/*-
 * Copyright (c) 2000-2015 Mark R V Murray
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer
 *    in this position and unchanged.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#include <sys/cdefs.h>
#ifdef _KERNEL
#include <sys/param.h>
#include <sys/malloc.h>
#include <sys/random.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#else /* !_KERNEL */
#include <sys/param.h>
#include <sys/types.h>
#include <assert.h>
#include <inttypes.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <threads.h>
#define KASSERT(x, y)   assert(x)
#define CTASSERT(x)     _Static_assert(x, "CTASSERT " #x)
#endif /* _KERNEL */

#define CHACHA_EMBED
#define KEYSTREAM_ONLY
#define CHACHA_NONCE0_CTR128
#include <crypto/chacha20/chacha.c>
#include <crypto/rijndael/rijndael-api-fst.h>
#include <crypto/sha2/sha256.h>

#include <dev/random/hash.h>
#ifdef _KERNEL
#include <dev/random/randomdev.h>
#endif

/* This code presumes that RANDOM_KEYSIZE is twice as large as RANDOM_BLOCKSIZE */
CTASSERT(RANDOM_KEYSIZE == 2*RANDOM_BLOCKSIZE);

/* Validate that full Chacha IV is as large as the 128-bit counter */
_Static_assert(CHACHA_STATELEN == RANDOM_BLOCKSIZE, "");

/*
 * Knob to control use of Chacha20-based PRF for Fortuna keystream primitive.
 *
 * Benefits include somewhat faster keystream generation compared with
 * unaccelerated AES-ICM; reseeding is much cheaper than computing AES key
 * schedules.
 */
bool random_chachamode __read_frequently = true;
#ifdef _KERNEL
SYSCTL_BOOL(_kern_random, OID_AUTO, use_chacha20_cipher, CTLFLAG_RDTUN,
    &random_chachamode, 0,
    "If non-zero, use the ChaCha20 cipher for randomdev PRF (default). "
    "If zero, use AES-ICM cipher for randomdev PRF (12.x default).");
#endif

/* Initialise the hash */
void
randomdev_hash_init(struct randomdev_hash *context)
{

        SHA256_Init(&context->sha);
}

/* Iterate the hash */
void
randomdev_hash_iterate(struct randomdev_hash *context, const void *data, size_t size)
{

        SHA256_Update(&context->sha, data, size);
}

/* Conclude by returning the hash in the supplied <*buf> which must be
 * RANDOM_KEYSIZE bytes long.
 */
void
randomdev_hash_finish(struct randomdev_hash *context, void *buf)
{

        SHA256_Final(buf, &context->sha);
}

/* Initialise the encryption routine by setting up the key schedule
 * from the supplied <*data> which must be RANDOM_KEYSIZE bytes of binary
 * data.
 */
void
randomdev_encrypt_init(union randomdev_key *context, const void *data)
{

        if (random_chachamode) {
                chacha_keysetup(&context->chacha, data, RANDOM_KEYSIZE * 8);
        } else {
                rijndael_cipherInit(&context->cipher, MODE_ECB, NULL);
                rijndael_makeKey(&context->key, DIR_ENCRYPT, RANDOM_KEYSIZE*8, data);
        }
}

/*
 * Create a pseudorandom output stream of 'bytecount' bytes using a CTR-mode
 * cipher or similar.  The 128-bit counter is supplied in the in-out parameter
 * 'ctr.'  The output stream goes to 'd_out.'
 *
 * If AES is used, 'bytecount' is guaranteed to be a multiple of
 * RANDOM_BLOCKSIZE.
 */
void
randomdev_keystream(union randomdev_key *context, uint128_t *ctr,
    void *d_out, size_t bytecount)
{
        size_t i, blockcount, read_chunk;

        if (random_chachamode) {
                uint128_t lectr;

                /*
                 * Chacha always encodes and increments the counter little
                 * endian.  So on BE machines, we must provide a swapped
                 * counter to chacha, and swap the output too.
                 */
                le128enc(&lectr, *ctr);

                chacha_ivsetup(&context->chacha, NULL, (const void *)&lectr);
                while (bytecount > 0) {
                        /*
                         * We are limited by the chacha_encrypt_bytes API to
                         * u32 bytes per chunk.
                         */
                        read_chunk = MIN(bytecount,
                            rounddown((size_t)UINT32_MAX, CHACHA_BLOCKLEN));

                        chacha_encrypt_bytes(&context->chacha, NULL, d_out,
                            read_chunk);

                        d_out = (char *)d_out + read_chunk;
                        bytecount -= read_chunk;
                }

                /*
                 * Decode Chacha-updated LE counter to native endian and store
                 * it back in the caller's in-out parameter.
                 */
                chacha_ctrsave(&context->chacha, (void *)&lectr);
                *ctr = le128dec(&lectr);

                explicit_bzero(&lectr, sizeof(lectr));
        } else {
                KASSERT(bytecount % RANDOM_BLOCKSIZE == 0,
                    ("%s: AES mode invalid bytecount, not a multiple of native "
                     "block size", __func__));

                blockcount = bytecount / RANDOM_BLOCKSIZE;
                for (i = 0; i < blockcount; i++) {
                        /*-
                         * FS&K - r = r|E(K,C)
                         *      - C = C + 1
                         */
                        rijndael_blockEncrypt(&context->cipher, &context->key,
                            (void *)ctr, RANDOM_BLOCKSIZE * 8, d_out);
                        d_out = (char *)d_out + RANDOM_BLOCKSIZE;
                        uint128_increment(ctr);
                }
        }
}

/*
 * Fetch a pointer to the relevant key material and its size.
 *
 * This API is expected to only be used only for reseeding, where the
 * endianness does not matter; the goal is to simply incorporate the key
 * material into the hash iterator that will produce key'.
 *
 * Do not expect the buffer pointed to by this API to match the exact
 * endianness, etc, as the key material that was supplied to
 * randomdev_encrypt_init().
 */
void
randomdev_getkey(union randomdev_key *context, const void **keyp, size_t *szp)
{

        if (!random_chachamode) {
                *keyp = &context->key.keyMaterial;
                *szp = context->key.keyLen / 8;
                return;
        }

        /* Chacha20 mode */
        *keyp = (const void *)&context->chacha.input[4];

        /* Sanity check keysize */
        if (context->chacha.input[0] == U8TO32_LITTLE(sigma) &&
            context->chacha.input[1] == U8TO32_LITTLE(&sigma[4]) &&
            context->chacha.input[2] == U8TO32_LITTLE(&sigma[8]) &&
            context->chacha.input[3] == U8TO32_LITTLE(&sigma[12])) {
                *szp = 32;
                return;
        }

#if 0
        /*
         * Included for the sake of completeness; as-implemented, Fortuna
         * doesn't need or use 128-bit Chacha20.
         */
        if (context->chacha->input[0] == U8TO32_LITTLE(tau) &&
            context->chacha->input[1] == U8TO32_LITTLE(&tau[4]) &&
            context->chacha->input[2] == U8TO32_LITTLE(&tau[8]) &&
            context->chacha->input[3] == U8TO32_LITTLE(&tau[12])) {
                *szp = 16;
                return;
        }
#endif

#ifdef _KERNEL
        panic("%s: Invalid chacha20 keysize: %16D\n", __func__,
            (void *)context->chacha.input, " ");
#else
        raise(SIGKILL);
#endif
}