buffered.h

#pragma once

#include <inttypes.h>
#include "algorithms.h"
#include "hc-128.h"
#include "rabbit.h"
#include "salsa20.h"
#include "sosemanuk.h"

typedef void (*extract_func_type)(void *state, uint8_t *stream);

typedef struct
{
  extract_func_type extract_func;
  uint16_t buffered_state_size;
  uint16_t buffer_offset;
  uint8_t chunk_size;
} cipher_attributes;

typedef struct
{
  const cipher_attributes *cipher;
  uint8_t available_count;
} buffered_state;

#define CIPHER_SPECIFICS_DECL(name,size)			\
  typedef struct {						\
    buffered_state header;					\
    name##_state state;						\
    /* Using uint32_t to ensure alignment: */			\
    uint32_t buffer[(size)/4];					\
  } name##_buffered_state;					\
  extern const cipher_attributes name##_cipher;			\
  extern const name##_buffered_state name##_static_initializer;

CIPHER_SPECIFICS_DECL(hc128, 4)
CIPHER_SPECIFICS_DECL(rabbit, 16)
CIPHER_SPECIFICS_DECL(salsa20, 64)
CIPHER_SPECIFICS_DECL(sosemanuk, 16)

#undef CIPHER_SPECIFICS_DECL

typedef enum
{
  BUFFERED_EXTRACT,
  BUFFERED_ENCDEC
} buffered_ops;

extern const cipher_attributes *cipher_attributes_map[LAST_CIPHER+1];

/** Gets the address of the cipher state contained in the buffered state.
 *
 * Low lever helper function to help writing generic code that works with
 * any cipher.
 *
 * @returns A value that can be cast to a pointer to one of the
 * <cipher>_state types, depending on what cipher this buffered state
 * was initialized to use.
 */
void *buffered_get_cipher_state(buffered_state *full_state);

/** Defines the cipher used for the buffered enc/decryption.
 *
 * The type buffered_state is the header of each of the specific <cipher>_buffered_state.
 * Before using the buffered API, this header must be initialized either with this
 * function or direct attribution from the static initializer <cipher>_static_initializer, like:
 *
 * hc128_buffered_state state = hc128_static_initializer;
 *
 * The header is updated by the buffered operations, so it is needed to reset it in case of
 * key or IV change. Use function buffered_reset() for this.
 *
 * @param state_header The pointer to the buffered state (or its header, their addresses must
 * coincide) that must be initialized.
 * @param cipher The cipher corresponding to the type of the buffered state.
 */
void buffered_init_header(buffered_state *state_header, cipher_type cipher);

/** Resets an buffered state to its initial state.
 *
 * Call this upon updating the cipher state with a key or IV change. It will discard any
 * buffered bytes generated by the previous key/IV combination. Currently this is as simple
 * as setting:
 *
 * @c state->header->available_count = 0;
 *
 * @param state_header The pointer to the buffered state (or its header, their addresses must
 * coincide).
 */
void buffered_reset(buffered_state *state_header);

/** Performs a buffered encryption, decryption or extraction operation.
 *
 * This function allows encryption or decryption of buffers of any size, independent of the
 * chunk size of the specific algorithm being used.
 *
 * @param full_state A properly initialized and valid buffered encryption state. One of the
 * <cipher>_buffered_state types. The full state (i.e. both the header and the cipher itself)
 * must be properly initialized before usage.
 * @param stream The buffer to be encrypted or decrypted in place, or to store the
 * extraction output.
 * @parem len The length of of the stream.
 * @param op What operation to perform, i.e. if to encrypt or decrypt (BUFFERED_ENCDEC) or
 * to just extract the len sized pseudorandom stream generated by the algorithm
 * (BUFFERED_EXTRACT). Notice that, for the kind of stream ciphers implemented, the encryption
 * and decryption operations are exactly the same.
 */
void buffered_action(buffered_state *full_state, uint8_t *stream, size_t len, buffered_ops op);

/** Discard an amount of bytes from the stream cipher output.
 *
 * This function is equivalent to calling buffered_action() with op BUFFERED_EXTRACT,
 * and discarding the output stream.
 *
 * @param full_state The properly initialized and valid buffered encryption state.
 * @param len How many bytes to skip from the current state of the buffered cipher.
 */
void buffered_skip(buffered_state *full_state, size_t len);