rc5.cpp

00001 // rc5.cpp - written and placed in the public domain by Wei Dai
00002 
00003 #include "pch.h"
00004 #include "rc5.h"
00005 #include "misc.h"
00006 
00007 NAMESPACE_BEGIN(CryptoPP)
00008 
00009 void RC5::Base::UncheckedSetKey(CipherDir direction, const byte *k, unsigned int keylen, unsigned int rounds)
00010 {
00011         AssertValidKeyLength(keylen);
00012         AssertValidRounds(rounds);
00013 
00014         r = rounds;
00015         sTable.New(2*(r+1));
00016 
00017         static const RC5_WORD MAGIC_P = 0xb7e15163L;    // magic constant P for wordsize
00018         static const RC5_WORD MAGIC_Q = 0x9e3779b9L;    // magic constant Q for wordsize
00019         static const int U=sizeof(RC5_WORD);
00020 
00021         const unsigned int c = STDMAX((keylen+U-1)/U, 1U);      // RC6 paper says c=1 if keylen==0
00022         SecBlock<RC5_WORD> l(c);
00023 
00024         GetUserKey(LITTLE_ENDIAN_ORDER, l.begin(), c, k, keylen);
00025 
00026         sTable[0] = MAGIC_P;
00027         for (unsigned j=1; j<sTable.size();j++)
00028                 sTable[j] = sTable[j-1] + MAGIC_Q;
00029 
00030         RC5_WORD a=0, b=0;
00031         const unsigned n = 3*STDMAX((unsigned int)sTable.size(), c);
00032 
00033         for (unsigned h=0; h < n; h++)
00034         {
00035                 a = sTable[h % sTable.size()] = rotlFixed((sTable[h % sTable.size()] + a + b), 3);
00036                 b = l[h % c] = rotlMod((l[h % c] + a + b), (a+b));
00037         }
00038 }
00039 
00040 typedef BlockGetAndPut<RC5::RC5_WORD, LittleEndian> Block;
00041 
00042 void RC5::Enc::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
00043 {
00044         const RC5_WORD *sptr = sTable;
00045         RC5_WORD a, b;
00046 
00047         Block::Get(inBlock)(a)(b);
00048         a += sptr[0];
00049         b += sptr[1];
00050         sptr += 2;
00051 
00052         for(unsigned i=0; i<r; i++)
00053         {
00054                 a = rotlMod(a^b,b) + sptr[2*i+0];
00055                 b = rotlMod(a^b,a) + sptr[2*i+1];
00056         }
00057 
00058         Block::Put(xorBlock, outBlock)(a)(b);
00059 }
00060 
00061 void RC5::Dec::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
00062 {
00063         const RC5_WORD *sptr = sTable.end();
00064         RC5_WORD a, b;
00065 
00066         Block::Get(inBlock)(a)(b);
00067 
00068         for (unsigned i=0; i<r; i++)
00069         {
00070                 sptr-=2;
00071                 b = rotrMod(b-sptr[1], a) ^ a;
00072                 a = rotrMod(a-sptr[0], b) ^ b;
00073         }
00074         b -= sTable[1];
00075         a -= sTable[0];
00076 
00077         Block::Put(xorBlock, outBlock)(a)(b);
00078 }
00079 
00080 NAMESPACE_END

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