/********************************************************************************/
/*										*/
/*	Math functions performed with canonical integers in byte buffers	*/
/*			     Written by Ken Goldman				*/
/*		       IBM Thomas J. Watson Research Center			*/
/*            $Id: MathOnByteBuffers.c 1519 2019-11-15 20:43:51Z kgoldman $	*/
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/* 9.11 MathOnByteBuffers.c */
/* 9.11.1 Introduction */
/* This file contains implementation of the math functions that are performed with canonical
   integers in byte buffers. The canonical integer is big-endian bytes. */
#include "Tpm.h"
/* 9.11.2.1 UnsignedCmpB */
/* This function compare two unsigned values. The values are byte-aligned, big-endian numbers (e.g,
   a hash). */
/* Return Values Meaning */
/* 1 if (a > b) */
/* 0 if (a = b) */
/* -1 if (a < b) */
LIB_EXPORT int
UnsignedCompareB(
		 UINT32           aSize,         // IN: size of a
		 const BYTE      *a,             // IN: a
		 UINT32           bSize,         // IN: size of b
		 const BYTE      *b              // IN: b
		 )
{
    UINT32             i;
    if(aSize > bSize)
	return 1;
    else if(aSize < bSize)
	return -1;
    else
	{
	    for(i = 0; i < aSize; i++)
		{
		    if(a[i] != b[i])
			return (a[i] > b[i]) ? 1 : -1;
		}
	}
    // Will return == if sizes are both zero
    return 0;
}
/* 9.11.2.2 SignedCompareB() */
/* Compare two signed integers: */
/* Return Values Meaning */
/* 1 if a > b */
/* 0 if a = b */
/* -1 if a < b */
int
SignedCompareB(
	       const UINT32     aSize,         // IN: size of a
	       const BYTE      *a,             // IN: a buffer
	       const UINT32     bSize,         // IN: size of b
	       const BYTE      *b              // IN: b buffer
	       )
{
    // are the signs different ?
    if(((a[0] ^ b[0]) & 0x80) > 0)
	// if the signs are different, then a is less than b if a is negative.
	return a[0] & 0x80 ? -1 : 1;
    else
	// do unsigned compare function
	return UnsignedCompareB(aSize, a, bSize, b);
}
/* 9.11.3.3 ModExpB */
/* This function is used to do modular exponentiation in support of RSA. The most typical uses are:
   c = m^e mod n (RSA encrypt) and m = c^d mod n (RSA decrypt).  When doing decryption, the e
   parameter of the function will contain the private exponent d instead of the public exponent
   e. */
/* If the results will not fit in the provided buffer, an error is returned
   (CRYPT_ERROR_UNDERFLOW). If the results is smaller than the buffer, the results is
   de-normalized. */
/* This version is intended for use with RSA and requires that m be less than n. */
/* Error Returns Meaning */
/* TPM_RC_SIZE number to exponentiate is larger than the modulus */
/* TPM_RC_NO_RESULT result will not fit into the provided buffer */
TPM_RC
ModExpB(
	UINT32           cSize,         // IN: the size of the output buffer. It will
	//     need to be the same size as the modulus
	BYTE            *c,             // OUT: the buffer to receive the results
	//     (c->size must be set to the maximum size
	//     for the returned value)
	const UINT32     mSize,
	const BYTE      *m,             // IN: number to exponentiate
	const UINT32     eSize,
	const BYTE      *e,             // IN: power
	const UINT32     nSize,
	const BYTE      *n              // IN: modulus
	)
{
    BN_MAX(bnC);
    BN_MAX(bnM);
    BN_MAX(bnE);
    BN_MAX(bnN);
    NUMBYTES         tSize = (NUMBYTES)nSize;
    TPM_RC           retVal = TPM_RC_SUCCESS;
    // Convert input parameters
    BnFromBytes(bnM, m, (NUMBYTES)mSize);
    BnFromBytes(bnE, e, (NUMBYTES)eSize);
    BnFromBytes(bnN, n, (NUMBYTES)nSize);
    // Make sure that the output is big enough to hold the result
    // and that 'm' is less than 'n' (the modulus)
    if(cSize < nSize)
	ERROR_RETURN(TPM_RC_NO_RESULT);
    if(BnUnsignedCmp(bnM, bnN) >= 0)
	ERROR_RETURN(TPM_RC_SIZE);
    BnModExp(bnC, bnM, bnE, bnN);
    BnToBytes(bnC, c, &tSize);
 Exit:
    return retVal;
}
/* 9.11.2.4 DivideB() */
/* Divide an integer (n) by an integer (d) producing a quotient (q) and a remainder (r). If q or r
   is not needed, then the pointer to them may be set to NULL. */
/* Error Returns Meaning */
/* TPM_RC_NO_RESULT q or r is too small to receive the result */
LIB_EXPORT TPM_RC
DivideB(
	const TPM2B     *n,             // IN: numerator
	const TPM2B     *d,             // IN: denominator
	TPM2B           *q,             // OUT: quotient
	TPM2B           *r              // OUT: remainder
	)
{
    BN_MAX_INITIALIZED(bnN, n);
    BN_MAX_INITIALIZED(bnD, d);
    BN_MAX(bnQ);
    BN_MAX(bnR);
    //
    // Do divide with converted values
    BnDiv(bnQ, bnR, bnN, bnD);
    // Convert the BIGNUM result back to 2B format using the size of the original
    // number
    if(q != NULL)
	if(!BnTo2B(bnQ, q, q->size))
	    return TPM_RC_NO_RESULT;
    if(r != NULL)
	if(!BnTo2B(bnR, r, r->size))
	    return TPM_RC_NO_RESULT;
    return TPM_RC_SUCCESS;
}
/* 9.11.2.5 AdjustNumberB() */
/* Remove/add leading zeros from a number in a TPM2B. Will try to make the number by adding or
   removing leading zeros. If the number is larger than the requested size, it will make the number
   as small as possible. Setting requestedSize to zero is equivalent to requesting that the number
   be normalized. */
UINT16
AdjustNumberB(
	      TPM2B           *num,
	      UINT16           requestedSize
	      )
{
    BYTE            *from;
    UINT16           i;
    // See if number is already the requested size
    if(num->size == requestedSize)
	return requestedSize;
    from = num->buffer;
    if (num->size > requestedSize)
	{
	    // This is a request to shift the number to the left (remove leading zeros)
	    // Find the first non-zero byte. Don't look past the point where removing
	    // more zeros would make the number smaller than requested, and don't throw
	    // away any significant digits.
	    for(i = num->size; *from == 0 && i > requestedSize; from++, i--);
	    if(i < num->size)
		{
		    num->size = i;
		    MemoryCopy(num->buffer, from, i);
		}
	}
    // This is a request to shift the number to the right (add leading zeros)
    else
	{
	    MemoryCopy(&num->buffer[requestedSize - num->size], num->buffer, num->size);
	    MemorySet(num->buffer, 0, requestedSize- num->size);
	    num->size = requestedSize;
	}
    return num->size;
}

/* 9.11.2.6 ShiftLeft() */
/* This function shifts a byte buffer (a TPM2B) one byte to the left. That is, the most significant
   bit of the most significant byte is lost. */
TPM2B *
ShiftLeft(
	  TPM2B       *value          // IN/OUT: value to shift and shifted value out
	  )
{
    UINT16       count = value->size;
    BYTE        *buffer = value->buffer;
    if(count > 0)
	{
	    for(count -= 1; count > 0; buffer++, count--)
		{
		    buffer[0] = (buffer[0] << 1) + ((buffer[1] & 0x80) ? 1 : 0);
		}
	    *buffer <<= 1;
	}
    return value;
}