u64 *const c) : "memory", "cc", "%rax", "%rbx", "%rcx", "%rdx"); } -static __always_inline void cswap(u64 bit, u64 *const px, u64 *const py) +static __always_inline void cswap(u8 bit, u64 *const px, u64 *const py) { - int i; - u64 mask = 0ULL - bit; + u64 temp; + asm volatile( + "test %9, %9 ;" + "movq %0, %8 ;" + "cmovnzq %4, %0 ;" + "cmovnzq %8, %4 ;" + "movq %1, %8 ;" + "cmovnzq %5, %1 ;" + "cmovnzq %8, %5 ;" + "movq %2, %8 ;" + "cmovnzq %6, %2 ;" + "cmovnzq %8, %6 ;" + "movq %3, %8 ;" + "cmovnzq %7, %3 ;" + "cmovnzq %8, %7 ;" + : "+r"(px[0]), "+r"(px[1]), "+r"(px[2]), "+r"(px[3]), + "+r"(py[0]), "+r"(py[1]), "+r"(py[2]), "+r"(py[3]), + "=r"(temp) + : "r"(bit) + : "cc" + ); +} - for (i = 0; i < NUM_WORDS_ELTFP25519; ++i) { - u64 t = mask & (px[i] ^ py[i]); - px[i] = px[i] ^ t; - py[i] = py[i] ^ t; - } +static __always_inline void cselect(u8 bit, u64 *const px, u64 *const py) +{ + asm volatile( + "test %4, %4 ;" + "cmovnzq %5, %0 ;" + "cmovnzq %6, %1 ;" + "cmovnzq %7, %2 ;" + "cmovnzq %8, %3 ;" + : "+r"(px[0]), "+r"(px[1]), "+r"(px[2]), "+r"(px[3]) + : "r"(bit), "rm"(py[0]), "rm"(py[1]), "rm"(py[2]), "rm"(py[3]) + : "cc" + ); } static void curve25519_adx(u8 shared[CURVE25519_POINT_SIZE], const u8 private_key[CURVE25519_POINT_SIZE], const u8 session_key[CURVE25519_POINT_SIZE]) @@ -1741,8 +1768,8 @@ static void curve25519_adx(u8 shared[CURVE25519_POINT_SIZE], const u8 private_ke sub_eltfp25519_1w(D, X3, Z3); /* D = (X3-Z3) */ mul_eltfp25519_2w_adx(DACB, AB, DC); /* [DA|CB] = [A|B]*[D|C] */ - cswap(swap, A, C); - cswap(swap, B, D); + cselect(swap, A, C); + cselect(swap, B, D); sqr_eltfp25519_2w_adx(AB); /* [AA|BB] = [A^2|B^2] */ add_eltfp25519_1w_adx(X3, DA, CB); /* X3 = (DA+CB) */ @@ -1940,8 +1967,8 @@ static void curve25519_bmi2(u8 shared[CURVE25519_POINT_SIZE], const u8 private_k sub_eltfp25519_1w(D, X3, Z3); /* D = (X3-Z3) */ mul_eltfp25519_2w_bmi2(DACB, AB, DC); /* [DA|CB] = [A|B]*[D|C] */ - cswap(swap, A, C); - cswap(swap, B, D); + cselect(swap, A, C); + cselect(swap, B, D); sqr_eltfp25519_2w_bmi2(AB); /* [AA|BB] = [A^2|B^2] */ add_eltfp25519_1w_bmi2(X3, DA, CB); /* X3 = (DA+CB) */ |