#define SHA256_DIGEST_SIZE  32
#define SHA256_BLOCK_SIZE   64

typedef struct
{
  uint32_t total[2];
  uint32_t state[8];
  uint32_t wbuf[16];
} sha256_context;

void sha256 (const unsigned char *input, unsigned int ilen,
	     unsigned char output[32]);
void sha256_start (sha256_context *ctx);
void sha256_finish (sha256_context *ctx, unsigned char output[32]);
void sha256_update (sha256_context *ctx, const unsigned char *input,
		    unsigned int ilen);
void sha256_process (sha256_context *ctx);