putty-source/crypto/aes-common.c

/*
 * Common variable definitions across all the AES implementations.
 */

#include "ssh.h"
#include "aes.h"

const uint8_t aes_key_setup_round_constants[10] = {
    /* The first few powers of X in GF(2^8), used during key setup.
     * This can safely be a lookup table without side channel risks,
     * because key setup iterates through it once in a standard way
     * regardless of the key. */
    0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36,
};
Break up crypto modules containing HW acceleration. This applies to all of AES, SHA-1, SHA-256 and SHA-512. All those source files previously contained multiple implementations of the algorithm, enabled or disabled by ifdefs detecting whether they would work on a given compiler. And in order to get advanced machine instructions like AES-NI or NEON crypto into the output file when the compile flags hadn't enabled them, we had to do nasty stuff with compiler-specific pragmas or attributes. Now we can do the detection at cmake time, and enable advanced instructions in the more sensible way, by compile-time flags. So I've broken up each of these modules into lots of sub-pieces: a file called (e.g.) 'foo-common.c' containing common definitions across all implementations (such as round constants), one called 'foo-select.c' containing the top-level vtable(s), and a separate file for each implementation exporting just the vtable(s) for that implementation. One advantage of this is that it depends a lot less on compiler- specific bodgery. My particular least favourite part of the previous setup was the part where I had to _manually_ define some Arm ACLE feature macros before including <arm_neon.h>, so that it would define the intrinsics I wanted. Now I'm enabling interesting architecture features in the normal way, on the compiler command line, there's no need for that kind of trick: the right feature macros are already defined and <arm_neon.h> does the right thing. Another change in this reorganisation is that I've stopped assuming there's just one hardware implementation per platform. Previously, the accelerated vtables were called things like sha256_hw, and varied between FOO-NI and NEON depending on platform; and the selection code would simply ask 'is hw available? if so, use hw, else sw'. Now, each HW acceleration strategy names its vtable its own way, and the selection vtable has a whole list of possibilities to iterate over looking for a supported one. So if someone feels like writing a second accelerated implementation of something for a given platform - for example, I've heard you can use plain NEON to speed up AES somewhat even without the crypto extension - then it will now have somewhere to drop in alongside the existing ones. 2021-04-19 05:42:12 +00:00			`/*`
			`* Common variable definitions across all the AES implementations.`
			`*/`

			`#include "ssh.h"`
			`#include "aes.h"`

			`const uint8_t aes_key_setup_round_constants[10] = {`
			`/* The first few powers of X in GF(2^8), used during key setup.`
			`* This can safely be a lookup table without side channel risks,`
			`* because key setup iterates through it once in a standard way`
			`* regardless of the key. */`
			`0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80, 0x1b, 0x36,`
			`};`