PX4-Autopilot/platforms/common/px4_sw_crypto/sw_crypto/crypto.c

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/**
 * @file crypto.c
 *
 * Wrapper for the monocypher crypto
 *
 */

#include <inttypes.h>
#include <stdbool.h>

#include <px4_platform_common/crypto_backend.h>
#include <lib/crypto/monocypher/src/optional/monocypher-ed25519.h>

/* room for 16 keys */
#define KEY_CACHE_LEN 16

#ifndef SECMEM_ALLOC
#define SECMEM_ALLOC malloc
#endif

#ifndef SECMEM_FREE
#define SECMEM_FREE free
#endif

/*
 * For now, this is just a dummy up/down counter for tracking open/close calls
 */
static int crypto_open_count = 0;

typedef struct {
	size_t key_size;
	uint8_t *key;
} volatile_key_t;

static volatile_key_t key_cache[KEY_CACHE_LEN];

/* Clear key cache */
static void clear_key_cache(void)
{
	for (int i = 0; i < KEY_CACHE_LEN ; i++) {
		SECMEM_FREE(key_cache[i].key);
		key_cache[i].key = NULL;
		key_cache[i].key_size = 0;
	}
}

/* Retrieve a direct pointer to the cached temporary/public key */
static const uint8_t *crypto_get_key_ptr(keystore_session_handle_t handle, uint8_t key_idx,
		size_t *len)
{
	uint8_t *ret;

	if (key_idx >= KEY_CACHE_LEN) {
		*len = 0;
		return NULL;
	}

	ret = key_cache[key_idx].key;

	/* if the key doesn't exist in the key cache, try to read it in there from keystore */
	if (ret == NULL) {

		/* First check if the key exists in the keystore and retrieve its length */
		*len = keystore_get_key(handle, key_idx, NULL, 0);

		if (*len > 0) {

			/* Allocate memory for the key in the cache */
			ret = SECMEM_ALLOC(*len);

			/* Retrieve the key from the keystore */
			if (ret) {
				if (keystore_get_key(handle, key_idx, ret, *len) > 0) {
					/* Success, store the key in cache */
					key_cache[key_idx].key_size = *len;
					key_cache[key_idx].key = ret;

				} else {
					/* key retrieval failed, free the memory */
					SECMEM_FREE(ret);
				}
			}
		}
	}

	*len = key_cache[key_idx].key_size;

	return ret;
}


void crypto_init()
{
	keystore_init();
	clear_key_cache();
}

crypto_session_handle_t crypto_open(px4_crypto_algorithm_t algorithm)
{
	crypto_session_handle_t ret;
	ret.algorithm = algorithm;
	ret.keystore_handle = keystore_open();

	if (keystore_session_handle_valid(ret.keystore_handle)) {
		ret.handle = ++crypto_open_count;

	} else {
		ret.handle = 0;
	}

	return ret;
}

void crypto_close(crypto_session_handle_t *handle)
{
	crypto_open_count--;
	handle->handle = 0;
	keystore_close(&handle->keystore_handle);
}

bool crypto_signature_check(crypto_session_handle_t handle,
			    uint8_t  key_index,
			    const uint8_t  *signature,
			    const uint8_t *message,
			    size_t message_size)
{
	bool ret = false;
	size_t keylen = 0;
	const uint8_t *public_key;

	if (crypto_session_handle_valid(handle)) {
		public_key = crypto_get_key_ptr(handle.keystore_handle, key_index, &keylen);
	}

	if (keylen == 0) {
		return false;
	}

	switch (handle.algorithm) {
	case CRYPTO_ED25519:
		ret = crypto_ed25519_check(signature, public_key, message, message_size) == 0;
		break;

	default:
		ret = false;
	}

	return ret;
}