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// rc6.cpp - written and placed in the public domain by Sean Woods
// based on Wei Dai's RC5 code.
#include "pch.h"
#include "rc6.h"
#include "misc.h"
NAMESPACE_BEGIN(CryptoPP)
void RC6::Base::UncheckedSetKey(CipherDir direction, const byte *k, unsigned int keylen, unsigned int rounds)
{
AssertValidKeyLength(keylen);
AssertValidRounds(rounds);
r = rounds;
sTable.New(2*(r+2));
static const RC6_WORD MAGIC_P = 0xb7e15163L; // magic constant P for wordsize
static const RC6_WORD MAGIC_Q = 0x9e3779b9L; // magic constant Q for wordsize
static const int U=sizeof(RC6_WORD);
const unsigned int c = STDMAX((keylen+U-1)/U, 1U); // RC6 paper says c=1 if keylen==0
SecBlock<RC6_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;
RC6_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()] = rotlFixed((sTable[h % sTable.size()] + a + b), 3);
b = l[h % c] = rotlMod((l[h % c] + a + b), (a+b));
}
}
typedef BlockGetAndPut<RC6::RC6_WORD, LittleEndian> Block;
void RC6::Enc::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
const RC6_WORD *sptr = sTable;
RC6_WORD a, b, c, d, t, u;
Block::Get(inBlock)(a)(b)(c)(d);
b += sptr[0];
d += sptr[1];
sptr += 2;
for(unsigned i=0; i<r; i++)
{
t = rotlFixed(b*(2*b+1), 5);
u = rotlFixed(d*(2*d+1), 5);
a = rotlMod(a^t,u) + sptr[0];
c = rotlMod(c^u,t) + sptr[1];
t = a; a = b; b = c; c = d; d = t;
sptr += 2;
}
a += sptr[0];
c += sptr[1];
Block::Put(xorBlock, outBlock)(a)(b)(c)(d);
}
void RC6::Dec::ProcessAndXorBlock(const byte *inBlock, const byte *xorBlock, byte *outBlock) const
{
const RC6_WORD *sptr = sTable.end();
RC6_WORD a, b, c, d, t, u;
Block::Get(inBlock)(a)(b)(c)(d);
sptr -= 2;
c -= sptr[1];
a -= sptr[0];
for (unsigned i=0; i < r; i++)
{
sptr -= 2;
t = a; a = d; d = c; c = b; b = t;
u = rotlFixed(d*(2*d+1), 5);
t = rotlFixed(b*(2*b+1), 5);
c = rotrMod(c-sptr[1], t) ^ u;
a = rotrMod(a-sptr[0], u) ^ t;
}
sptr -= 2;
d -= sTable[1];
b -= sTable[0];
Block::Put(xorBlock, outBlock)(a)(b)(c)(d);
}
NAMESPACE_END
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