openssl/crypto/include/internal/chacha.h

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#ifndef HEADER_CHACHA_H
#define HEADER_CHACHA_H

#include <stddef.h>

#ifdef __cplusplus
extern "C" {
#endif

# ifdef OPENSSL_NO_CHACHA
#  error CHACHA is disabled.
# endif

/*
 * ChaCha20_ctr32 encrypts |len| bytes from |inp| with the given key and
 * nonce and writes the result to |out|, which may be equal to |inp|.
 * The |key| is not 32 bytes of verbatim key material though, but the
 * said material collected into 8 32-bit elements array in host byte
 * order. Same approach applies to nonce: the |counter| argument is
 * pointer to concatenated nonce and counter values collected into 4
 * 32-bit elements. This, passing crypto material collected into 32-bit
 * elements as opposite to passing verbatim byte vectors, is chosen for
 * efficiency in multi-call scenarios.
 */
void ChaCha20_ctr32(unsigned char *out, const unsigned char *inp,
                    size_t len, const unsigned int key[8],
                    const unsigned int counter[4]);
/*
 * You can notice that there is no key setup procedure. Because it's
 * as trivial as collecting bytes into 32-bit elements, it's reckoned
 * that below macro is sufficient.
 */
#define CHACHA_U8TOU32(p)  ( \
                ((unsigned int)(p)[0])     | ((unsigned int)(p)[1]<<8) | \
                ((unsigned int)(p)[2]<<16) | ((unsigned int)(p)[3]<<24)  )

#define CHACHA_KEY_SIZE		32
#define CHACHA_CTR_SIZE		16
#define CHACHA_BLK_SIZE		64

#ifdef __cplusplus
}
#endif
#endif