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40
41 /*
42 // Intel(R) Integrated Performance Primitives. Cryptography Primitives.
43 //
44 // Context:
45 // cpFastMontMultiExp()
46 //
47 */
48
49 #include "owndefs.h"
50 #include "owncp.h"
51 #include "pcpbn.h"
52 #include "pcpmontgomery.h"
53
54
GetIndex(const Ipp8u ** ppE,cpSize numItems,cpSize nBit)55 static cpSize GetIndex(const Ipp8u** ppE, cpSize numItems, cpSize nBit)
56 {
57 cpSize shift = nBit%BYTESIZE;
58 cpSize offset= nBit/BYTESIZE;
59 cpSize index = 0;
60
61 cpSize n;
62 for(n=numItems; n>0; n--) {
63 const Ipp8u* pE = ppE[n-1] + offset;
64 Ipp8u e = pE[0];
65 index <<= 1;
66 index += (e>>shift) &1;
67 }
68 return index;
69 }
70
71 /*
72 // Computes multi-exponentiation
73 // y = x[0]^e[0] * x[1]^e[1] *...* x[numItems-1]^e[numItems-1] mod M
74 //
75 // Input:
76 // - table pTbl of precomuted values pTbl[i] = x[0]^i[0] * x[1]^i[1] *...* x[numItems-1]^i[numItems-1] mod M,
77 // where i[0], i[1], ..., i[numItems-1] are bits of i value;
78 // each entry has sizeM length (i.e. equial to modulo M size)
79 // - array of pointers to the BNU exponents e[0], e[1],...,e[numItems-1]
80 // - pointer to the Montgomery engine
81 */
cpFastMontMultiExp(BNU_CHUNK_T * pY,const BNU_CHUNK_T * pPrecomTbl,const Ipp8u ** ppE,cpSize eItemBitSize,cpSize numItems,gsModEngine * pModEngine)82 void cpFastMontMultiExp(BNU_CHUNK_T* pY,
83 const BNU_CHUNK_T* pPrecomTbl,
84 const Ipp8u** ppE, cpSize eItemBitSize,
85 cpSize numItems,
86 gsModEngine* pModEngine)
87 {
88 cpSize sizeM = MOD_LEN(pModEngine);
89
90 /* find 1-st non zero index */
91 cpSize eBitNumber;
92 cpSize tblIdx;
93 for(eBitNumber=eItemBitSize-1, tblIdx=0; !tblIdx && eBitNumber>=0; eBitNumber--)
94 tblIdx =GetIndex(ppE, numItems, eBitNumber);
95
96 COPY_BNU(pY, pPrecomTbl+tblIdx*sizeM, sizeM);
97
98 for(; eBitNumber>=0; eBitNumber--) {
99 cpMontMul_BNU(pY,
100 pY,
101 pY,
102 pModEngine);
103
104 tblIdx = GetIndex(ppE, numItems, eBitNumber);
105
106 if(tblIdx)
107 cpMontMul_BNU(pY,
108 pY,
109 pPrecomTbl+tblIdx*sizeM,
110 pModEngine);
111 }
112 }
113