/********************************************************************************/
/*										*/
/*	Functions that are used for the two-phase, ECC, key-exchange protocols	*/
/*			     Written by Ken Goldman				*/
/*		       IBM Thomas J. Watson Research Center			*/
/*            $Id: CryptEccKeyExchange.c 1594 2020-03-26 22:15:48Z kgoldman $	*/
/*										*/
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/* 10.2.11 CryptEccKeyExchange.c */
#include "Tpm.h"

LIB_EXPORT TPM_RC
SM2KeyExchange(
	       TPMS_ECC_POINT        *outZ,         // OUT: the computed point
	       TPM_ECC_CURVE          curveId,      // IN: the curve for the computations
	       TPM2B_ECC_PARAMETER   *dsAIn,        // IN: static private TPM key
	       TPM2B_ECC_PARAMETER   *deAIn,        // IN: ephemeral private TPM key
	       TPMS_ECC_POINT        *QsBIn,        // IN: static public party B key
	       TPMS_ECC_POINT        *QeBIn         // IN: ephemeral public party B key
	       );

#if CC_ZGen_2Phase == YES
#if ALG_ECMQV
/*     10.2.11.1.1 avf1() */
/* This function does the associated value computation required by MQV key exchange. Process: */
/* a) Convert xQ to an integer xqi using the convention specified in Appendix C.3. */
/* b) Calculate xqm = xqi mod 2^ceil(f/2) (where f = ceil(log2(n)). */
/* c) Calculate the associate value function avf(Q) = xqm + 2ceil(f / 2) */
/*  Always returns TRUE(1). */
static BOOL
avf1(
     bigNum               bnX,           // IN/OUT: the reduced value
     bigNum               bnN            // IN: the order of the curve
     )
{
    // compute f = 2^(ceil(ceil(log2(n)) / 2))
    int                      f = (BnSizeInBits(bnN) + 1) / 2;
    // x' = 2^f + (x mod 2^f)
    BnMaskBits(bnX, f);   // This is mod 2*2^f but it doesn't matter because
    // the next operation will SET the extra bit anyway
    BnSetBit(bnX, f);
    return TRUE;
}
/* 	  10.2.11.1.2 C_2_2_MQV() */
/* This function performs the key exchange defined in SP800-56A 6.1.1.4 Full MQV, C(2, 2, ECC
   MQV). */
/* CAUTION: Implementation of this function may require use of essential claims in patents not owned
   by TCG members. */
/* Points QsB() and QeB() are required to be on the curve of inQsA. The function will fail, possibly
   catastrophically, if this is not the case. */
/* Error Returns Meaning */
/* TPM_RC_NO_RESULT the value for dsA does not give a valid point on the curve */
static TPM_RC
C_2_2_MQV(
	  TPMS_ECC_POINT        *outZ,         // OUT: the computed point
	  TPM_ECC_CURVE          curveId,      // IN: the curve for the computations
	  TPM2B_ECC_PARAMETER   *dsA,          // IN: static private TPM key
	  TPM2B_ECC_PARAMETER   *deA,          // IN: ephemeral private TPM key
	  TPMS_ECC_POINT        *QsB,          // IN: static public party B key
	  TPMS_ECC_POINT        *QeB           // IN: ephemeral public party B key
	  )
{
    CURVE_INITIALIZED(E, curveId);
    const ECC_CURVE_DATA          *C;
    POINT(pQeA);
    POINT_INITIALIZED(pQeB, QeB);
    POINT_INITIALIZED(pQsB, QsB);
    ECC_NUM(bnTa);
    ECC_INITIALIZED(bnDeA, deA);
    ECC_INITIALIZED(bnDsA, dsA);
    ECC_NUM(bnN);
    ECC_NUM(bnXeB);
    TPM_RC                 retVal;
    //
    // Parameter checks
    if(E == NULL)
	ERROR_RETURN(TPM_RC_VALUE);
    pAssert(outZ != NULL && pQeB != NULL && pQsB != NULL && deA != NULL
	    && dsA != NULL);
    C = AccessCurveData(E);
    // Process:
    //  1. implicitsigA = (de,A + avf(Qe,A)ds,A ) mod n.
    //  2. P = h(implicitsigA)(Qe,B + avf(Qe,B)Qs,B).
    //  3. If P = O, output an error indicator.
    //  4. Z=xP, where xP is the x-coordinate of P.
    // Compute the public ephemeral key pQeA = [de,A]G
    if((retVal = BnPointMult(pQeA, CurveGetG(C), bnDeA, NULL, NULL, E))
       != TPM_RC_SUCCESS)
	goto Exit;
    //  1. implicitsigA = (de,A + avf(Qe,A)ds,A ) mod n.
    //  tA := (ds,A + de,A  avf(Xe,A)) mod n    (3)
    //  Compute 'tA' = ('deA' +  'dsA'  avf('XeA')) mod n
    // Ta = avf(XeA);
    BnCopy(bnTa, pQeA->x);
    avf1(bnTa, bnN);
    // do Ta = ds,A * Ta mod n = dsA * avf(XeA) mod n
    BnModMult(bnTa, bnDsA, bnTa, bnN);
    // now Ta = deA + Ta mod n =  deA + dsA * avf(XeA) mod n
    BnAdd(bnTa, bnTa, bnDeA);
    BnMod(bnTa, bnN);
    //  2. P = h(implicitsigA)(Qe,B + avf(Qe,B)Qs,B).
    // Put this in because almost every case of h is == 1 so skip the call when
    // not necessary.
    if(!BnEqualWord(CurveGetCofactor(C), 1))
	// Cofactor is not 1 so compute Ta := Ta * h mod n
	BnModMult(bnTa, bnTa, CurveGetCofactor(C), CurveGetOrder(C));
    // Now that 'tA' is (h * 'tA' mod n)
    // 'outZ' = (tA)(Qe,B + avf(Qe,B)Qs,B).
    // first, compute XeB = avf(XeB)
    avf1(bnXeB, bnN);
    // QsB := [XeB]QsB
    BnPointMult(pQsB, pQsB, bnXeB, NULL, NULL, E);
    BnEccAdd(pQeB, pQeB, pQsB, E);
    // QeB := [tA]QeB = [tA](QsB + [Xe,B]QeB) and check for at infinity
    // If the result is not the point at infinity, return QeB
    BnPointMult(pQeB, pQeB, bnTa, NULL, NULL, E);
    if(BnEqualZero(pQeB->z))
	ERROR_RETURN(TPM_RC_NO_RESULT);
    // Convert BIGNUM E to TPM2B E
    BnPointTo2B(outZ, pQeB, E);
 Exit:
    CURVE_FREE(E);
    return retVal;
}
#endif // ALG_ECMQV
/* 10.2.11.1.3 C_2_2_ECDH() */
/* This function performs the two phase key exchange defined in SP800-56A, 6.1.1.2 Full Unified
   Model, C(2, 2, ECC CDH). */
static TPM_RC
C_2_2_ECDH(
	   TPMS_ECC_POINT          *outZs,         // OUT: Zs
	   TPMS_ECC_POINT          *outZe,         // OUT: Ze
	   TPM_ECC_CURVE            curveId,       // IN: the curve for the computations
	   TPM2B_ECC_PARAMETER     *dsA,           // IN: static private TPM key
	   TPM2B_ECC_PARAMETER     *deA,           // IN: ephemeral private TPM key
	   TPMS_ECC_POINT          *QsB,           // IN: static public party B key
	   TPMS_ECC_POINT          *QeB            // IN: ephemeral public party B key
	   )
{
    CURVE_INITIALIZED(E, curveId);
    ECC_INITIALIZED(bnAs, dsA);
    ECC_INITIALIZED(bnAe, deA);
    POINT_INITIALIZED(ecBs, QsB);
    POINT_INITIALIZED(ecBe, QeB);
    POINT(ecZ);
    TPM_RC            retVal;
    //
    // Parameter checks
    if(E == NULL)
	ERROR_RETURN(TPM_RC_CURVE);
    pAssert(outZs != NULL && dsA != NULL && deA != NULL && QsB != NULL
	    && QeB != NULL);
    // Do the point multiply for the Zs value ([dsA]QsB)
    retVal = BnPointMult(ecZ, ecBs, bnAs, NULL, NULL, E);
    if(retVal == TPM_RC_SUCCESS)
	{
	    // Convert the Zs value.
	    BnPointTo2B(outZs, ecZ, E);
	    // Do the point multiply for the Ze value ([deA]QeB)
	    retVal = BnPointMult(ecZ, ecBe, bnAe, NULL, NULL, E);
	    if(retVal == TPM_RC_SUCCESS)
		BnPointTo2B(outZe, ecZ, E);
	}
 Exit:
    CURVE_FREE(E);
    return retVal;
}
/* 10.2.11.1.4 CryptEcc2PhaseKeyExchange() */
/* This function is the dispatch routine for the EC key exchange functions that use two ephemeral
   and two static keys. */
/* Error Returns Meaning */
/* TPM_RC_SCHEME scheme is not defined */
LIB_EXPORT TPM_RC
CryptEcc2PhaseKeyExchange(
			  TPMS_ECC_POINT          *outZ1,         // OUT: a computed point
			  TPMS_ECC_POINT          *outZ2,         // OUT: and optional second point
			  TPM_ECC_CURVE            curveId,   // IN: the curve for the computations
			  TPM_ALG_ID               scheme,        // IN: the key exchange scheme
			  TPM2B_ECC_PARAMETER     *dsA,           // IN: static private TPM key
			  TPM2B_ECC_PARAMETER     *deA,           // IN: ephemeral private TPM key
			  TPMS_ECC_POINT          *QsB,           // IN: static public party B key
			  TPMS_ECC_POINT          *QeB            // IN: ephemeral public party B key
			  )
{
    pAssert(outZ1 != NULL
	    && dsA != NULL && deA != NULL
	    && QsB != NULL && QeB != NULL);
    // Initialize the output points so that they are empty until one of the
    // functions decides otherwise
    outZ1->x.b.size = 0;
    outZ1->y.b.size = 0;
    if(outZ2 != NULL)
	{
	    outZ2->x.b.size = 0;
	    outZ2->y.b.size = 0;
	}
    switch(scheme)
	{
	  case ALG_ECDH_VALUE:
	    return C_2_2_ECDH(outZ1, outZ2, curveId, dsA, deA, QsB, QeB);
	    break;
#if ALG_ECMQV
	  case ALG_ECMQV_VALUE:
	    return C_2_2_MQV(outZ1, curveId, dsA, deA, QsB, QeB);
	    break;
#endif
#if ALG_SM2
	  case ALG_SM2_VALUE:
	    return SM2KeyExchange(outZ1, curveId, dsA, deA, QsB, QeB);
	    break;
#endif
	  default:
	    return TPM_RC_SCHEME;
	}
}
#if ALG_SM2
/* 10.2.11.1.5 ComputeWForSM2() */
/* Compute the value for w used by SM2 */
static UINT32
ComputeWForSM2(
	       bigCurve        E
	       )
{
    //  w := ceil(ceil(log2(n)) / 2) - 1
    return (BnMsb(CurveGetOrder(AccessCurveData(E))) / 2 - 1);
}
/* 10.2.11.1.6 avfSm2() */
/* This function does the associated value computation required by SM2 key exchange. This is
   different form the avf() in the international standards because it returns a value that is half
   the size of the value returned by the standard avf. For example, if n is 15, Ws (w in the
   standard) is 2 but the W here is 1. This means that an input value of 14 (1110b) would return a
   value of 110b with the standard but 10b with the scheme in SM2. */
static bigNum
avfSm2(
       bigNum              bn,           // IN/OUT: the reduced value
       UINT32              w              // IN: the value of w
       )
{
    // a)   set w := ceil(ceil(log2(n)) / 2) - 1
    // b)   set x' := 2^w + ( x & (2^w - 1))
    // This is just like the avf for MQV where x' = 2^w + (x mod 2^w)
    BnMaskBits(bn, w);   // as with avf1, this is too big by a factor of 2 but
    // it doesn't matter because we SET the extra bit
    // anyway
    BnSetBit(bn, w);
    return bn;
}
/* SM2KeyExchange() This function performs the key exchange defined in SM2. The first step is to
   compute tA = (dsA + deA avf(Xe,A)) mod n Then, compute the Z value from outZ = (h tA mod n) (QsA
   + [avf(QeB().x)](QeB())). The function will compute the ephemeral public key from the ephemeral
   private key. All points are required to be on the curve of inQsA. The function will fail
   catastrophically if this is not the case */
/* Error Returns Meaning */
/* TPM_RC_NO_RESULT the value for dsA does not give a valid point on the curve */
LIB_EXPORT TPM_RC
SM2KeyExchange(
	       TPMS_ECC_POINT        *outZ,         // OUT: the computed point
	       TPM_ECC_CURVE          curveId,      // IN: the curve for the computations
	       TPM2B_ECC_PARAMETER   *dsAIn,        // IN: static private TPM key
	       TPM2B_ECC_PARAMETER   *deAIn,        // IN: ephemeral private TPM key
	       TPMS_ECC_POINT        *QsBIn,        // IN: static public party B key
	       TPMS_ECC_POINT        *QeBIn         // IN: ephemeral public party B key
	       )
{
    CURVE_INITIALIZED(E, curveId);
    const ECC_CURVE_DATA      *C;
    ECC_INITIALIZED(dsA, dsAIn);
    ECC_INITIALIZED(deA, deAIn);
    POINT_INITIALIZED(QsB, QsBIn);
    POINT_INITIALIZED(QeB, QeBIn);
    BN_WORD_INITIALIZED(One, 1);
    POINT(QeA);
    ECC_NUM(XeB);
    POINT(Z);
    ECC_NUM(Ta);
    UINT32                   w;
    TPM_RC                 retVal = TPM_RC_NO_RESULT;
    //
    // Parameter checks
    if(E == NULL)
	ERROR_RETURN(TPM_RC_CURVE);
    C = AccessCurveData(E);
    pAssert(outZ != NULL && dsA != NULL && deA != NULL &&  QsB != NULL
	    && QeB != NULL);
    // Compute the value for w
    w = ComputeWForSM2(E);
    // Compute the public ephemeral key pQeA = [de,A]G
    if(!BnEccModMult(QeA, CurveGetG(C), deA, E))
	goto Exit;
    //  tA := (ds,A + de,A  avf(Xe,A)) mod n    (3)
    //  Compute 'tA' = ('dsA' +  'deA'  avf('XeA')) mod n
    // Ta = avf(XeA);
    // do Ta = de,A * Ta = deA * avf(XeA)
    BnMult(Ta, deA, avfSm2(QeA->x, w));
    // now Ta = dsA + Ta =  dsA + deA * avf(XeA)
    BnAdd(Ta, dsA, Ta);
    BnMod(Ta, CurveGetOrder(C));
    //  outZ = [h  tA mod n] (Qs,B + [avf(Xe,B)](Qe,B)) (4)
    // Put this in because almost every case of h is == 1 so skip the call when
    // not necessary.
    if(!BnEqualWord(CurveGetCofactor(C), 1))
	// Cofactor is not 1 so compute Ta := Ta * h mod n
	BnModMult(Ta, Ta, CurveGetCofactor(C), CurveGetOrder(C));
    // Now that 'tA' is (h * 'tA' mod n)
    // 'outZ' = ['tA'](QsB + [avf(QeB.x)](QeB)).
    BnCopy(XeB, QeB->x);
    if(!BnEccModMult2(Z, QsB, One, QeB, avfSm2(XeB, w), E))
	goto Exit;
    // QeB := [tA]QeB = [tA](QsB + [Xe,B]QeB) and check for at infinity
    if(!BnEccModMult(Z, Z, Ta, E))
	goto Exit;
    // Convert BIGNUM E to TPM2B E
    BnPointTo2B(outZ, Z, E);
    retVal = TPM_RC_SUCCESS;
 Exit:
    CURVE_FREE(E);
    return retVal;
}
#endif
#endif // CC_ZGen_2Phase
