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# 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