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40
41 /*
42 //
43 // Purpose:
44 // Cryptography Primitive.
45 // Modular Exponentiation (binary version)
46 //
47 // Contents:
48 // cpMontExpBin_BNU()
49 */
50
51 #include "owndefs.h"
52 #include "owncp.h"
53 #include "pcpbn.h"
54 #include "pcpmontgomery.h"
55
56 //tbcd: temporary excluded: #include <assert.h>
57
58 /*F*
59 // Name: cpMontExpBin_BNU
60 //
61 // Purpose: computes the Montgomery exponentiation with exponent
62 // BNU_CHUNK_T *dataE to the given big number integer of Montgomery form
63 // BNU_CHUNK_T *dataX with respect to the modulus gsModEngine *pModEngine.
64 //
65 // Returns:
66 // Length of modulus
67 //
68 //
69 // Parameters:
70 // dataX big number integer of Montgomery form within the
71 // range [0,m-1]
72 // dataE big number exponent
73 // pModEngine Montgomery modulus of IppsMontState.
74 / dataY the Montgomery exponentation result.
75 //
76 // Notes: IppsBigNumState *r should possess enough memory space as to hold the result
77 // of the operation. i.e. both pointers r->d and r->buffer should possess
78 // no less than (m->n->length) number of 32-bit words.
79 *F*/
80
cpMontExpBin_BNU(BNU_CHUNK_T * dataY,const BNU_CHUNK_T * dataX,cpSize nsX,const BNU_CHUNK_T * dataE,cpSize nsE,gsModEngine * pModEngine)81 cpSize cpMontExpBin_BNU(BNU_CHUNK_T* dataY,
82 const BNU_CHUNK_T* dataX, cpSize nsX,
83 const BNU_CHUNK_T* dataE, cpSize nsE,
84 gsModEngine* pModEngine)
85 {
86 cpSize nsM = MOD_LEN( pModEngine );
87
88 /*
89 // test for special cases:
90 // x^0 = 1
91 // 0^e = 0
92 */
93 if( cpEqu_BNU_CHUNK(dataE, nsE, 0) ) {
94 COPY_BNU(dataY, MOD_MNT_R( pModEngine ), nsM);
95 }
96 else if( cpEqu_BNU_CHUNK(dataX, nsX, 0) ) {
97 ZEXPAND_BNU(dataY, 0, nsM);
98 }
99
100 /* general case */
101 else {
102 /* Montgomery engine buffers */
103 const int usedPoolLen = 1;
104 BNU_CHUNK_T* dataT = gsModPoolAlloc(pModEngine, usedPoolLen);
105 //tbcd: temporary excluded: assert(NULL!=dataT);
106
107 {
108 /* execute most significant part pE */
109 BNU_CHUNK_T eValue = dataE[nsE-1];
110 int n = cpNLZ_BNU(eValue)+1;
111
112 /* expand base and init result */
113 ZEXPAND_COPY_BNU(dataT, nsM, dataX, nsX);
114 COPY_BNU(dataY, dataT, nsM);
115
116 eValue <<= n;
117 for(; n<BNU_CHUNK_BITS; n++, eValue<<=1) {
118 /* squaring R = R*R mod Modulus */
119 MOD_METHOD( pModEngine )->sqr(dataY, dataY, pModEngine);
120
121 /* and multiply R = R*X mod Modulus */
122 if(eValue & ((BNU_CHUNK_T)1<<(BNU_CHUNK_BITS-1)))
123 MOD_METHOD( pModEngine )->mul(dataY, dataY, dataT, pModEngine);
124 }
125
126 /* execute rest bits of E */
127 for(--nsE; nsE>0; nsE--) {
128 eValue = dataE[nsE-1];
129
130 for(n=0; n<BNU_CHUNK_BITS; n++, eValue<<=1) {
131 /* squaring: R = R*R mod Modulus */
132 MOD_METHOD( pModEngine )->sqr(dataY, dataY, pModEngine);
133
134 if(eValue & ((BNU_CHUNK_T)1<<(BNU_CHUNK_BITS-1)))
135 MOD_METHOD( pModEngine )->mul(dataY, dataY, dataT, pModEngine);
136 }
137 }
138 }
139
140 gsModPoolFree(pModEngine, usedPoolLen);
141 }
142
143 return nsM;
144 }
145