/*
 *  Entropy accumulator implementation
 *
 *  Copyright (C) 2006-2016, ARM Limited, All Rights Reserved
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *  This file is part of mbed TLS (https://tls.mbed.org)
 */

#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/mbedtls_config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif

#if defined(MBEDTLS_ENTROPY_C)

#if defined(MBEDTLS_TEST_NULL_ENTROPY)
#warning "**** WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined! "
#warning "**** THIS BUILD HAS NO DEFINED ENTROPY SOURCES "
#warning "**** THIS BUILD IS *NOT* SUITABLE FOR PRODUCTION USE "
#endif

#include "mbedtls/entropy.h"
#include "mbedtls/entropy_poll.h"

#include <string.h>

#if defined(MBEDTLS_FS_IO)
#include <stdio.h>
#endif

#if defined(MBEDTLS_SELF_TEST)
#if defined(MBEDTLS_PLATFORM_C)
#include "mbedtls/platform.h"
#else
#include <stdio.h>
#define mbedtls_printf     printf
#endif /* MBEDTLS_PLATFORM_C */
#endif /* MBEDTLS_SELF_TEST */

#if defined(MBEDTLS_HAVEGE_C)
#include "mbedtls/havege.h"
#endif

/* Implementation that should never be optimized out by the compiler */
static void mbedtls_zeroize(void *v, size_t n)
{
    volatile unsigned char *p = v;
    while (n--) {
        *p++ = 0;
    }
}

#define ENTROPY_MAX_LOOP    256     /**< Maximum amount to loop before error */

void mbedtls_entropy_init(mbedtls_entropy_context *ctx)
{
    memset(ctx, 0, sizeof(mbedtls_entropy_context));

#if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_init(&ctx->mutex);
#endif

#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
    mbedtls_sha512_starts(&ctx->accumulator, 0);
#else
    mbedtls_sha256_starts(&ctx->accumulator, 0);
#endif
#if defined(MBEDTLS_HAVEGE_C)
    mbedtls_havege_init(&ctx->havege_data);
#endif

#if defined(MBEDTLS_TEST_NULL_ENTROPY)
    mbedtls_entropy_add_source(ctx, mbedtls_null_entropy_poll, NULL,
                               1, MBEDTLS_ENTROPY_SOURCE_STRONG);
#endif

#if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
#if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
    mbedtls_entropy_add_source(ctx, mbedtls_platform_entropy_poll, NULL,
                               MBEDTLS_ENTROPY_MIN_PLATFORM,
                               MBEDTLS_ENTROPY_SOURCE_STRONG);
#endif
#if defined(MBEDTLS_TIMING_C)
    mbedtls_entropy_add_source(ctx, mbedtls_hardclock_poll, NULL,
                               MBEDTLS_ENTROPY_MIN_HARDCLOCK,
                               MBEDTLS_ENTROPY_SOURCE_WEAK);
#endif
#if defined(MBEDTLS_HAVEGE_C)
    mbedtls_entropy_add_source(ctx, mbedtls_havege_poll, &ctx->havege_data,
                               MBEDTLS_ENTROPY_MIN_HAVEGE,
                               MBEDTLS_ENTROPY_SOURCE_STRONG);
#endif
#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
    mbedtls_entropy_add_source(ctx, mbedtls_hardware_poll, NULL,
                               MBEDTLS_ENTROPY_MIN_HARDWARE,
                               MBEDTLS_ENTROPY_SOURCE_STRONG);
#endif
#if defined(MBEDTLS_ENTROPY_NV_SEED)
    mbedtls_entropy_add_source(ctx, mbedtls_nv_seed_poll, NULL,
                               MBEDTLS_ENTROPY_BLOCK_SIZE,
                               MBEDTLS_ENTROPY_SOURCE_STRONG);
#endif
#endif /* MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES */
}

void mbedtls_entropy_free(mbedtls_entropy_context *ctx)
{
#if defined(MBEDTLS_HAVEGE_C)
    mbedtls_havege_free(&ctx->havege_data);
#endif
#if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_free(&ctx->mutex);
#endif
    mbedtls_zeroize(ctx, sizeof(mbedtls_entropy_context));
}

int mbedtls_entropy_add_source(mbedtls_entropy_context *ctx,
                               mbedtls_entropy_f_source_ptr f_source, void *p_source,
                               size_t threshold, int strong)
{
    int index, ret = 0;

#if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
        return (ret);
    }
#endif

    index = ctx->source_count;
    if (index >= MBEDTLS_ENTROPY_MAX_SOURCES) {
        ret = MBEDTLS_ERR_ENTROPY_MAX_SOURCES;
        goto exit;
    }

    ctx->source[index].f_source  = f_source;
    ctx->source[index].p_source  = p_source;
    ctx->source[index].threshold = threshold;
    ctx->source[index].strong    = strong;

    ctx->source_count++;

exit:
#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
        return (MBEDTLS_ERR_THREADING_MUTEX_ERROR);
    }
#endif

    return (ret);
}

/*
 * Entropy accumulator update
 */
static int entropy_update(mbedtls_entropy_context *ctx, unsigned char source_id,
                          const unsigned char *data, size_t len)
{
    unsigned char header[2];
    unsigned char tmp[MBEDTLS_ENTROPY_BLOCK_SIZE];
    size_t use_len = len;
    const unsigned char *p = data;

    if (use_len > MBEDTLS_ENTROPY_BLOCK_SIZE) {
#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
        mbedtls_sha512(data, len, tmp, 0);
#else
        mbedtls_sha256(data, len, tmp, 0);
#endif
        p = tmp;
        use_len = MBEDTLS_ENTROPY_BLOCK_SIZE;
    }

    header[0] = source_id;
    header[1] = use_len & 0xFF;

#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
    mbedtls_sha512_update(&ctx->accumulator, header, 2);
    mbedtls_sha512_update(&ctx->accumulator, p, use_len);
#else
    mbedtls_sha256_update(&ctx->accumulator, header, 2);
    mbedtls_sha256_update(&ctx->accumulator, p, use_len);
#endif

    return (0);
}

int mbedtls_entropy_update_manual(mbedtls_entropy_context *ctx,
                                  const unsigned char *data, size_t len)
{
    int ret;

#if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
        return (ret);
    }
#endif

    ret = entropy_update(ctx, MBEDTLS_ENTROPY_SOURCE_MANUAL, data, len);

#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
        return (MBEDTLS_ERR_THREADING_MUTEX_ERROR);
    }
#endif

    return (ret);
}

/*
 * Run through the different sources to add entropy to our accumulator
 */
static int entropy_gather_internal(mbedtls_entropy_context *ctx)
{
    int ret, i, have_one_strong = 0;
    unsigned char buf[MBEDTLS_ENTROPY_MAX_GATHER];
    size_t olen;

    if (ctx->source_count == 0) {
        return (MBEDTLS_ERR_ENTROPY_NO_SOURCES_DEFINED);
    }

    /*
     * Run through our entropy sources
     */
    for (i = 0; i < ctx->source_count; i++) {
        if (ctx->source[i].strong == MBEDTLS_ENTROPY_SOURCE_STRONG) {
            have_one_strong = 1;
        }

        olen = 0;
        if ((ret = ctx->source[i].f_source(ctx->source[i].p_source,
                                           buf, MBEDTLS_ENTROPY_MAX_GATHER, &olen)) != 0) {
            return (ret);
        }

        /*
         * Add if we actually gathered something
         */
        if (olen > 0) {
            entropy_update(ctx, (unsigned char) i, buf, olen);
            ctx->source[i].size += olen;
        }
    }

    if (have_one_strong == 0) {
        return (MBEDTLS_ERR_ENTROPY_NO_STRONG_SOURCE);
    }

    return (0);
}

/*
 * Thread-safe wrapper for entropy_gather_internal()
 */
int mbedtls_entropy_gather(mbedtls_entropy_context *ctx)
{
    int ret;

#if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
        return (ret);
    }
#endif

    ret = entropy_gather_internal(ctx);

#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
        return (MBEDTLS_ERR_THREADING_MUTEX_ERROR);
    }
#endif

    return (ret);
}

int mbedtls_entropy_func(void *data, unsigned char *output, size_t len)
{
    int ret, count = 0, i, done;
    mbedtls_entropy_context *ctx = (mbedtls_entropy_context *) data;
    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

    if (len > MBEDTLS_ENTROPY_BLOCK_SIZE) {
        return (MBEDTLS_ERR_ENTROPY_SOURCE_FAILED);
    }

#if defined(MBEDTLS_ENTROPY_NV_SEED)
    /* Update the NV entropy seed before generating any entropy for outside
     * use.
     */
    if (ctx->initial_entropy_run == 0) {
        ctx->initial_entropy_run = 1;
        if ((ret = mbedtls_entropy_update_nv_seed(ctx)) != 0) {
            return (ret);
        }
    }
#endif

#if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0) {
        return (ret);
    }
#endif

    /*
     * Always gather extra entropy before a call
     */
    do {
        if (count++ > ENTROPY_MAX_LOOP) {
            ret = MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
            goto exit;
        }

        if ((ret = entropy_gather_internal(ctx)) != 0) {
            goto exit;
        }

        done = 1;
        for (i = 0; i < ctx->source_count; i++)
            if (ctx->source[i].size < ctx->source[i].threshold) {
                done = 0;
            }
    } while (! done);

    memset(buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE);

#if defined(MBEDTLS_ENTROPY_SHA512_ACCUMULATOR)
    mbedtls_sha512_finish(&ctx->accumulator, buf);

    /*
     * Reset accumulator and counters and recycle existing entropy
     */
    memset(&ctx->accumulator, 0, sizeof(mbedtls_sha512_context));
    mbedtls_sha512_starts(&ctx->accumulator, 0);
    mbedtls_sha512_update(&ctx->accumulator, buf, MBEDTLS_ENTROPY_BLOCK_SIZE);

    /*
     * Perform second SHA-512 on entropy
     */
    mbedtls_sha512(buf, MBEDTLS_ENTROPY_BLOCK_SIZE, buf, 0);
#else /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */
    mbedtls_sha256_finish(&ctx->accumulator, buf);

    /*
     * Reset accumulator and counters and recycle existing entropy
     */
    memset(&ctx->accumulator, 0, sizeof(mbedtls_sha256_context));
    mbedtls_sha256_starts(&ctx->accumulator, 0);
    mbedtls_sha256_update(&ctx->accumulator, buf, MBEDTLS_ENTROPY_BLOCK_SIZE);

    /*
     * Perform second SHA-256 on entropy
     */
    mbedtls_sha256(buf, MBEDTLS_ENTROPY_BLOCK_SIZE, buf, 0);
#endif /* MBEDTLS_ENTROPY_SHA512_ACCUMULATOR */

    for (i = 0; i < ctx->source_count; i++) {
        ctx->source[i].size = 0;
    }

    memcpy(output, buf, len);

    ret = 0;

exit:
#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&ctx->mutex) != 0) {
        return (MBEDTLS_ERR_THREADING_MUTEX_ERROR);
    }
#endif

    return (ret);
}

#if defined(MBEDTLS_ENTROPY_NV_SEED)
int mbedtls_entropy_update_nv_seed(mbedtls_entropy_context *ctx)
{
    int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
    unsigned char buf[ MBEDTLS_ENTROPY_MAX_SEED_SIZE ];

    /* Read new seed  and write it to NV */
    if ((ret = mbedtls_entropy_func(ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE)) != 0) {
        return (ret);
    }

    if (mbedtls_nv_seed_write(buf, MBEDTLS_ENTROPY_BLOCK_SIZE) < 0) {
        return (MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR);
    }

    /* Manually update the remaining stream with a separator value to diverge */
    memset(buf, 0, MBEDTLS_ENTROPY_BLOCK_SIZE);
    mbedtls_entropy_update_manual(ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE);

    return (0);
}
#endif /* MBEDTLS_ENTROPY_NV_SEED */

#if defined(MBEDTLS_FS_IO)
int mbedtls_entropy_write_seed_file(mbedtls_entropy_context *ctx, const char *path)
{
    int ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
    FILE *f;
    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE];

    if ((f = fopen(path, "wb")) == NULL) {
        return (MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR);
    }

    if ((ret = mbedtls_entropy_func(ctx, buf, MBEDTLS_ENTROPY_BLOCK_SIZE)) != 0) {
        goto exit;
    }

    if (fwrite(buf, 1, MBEDTLS_ENTROPY_BLOCK_SIZE, f) != MBEDTLS_ENTROPY_BLOCK_SIZE) {
        ret = MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR;
        goto exit;
    }

    ret = 0;

exit:
    fclose(f);
    return (ret);
}

int mbedtls_entropy_update_seed_file(mbedtls_entropy_context *ctx, const char *path)
{
    FILE *f;
    size_t n;
    unsigned char buf[ MBEDTLS_ENTROPY_MAX_SEED_SIZE ];

    if ((f = fopen(path, "rb")) == NULL) {
        return (MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR);
    }

    fseek(f, 0, SEEK_END);
    n = (size_t) ftell(f);
    fseek(f, 0, SEEK_SET);

    if (n > MBEDTLS_ENTROPY_MAX_SEED_SIZE) {
        n = MBEDTLS_ENTROPY_MAX_SEED_SIZE;
    }

    if (fread(buf, 1, n, f) != n) {
        fclose(f);
        return (MBEDTLS_ERR_ENTROPY_FILE_IO_ERROR);
    }

    fclose(f);

    mbedtls_entropy_update_manual(ctx, buf, n);

    return (mbedtls_entropy_write_seed_file(ctx, path));
}
#endif /* MBEDTLS_FS_IO */

#if defined(MBEDTLS_SELF_TEST)
/*
 * Dummy source function
 */
static int entropy_dummy_source(void *data, unsigned char *output,
                                size_t len, size_t *olen)
{
    ((void) data);

    memset(output, 0x2a, len);
    *olen = len;

    return (0);
}

/*
 * The actual entropy quality is hard to test, but we can at least
 * test that the functions don't cause errors and write the correct
 * amount of data to buffers.
 */
int mbedtls_entropy_self_test(int verbose)
{
    int ret = 0;
    mbedtls_entropy_context ctx;
    unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
    unsigned char acc[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
    size_t i, j;

    if (verbose != 0) {
        mbedtls_printf("  ENTROPY test: ");
    }

    mbedtls_entropy_init(&ctx);

    /* First do a gather to make sure we have default sources */
    if ((ret = mbedtls_entropy_gather(&ctx)) != 0) {
        goto cleanup;
    }

    ret = mbedtls_entropy_add_source(&ctx, entropy_dummy_source, NULL, 16,
                                     MBEDTLS_ENTROPY_SOURCE_WEAK);
    if (ret != 0) {
        goto cleanup;
    }

    if ((ret = mbedtls_entropy_update_manual(&ctx, buf, sizeof buf)) != 0) {
        goto cleanup;
    }

    /*
     * To test that mbedtls_entropy_func writes correct number of bytes:
     * - use the whole buffer and rely on ASan to detect overruns
     * - collect entropy 8 times and OR the result in an accumulator:
     *   any byte should then be 0 with probably 2^(-64), so requiring
     *   each of the 32 or 64 bytes to be non-zero has a false failure rate
     *   of at most 2^(-58) which is acceptable.
     */
    for (i = 0; i < 8; i++) {
        if ((ret = mbedtls_entropy_func(&ctx, buf, sizeof(buf))) != 0) {
            goto cleanup;
        }

        for (j = 0; j < sizeof(buf); j++) {
            acc[j] |= buf[j];
        }
    }

    for (j = 0; j < sizeof(buf); j++) {
        if (acc[j] == 0) {
            ret = 1;
            goto cleanup;
        }
    }

cleanup:
    mbedtls_entropy_free(&ctx);

    if (verbose != 0) {
        if (ret != 0) {
            mbedtls_printf("failed\n");
        } else {
            mbedtls_printf("passed\n");
        }

        mbedtls_printf("\n");
    }

    return (ret != 0);
}
#endif /* MBEDTLS_SELF_TEST */

#endif /* MBEDTLS_ENTROPY_C */