path: root/xchapolybox.c

/* SPDX-License-Identifier: MIT
 *
 * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
 */

#include "xchapolybox.h"

#include <stdint.h>
#include <stdbool.h>
#include <assert.h>
#include <string.h>
#include <sys/types.h>

#ifndef __BYTE_ORDER__
#include <sys/param.h>
#if !defined(BYTE_ORDER) || !defined(BIG_ENDIAN) || !defined(LITTLE_ENDIAN)
#error "Unable to determine endianness."
#endif
#define __BYTE_ORDER__ BYTE_ORDER
#define __ORDER_BIG_ENDIAN__ BIG_ENDIAN
#define __ORDER_LITTLE_ENDIAN__ LITTLE_ENDIAN
#endif
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
#define le32_to_cpup(a) __builtin_bswap32(*(a))
#define le64_to_cpup(a) __builtin_bswap64(*(a))
#define cpu_to_le32(a) __builtin_bswap32(a)
#define cpu_to_le64(a) __builtin_bswap64(a)
#else
#define le32_to_cpup(a) (*(a))
#define le64_to_cpup(a) (*(a))
#define cpu_to_le32(a) (a)
#define cpu_to_le64(a) (a)
#endif

#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))

static inline uint32_t get_unaligned_le32(const uint8_t *a)
{
	uint32_t l;
	__builtin_memcpy(&l, a, sizeof(l));
	return le32_to_cpup(&l);
}
static inline uint64_t get_unaligned_le64(const uint8_t *a)
{
	uint64_t l;
	__builtin_memcpy(&l, a, sizeof(l));
	return le64_to_cpup(&l);
}
static inline void put_unaligned_le32(uint32_t s, uint8_t *d)
{
	uint32_t l = cpu_to_le32(s);
	__builtin_memcpy(d, &l, sizeof(l));
}
static inline void put_unaligned_le64(uint64_t s, uint8_t *d)
{
	uint64_t l = cpu_to_le64(s);
	__builtin_memcpy(d, &l, sizeof(l));
}
static inline void cpu_to_le32_array(uint32_t *buf, unsigned int words)
{
        while (words--) {
		*buf = cpu_to_le32(*buf);
		++buf;
	}
}
static inline uint32_t rol32(uint32_t word, unsigned int shift)
{
        return (word << shift) | (word >> ((-shift) & 31));
}
static __attribute__((noinline)) void memzero_explicit(void *s, size_t len)
{
	memset(s, 0, len);
	asm volatile("": :"r"(s) : "memory");
}
static __attribute__((noinline)) bool
memeq(const uint8_t *src1, const uint8_t *src2, size_t len)
{
	volatile uint8_t acc = 0;
	size_t i;

	for (i = 0; i < len; ++i) {
		acc |= src1[i] ^ src2[i];
		asm volatile("" : "=r"(acc) : "0"(acc));
	}
	return 1 & ((acc - 1) >> 8);
}
static void xor_cpy(uint8_t *dst, const uint8_t *src1, const uint8_t *src2,
		    size_t len)
{
	size_t i;

	for (i = 0; i < len; ++i)
		dst[i] = src1[i] ^ src2[i];
}
#ifdef __APPLE__
#include <CommonCrypto/CommonRandom.h>
static inline void get_random_bytes(uint8_t *out, size_t len)
{
	assert(CCRandomGenerateBytes(out, len) == kCCSuccess);
}
#else
#include <sys/random.h>
static inline void get_random_bytes(uint8_t *out, size_t len)
{
	assert(!getentropy(out, len));
}
#endif

#define QUARTER_ROUND(x, a, b, c, d) ( \
	x[a] += x[b], \
	x[d] = rol32((x[d] ^ x[a]), 16), \
	x[c] += x[d], \
	x[b] = rol32((x[b] ^ x[c]), 12), \
	x[a] += x[b], \
	x[d] = rol32((x[d] ^ x[a]), 8), \
	x[c] += x[d], \
	x[b] = rol32((x[b] ^ x[c]), 7) \
)

#define C(i, j) (i * 4 + j)

#define DOUBLE_ROUND(x) ( \
	/* Column Round */ \
	QUARTER_ROUND(x, C(0, 0), C(1, 0), C(2, 0), C(3, 0)), \
	QUARTER_ROUND(x, C(0, 1), C(1, 1), C(2, 1), C(3, 1)), \
	QUARTER_ROUND(x, C(0, 2), C(1, 2), C(2, 2), C(3, 2)), \
	QUARTER_ROUND(x, C(0, 3), C(1, 3), C(2, 3), C(3, 3)), \
	/* Diagonal Round */ \
	QUARTER_ROUND(x, C(0, 0), C(1, 1), C(2, 2), C(3, 3)), \
	QUARTER_ROUND(x, C(0, 1), C(1, 2), C(2, 3), C(3, 0)), \
	QUARTER_ROUND(x, C(0, 2), C(1, 3), C(2, 0), C(3, 1)), \
	QUARTER_ROUND(x, C(0, 3), C(1, 0), C(2, 1), C(3, 2)) \
)

#define TWENTY_ROUNDS(x) ( \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x), \
	DOUBLE_ROUND(x) \
)

enum chacha20_lengths {
	CHACHA20_NONCE_SIZE = 16,
	CHACHA20_KEY_SIZE = 32,
	CHACHA20_KEY_WORDS = CHACHA20_KEY_SIZE / sizeof(uint32_t),
	CHACHA20_BLOCK_SIZE = 64,
	CHACHA20_BLOCK_WORDS = CHACHA20_BLOCK_SIZE / sizeof(uint32_t),
	HCHACHA20_NONCE_SIZE = CHACHA20_NONCE_SIZE,
	HCHACHA20_KEY_SIZE = CHACHA20_KEY_SIZE
};

enum chacha20_constants { /* expand 32-byte k */
	CHACHA20_CONSTANT_EXPA = 0x61707865U,
	CHACHA20_CONSTANT_ND_3 = 0x3320646eU,
	CHACHA20_CONSTANT_2_BY = 0x79622d32U,
	CHACHA20_CONSTANT_TE_K = 0x6b206574U
};

struct chacha20_ctx {
	union {
		uint32_t state[16];
		struct {
			uint32_t constant[4];
			uint32_t key[8];
			uint32_t counter[4];
		};
	};
};

static void chacha20_init(struct chacha20_ctx *ctx,
			  const uint8_t key[CHACHA20_KEY_SIZE],
			  const uint64_t nonce)
{
	ctx->constant[0] = CHACHA20_CONSTANT_EXPA;
	ctx->constant[1] = CHACHA20_CONSTANT_ND_3;
	ctx->constant[2] = CHACHA20_CONSTANT_2_BY;
	ctx->constant[3] = CHACHA20_CONSTANT_TE_K;
	ctx->key[0] = get_unaligned_le32(key + 0);
	ctx->key[1] = get_unaligned_le32(key + 4);
	ctx->key[2] = get_unaligned_le32(key + 8);
	ctx->key[3] = get_unaligned_le32(key + 12);
	ctx->key[4] = get_unaligned_le32(key + 16);
	ctx->key[5] = get_unaligned_le32(key + 20);
	ctx->key[6] = get_unaligned_le32(key + 24);
	ctx->key[7] = get_unaligned_le32(key + 28);
	ctx->counter[0] = 0;
	ctx->counter[1] = 0;
	ctx->counter[2] = nonce & 0xffffffffU;
	ctx->counter[3] = nonce >> 32;
}

static void chacha20_block(struct chacha20_ctx *ctx, uint32_t *stream)
{
	uint32_t x[CHACHA20_BLOCK_WORDS];
	int i;

	for (i = 0; i < ARRAY_SIZE(x); ++i)
		x[i] = ctx->state[i];

	TWENTY_ROUNDS(x);

	for (i = 0; i < ARRAY_SIZE(x); ++i)
		stream[i] = cpu_to_le32(x[i] + ctx->state[i]);

	ctx->counter[0] += 1;
}

static void chacha20(struct chacha20_ctx *ctx, uint8_t *out, const uint8_t *in,
		     uint32_t len)
{
	uint32_t buf[CHACHA20_BLOCK_WORDS];

	while (len >= CHACHA20_BLOCK_SIZE) {
		chacha20_block(ctx, buf);
		xor_cpy(out, in, (uint8_t *)buf, CHACHA20_BLOCK_SIZE);
		len -= CHACHA20_BLOCK_SIZE;
		out += CHACHA20_BLOCK_SIZE;
		in += CHACHA20_BLOCK_SIZE;
	}
	if (len) {
		chacha20_block(ctx, buf);
		xor_cpy(out, in, (uint8_t *)buf, len);
	}
}

static void hchacha20(uint32_t derived_key[CHACHA20_KEY_WORDS],
		      const uint8_t nonce[HCHACHA20_NONCE_SIZE],
		      const uint8_t key[HCHACHA20_KEY_SIZE])
{
	uint32_t x[] = { CHACHA20_CONSTANT_EXPA,
		    CHACHA20_CONSTANT_ND_3,
		    CHACHA20_CONSTANT_2_BY,
		    CHACHA20_CONSTANT_TE_K,
		    get_unaligned_le32(key +  0),
		    get_unaligned_le32(key +  4),
		    get_unaligned_le32(key +  8),
		    get_unaligned_le32(key + 12),
		    get_unaligned_le32(key + 16),
		    get_unaligned_le32(key + 20),
		    get_unaligned_le32(key + 24),
		    get_unaligned_le32(key + 28),
		    get_unaligned_le32(nonce +  0),
		    get_unaligned_le32(nonce +  4),
		    get_unaligned_le32(nonce +  8),
		    get_unaligned_le32(nonce + 12)
	};

	TWENTY_ROUNDS(x);

	memcpy(derived_key + 0, x +  0, sizeof(uint32_t) * 4);
	memcpy(derived_key + 4, x + 12, sizeof(uint32_t) * 4);
}

enum poly1305_lengths {
	POLY1305_BLOCK_SIZE = 16,
	POLY1305_KEY_SIZE = 32,
	POLY1305_MAC_SIZE = 16
};

struct poly1305_internal {
	uint32_t h[5];
	uint32_t r[5];
	uint32_t s[4];
};

struct poly1305_ctx {
	struct poly1305_internal state;
	uint32_t nonce[4];
	uint8_t data[POLY1305_BLOCK_SIZE];
	size_t num;
};

static void poly1305_init_core(struct poly1305_internal *st,
			       const uint8_t key[16])
{
	/* r &= 0xffffffc0ffffffc0ffffffc0fffffff */
	st->r[0] = (get_unaligned_le32(&key[0])) & 0x3ffffff;
	st->r[1] = (get_unaligned_le32(&key[3]) >> 2) & 0x3ffff03;
	st->r[2] = (get_unaligned_le32(&key[6]) >> 4) & 0x3ffc0ff;
	st->r[3] = (get_unaligned_le32(&key[9]) >> 6) & 0x3f03fff;
	st->r[4] = (get_unaligned_le32(&key[12]) >> 8) & 0x00fffff;

	/* s = 5*r */
	st->s[0] = st->r[1] * 5;
	st->s[1] = st->r[2] * 5;
	st->s[2] = st->r[3] * 5;
	st->s[3] = st->r[4] * 5;

	/* h = 0 */
	st->h[0] = 0;
	st->h[1] = 0;
	st->h[2] = 0;
	st->h[3] = 0;
	st->h[4] = 0;
}

static void poly1305_blocks_core(struct poly1305_internal *st,
				 const uint8_t *input, size_t len,
				 const uint32_t padbit)
{
	const uint32_t hibit = padbit << 24;
	uint32_t r0, r1, r2, r3, r4;
	uint32_t s1, s2, s3, s4;
	uint32_t h0, h1, h2, h3, h4;
	uint64_t d0, d1, d2, d3, d4;
	uint32_t c;

	r0 = st->r[0];
	r1 = st->r[1];
	r2 = st->r[2];
	r3 = st->r[3];
	r4 = st->r[4];

	s1 = st->s[0];
	s2 = st->s[1];
	s3 = st->s[2];
	s4 = st->s[3];

	h0 = st->h[0];
	h1 = st->h[1];
	h2 = st->h[2];
	h3 = st->h[3];
	h4 = st->h[4];

	while (len >= POLY1305_BLOCK_SIZE) {
		/* h += m[i] */
		h0 += (get_unaligned_le32(&input[0])) & 0x3ffffff;
		h1 += (get_unaligned_le32(&input[3]) >> 2) & 0x3ffffff;
		h2 += (get_unaligned_le32(&input[6]) >> 4) & 0x3ffffff;
		h3 += (get_unaligned_le32(&input[9]) >> 6) & 0x3ffffff;
		h4 += (get_unaligned_le32(&input[12]) >> 8) | hibit;

		/* h *= r */
		d0 = ((uint64_t)h0 * r0) + ((uint64_t)h1 * s4) +
		     ((uint64_t)h2 * s3) + ((uint64_t)h3 * s2) +
		     ((uint64_t)h4 * s1);
		d1 = ((uint64_t)h0 * r1) + ((uint64_t)h1 * r0) +
		     ((uint64_t)h2 * s4) + ((uint64_t)h3 * s3) +
		     ((uint64_t)h4 * s2);
		d2 = ((uint64_t)h0 * r2) + ((uint64_t)h1 * r1) +
		     ((uint64_t)h2 * r0) + ((uint64_t)h3 * s4) +
		     ((uint64_t)h4 * s3);
		d3 = ((uint64_t)h0 * r3) + ((uint64_t)h1 * r2) +
		     ((uint64_t)h2 * r1) + ((uint64_t)h3 * r0) +
		     ((uint64_t)h4 * s4);
		d4 = ((uint64_t)h0 * r4) + ((uint64_t)h1 * r3) +
		     ((uint64_t)h2 * r2) + ((uint64_t)h3 * r1) +
		     ((uint64_t)h4 * r0);

		/* (partial) h %= p */
		c = (uint32_t)(d0 >> 26);
		h0 = (uint32_t)d0 & 0x3ffffff;
		d1 += c;
		c = (uint32_t)(d1 >> 26);
		h1 = (uint32_t)d1 & 0x3ffffff;
		d2 += c;
		c = (uint32_t)(d2 >> 26);
		h2 = (uint32_t)d2 & 0x3ffffff;
		d3 += c;
		c = (uint32_t)(d3 >> 26);
		h3 = (uint32_t)d3 & 0x3ffffff;
		d4 += c;
		c = (uint32_t)(d4 >> 26);
		h4 = (uint32_t)d4 & 0x3ffffff;
		h0 += c * 5;
		c = (h0 >> 26);
		h0 = h0 & 0x3ffffff;
		h1 += c;

		input += POLY1305_BLOCK_SIZE;
		len -= POLY1305_BLOCK_SIZE;
	}

	st->h[0] = h0;
	st->h[1] = h1;
	st->h[2] = h2;
	st->h[3] = h3;
	st->h[4] = h4;
}

static void poly1305_emit_core(struct poly1305_internal *st, uint8_t mac[16],
			       const uint32_t nonce[4])
{
	uint32_t h0, h1, h2, h3, h4, c;
	uint32_t g0, g1, g2, g3, g4;
	uint64_t f;
	uint32_t mask;

	/* fully carry h */
	h0 = st->h[0];
	h1 = st->h[1];
	h2 = st->h[2];
	h3 = st->h[3];
	h4 = st->h[4];

	c = h1 >> 26;
	h1 = h1 & 0x3ffffff;
	h2 += c;
	c = h2 >> 26;
	h2 = h2 & 0x3ffffff;
	h3 += c;
	c = h3 >> 26;
	h3 = h3 & 0x3ffffff;
	h4 += c;
	c = h4 >> 26;
	h4 = h4 & 0x3ffffff;
	h0 += c * 5;
	c = h0 >> 26;
	h0 = h0 & 0x3ffffff;
	h1 += c;

	/* compute h + -p */
	g0 = h0 + 5;
	c = g0 >> 26;
	g0 &= 0x3ffffff;
	g1 = h1 + c;
	c = g1 >> 26;
	g1 &= 0x3ffffff;
	g2 = h2 + c;
	c = g2 >> 26;
	g2 &= 0x3ffffff;
	g3 = h3 + c;
	c = g3 >> 26;
	g3 &= 0x3ffffff;
	g4 = h4 + c - (1UL << 26);

	/* select h if h < p, or h + -p if h >= p */
	mask = (g4 >> ((sizeof(uint32_t) * 8) - 1)) - 1;
	g0 &= mask;
	g1 &= mask;
	g2 &= mask;
	g3 &= mask;
	g4 &= mask;
	mask = ~mask;

	h0 = (h0 & mask) | g0;
	h1 = (h1 & mask) | g1;
	h2 = (h2 & mask) | g2;
	h3 = (h3 & mask) | g3;
	h4 = (h4 & mask) | g4;

	/* h = h % (2^128) */
	h0 = ((h0) | (h1 << 26)) & 0xffffffff;
	h1 = ((h1 >> 6) | (h2 << 20)) & 0xffffffff;
	h2 = ((h2 >> 12) | (h3 << 14)) & 0xffffffff;
	h3 = ((h3 >> 18) | (h4 << 8)) & 0xffffffff;

	/* mac = (h + nonce) % (2^128) */
	f = (uint64_t)h0 + nonce[0];
	h0 = (uint32_t)f;
	f = (uint64_t)h1 + nonce[1] + (f >> 32);
	h1 = (uint32_t)f;
	f = (uint64_t)h2 + nonce[2] + (f >> 32);
	h2 = (uint32_t)f;
	f = (uint64_t)h3 + nonce[3] + (f >> 32);
	h3 = (uint32_t)f;

	put_unaligned_le32(h0, &mac[0]);
	put_unaligned_le32(h1, &mac[4]);
	put_unaligned_le32(h2, &mac[8]);
	put_unaligned_le32(h3, &mac[12]);
}

static void poly1305_init(struct poly1305_ctx *ctx,
			  const uint8_t key[POLY1305_KEY_SIZE])
{
	ctx->nonce[0] = get_unaligned_le32(&key[16]);
	ctx->nonce[1] = get_unaligned_le32(&key[20]);
	ctx->nonce[2] = get_unaligned_le32(&key[24]);
	ctx->nonce[3] = get_unaligned_le32(&key[28]);

	poly1305_init_core(&ctx->state, key);

	ctx->num = 0;
}

static void poly1305_update(struct poly1305_ctx *ctx, const uint8_t *input,
			    size_t len)
{
	const size_t num = ctx->num;
	size_t rem;

	if (num) {
		rem = POLY1305_BLOCK_SIZE - num;
		if (len < rem) {
			memcpy(ctx->data + num, input, len);
			ctx->num = num + len;
			return;
		}
		memcpy(ctx->data + num, input, rem);
		poly1305_blocks_core(&ctx->state, ctx->data,
				     POLY1305_BLOCK_SIZE, 1);
		input += rem;
		len -= rem;
	}

	rem = len % POLY1305_BLOCK_SIZE;
	len -= rem;

	if (len >= POLY1305_BLOCK_SIZE) {
		poly1305_blocks_core(&ctx->state, input, len, 1);
		input += len;
	}

	if (rem)
		memcpy(ctx->data, input, rem);

	ctx->num = rem;
}

static void poly1305_final(struct poly1305_ctx *ctx,
			   uint8_t mac[POLY1305_MAC_SIZE])
{
	size_t num = ctx->num;

	if (num) {
		ctx->data[num++] = 1;
		while (num < POLY1305_BLOCK_SIZE)
			ctx->data[num++] = 0;
		poly1305_blocks_core(&ctx->state, ctx->data,
				     POLY1305_BLOCK_SIZE, 0);
	}

	poly1305_emit_core(&ctx->state, mac, ctx->nonce);

	memzero_explicit(ctx, sizeof(*ctx));
}

enum chacha20poly1305_lengths {
	XCHACHA20POLY1305_NONCE_SIZE = 24,
	CHACHA20POLY1305_KEY_SIZE = 32,
	CHACHA20POLY1305_AUTHTAG_SIZE = 16
};

static const uint8_t pad0[16] = { 0 };

static void
chacha20poly1305_encrypt(uint8_t *dst, const uint8_t *src, const size_t src_len,
			 const uint8_t *ad, const size_t ad_len,
			 const uint64_t nonce,
			 const uint8_t key[CHACHA20POLY1305_KEY_SIZE])
{
	struct poly1305_ctx poly1305_state;
	struct chacha20_ctx chacha20_state;
	union {
		uint8_t block0[POLY1305_KEY_SIZE];
		uint64_t lens[2];
	} b = { { 0 } };

	chacha20_init(&chacha20_state, key, nonce);
	chacha20(&chacha20_state, b.block0, b.block0, sizeof(b.block0));
	poly1305_init(&poly1305_state, b.block0);

	poly1305_update(&poly1305_state, ad, ad_len);
	poly1305_update(&poly1305_state, pad0, (0x10 - ad_len) & 0xf);

	chacha20(&chacha20_state, dst, src, src_len);

	poly1305_update(&poly1305_state, dst, src_len);
	poly1305_update(&poly1305_state, pad0, (0x10 - src_len) & 0xf);

	b.lens[0] = cpu_to_le64(ad_len);
	b.lens[1] = cpu_to_le64(src_len);
	poly1305_update(&poly1305_state, (uint8_t *)b.lens, sizeof(b.lens));

	poly1305_final(&poly1305_state, dst + src_len);

	memzero_explicit(&chacha20_state, sizeof(chacha20_state));
	memzero_explicit(&b, sizeof(b));
}

static bool
chacha20poly1305_decrypt(uint8_t *dst, const uint8_t *src, const size_t src_len,
			 const uint8_t *ad, const size_t ad_len,
			 const uint64_t nonce,
			 const uint8_t key[CHACHA20POLY1305_KEY_SIZE])
{
	struct poly1305_ctx poly1305_state;
	struct chacha20_ctx chacha20_state;
	bool ret;
	size_t dst_len;
	union {
		uint8_t block0[POLY1305_KEY_SIZE];
		uint8_t mac[POLY1305_MAC_SIZE];
		uint64_t lens[2];
	} b = { { 0 } };

	if (src_len < POLY1305_MAC_SIZE)
		return false;

	chacha20_init(&chacha20_state, key, nonce);
	chacha20(&chacha20_state, b.block0, b.block0, sizeof(b.block0));
	poly1305_init(&poly1305_state, b.block0);

	poly1305_update(&poly1305_state, ad, ad_len);
	poly1305_update(&poly1305_state, pad0, (0x10 - ad_len) & 0xf);

	dst_len = src_len - POLY1305_MAC_SIZE;
	poly1305_update(&poly1305_state, src, dst_len);
	poly1305_update(&poly1305_state, pad0, (0x10 - dst_len) & 0xf);

	b.lens[0] = cpu_to_le64(ad_len);
	b.lens[1] = cpu_to_le64(dst_len);
	poly1305_update(&poly1305_state, (uint8_t *)b.lens, sizeof(b.lens));

	poly1305_final(&poly1305_state, b.mac);

	ret = memeq(b.mac, src + dst_len, POLY1305_MAC_SIZE);
	if (ret)
		chacha20(&chacha20_state, dst, src, dst_len);

	memzero_explicit(&chacha20_state, sizeof(chacha20_state));
	memzero_explicit(&b, sizeof(b));

	return ret;
}

static void
xchacha20poly1305_encrypt(uint8_t *dst, const uint8_t *src,
			  const size_t src_len, const uint8_t *ad,
			  const size_t ad_len,
			  const uint8_t nonce[XCHACHA20POLY1305_NONCE_SIZE],
			  const uint8_t key[CHACHA20POLY1305_KEY_SIZE])
{
	uint32_t derived_key[CHACHA20_KEY_WORDS] __attribute__((aligned(16)));

	hchacha20(derived_key, nonce, key);
	cpu_to_le32_array(derived_key, ARRAY_SIZE(derived_key));
	chacha20poly1305_encrypt(dst, src, src_len, ad, ad_len,
				 get_unaligned_le64(nonce + 16),
				 (uint8_t *)derived_key);
	memzero_explicit(derived_key, CHACHA20POLY1305_KEY_SIZE);
}

static bool
xchacha20poly1305_decrypt(uint8_t *dst, const uint8_t *src,
			  const size_t src_len,  const uint8_t *ad,
			  const size_t ad_len,
			  const uint8_t nonce[XCHACHA20POLY1305_NONCE_SIZE],
			  const uint8_t key[CHACHA20POLY1305_KEY_SIZE])
{
	bool ret;
	uint32_t derived_key[CHACHA20_KEY_WORDS] __attribute__((aligned(16)));

	hchacha20(derived_key, nonce, key);
	cpu_to_le32_array(derived_key, ARRAY_SIZE(derived_key));
	ret = chacha20poly1305_decrypt(dst, src, src_len, ad, ad_len,
				       get_unaligned_le64(nonce + 16),
				       (uint8_t *)derived_key);
	memzero_explicit(derived_key, CHACHA20POLY1305_KEY_SIZE);
	return ret;
}

void xchapolybox_seal(uint8_t *dst, const uint8_t *src, size_t src_len,
		      const uint8_t key[static XCHAPOLYBOX_KEY_LEN])
{
	get_random_bytes(dst, XCHACHA20POLY1305_NONCE_SIZE);
	xchacha20poly1305_encrypt(dst + XCHACHA20POLY1305_NONCE_SIZE, src,
				  src_len, NULL, 0, dst, key);
}

bool xchapolybox_open(uint8_t *dst, const uint8_t *src, size_t src_len,
		      const uint8_t key[static XCHAPOLYBOX_KEY_LEN])
{
	if (src_len < XCHAPOLYBOX_OVERHEAD_LEN)
		return false;
	return xchacha20poly1305_decrypt(dst,
					 src + XCHACHA20POLY1305_NONCE_SIZE,
					 src_len - XCHACHA20POLY1305_NONCE_SIZE,
					 NULL, 0, src, key);
}

void xchapolybox_genkey(uint8_t key[static XCHAPOLYBOX_KEY_LEN])
{
	get_random_bytes(key, XCHAPOLYBOX_KEY_LEN);
}