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// rc5.cpp - originally written and placed in the public domain by Wei Dai
#include "pch.h"
#include "rc5.h"
#include "misc.h"
#include "secblock.h"
NAMESPACE_BEGIN(CryptoPP)
void RC5::Base::UncheckedSetKey(const byte *k, unsigned int keylen, const NameValuePairs ¶ms)
{
AssertValidKeyLength(keylen);
r = GetRoundsAndThrowIfInvalid(params, this);
sTable.New(2*(r+1));
static const RC5_WORD MAGIC_P = 0xb7e15163L; // magic constant P for wordsize
static const RC5_WORD MAGIC_Q = 0x9e3779b9L; // magic constant Q for wordsize
static const int U=sizeof(RC5_WORD);
const unsigned int c = STDMAX((keylen+U-1)/U, 1U); // RC6 paper says c=1 if keylen==0
SecBlock<RC5_WORD> l(c);
GetUserKey(LITTLE_ENDIAN_ORDER, l.begin(), c, k, keylen);
sTable[0] = MAGIC_P;
for (unsigned j=1; j<sTable.size();j++)
sTable[j] = sTable[j-1] + MAGIC_Q;
RC5_WORD a=0, b=0;
const unsigned n = 3*STDMAX((unsigned int)sTable.size(), c);
for (unsigned h=0; h < n; h++)
{
a = sTable[h % sTable.size()] = rotlConstant<3>((sTable[h % sTable.size()] + a + b));
b = l[h % c] = rotlMod((l[h % c] + a + b), (a+b));
}
}
typedef BlockGetAndPut<RC5::RC5_WORD, LittleEndian> Block;
void RC5::Enc::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
const RC5_WORD *sptr = sTable;
RC5_WORD a, b;
Block::Get(inBlock)(a)(b);
a += sptr[0];
b += sptr[1];
sptr += 2;
for(unsigned i=0; i<r; i++)
{
a = rotlMod(a^b,b) + sptr[2*i+0];
b = rotlMod(a^b,a) + sptr[2*i+1];
}
Block::Put(xorBlock, outBlock)(a)(b);
}
void RC5::Dec::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
const RC5_WORD *sptr = sTable.end();
RC5_WORD a, b;
Block::Get(inBlock)(a)(b);
for (unsigned i=0; i<r; i++)
{
sptr-=2;
b = rotrMod(b-sptr[1], a) ^ a;
a = rotrMod(a-sptr[0], b) ^ b;
}
b -= sTable[1];
a -= sTable[0];
Block::Put(xorBlock, outBlock)(a)(b);
}
NAMESPACE_END
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