/********************************************************************************/
/*										*/
/*	conversion functions that will convert TPM2B to/from internal format	*/
/*			     Written by Ken Goldman				*/
/*		       IBM Thomas J. Watson Research Center			*/
/*            $Id: BnConvert.c 1047 2017-07-20 18:27:34Z kgoldman $		*/
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/* 10.2.2 BnConvert.c */
/* 10.2.2.1 Introduction */
/* This file contains the basic conversion functions that will convert TPM2B to/from the internal
   format. The internal format is a bigNum, */
/* 10.2.2.2 Includes */
#include "Tpm.h"
/* 10.2.2.3 Functions */
/* 10.2.2.3.1 BnFromBytes() */
/* This function will convert a big-endian byte array to the internal number format. If bn is NULL,
   then the output is NULL. If bytes is null or the required size is 0, then the output is set to
   zero */
LIB_EXPORT bigNum
BnFromBytes(
	    bigNum           bn,
	    const BYTE      *bytes,
	    NUMBYTES         nBytes
	    )
{
    const BYTE      *pFrom; // 'p' points to the least significant bytes of source
    BYTE            *pTo;   // points to least significant bytes of destination
    crypt_uword_t    size;
    //
    size = (bytes != NULL) ? BYTES_TO_CRYPT_WORDS(nBytes) : 0;
    // If nothing in, nothing out
    if(bn == NULL)
	return NULL;
    // make sure things fit
    pAssert(BnGetAllocated(bn) >= size);
    if(size > 0)
	{
	    // Clear the topmost word in case it is not filled with data
	    bn->d[size - 1] = 0;
	    // Moving the input bytes from the end of the list (LSB) end
	    pFrom = bytes + nBytes - 1;
	    // To the LS0 of the LSW of the bigNum.
	    pTo = (BYTE *)bn->d;
	    for(; nBytes != 0; nBytes--)
		*pTo++ = *pFrom--;
	    // For a little-endian machine, the conversion is a straight byte
	    // reversal. For a big-endian machine, we have to put the words in
	    // big-endian byte order
#if BIG_ENDIAN_TPM
	    {
		crypt_word_t   t;
		for(t = (crypt_word_t)size - 1; t >= 0; t--)
		    bn->d[t] = SWAP_CRYPT_WORD(bn->d[t]);
	    }
#endif
	}
    BnSetTop(bn, size);
    return bn;
}
/* 10.2.2.3.2 BnFrom2B() */
/* Convert an TPM2B to a BIG_NUM. If the input value does not exist, or the output does not exist,
   or the input will not fit into the output the function returns NULL */
LIB_EXPORT bigNum
BnFrom2B(
	 bigNum           bn,         // OUT:
	 const TPM2B     *a2B         // IN: number to convert
	 )
{
    if(a2B != NULL)
	return BnFromBytes(bn, a2B->buffer, a2B->size);
    // Make sure that the number has an initialized value rather than whatever
    // was there before
    BnSetTop(bn, 0);
    return NULL;
}
/* 10.2.2.3.3 BnFromHex() */
/* Convert a hex string into a bigNum. This is primarily used in debugging. */
LIB_EXPORT bigNum
BnFromHex(
	  bigNum          bn,         // OUT:
	  const char      *hex        // IN:
	  )
{
#define FromHex(a)  ((a) - (((a) > 'a') ? ('a' + 10)			\
			    : ((a) > 'A') ? ('A' - 10) : '0'))
    unsigned             i;
    unsigned             wordCount;
    const char          *p;
    BYTE                *d = (BYTE *)&(bn->d[0]);
    i = strlen(hex);
    wordCount = BYTES_TO_CRYPT_WORDS((i + 1) / 2);
    if((i == 0) || (wordCount >= BnGetAllocated(bn)))
	BnSetWord(bn, 0);
    else
	{
	    bn->d[wordCount - 1] = 0;
	    p = hex + i - 1;
	    for(;i > 1; i -= 2)
		{
		    BYTE a;
		    a = FromHex(*p);
		    p--;
		    *d++ = a + (FromHex(*p) << 4);
		    p--;
		}
	    if(i == 1)
		*d = FromHex(*p);
	}
#if !BIG_ENDIAN_TPM
    for(i = 0; i < wordCount; i++)
	bn->d[i] = SWAP_CRYPT_WORD(bn->d[i]);
#endif // BIG_ENDIAN_TPM
    BnSetTop(bn, wordCount);
    return bn;
}
/* 10.2.2.3.4 BnToBytes() */
/* This function converts a BIG_NUM to a byte array. If size is not large enough to hold the bigNum
   value, then the function return FALSE. Otherwise, it converts the bigNum to a big-endian byte
   string and sets size to the normalized value. If size is an input 0, then the receiving buffer is
   guaranteed to be large enough for the result and the size will be set to the size required for
   bigNum (leading zeros suppressed). */
/* The conversion for a little-endian machine simply requires that all significant bytes of the
   bigNum be reversed. For a big-endian machine, rather than process unpack each word individually,
   the bigNum is converted to little-endian words, copied, and then converted back to big-endian. */
LIB_EXPORT BOOL
BnToBytes(
	  bigConst             bn,
	  BYTE                *buffer,
	  NUMBYTES            *size           // This the number of bytes that are
	  // available in the buffer. The result
	  // should be this big.
	  )
{
    crypt_uword_t        requiredSize;
    BYTE                *pFrom;
    BYTE                *pTo;
    crypt_uword_t        count;
    //
    // validate inputs
    pAssert(bn != NULL && buffer != NULL && size != NULL);
    requiredSize = (BnSizeInBits(bn) + 7) / 8;
    if(requiredSize == 0)
	{
	    // If the input value is 0, return a byte of zero
	    *size = 1;
	    *buffer = 0;
	}
    else
	{
#if BIG_ENDIAN_TPM
	    // Copy the constant input value into a modifiable value
	    BN_VAR(bnL, LARGEST_NUMBER_BITS * 2);
	    BnCopy(bnL, bn);
	    // byte swap the words in the local value to make them little-endian
	    for(count = 0; count < bnL->size; count++)
		bnL->d[count] = SWAP_CRYPT_WORD(bnL->d[count]);
	    bn = (bigConst)bnL;
#endif
	    if(*size == 0)
		*size = (NUMBYTES)requiredSize;
	    pAssert(requiredSize <= *size);
	    // Byte swap the number (not words but the whole value)
	    count = *size;
	    // Start from the least significant word and offset to the most significant
	    // byte which is in some high word
	    pFrom = (BYTE *)(&bn->d[0]) + requiredSize - 1;
	    pTo = buffer;
	    // If the number of output bytes is larger than the number bytes required
	    // for the input number, pad with zeros
	    for(count = *size; count > requiredSize; count--)
		*pTo++ = 0;
	    // Move the most significant byte at the end of the BigNum to the next most
	    // significant byte position of the 2B and repeat for all significant bytes.
	    for(; requiredSize > 0; requiredSize--)
		*pTo++ = *pFrom--;
	}
    return TRUE;
}
/* 10.2.2.3.5 BnTo2B() */
/* Function to convert a BIG_NUM to TPM2B. The TPM2B size is set to the requested size which may
   require padding. If size is non-zero and less than required by the value in bn then an error is
   returned. If size is zero, then the TPM2B is assumed to be large enough for the data and
   a2b->size will be adjusted accordingly. */
LIB_EXPORT BOOL
BnTo2B(
       bigConst         bn,                // IN:
       TPM2B           *a2B,               // OUT:
       NUMBYTES         size               // IN: the desired size
       )
{
    // Set the output size
    a2B->size = size;
    return BnToBytes(bn, a2B->buffer, &a2B->size);
}
#ifdef TPM_ALG_ECC
/* 10.2.2.3.6 BnPointFrom2B() */
/* Function to create a BIG_POINT structure from a 2B point. A point is going to be two ECC values
   in the same buffer. The values are going to be the size of the modulus.  They are in modular
   form. */
LIB_EXPORT bn_point_t   *
BnPointFrom2B(
	      bigPoint             ecP,         // OUT: the preallocated point structure
	      TPMS_ECC_POINT      *p            // IN: the number to convert
	      )
{
    if(p == NULL)
	return NULL;
    if(NULL != ecP)
	{
	    BnFrom2B(ecP->x, &p->x.b);
	    BnFrom2B(ecP->y, &p->y.b);
	    BnSetWord(ecP->z, 1);
	}
    return ecP;
}
/* 10.2.2.3.7 BnPointTo2B() */
/* This function converts a BIG_POINT into a TPMS_ECC_POINT. A TPMS_ECC_POINT contains two
   TPM2B_ECC_PARAMETER values. The maximum size of the parameters is dependent on the maximum EC key
   size used in an implementation. The presumption is that the TPMS_ECC_POINT is large enough to
   hold 2 TPM2B values, each as large as a MAX_ECC_PARAMETER_BYTES */
LIB_EXPORT BOOL
BnPointTo2B(
	    TPMS_ECC_POINT  *p,             // OUT: the converted 2B structure
	    bigPoint         ecP,           // IN: the values to be converted
	    bigCurve         E              // IN: curve descriptor for the point
	    )
{
    UINT16           size = (UINT16)BITS_TO_BYTES(
						  BnMsb(CurveGetOrder(AccessCurveData(E))));
    pAssert(p && ecP && E);
    pAssert(BnEqualWord(ecP->z, 1));
    BnTo2B(ecP->x, &p->x.b, size);
    BnTo2B(ecP->y, &p->y.b, size);
    return TRUE;
}
#endif // TPM_ALG_ECC

LIB_EXPORT int
Bn2bin(bigConst       bn,
       unsigned char *buffer,
       size_t         buffer_len)
{
    int i = bn->size;
    int bits, j, t = 0;
    const size_t sz = sizeof(crypt_uword_t);
    unsigned char *pFrom;

    if (i > 0) {
        i -= 1;
        bits = i * BN_BITS2 + BN_num_bits_word(bn->d[i]);
        t = BITS_TO_BYTES(bits);
        j = t - 1;

        pAssert(t < (int)buffer_len)

#if BIG_ENDIAN_TPM
        unsigned int count;
	// Copy the constant input value into a modifiable value
	BN_VAR(bnL, LARGEST_NUMBER_BITS * 2);
	BnCopy(bnL, bn);
	// byte swap the words in the local value to make them little-endian
	for(count = 0; count < bnL->size; count++)
	    bnL->d[count] = SWAP_CRYPT_WORD(bnL->d[count]);
	bn = (bigConst)bnL;
#endif
	pFrom = (unsigned char *)&bn->d[j / sz] + (j % sz);

        for (;j >= 0; j--)
            *buffer++ = *pFrom--;
    }

    return t;
}
