DES 전문가 계십니까?
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DES공부하다가 리차드의 초기치환법이라는게 나왔는데 도통 이해할 수가 없습니다;; 너무 무리한 부탁인건 알지만 원리 좀 설명해 주시면 감사하겠습니다;; 진짜 눈물 날것 같습니다ㅠㅠㅠ;;
private void des( int[] inInts, int[] outInts, int[] keys )
{
int fval, work, right, leftt;
int round;
int keysi = 0;
leftt = inInts[0];
right = inInts[1];
work = ((leftt >> 4) ^ right) & 0x0f0f0f0f;
right ^= work;
leftt ^= (work << 4);
work = ((leftt >> 16) ^ right) & 0x0000ffff;
right ^= work;
leftt ^= (work << 16);
work = ((right >> 2) ^ leftt) & 0x33333333;
leftt ^= work;
right ^= (work << 2);
work = ((right >> 8) ^ leftt) & 0x00ff00ff;
leftt ^= work;
right ^= (work << 8);
right = (right << 1) | ((right >> 31) & 1);
work = (leftt ^ right) & 0xaaaaaaaa;
leftt ^= work;
right ^= work;
leftt = (leftt << 1) | ((leftt >> 31) & 1);
for ( round = 0; round < 8; ++round )
{
work = (right << 28) | (right >> 4);
work ^= keys[keysi++];
fval = SP7[ work & 0x0000003f ];
fval |= SP5[(work >> 8) & 0x0000003f ];
fval |= SP3[(work >> 16) & 0x0000003f ];
fval |= SP1[(work >> 24) & 0x0000003f ];
work = right ^ keys[keysi++];
fval |= SP8[ work & 0x0000003f ];
fval |= SP6[(work >> 8) & 0x0000003f ];
fval |= SP4[(work >> 16) & 0x0000003f ];
fval |= SP2[(work >> 24) & 0x0000003f ];
leftt ^= fval;
work = (leftt << 28) | (leftt >> 4);
work ^= keys[keysi++];
fval = SP7[ work & 0x0000003f ];
fval |= SP5[(work >> 8) & 0x0000003f ];
fval |= SP3[(work >> 16) & 0x0000003f ];
fval |= SP1[(work >> 24) & 0x0000003f ];
work = leftt ^ keys[keysi++];
fval |= SP8[ work & 0x0000003f ];
fval |= SP6[(work >> 8) & 0x0000003f ];
fval |= SP4[(work >> 16) & 0x0000003f ];
fval |= SP2[(work >> 24) & 0x0000003f ];
right ^= fval;
}
right = (right << 31) | (right >>> 1);
work = (leftt ^ right) & 0xaaaaaaaa;
leftt ^= work;
right ^= work;
leftt = (leftt << 31) | (leftt >>> 1);
work = ((leftt >>> 8) ^ right) & 0x00ff00ff;
right ^= work;
leftt ^= (work << 8);
work = ((leftt >>> 2) ^ right) & 0x33333333;
right ^= work;
leftt ^= (work << 2);
work = ((right >>> 16) ^ leftt) & 0x0000ffff;
leftt ^= work;
right ^= (work << 16);
work = ((right >>> 4) ^ leftt) & 0x0f0f0f0f;
leftt ^= work;
right ^= (work << 4);
outInts[0] = right;
outInts[1] = leftt;
}
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