/*
 * crypting: Hashes and Crypto in GAP
 */

#include "gap_all.h"   // GAP headers

static Obj CRYPTING_SHA256_State_Type;

/* Implements the SHA256 hash function as per the description in
 * https://web.archive.org/web/20130526224224/http://csrc.nist.gov/groups/STM/cavp/documents/shs/sha256-384-512.pdf
 */


/* For the moment we assume the input is a
   string, we should probably have a list of bytes,
   or words or something */


static inline UInt4 RotateRight(UInt4 x, const UInt4 n)
{
    return (x >> n) | (x << (32 - n));
}

static inline UInt4 Ch(UInt4 x, UInt4 y, UInt4 z)
{ return (x & y) ^ (~x & z); }

static inline UInt4 Maj(UInt4 x, UInt4 y, UInt4 z)
{ return (x & y) ^ (x & z) ^ (y & z); }

static inline UInt4 Sigma0(UInt4 x)
{ return RotateRight(x, 2) ^ RotateRight(x, 13) ^ RotateRight(x, 22); }

static inline UInt4 Sigma1(UInt4 x)
{ return RotateRight(x, 6) ^ RotateRight(x, 11) ^ RotateRight(x, 25); }

static inline UInt4 sigma0(UInt4 x)
{ return RotateRight(x, 7) ^ RotateRight(x, 18) ^ (x >> 3); }

static inline UInt4 sigma1(UInt4 x)
{ return RotateRight(x, 17) ^ RotateRight(x, 19) ^ (x >> 10); }

static const UInt4 k[] = {
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
    0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
    0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
    0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
    0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
    0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
    0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
};

static const UInt4 rinit[] = {
    0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
    0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19 };

// determine endianess, the lazy way (the proper way
// would be using a configure script and checking by test-compiling
// some code and using the result to #define a suitable flag)
#if defined(__BYTE_ORDER__)
  #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
  #define WORDS_BIGENDIAN 1
  #elif __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
  #undef WORDS_BIGENDIAN
  #else
  #error Unsupported __BYTE_ORDER__
  #endif
#elif defined(__BIG_ENDIAN__) && __BIG_ENDIAN__
#define WORDS_BIGENDIAN 1
#elif defined(__LITTLE_ENDIAN__) && __LITTLE_ENDIAN__
#undef WORDS_BIGENDIAN
#else
#error Could not determine endianess
#endif

#ifdef WORDS_BIGENDIAN
#include <string.h>
#define be32decode(dst, src, len) memcpy(dst, src, len)
#define be32encode(dst, src, len) memcpy(dst, src, len)
#define store64be(dst, x) *dst = x
#else
static void be32decode(UInt4 *dst, const UInt1 *src, UInt len)
{
    UInt i;
    for(i=0;i<(len >> 2);i++) {
        dst[i] = (src[i*4] << 24)
            | (src[i*4 + 1] << 16)
            | (src[i*4 + 2] << 8)
            | (src[i*4 + 3]);
    }
}

static void be32encode(UInt1 *dst, const UInt4 *src, UInt len)
{
    UInt i;
    for(i=0;i<(len >> 2);i++) {
        dst[4*i+0] = (src[i] & 0xff000000) >> 24;
        dst[4*i+1] = (src[i] & 0xff0000) >> 16;
        dst[4*i+2] = (src[i] & 0xff00) >> 8;
        dst[4*i+3] = (src[i] & 0xff);
    }
}

static void store64be(UInt8 *dst, UInt8 x)
{
    *dst = (((x >> 56) |
            ((x >> 40) & 0xff00) |
            ((x >> 24) & 0xff0000) |
            ((x >> 8) & 0xff000000) |
            ((x << 8) & ((UInt8)0xff << 32)) |
            ((x << 24) & ((UInt8)0xff << 40)) |
            ((x << 40) & ((UInt8)0xff << 48)) |
            ((x << 56))));
}
#endif

typedef struct sha256_state_t {
    UInt4 r[8];      /* Current hash value register */
    UInt count;      /* Nr of bits already hashed */
    UInt1 buf[64];   /* One chunk, 512 bits */
} sha256_state_t;

static int sha256_init(sha256_state_t *state)
{
    memcpy(state->r, rinit, sizeof(rinit));
    state->count = 0UL;
    memset(state->buf, 0, 64);

    return 0;
}

static void sha256_transform(UInt4 state[8], const UInt1 block[64], UInt4 w[64], UInt4 r[8])
{
    UInt i;
    UInt4 temp1, temp2;

    memcpy(r, state, 32);
    be32decode(w, block, 64);
    for(i=16;i<64;i++) {
        w[i] = sigma1(w[i-2]) + w[i-7] + sigma0(w[i-15]) + w[i-16];
    }

    /* A block is 512bit = 64bytes */
    for(i=0;i<64;i++) {
        temp1 = r[7] + Sigma1(r[4]) + Ch(r[4], r[5], r[6]) + k[i] + w[i];
        temp2 = Sigma0(r[0]) + Maj(r[0],r[1],r[2]);
        r[7] = r[6];
        r[6] = r[5];
        r[5] = r[4];
        r[4] = r[3] + temp1;
        r[3] = r[2];
        r[2] = r[1];
        r[1] = r[0];
        r[0] = temp1 + temp2;
    }
    for(i=0;i<8;i++) {
        state[i] += r[i];
    }
}

static int sha256_update(sha256_state_t *state, const UChar *buf, UInt8 len)
{
    UInt4 i,rem;
    UInt4 w[64];
    UInt4 r[8];

    /* If there is buffered stuff in state, fill block */
    rem = (state->count >> 3) & 0x3f;
    /* Number of bits already hashed. Needed for continuation, and for
       padding */
    state->count += len << 3;

    /* Not enough to hash full block, just buffer */
    if (len < 64 - rem) {
        for (i=0; i<len; i++) {
            state->buf[rem + i] = buf[i];
        }
        return 0;
    }
    for (i=0; i<64-rem; i++) {
        state->buf[rem+i] = buf[i];
    }
    /* Filled a block, do the SHA256 transform */
    sha256_transform(state->r, state->buf, w, r);
    buf += (UInt4)64 - rem;
    len -= (UInt4)64 - rem;

    /* Hash full blocks */
    while(len >= 64) {
        sha256_transform(state->r, (const UInt1 *)buf, w, r);
        buf += 64;
        len -= 64;
    }

    /* Store remainder in buffer */
    for(i=0;i<len;i++) {
        state->buf[i] = buf[i];
    }
    memset(w, 0x0, sizeof(w));
    memset(r, 0x0, sizeof(r));

    return 0;
}

static int sha256_final(sha256_state_t *state)
{
    UInt8 rem;
    UInt8 i;
    UInt4 w[64];
    UInt4 r[8];

    rem = (state->count >> 3) & 0x3f;
    state->buf[rem] = 0x80;
    if(rem<56) {
        for(i=1;i<56-rem;i++) {
            state->buf[rem+i] = 0x00;
        }
    } else {
        for(i=1;i<(UInt4)64-rem;i++) {
            state->buf[rem + i] = 0x00;
        }
        sha256_transform(state->r, state->buf, w, r);
        memset(state->buf, 0, 56);
    }
    store64be((UInt8 *)(&state->buf[56]), state->count);

    sha256_transform(state->r, state->buf, w, r);

    return 0;
}

Obj FuncCRYPTING_SHA256_INIT(Obj self)
{
    Obj result;
    sha256_state_t *sptr;

    result = NewBag(T_DATOBJ, sizeof(UInt4) + sizeof(sha256_state_t));
    SET_TYPE_OBJ(result, CRYPTING_SHA256_State_Type);

    sptr = (sha256_state_t *)(&ADDR_OBJ(result)[1]);
    sha256_init(sptr);

    return result;
}

Obj FuncCRYPTING_SHA256_UPDATE(Obj self, Obj state, Obj bytes)
{
    sha256_state_t *sptr;
    if (!IS_STRING(bytes) || !IS_STRING_REP(bytes)) {
        ErrorQuit("usage: bytes has to be a string in IsStringRep", 0L, 0L);
        return Fail;
    }

    sptr = (sha256_state_t *)(&ADDR_OBJ(state)[1]);
    sha256_update(sptr, CHARS_STRING(bytes), GET_LEN_STRING(bytes));
    CHANGED_BAG(state);

    return 0;
}

Obj FuncCRYPTING_SHA256_FINAL(Obj self, Obj state)
{
    Obj result;
    sha256_state_t *sptr;
    int i;

    result = NEW_PLIST(T_PLIST, 8);
    SET_LEN_PLIST(result, 8);

    sptr = (sha256_state_t *)(&ADDR_OBJ(state)[1]);
    sha256_final(sptr);
    CHANGED_BAG(state);

    for(i=0;i<8;i++) {
        SET_ELM_PLIST(result, i+1, ObjInt_UInt(sptr->r[i]));
        CHANGED_BAG(result);
    }
    return result;
}

Obj FuncCRYPTING_SHA256_HMAC(Obj self, Obj key, Obj text)
{
    UInt i, klen;
    UInt1 k_ipad[64], k_opad[64];
    UInt1 digest[32];
    sha256_state_t st;
    Obj result;

    if (!IS_STRING(key) || !IS_STRING_REP(key)) {
        ErrorQuit("usage: key has to be a string in IsStringRep", 0L, 0L);
        return Fail;
    }
    if (!IS_STRING(text) || !IS_STRING_REP(text)) {
        ErrorQuit("usage: text has to be a string in IsStringRep", 0L, 0L);
        return Fail;
    }

    memset(k_ipad, 0x36, sizeof(k_ipad));
    memset(k_opad, 0x5c, sizeof(k_opad));

    klen = GET_LEN_STRING(key);
    if(GET_LEN_STRING(key) > 64) {
        sha256_init(&st);
        sha256_update(&st, CHARS_STRING(key), klen);
        sha256_final(&st);

        be32encode(digest, st.r, sizeof(digest));
        klen = 32;

        for (i=0;i<klen;i++) {
            k_ipad[i] ^= digest[i];
            k_opad[i] ^= digest[i];
        }
    } else {
        for (i=0;i<klen;i++) {
            k_ipad[i] ^= CHARS_STRING(key)[i];
            k_opad[i] ^= CHARS_STRING(key)[i];
        }
    }

    sha256_init(&st);
    sha256_update(&st, k_ipad, 64);
    sha256_update(&st, CHARS_STRING(text), GET_LEN_STRING(text));
    sha256_final(&st);

    be32encode(digest, st.r, sizeof(digest));
    sha256_init(&st);
    sha256_update(&st, k_opad, 64);
    sha256_update(&st, digest, 32);
    sha256_final(&st);

    result = NEW_PLIST(T_PLIST, 8);
    SET_LEN_PLIST(result, 8);
    for(i=0;i<8;i++) {
        SET_ELM_PLIST(result, i+1, ObjInt_UInt(st.r[i]));
        CHANGED_BAG(result);
    }
    return result;
}

// Table of functions to export
static StructGVarFunc GVarFuncs [] = {
    GVAR_FUNC(CRYPTING_SHA256_INIT, 0, ""),
    GVAR_FUNC(CRYPTING_SHA256_UPDATE, 2, "state, bytes"),
    GVAR_FUNC(CRYPTING_SHA256_FINAL, 1, "state"),
    GVAR_FUNC(CRYPTING_SHA256_HMAC, 2, "key, text"),

    { 0 } /* Finish with an empty entry */
};

/******************************************************************************
*F  InitKernel( <module> )  . . . . . . . . initialise kernel data structures
*/
static Int InitKernel( StructInitInfo *module )
{
    ImportGVarFromLibrary( "CRYPTING_SHA256_State_Type", &CRYPTING_SHA256_State_Type);

    /* init filters and functions */
    InitHdlrFuncsFromTable( GVarFuncs );

    /* return success */
    return 0;
}

/******************************************************************************
*F  InitLibrary( <module> ) . . . . . . .  initialise library data structures
*/
static Int InitLibrary( StructInitInfo *module )
{
    /* init filters and functions */
    InitGVarFuncsFromTable( GVarFuncs );

    return 0;
}

/******************************************************************************
*F  InitInfopl()  . . . . . . . . . . . . . . . . . table of init functions
*/
static StructInitInfo module = {
    .type = MODULE_DYNAMIC,
    .name = "crypting",
    .initKernel = InitKernel,
    .initLibrary = InitLibrary,
};

StructInitInfo *Init__Dynamic( void )
{
    return &module;
}
