// 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"

#include "secblock.h"

NAMESPACE_BEGIN(CryptoPP)

void RC6::Base::UncheckedSetKey(const byte *k, unsigned int keylen, const NameValuePairs &params)

{

  AssertValidKeyLength(keylen);

  r = GetRoundsAndThrowIfInvalid(params, this);

  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()] = rotlConstant<3>((sTable[h % sTable.size()] + a + b));

    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 = rotlConstant<5>(b*(2*b+1));

    u = rotlConstant<5>(d*(2*d+1));

    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 = rotlConstant<5>(d*(2 * d + 1));

    t = rotlConstant<5>(b*(2 * b + 1));

    c = rotrMod(c-sptr[1], t) ^ u;

    a = rotrMod(a-sptr[0], u) ^ t;

  }

  d -= sTable[1];

  b -= sTable[0];

  Block::Put(xorBlock, outBlock)(a)(b)(c)(d);

}

NAMESPACE_END