// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <stddef.h>
#include <stdint.h>
#include <string.h>

#include <crypto/digest.h>
#include <crypto/hkdf.h>
#include <explicit-memory/bytes.h>
#include <fbl/auto_call.h>
#include <lib/zircon-internal/debug.h>
#include <zircon/errors.h>
#include <zircon/types.h>

// See note in //zircon/third_party/ulib/uboringssl/rules.mk
#define BORINGSSL_NO_CXX
#include <openssl/digest.h>
#include <openssl/hkdf.h>

#include "error.h"

#define ZXDEBUG 0

namespace crypto {
namespace {

const uint16_t kAllFlags = HKDF::ALLOW_WEAK_KEY;
}
// Public methods

HKDF::HKDF() : digest_(digest::kUninitialized) {}
HKDF::~HKDF() {}

zx_status_t HKDF::Init(digest::Algorithm digest, const Secret& key, const Bytes& salt,
                       uint16_t flags) {
    zx_status_t rc;

    if ((flags & (~kAllFlags)) != 0) {
        xprintf("invalid flags: %04x\n", flags);
        return ZX_ERR_INVALID_ARGS;
    }

    uintptr_t ptr;
    if ((rc = digest::GetDigest(digest, &ptr)) != ZX_OK) {
        return rc;
    }
    digest_ = digest;
    const EVP_MD* md = reinterpret_cast<const EVP_MD*>(ptr);

    // Reserve space for the pseudo-random key.
    uint8_t *prk;
    size_t prk_len = EVP_MD_size(md);
    if ((rc = prk_.Allocate(prk_len, &prk)) != ZX_OK) {
        return rc;
    }

    // Recommended minimum length for the key is the digest output length (RFC 2104, section 2).
    if ((flags & ALLOW_WEAK_KEY) == 0 && key.len() < prk_len) {
        xprintf("weak parameter(s): key_len=%zu", key.len());
        return ZX_ERR_INVALID_ARGS;
    }

    // Extract the PRK used to generate other keys.
    if (HKDF_extract(prk, &prk_len, md, key.get(), key.len(), salt.get(), salt.len()) < 0) {
        xprintf_crypto_errors(&rc);
        return rc;
    }
    ZX_DEBUG_ASSERT(prk_len == prk_.len());

    return ZX_OK;
}

zx_status_t HKDF::Derive(const char* label, size_t len, Bytes* out) {
    zx_status_t rc;

    if ((rc = out->Resize(len)) != ZX_OK ||
        (rc = Derive(label, out->get(), len)) != ZX_OK) {
        return rc;
    }

    return ZX_OK;
}

zx_status_t HKDF::Derive(const char* label, size_t len, Secret* out) {
    zx_status_t rc;

    uint8_t *buf;
    if ((rc = out->Allocate(len, &buf)) != ZX_OK ||
        (rc = Derive(label, buf, len)) != ZX_OK) {
        return rc;
    }

    return ZX_OK;
}

zx_status_t HKDF::Derive(const char* label, uint8_t* out, size_t out_len) {
    zx_status_t rc;

    if (!out || out_len == 0) {
        xprintf("bad parameter(s): out=%p, out_len=%zu\n", out, out_len);
        return ZX_ERR_INVALID_ARGS;
    }

    uintptr_t ptr;
    if ((rc = digest::GetDigest(digest_, &ptr)) != ZX_OK) {
        return rc;
    }
    const EVP_MD* md = reinterpret_cast<const EVP_MD*>(ptr);

    // Maybe the platform is weird...
    static_assert(sizeof(uint8_t) == sizeof(char), "can't convert char to uint8_t");
    const uint8_t* info = reinterpret_cast<const uint8_t*>(label);
    size_t info_len = label ? strlen(label) : 0;

    // Generate the key
    if (HKDF_expand(out, out_len, md, prk_.get(), prk_.len(), info, info_len) < 0) {
        xprintf_crypto_errors(&rc);
        return rc;
    }

    return ZX_OK;
}

} // namespace crypto