/*
chacha-merged.c version 20080118
D. J. Bernstein
Public domain.
*/

#include "../system.h"

#include "chacha.h"

typedef struct chacha_ctx chacha_ctx;

#define U8C(v) (v##U)
#define U32C(v) (v##U)

#define U8V(v) ((uint8_t)(v) & U8C(0xFF))
#define U32V(v) ((uint32_t)(v) & U32C(0xFFFFFFFF))

#define ROTL32(v, n) \
	(U32V((v) << (n)) | ((v) >> (32 - (n))))

#define U8TO32_LITTLE(p) \
	(((uint32_t)((p)[0])      ) | \
	 ((uint32_t)((p)[1]) <<  8) | \
	 ((uint32_t)((p)[2]) << 16) | \
	 ((uint32_t)((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";

void chacha_keysetup(chacha_ctx *x, const uint8_t *k, uint32_t kbits) {
	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);
}

void chacha_ivsetup(chacha_ctx *x, const uint8_t *iv, const uint8_t *counter) {
	x->input[12] = counter == NULL ? 0 : U8TO32_LITTLE(counter + 0);
	x->input[13] = counter == NULL ? 0 : U8TO32_LITTLE(counter + 4);
	x->input[14] = U8TO32_LITTLE(iv + 0);
	x->input[15] = U8TO32_LITTLE(iv + 4);
}

void
chacha_encrypt_bytes(chacha_ctx *x, const uint8_t *m, uint8_t *c, uint32_t bytes) {
	uint32_t x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
	uint32_t j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;
	uint8_t *ctarget = NULL;
	uint8_t tmp[64];
	uint32_t 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);

		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));

		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;
		m += 64;
	}
}