/*

chacha-merged.c version 20080118

D. J. Bernstein

Public domain.

*/

/* $OpenBSD: chacha_private.h,v 1.2 2013/10/04 07:02:27 djm Exp $ */

typedef unsigned char u8;

typedef unsigned int u32;

typedef struct

{

  u32 input[16]; /* could be compressed */

} chacha_ctx;

#define U8C(v) (v##U)

#define U32C(v) (v##U)

#define U8V(v) ((u8)(v) & U8C(0xFF))

#define U32V(v) ((u32)(v) & U32C(0xFFFFFFFF))

#define ROTL32(v, n) \

  (U32V((v) << (n)) | ((v) >> (32 - (n))))

#define U8TO32_LITTLE(p) \

  (((u32)((p)[0])      ) | \

   ((u32)((p)[1]) <<  8) | \

   ((u32)((p)[2]) << 16) | \

   ((u32)((p)[3]) << 24))

#define U32TO8_LITTLE(p, v) \

  do { \

    (p)[0] = U8V((v)      ); \

    (p)[1] = U8V((v) >>  8); \

    (p)[2] = U8V((v) >> 16); \

    (p)[3] = U8V((v) >> 24); \

  } while (0)

#define ROTATE(v,c) (ROTL32(v,c))

#define XOR(v,w) ((v) ^ (w))

#define PLUS(v,w) (U32V((v) + (w)))

#define PLUSONE(v) (PLUS((v),1))

#define QUARTERROUND(a,b,c,d) \

  a = PLUS(a,b); d = ROTATE(XOR(d,a),16); \

  c = PLUS(c,d); b = ROTATE(XOR(b,c),12); \

  a = PLUS(a,b); d = ROTATE(XOR(d,a), 8); \

  c = PLUS(c,d); b = ROTATE(XOR(b,c), 7);

static const char sigma[16] = "expand 32-byte k";

static const char tau[16] = "expand 16-byte k";

static void

chacha_keysetup(chacha_ctx *x,const u8 *k,u32 kbits,u32 ivbits)

{

  const char *constants;

  x->input[4] = U8TO32_LITTLE(k + 0);

  x->input[5] = U8TO32_LITTLE(k + 4);

  x->input[6] = U8TO32_LITTLE(k + 8);

  x->input[7] = U8TO32_LITTLE(k + 12);

  if (kbits == 256) { /* recommended */

    k += 16;

    constants = sigma;

  } else { /* kbits == 128 */

    constants = tau;

  }

  x->input[8] = U8TO32_LITTLE(k + 0);

  x->input[9] = U8TO32_LITTLE(k + 4);

  x->input[10] = U8TO32_LITTLE(k + 8);

  x->input[11] = U8TO32_LITTLE(k + 12);

  x->input[0] = U8TO32_LITTLE(constants + 0);

  x->input[1] = U8TO32_LITTLE(constants + 4);

  x->input[2] = U8TO32_LITTLE(constants + 8);

  x->input[3] = U8TO32_LITTLE(constants + 12);

}

static void

chacha_ivsetup(chacha_ctx *x,const u8 *iv)

{

  x->input[12] = 0;

  x->input[13] = 0;

  x->input[14] = U8TO32_LITTLE(iv + 0);

  x->input[15] = U8TO32_LITTLE(iv + 4);

}

static void

chacha_encrypt_bytes(chacha_ctx *x,const u8 *m,u8 *c,u32 bytes)

{

  u32 x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;

  u32 j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;

  u8 *ctarget = NULL;

  u8 tmp[64];

  u32 i;

  if (!bytes) return;

  j0 = x->input[0];

  j1 = x->input[1];

  j2 = x->input[2];

  j3 = x->input[3];

  j4 = x->input[4];

  j5 = x->input[5];

  j6 = x->input[6];

  j7 = x->input[7];

  j8 = x->input[8];

  j9 = x->input[9];

  j10 = x->input[10];

  j11 = x->input[11];

  j12 = x->input[12];

  j13 = x->input[13];

  j14 = x->input[14];

  j15 = x->input[15];

  for (;;) {

    if (bytes < 64) {

      for (i = 0;i < bytes;++i) tmp[i] = m[i];

      m = tmp;

      ctarget = c;

      c = tmp;

    }

    x0 = j0;

    x1 = j1;

    x2 = j2;

    x3 = j3;

    x4 = j4;

    x5 = j5;

    x6 = j6;

    x7 = j7;

    x8 = j8;

    x9 = j9;

    x10 = j10;

    x11 = j11;

    x12 = j12;

    x13 = j13;

    x14 = j14;

    x15 = j15;

    for (i = 20;i > 0;i -= 2) {

      QUARTERROUND( x0, x4, x8,x12)

      QUARTERROUND( x1, x5, x9,x13)

      QUARTERROUND( x2, x6,x10,x14)

      QUARTERROUND( x3, x7,x11,x15)

      QUARTERROUND( x0, x5,x10,x15)

      QUARTERROUND( x1, x6,x11,x12)

      QUARTERROUND( x2, x7, x8,x13)

      QUARTERROUND( x3, x4, x9,x14)

    }

    x0 = PLUS(x0,j0);

    x1 = PLUS(x1,j1);

    x2 = PLUS(x2,j2);

    x3 = PLUS(x3,j3);

    x4 = PLUS(x4,j4);

    x5 = PLUS(x5,j5);

    x6 = PLUS(x6,j6);

    x7 = PLUS(x7,j7);

    x8 = PLUS(x8,j8);

    x9 = PLUS(x9,j9);

    x10 = PLUS(x10,j10);

    x11 = PLUS(x11,j11);

    x12 = PLUS(x12,j12);

    x13 = PLUS(x13,j13);

    x14 = PLUS(x14,j14);

    x15 = PLUS(x15,j15);

#ifndef KEYSTREAM_ONLY

    x0 = XOR(x0,U8TO32_LITTLE(m + 0));

    x1 = XOR(x1,U8TO32_LITTLE(m + 4));

    x2 = XOR(x2,U8TO32_LITTLE(m + 8));

    x3 = XOR(x3,U8TO32_LITTLE(m + 12));

    x4 = XOR(x4,U8TO32_LITTLE(m + 16));

    x5 = XOR(x5,U8TO32_LITTLE(m + 20));

    x6 = XOR(x6,U8TO32_LITTLE(m + 24));

    x7 = XOR(x7,U8TO32_LITTLE(m + 28));

    x8 = XOR(x8,U8TO32_LITTLE(m + 32));

    x9 = XOR(x9,U8TO32_LITTLE(m + 36));

    x10 = XOR(x10,U8TO32_LITTLE(m + 40));

    x11 = XOR(x11,U8TO32_LITTLE(m + 44));

    x12 = XOR(x12,U8TO32_LITTLE(m + 48));

    x13 = XOR(x13,U8TO32_LITTLE(m + 52));

    x14 = XOR(x14,U8TO32_LITTLE(m + 56));

    x15 = XOR(x15,U8TO32_LITTLE(m + 60));

#endif

    j12 = PLUSONE(j12);

    if (!j12) {

      j13 = PLUSONE(j13);

      /* stopping at 2^70 bytes per nonce is user's responsibility */

    }

    U32TO8_LITTLE(c + 0,x0);

    U32TO8_LITTLE(c + 4,x1);

    U32TO8_LITTLE(c + 8,x2);

    U32TO8_LITTLE(c + 12,x3);

    U32TO8_LITTLE(c + 16,x4);

    U32TO8_LITTLE(c + 20,x5);

    U32TO8_LITTLE(c + 24,x6);

    U32TO8_LITTLE(c + 28,x7);

    U32TO8_LITTLE(c + 32,x8);

    U32TO8_LITTLE(c + 36,x9);

    U32TO8_LITTLE(c + 40,x10);

    U32TO8_LITTLE(c + 44,x11);

    U32TO8_LITTLE(c + 48,x12);

    U32TO8_LITTLE(c + 52,x13);

    U32TO8_LITTLE(c + 56,x14);

    U32TO8_LITTLE(c + 60,x15);

    if (bytes <= 64) {

      if (bytes < 64) {

        for (i = 0;i < bytes;++i) ctarget[i] = c[i];

      }

      x->input[12] = j12;

      x->input[13] = j13;

      return;

    }

    bytes -= 64;

    c += 64;

#ifndef KEYSTREAM_ONLY

    m += 64;

#endif

  }

}