50 lines
1.1 KiB
C
50 lines
1.1 KiB
C
#include "sc25519.h"
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void sc25519_slide(signed char r[256], const sc25519 *s, int swindowsize)
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{
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int i,j,k,b,m=(1<<(swindowsize-1))-1, soplen=256;
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unsigned long long sv0 = s->v[0];
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unsigned long long sv1 = s->v[1];
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unsigned long long sv2 = s->v[2];
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unsigned long long sv3 = s->v[3];
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/* first put the binary expansion into r */
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for(i=0;i<64;i++) {
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r[i] = sv0 & 1;
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r[i+64] = sv1 & 1;
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r[i+128] = sv2 & 1;
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r[i+192] = sv3 & 1;
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sv0 >>= 1;
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sv1 >>= 1;
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sv2 >>= 1;
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sv3 >>= 1;
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}
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/* Making it sliding window */
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for (j = 0;j < soplen;++j)
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{
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if (r[j]) {
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for (b = 1;b < soplen - j && b <= 6;++b) {
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if (r[j] + (r[j + b] << b) <= m)
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{
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r[j] += r[j + b] << b; r[j + b] = 0;
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}
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else if (r[j] - (r[j + b] << b) >= -m)
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{
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r[j] -= r[j + b] << b;
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for (k = j + b;k < soplen;++k)
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{
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if (!r[k]) {
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r[k] = 1;
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break;
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}
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r[k] = 0;
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}
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}
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else if (r[j + b])
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break;
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}
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}
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}
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}
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