sha256.h

#ifndef Sha256_h
#define Sha256_h

#include <inttypes.h>
#include "Print.h"

#define HASH_LENGTH 32
#define BLOCK_LENGTH 64

class Sha256 : public Print {

  union Buffer {
    uint8_t b[BLOCK_LENGTH];
    uint32_t w[BLOCK_LENGTH / 4];
  };

  union State {
    uint8_t b[HASH_LENGTH];
    uint32_t w[HASH_LENGTH / 4];
  };

  public:
    void init(void);
    void initHmac(const uint8_t *key, size_t keyLength);

    // Reset to initial state, but preserve key material.
    void reset(void);

    uint8_t* result(void);
    uint8_t* resultHmac(void);
#if defined(ARDUINO) && ARDUINO >= 100
    virtual size_t write(uint8_t);
#else
    virtual void write(uint8_t);
#endif
    using Print::write;

  private:
    void hashBlock();
    void padBlock();
    void push(uint8_t data);

    uint32_t byteCount;

    uint8_t keyBuffer[BLOCK_LENGTH];
    uint8_t innerHash[HASH_LENGTH];

    State state;
    Buffer buffer;
    uint8_t bufferOffset;
};

#endif