/* sha256.h - TinyCrypt interface to a SHA-256 implementation */

/*
    Copyright (C) 2017 by Intel Corporation, All Rights Reserved.

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*/

/**
    @file
    @brief Interface to a SHA-256 implementation.

    Overview:   SHA-256 is a NIST approved cryptographic hashing algorithm
                specified in FIPS 180. A hash algorithm maps data of arbitrary
                size to data of fixed length.

    Security:   SHA-256 provides 128 bits of security against collision attacks
                and 256 bits of security against pre-image attacks. SHA-256 does
                NOT behave like a random oracle, but it can be used as one if
                the string being hashed is prefix-free encoded before hashing.

    Usage:      1) call tc_sha256_init to initialize a struct
                tc_sha256_state_struct before hashing a new string.

                2) call tc_sha256_update to hash the next string segment;
                tc_sha256_update can be called as many times as needed to hash
                all of the segments of a string; the order is important.

                3) call tc_sha256_final to out put the digest from a hashing
                operation.
*/

#ifndef __TC_SHA256_H__
#define __TC_SHA256_H__

#include <stddef.h>
#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif

#define TC_SHA256_BLOCK_SIZE (64)
#define TC_SHA256_DIGEST_SIZE (32)
#define TC_SHA256_STATE_BLOCKS (TC_SHA256_DIGEST_SIZE/4)

struct tc_sha256_state_struct
{
    unsigned int iv[TC_SHA256_STATE_BLOCKS];
    uint64_t bits_hashed;
    uint8_t leftover[TC_SHA256_BLOCK_SIZE];
    size_t leftover_offset;
};

typedef struct tc_sha256_state_struct* TCSha256State_t;

/**
    @brief SHA256 initialization procedure
    Initializes s
    @return returns TC_CRYPTO_SUCCESS (1)
            returns TC_CRYPTO_FAIL (0) if s == NULL
    @param s Sha256 state struct
*/
int tc_sha256_init(TCSha256State_t s);

/**
    @brief SHA256 update procedure
    Hashes data_length bytes addressed by data into state s
    @return returns TC_CRYPTO_SUCCESS (1)
            returns TC_CRYPTO_FAIL (0) if:
                  s == NULL,
                  s->iv == NULL,
                  data == NULL
    @note Assumes s has been initialized by tc_sha256_init
    @warning The state buffer 'leftover' is left in memory after processing
             If your application intends to have sensitive data in this
             buffer, remind to erase it after the data has been processed
    @param s Sha256 state struct
    @param data message to hash
    @param datalen length of message to hash
*/
int tc_sha256_update (TCSha256State_t s, const uint8_t* data, size_t datalen);

/**
    @brief SHA256 final procedure
    Inserts the completed hash computation into digest
    @return returns TC_CRYPTO_SUCCESS (1)
            returns TC_CRYPTO_FAIL (0) if:
                  s == NULL,
                  s->iv == NULL,
                  digest == NULL
    @note Assumes: s has been initialized by tc_sha256_init
          digest points to at least TC_SHA256_DIGEST_SIZE bytes
    @warning The state buffer 'leftover' is left in memory after processing
             If your application intends to have sensitive data in this
             buffer, remind to erase it after the data has been processed
    @param digest unsigned eight bit integer
    @param Sha256 state struct
*/
int tc_sha256_final(uint8_t* digest, TCSha256State_t s);

#ifdef __cplusplus
}
#endif

#endif /* __TC_SHA256_H__ */
