include/openssl/chacha.h

// Copyright 2014 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_CHACHA_H
#define OPENSSL_HEADER_CHACHA_H

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

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

// ChaCha20.
//
// ChaCha20 is a stream cipher. See https://tools.ietf.org/html/rfc8439.


// CRYPTO_chacha_20 encrypts `in_len` bytes from `in` with the given key and
// nonce and writes the result to `out`. If `in` and `out` alias, they must be
// equal. The initial block counter is specified by `counter`.
//
// This function implements a 32-bit block counter as in RFC 8439. On overflow,
// the counter wraps. Reusing a key, nonce, and block counter combination is not
// secure, so wrapping is usually a bug in the caller. While it is possible to
// wrap without reuse with a large initial block counter, this is not
// recommended and may not be portable to other ChaCha20 implementations.
OPENSSL_EXPORT void CRYPTO_chacha_20(uint8_t *out, const uint8_t *in,
                                     size_t in_len, const uint8_t key[32],
                                     const uint8_t nonce[12], uint32_t counter);


#if defined(__cplusplus)
}  // extern C
#endif

#endif  // OPENSSL_HEADER_CHACHA_H