core/cortex-m0/curve25519: Integrate fast curve25519 implementation

- Move generic implementation to curve25519-generic.o
- Always use optimized version on cortex-m0.

- Rename .s files to .S, remove unnecessary lines in assembly files.
- Rename crypto_scalarmult_curve25519 to x25519_scalar_mult to match
  the signature provided by the generic implementation.
- Replace some handcoded memcpy with function calls
- Remove unnecessary "volatile" specifications in the code.

 Conflicts:
	common/build.mk
	core/cortex-m0/curve25519/mpy121666.S
	core/cortex-m0/curve25519/mul.S
	core/cortex-m0/curve25519/reduce25519.S
	core/cortex-m0/curve25519/scalarmult.c
	core/cortex-m0/curve25519/sqr.S

BRANCH=none
BUG=b:62813194
TEST=To test old implementation only:
        - Increase CONFIG_RO_SIZE to 60kb
        - Increase console stack size to 2048
     make BOARD=hammer PROJECT=x25519 TEST_BUILD=y
     ./util/flash_ec --board=hammer --image=build/hammer/x25519.bin
     EC console: runtest, taskinfo
     => Used to takes ~4'17" to run (X25519 duration 256347 us).
        1496/2048 stack size usage in CONSOLE task
     => Now takes ~1'25" to run (X25519 duration 84520 us)
        732/2048 stack size usage in CONSOLE task
TEST=In test/x25519.c, uncomment #define TEST_X25519_1M_ITERATIONS
     make BOARD=hammer PROJECT=x25519 TEST_BUILD=y
     ./util/flash_ec --board=hammer --image=build/hammer/x25519.bin
     EC console: runtest, wait ~23 hours, test passes.
TEST=- Define CONFIG_CURVE25519_CORTEXM0 (next patch)
     makes newsizes
     build/hammer/RW/ec.RW.flat shrank by 1888 bytes: (52208 to 50320)

Change-Id: Icce38d3c32f431a85ac0f951cf34456b490dc665
Reviewed-on: https://chromium-review.googlesource.com/540962
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>
(cherry picked from commit edc668ea6cca1d4f3e53c211406d6a8bf5fe6364)
Reviewed-on: https://chromium-review.googlesource.com/734797
Commit-Queue: Vadim Bendebury <vbendeb@chromium.org>
Tested-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/curve25519.h b/include/curve25519.h
index 4b75373da1..8287c94466 100644
--- a/include/curve25519.h
+++ b/include/curve25519.h
@@ -59,4 +59,12 @@ int X25519(uint8_t out_shared_key[32], const uint8_t private_key[32],
 void X25519_public_from_private(uint8_t out_public_value[32],
 				const uint8_t private_key[32]);
 
+/*
+ * Low-level x25519 function, defined by either the generic or cortex-m0
+ * implementation. Must not be called directly.
+ */
+void x25519_scalar_mult(uint8_t out[32],
+			const uint8_t scalar[32],
+			const uint8_t point[32]);
+
 #endif /* __CROS_EC_CURVE25519_H */