// Copyright 2022 The BoringSSL Authors
//
// 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
//
//     https://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.

#ifndef OPENSSL_HEADER_CTRDRBG_H
#define OPENSSL_HEADER_CTRDRBG_H

#include <openssl/base.h>  // IWYU pragma: export

#if defined(__cplusplus)
extern "C" {
#endif


// FIPS pseudo-random number generator.


// CTR-DRBG state objects.
//
// CTR_DRBG_STATE contains the state of a FIPS AES-CTR-based pseudo-random
// number generator. If BoringSSL was built in FIPS mode then this is a FIPS
// Approved algorithm. BoringSSL supports CTR-DRBG both with, and without, a
// derivation function.

// CTR_DRBG_MIN_ENTROPY_LEN is the minimum number of bytes of input entropy
// when using a derivation function. See SP 800-90Ar1, table 3.
#define CTR_DRBG_MIN_ENTROPY_LEN 32

// CTR_DRBG_MAX_ENTROPY_LEN is the maximum number of bytes of input entropy
// when using a derivation function. This is an implementation limitation.
#define CTR_DRBG_MAX_ENTROPY_LEN 64

// CTR_DRBG_ENTROPY_LEN is a fixed amount of entropy required when not using a
// derivation function.
#define CTR_DRBG_ENTROPY_LEN 48

// The length of a seed, when using a derivation function. See SP 800-90Ar1,
// table 3.
#define CTR_DRBG_SEED_LEN (32 + CTR_DRBG_NONCE_LEN)

// CTR_DRBG_NONCE_LEN is the number of bytes of input nonce. This only applies
// when using a derivation function.
#define CTR_DRBG_NONCE_LEN 16

// CTR_DRBG_MAX_GENERATE_LENGTH is the maximum number of bytes that can be
// generated in a single call to `CTR_DRBG_generate`.
#define CTR_DRBG_MAX_GENERATE_LENGTH 65536

// CTR_DRBG_new returns an initialized `CTR_DRBG_STATE`, or NULL if either
// allocation failed or if `personalization_len` is invalid. This DRBG will not
// use a derivation function.
OPENSSL_EXPORT CTR_DRBG_STATE *CTR_DRBG_new(
    const uint8_t entropy[CTR_DRBG_ENTROPY_LEN], const uint8_t *personalization,
    size_t personalization_len);

// CTR_DRBG_new_df returns an initialized `CTR_DRBG_STATE`, or NULL if either
// allocation failed or if an argument is invalid. This DRBG will use a
// derivation function.
OPENSSL_EXPORT CTR_DRBG_STATE *CTR_DRBG_new_df(
    const uint8_t *entropy, size_t entropy_len,
    const uint8_t nonce[CTR_DRBG_NONCE_LEN], const uint8_t *personalization,
    size_t personalization_len);

// CTR_DRBG_free frees `state` if non-NULL, or else does nothing.
OPENSSL_EXPORT void CTR_DRBG_free(CTR_DRBG_STATE *state);

// CTR_DRBG_reseed reseeds `drbg` given `CTR_DRBG_ENTROPY_LEN` bytes of entropy
// in `entropy` and, optionally, up to `CTR_DRBG_SEED_LEN` bytes of
// additional data. It returns one on success or zero on error.
OPENSSL_EXPORT int CTR_DRBG_reseed(CTR_DRBG_STATE *drbg,
                                   const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],
                                   const uint8_t *additional_data,
                                   size_t additional_data_len);

// CTR_DRBG_reseed_ex acts like `CTR_DRBG_reseed` but with variable-length
// entropy input, up to `CTR_DRBG_MAX_ENTROPY_LEN`.
OPENSSL_EXPORT int CTR_DRBG_reseed_ex(CTR_DRBG_STATE *drbg,
                                      const uint8_t *entropy,
                                      size_t entropy_len,
                                      const uint8_t *additional_data,
                                      size_t additional_data_len);

// CTR_DRBG_generate processes to up `CTR_DRBG_ENTROPY_LEN` bytes of additional
// data (if any) and then writes `out_len` random bytes to `out`, where
// `out_len` <= `CTR_DRBG_MAX_GENERATE_LENGTH`. It returns one on success or
// zero on error.
OPENSSL_EXPORT int CTR_DRBG_generate(CTR_DRBG_STATE *drbg, uint8_t *out,
                                     size_t out_len,
                                     const uint8_t *additional_data,
                                     size_t additional_data_len);

// CTR_DRBG_clear zeroises the state of `drbg`.
OPENSSL_EXPORT void CTR_DRBG_clear(CTR_DRBG_STATE *drbg);


#if defined(__cplusplus)
}  // extern C

extern "C++" {
BSSL_NAMESPACE_BEGIN
BORINGSSL_MAKE_DELETER(CTR_DRBG_STATE, CTR_DRBG_free)
BSSL_NAMESPACE_END
}  // extern C++
#endif

#endif  // OPENSSL_HEADER_CTRDRBG_H