/********************************************************************************/
/*										*/
/*			    Code for prime validation. 				*/
/*			     Written by Ken Goldman				*/
/*		       IBM Thomas J. Watson Research Center			*/
/*            $Id: CryptPrime.c 1529 2019-11-21 23:29:01Z kgoldman $		*/
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/* 10.2.14 CryptPrime.c */
/* 10.2.14.1	Introduction */
/* This file contains the code for prime validation. */

#include "Tpm.h"
#include "CryptPrime_fp.h"
//#define CPRI_PRIME
//#include "PrimeTable.h"
#include "CryptPrimeSieve_fp.h"
extern const uint32_t      s_LastPrimeInTable;
extern const uint32_t      s_PrimeTableSize;
extern const uint32_t      s_PrimesInTable;
extern const unsigned char s_PrimeTable[];
extern bigConst            s_CompositeOfSmallPrimes;

/* 10.2.14.1.1 Root2() */
/* This finds ceil(sqrt(n)) to use as a stopping point for searching the prime table. */
static uint32_t
Root2(
      uint32_t             n
      )
{
    int32_t              last = (int32_t)(n >> 2);
    int32_t              next = (int32_t)(n >> 1);
    int32_t              diff;
    int32_t              stop = 10;
    //
    // get a starting point
    for(; next != 0; last >>= 1, next >>= 2);
    last++;
    do
	{
	    next = (last + (n / last)) >> 1;
	    diff = next - last;
	    last = next;
	    if(stop-- == 0)
		FAIL(FATAL_ERROR_INTERNAL);
	} while(diff < -1 || diff > 1);
    if((n / next) > (unsigned)next)
	next++;
    pAssert(next != 0);
    pAssert(((n / next) <= (unsigned)next) && (n / (next + 1) < (unsigned)next));
    return next;
}
/* 10.2.14.1.2 IsPrimeInt() */
/* This will do a test of a word of up to 32-bits in size. */
BOOL
IsPrimeInt(
	   uint32_t            n
	   )
{
    uint32_t            i;
    uint32_t            stop;
    if(n < 3 || ((n & 1) == 0))
	return (n == 2);
    if(n <= s_LastPrimeInTable)
	{
	    n >>= 1;
	    return ((s_PrimeTable[n >> 3] >> (n & 7)) & 1);
	}
    // Need to search
    stop = Root2(n) >> 1;
    // starting at 1 is equivalent to staring at  (1 << 1) + 1 = 3
    for(i = 1; i < stop; i++)
	{
	    if((s_PrimeTable[i >> 3] >> (i & 7)) & 1)
		// see if this prime evenly divides the number
		if((n % ((i << 1) + 1)) == 0)
		    return FALSE;
	}
    return TRUE;
}
/* 10.2.14.1.3 BnIsProbablyPrime() */
/* This function is used when the key sieve is not implemented. This function Will try to eliminate
   some of the obvious things before going on to perform MillerRabin() as a final verification of
   primeness. */
BOOL
BnIsProbablyPrime(
		  bigNum          prime,           // IN:
		  RAND_STATE      *rand            // IN: the random state just
		  //     in case Miller-Rabin is required
		  )
{
#if RADIX_BITS > 32
    if(BnUnsignedCmpWord(prime, UINT32_MAX) <= 0)
#else
	if(BnGetSize(prime) == 1)
#endif
	    return IsPrimeInt((uint32_t)prime->d[0]);
    if(BnIsEven(prime))
	return FALSE;
    if(BnUnsignedCmpWord(prime, s_LastPrimeInTable) <= 0)
	{
	    crypt_uword_t       temp = prime->d[0] >> 1;
	    return ((s_PrimeTable[temp >> 3] >> (temp & 7)) & 1);
	}
    {
	BN_VAR(n, LARGEST_NUMBER_BITS);
	BnGcd(n, prime, s_CompositeOfSmallPrimes);
	if(!BnEqualWord(n, 1))
	    return FALSE;
    }
    return MillerRabin(prime, rand);
}
/* 10.2.14.1.4 MillerRabinRounds() */
/* Function returns the number of Miller-Rabin rounds necessary to give an error probability equal
   to the security strength of the prime. These values are from FIPS 186-3. */
UINT32
MillerRabinRounds(
		  UINT32           bits           // IN: Number of bits in the RSA prime
		  )
{
    if(bits < 511) return 8;    // don't really expect this
    if(bits < 1536) return 5;   // for 512 and 1K primes
    return 4;                   // for 3K public modulus and greater
}
/* 10.2.14.1.5 MillerRabin() */
/* This function performs a Miller-Rabin test from FIPS 186-3. It does iterations trials on the
   number. In all likelihood, if the number is not prime, the first test fails. */
/* Return Values Meaning */
/* TRUE probably prime */
/* FALSE composite */
BOOL
MillerRabin(
	    bigNum           bnW,
	    RAND_STATE      *rand
	    )
{
    BN_MAX(bnWm1);
    BN_PRIME(bnM);
    BN_PRIME(bnB);
    BN_PRIME(bnZ);
    BOOL             ret = FALSE;   // Assumed composite for easy exit
    unsigned int     a;
    unsigned int     j;
    int              wLen;
    int              i;
    int              iterations = MillerRabinRounds(BnSizeInBits(bnW));
    //
    INSTRUMENT_INC(MillerRabinTrials[PrimeIndex]);
    
    pAssert(bnW->size > 1);
    // Let a be the largest integer such that 2^a divides w1.
    BnSubWord(bnWm1, bnW, 1);
    pAssert(bnWm1->size != 0);
    
    // Since w is odd (w-1) is even so start at bit number 1 rather than 0
    // Get the number of bits in bnWm1 so that it doesn't have to be recomputed
    // on each iteration.
    i = (int)(bnWm1->size * RADIX_BITS);
    // Now find the largest power of 2 that divides w1
    for(a = 1;
	(a < (bnWm1->size * RADIX_BITS)) &&
	    (BnTestBit(bnWm1, a) == 0);
	a++);
    // 2. m = (w1) / 2^a
    BnShiftRight(bnM, bnWm1, a);
    // 3. wlen = len (w).
    wLen = BnSizeInBits(bnW);
    // 4. For i = 1 to iterations do
    for(i = 0; i < iterations; i++)
	{
	    // 4.1 Obtain a string b of wlen bits from an RBG.
	    // Ensure that 1 < b < w1.
	    // 4.2 If ((b <= 1) or (b >= w1)), then go to step 4.1.
	    while(BnGetRandomBits(bnB, wLen, rand) && ((BnUnsignedCmpWord(bnB, 1) <= 0)
						       || (BnUnsignedCmp(bnB, bnWm1) >= 0)));
	    if(g_inFailureMode)
		return FALSE;
	    
	    // 4.3 z = b^m mod w.
	    // if ModExp fails, then say this is not
	    // prime and bail out.
	    BnModExp(bnZ, bnB, bnM, bnW);
	    
	    // 4.4 If ((z == 1) or (z = w == 1)), then go to step 4.7.
	    if((BnUnsignedCmpWord(bnZ, 1) == 0)
	       || (BnUnsignedCmp(bnZ, bnWm1) == 0))
		goto step4point7;
	    // 4.5 For j = 1 to a  1 do.
	    for(j = 1; j < a; j++)
		{
		    // 4.5.1 z = z^2 mod w.
		    BnModMult(bnZ, bnZ, bnZ, bnW);
		    // 4.5.2 If (z = w1), then go to step 4.7.
		    if(BnUnsignedCmp(bnZ, bnWm1) == 0)
			goto step4point7;
		    // 4.5.3 If (z = 1), then go to step 4.6.
		    if(BnEqualWord(bnZ, 1))
			goto step4point6;
		}
	    // 4.6 Return COMPOSITE.
	step4point6:
	    INSTRUMENT_INC(failedAtIteration[i]);
	    goto end;
	    // 4.7 Continue. Comment: Increment i for the do-loop in step 4.
	step4point7:
	    continue;
	}
    // 5. Return PROBABLY PRIME
    ret = TRUE;
 end:
    return ret;
}
#if ALG_RSA
/* 10.2.14.1.6 RsaCheckPrime() */
/* This will check to see if a number is prime and appropriate for an RSA prime. */
/* This has different functionality based on whether we are using key sieving or not. If not, the
   number checked to see if it is divisible by the public exponent, then the number is adjusted
   either up or down in order to make it a better candidate. It is then checked for being probably
   prime. */
/* If sieving is used, the number is used to root a sieving process. */
TPM_RC
RsaCheckPrime(
	      bigNum           prime,
	      UINT32           exponent,
	      RAND_STATE      *rand
	      )
{
#if !RSA_KEY_SIEVE
    TPM_RC          retVal = TPM_RC_SUCCESS;
    UINT32          modE = BnModWord(prime, exponent);
    NOT_REFERENCED(rand);
    if(modE == 0)
	// evenly divisible so add two keeping the number odd
	BnAddWord(prime, prime, 2);
    // want 0 != (p - 1) mod e
    // which is 1 != p mod e
    else if(modE == 1)
	// subtract 2 keeping number odd and insuring that
	// 0 != (p - 1) mod e
	BnSubWord(prime, prime, 2);
    if(BnIsProbablyPrime(prime, rand) == 0)
	ERROR_RETURN(g_inFailureMode ? TPM_RC_FAILURE : TPM_RC_VALUE);
 Exit:
    return retVal;
#else
    return PrimeSelectWithSieve(prime, exponent, rand);
#endif
}
/* 10.2.14.1.7 RsaAdjustPrimeCandidate() */

/* For this math, we assume that the RSA numbers are fixed-point numbers with the decimal point to
   the left of the most significant bit. This approach helps make it clear what is happening with
   the MSb of the values. The two RSA primes have to be large enough so that their product will be a
   number with the necessary number of significant bits. For example, we want to be able to multiply
   two 1024-bit numbers to produce a number with 2048 significant bits. If we accept any 1024-bit
   prime that has its MSb set, then it is possible to produce a product that does not have the MSb
   SET. For example, if we use tiny keys of 16 bits and have two 8-bit primes of 0x80, then the
   public key would be 0x4000 which is only 15-bits. So, what we need to do is made sure that each
   of the primes is large enough so that the product of the primes is twice as large as each
   prime. A little arithmetic will show that the only way to do this is to make sure that each of
   the primes is no less than root(2)/2. That's what this functions does. This function adjusts the
   candidate prime so that it is odd and >= root(2)/2. This allows the product of these two numbers
   to be .5, which, in fixed point notation means that the most significant bit is 1. For this
   routine, the root(2)/2 (0.7071067811865475) approximated with 0xB505 which is, in fixed point,
   0.7071075439453125 or an error of 0.000108%. Just setting the upper two bits would give a value >
   0.75 which is an error of > 6%. Given the amount of time all the other computations take,
   reducing the error is not much of a cost, but it isn't totally required either. */
/* This function can be replaced with a function that just sets the two most significant bits of
   each prime candidate without introducing any computational issues. */

LIB_EXPORT void
RsaAdjustPrimeCandidate(
			bigNum          prime
			)
{
    UINT32          msw;
    UINT32          adjusted;
    
    // If the radix is 32, the compiler should turn this into a simple assignment
    msw = prime->d[prime->size - 1] >> ((RADIX_BITS == 64) ? 32 : 0);
    // Multiplying 0xff...f by 0x4AFB gives 0xff..f - 0xB5050...0
    adjusted = (msw >> 16) * 0x4AFB;
    adjusted += ((msw & 0xFFFF) * 0x4AFB) >> 16;
    adjusted += 0xB5050000UL;
#if RADIX_BITS == 64
    // Save the low-order 32 bits
    prime->d[prime->size - 1] &= 0xFFFFFFFFUL;
    // replace the upper 32-bits
    prime->d[prime->size -1] |= ((crypt_uword_t)adjusted << 32);
#else
    prime->d[prime->size - 1] = (crypt_uword_t)adjusted;
#endif
    // make sure the number is odd
    prime->d[0] |= 1;
}


/* 10.2.14.1.8 BnGeneratePrimeForRSA() */
/* Function to generate a prime of the desired size with the proper attributes for an RSA prime. */

TPM_RC
BnGeneratePrimeForRSA(
		      bigNum          prime,          // IN/OUT: points to the BN that will get the
		      //  random value
		      UINT32          bits,           // IN: number of bits to get
		      UINT32          exponent,       // IN: the exponent
		      RAND_STATE      *rand           // IN: the random state
		      )
{
    BOOL            found = FALSE;
    //
    // Make sure that the prime is large enough
    pAssert(prime->allocated >= BITS_TO_CRYPT_WORDS(bits));
    // Only try to handle specific sizes of keys in order to save overhead
    pAssert((bits % 32) == 0);
    
    prime->size = BITS_TO_CRYPT_WORDS(bits);
    
    while(!found)
	{
	    // The change below is to make sure that all keys that are generated from the same
	    // seed value will be the same regardless of the endianess or word size of the CPU.
	    //       DRBG_Generate(rand, (BYTE *)prime->d, (UINT16)BITS_TO_BYTES(bits));// old
	    //       if(g_inFailureMode)                                                // old
	    if(!BnGetRandomBits(prime, bits, rand))                              // new
		return TPM_RC_FAILURE;
	    RsaAdjustPrimeCandidate(prime);
	    found = RsaCheckPrime(prime, exponent, rand) == TPM_RC_SUCCESS;
	}
    return TPM_RC_SUCCESS;
}

#endif // TPM_ALG_RSA
