crypto/cipher_extra/e_chacha20poly1305.c - boringssl - Git at Google

 /* Copyright (c) 2014, Google Inc.
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
  * copyright notice and this permission notice appear in all copies.
  *
  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

 #include <openssl/aead.h>

 #include <assert.h>
 #include <string.h>

 #include <openssl/chacha.h>
 #include <openssl/cipher.h>
 #include <openssl/err.h>
 #include <openssl/mem.h>
 #include <openssl/poly1305.h>

 #include "internal.h"
 #include "../chacha/internal.h"
 #include "../fipsmodule/cipher/internal.h"
 #include "../internal.h"

 struct aead_chacha20_poly1305_ctx {
   uint8_t key[32];
 };

 static_assert(sizeof(((EVP_AEAD_CTX *)NULL)->state) >=
                   sizeof(struct aead_chacha20_poly1305_ctx),
               "AEAD state is too small");
 static_assert(alignof(union evp_aead_ctx_st_state) >=
                   alignof(struct aead_chacha20_poly1305_ctx),
               "AEAD state has insufficient alignment");

 static int aead_chacha20_poly1305_init(EVP_AEAD_CTX *ctx, const uint8_t *key,
                                        size_t key_len, size_t tag_len) {
   struct aead_chacha20_poly1305_ctx *c20_ctx =
       (struct aead_chacha20_poly1305_ctx *)&ctx->state;

   if (tag_len == 0) {
     tag_len = POLY1305_TAG_LEN;
   }

   if (tag_len > POLY1305_TAG_LEN) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
     return 0;
   }

   if (key_len != sizeof(c20_ctx->key)) {
     return 0;  // internal error - EVP_AEAD_CTX_init should catch this.
   }

   OPENSSL_memcpy(c20_ctx->key, key, key_len);
   ctx->tag_len = tag_len;

   return 1;
 }

 static void aead_chacha20_poly1305_cleanup(EVP_AEAD_CTX *ctx) {}

 static void poly1305_update_length(poly1305_state *poly1305, size_t data_len) {
   uint8_t length_bytes[8];

   for (unsigned i = 0; i < sizeof(length_bytes); i++) {
     length_bytes[i] = data_len;
     data_len >>= 8;
   }

   CRYPTO_poly1305_update(poly1305, length_bytes, sizeof(length_bytes));
 }

 // calc_tag fills |tag| with the authentication tag for the given inputs.
 static void calc_tag(uint8_t tag[POLY1305_TAG_LEN], const uint8_t *key,
                      const uint8_t nonce[12], const uint8_t *ad, size_t ad_len,
                      const uint8_t *ciphertext, size_t ciphertext_len,
                      const uint8_t *ciphertext_extra,
                      size_t ciphertext_extra_len) {
   alignas(16) uint8_t poly1305_key[32];
   OPENSSL_memset(poly1305_key, 0, sizeof(poly1305_key));
   CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key), key, nonce,
                    0);

   static const uint8_t padding[16] = { 0 };  // Padding is all zeros.
   poly1305_state ctx;
   CRYPTO_poly1305_init(&ctx, poly1305_key);
   CRYPTO_poly1305_update(&ctx, ad, ad_len);
   if (ad_len % 16 != 0) {
     CRYPTO_poly1305_update(&ctx, padding, sizeof(padding) - (ad_len % 16));
   }
   CRYPTO_poly1305_update(&ctx, ciphertext, ciphertext_len);
   CRYPTO_poly1305_update(&ctx, ciphertext_extra, ciphertext_extra_len);
   const size_t ciphertext_total = ciphertext_len + ciphertext_extra_len;
   if (ciphertext_total % 16 != 0) {
     CRYPTO_poly1305_update(&ctx, padding,
                            sizeof(padding) - (ciphertext_total % 16));
   }
   poly1305_update_length(&ctx, ad_len);
   poly1305_update_length(&ctx, ciphertext_total);
   CRYPTO_poly1305_finish(&ctx, tag);
 }

 static int chacha20_poly1305_seal_scatter(
     const uint8_t *key, uint8_t *out, uint8_t *out_tag,
     size_t *out_tag_len, size_t max_out_tag_len, const uint8_t *nonce,
     size_t nonce_len, const uint8_t *in, size_t in_len, const uint8_t *extra_in,
     size_t extra_in_len, const uint8_t *ad, size_t ad_len, size_t tag_len) {
   if (extra_in_len + tag_len < tag_len) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
     return 0;
   }
   if (max_out_tag_len < tag_len + extra_in_len) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
     return 0;
   }
   if (nonce_len != 12) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
     return 0;
   }

   // |CRYPTO_chacha_20| uses a 32-bit block counter. Therefore we disallow
   // individual operations that work on more than 256GB at a time.
   // |in_len_64| is needed because, on 32-bit platforms, size_t is only
   // 32-bits and this produces a warning because it's always false.
   // Casting to uint64_t inside the conditional is not sufficient to stop
   // the warning.
   const uint64_t in_len_64 = in_len;
   if (in_len_64 >= (UINT64_C(1) << 32) * 64 - 64) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
     return 0;
   }

   if (max_out_tag_len < tag_len) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
     return 0;
   }

   // The the extra input is given, it is expected to be very short and so is
   // encrypted byte-by-byte first.
   if (extra_in_len) {
     static const size_t kChaChaBlockSize = 64;
     uint32_t block_counter = 1 + (in_len / kChaChaBlockSize);
     size_t offset = in_len % kChaChaBlockSize;
     uint8_t block[64 /* kChaChaBlockSize */];

     for (size_t done = 0; done < extra_in_len; block_counter++) {
       memset(block, 0, sizeof(block));
       CRYPTO_chacha_20(block, block, sizeof(block), key, nonce,
                        block_counter);
       for (size_t i = offset; i < sizeof(block) && done < extra_in_len;
            i++, done++) {
         out_tag[done] = extra_in[done] ^ block[i];
       }
       offset = 0;
     }
   }

   union chacha20_poly1305_seal_data data;
   if (chacha20_poly1305_asm_capable()) {
     OPENSSL_memcpy(data.in.key, key, 32);
     data.in.counter = 0;
     OPENSSL_memcpy(data.in.nonce, nonce, 12);
     data.in.extra_ciphertext = out_tag;
     data.in.extra_ciphertext_len = extra_in_len;
     chacha20_poly1305_seal(out, in, in_len, ad, ad_len, &data);
   } else {
     CRYPTO_chacha_20(out, in, in_len, key, nonce, 1);
     calc_tag(data.out.tag, key, nonce, ad, ad_len, out, in_len, out_tag,
              extra_in_len);
   }

   OPENSSL_memcpy(out_tag + extra_in_len, data.out.tag, tag_len);
   *out_tag_len = extra_in_len + tag_len;
   return 1;
 }

 static int aead_chacha20_poly1305_seal_scatter(
     const EVP_AEAD_CTX *ctx, uint8_t *out, uint8_t *out_tag,
     size_t *out_tag_len, size_t max_out_tag_len, const uint8_t *nonce,
     size_t nonce_len, const uint8_t *in, size_t in_len, const uint8_t *extra_in,
     size_t extra_in_len, const uint8_t *ad, size_t ad_len) {
   const struct aead_chacha20_poly1305_ctx *c20_ctx =
       (struct aead_chacha20_poly1305_ctx *)&ctx->state;

   return chacha20_poly1305_seal_scatter(
       c20_ctx->key, out, out_tag, out_tag_len, max_out_tag_len, nonce,
       nonce_len, in, in_len, extra_in, extra_in_len, ad, ad_len, ctx->tag_len);
 }

 static int aead_xchacha20_poly1305_seal_scatter(
     const EVP_AEAD_CTX *ctx, uint8_t *out, uint8_t *out_tag,
     size_t *out_tag_len, size_t max_out_tag_len, const uint8_t *nonce,
     size_t nonce_len, const uint8_t *in, size_t in_len, const uint8_t *extra_in,
     size_t extra_in_len, const uint8_t *ad, size_t ad_len) {
   const struct aead_chacha20_poly1305_ctx *c20_ctx =
       (struct aead_chacha20_poly1305_ctx *)&ctx->state;

   if (nonce_len != 24) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
     return 0;
   }

   alignas(4) uint8_t derived_key[32];
   alignas(4) uint8_t derived_nonce[12];
   CRYPTO_hchacha20(derived_key, c20_ctx->key, nonce);
   OPENSSL_memset(derived_nonce, 0, 4);
   OPENSSL_memcpy(&derived_nonce[4], &nonce[16], 8);

   return chacha20_poly1305_seal_scatter(
       derived_key, out, out_tag, out_tag_len, max_out_tag_len,
       derived_nonce, sizeof(derived_nonce), in, in_len, extra_in, extra_in_len,
       ad, ad_len, ctx->tag_len);
 }

 static int chacha20_poly1305_open_gather(
     const uint8_t *key, uint8_t *out, const uint8_t *nonce,
     size_t nonce_len, const uint8_t *in, size_t in_len, const uint8_t *in_tag,
     size_t in_tag_len, const uint8_t *ad, size_t ad_len, size_t tag_len) {
   if (nonce_len != 12) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
     return 0;
   }

   if (in_tag_len != tag_len) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
     return 0;
   }

   // |CRYPTO_chacha_20| uses a 32-bit block counter. Therefore we disallow
   // individual operations that work on more than 256GB at a time.
   // |in_len_64| is needed because, on 32-bit platforms, size_t is only
   // 32-bits and this produces a warning because it's always false.
   // Casting to uint64_t inside the conditional is not sufficient to stop
   // the warning.
   const uint64_t in_len_64 = in_len;
   if (in_len_64 >= (UINT64_C(1) << 32) * 64 - 64) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
     return 0;
   }

   union chacha20_poly1305_open_data data;
   if (chacha20_poly1305_asm_capable()) {
     OPENSSL_memcpy(data.in.key, key, 32);
     data.in.counter = 0;
     OPENSSL_memcpy(data.in.nonce, nonce, 12);
     chacha20_poly1305_open(out, in, in_len, ad, ad_len, &data);
   } else {
     calc_tag(data.out.tag, key, nonce, ad, ad_len, in, in_len, NULL, 0);
     CRYPTO_chacha_20(out, in, in_len, key, nonce, 1);
   }

   if (CRYPTO_memcmp(data.out.tag, in_tag, tag_len) != 0) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
     return 0;
   }

   return 1;
 }

 static int aead_chacha20_poly1305_open_gather(
     const EVP_AEAD_CTX *ctx, uint8_t *out, const uint8_t *nonce,
     size_t nonce_len, const uint8_t *in, size_t in_len, const uint8_t *in_tag,
     size_t in_tag_len, const uint8_t *ad, size_t ad_len) {
   const struct aead_chacha20_poly1305_ctx *c20_ctx =
       (struct aead_chacha20_poly1305_ctx *)&ctx->state;

   return chacha20_poly1305_open_gather(c20_ctx->key, out, nonce, nonce_len, in,
                                        in_len, in_tag, in_tag_len, ad, ad_len,
                                        ctx->tag_len);
 }

 static int aead_xchacha20_poly1305_open_gather(
     const EVP_AEAD_CTX *ctx, uint8_t *out, const uint8_t *nonce,
     size_t nonce_len, const uint8_t *in, size_t in_len, const uint8_t *in_tag,
     size_t in_tag_len, const uint8_t *ad, size_t ad_len) {
   const struct aead_chacha20_poly1305_ctx *c20_ctx =
       (struct aead_chacha20_poly1305_ctx *)&ctx->state;

   if (nonce_len != 24) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
     return 0;
   }

   alignas(4) uint8_t derived_key[32];
   alignas(4) uint8_t derived_nonce[12];
   CRYPTO_hchacha20(derived_key, c20_ctx->key, nonce);
   OPENSSL_memset(derived_nonce, 0, 4);
   OPENSSL_memcpy(&derived_nonce[4], &nonce[16], 8);

   return chacha20_poly1305_open_gather(
       derived_key, out, derived_nonce, sizeof(derived_nonce), in, in_len,
       in_tag, in_tag_len, ad, ad_len, ctx->tag_len);
 }

 static const EVP_AEAD aead_chacha20_poly1305 = {
     32,                // key len
     12,                // nonce len
     POLY1305_TAG_LEN,  // overhead
     POLY1305_TAG_LEN,  // max tag length
     1,                 // seal_scatter_supports_extra_in

     aead_chacha20_poly1305_init,
     NULL,  // init_with_direction
     aead_chacha20_poly1305_cleanup,
     NULL /* open */,
     aead_chacha20_poly1305_seal_scatter,
     aead_chacha20_poly1305_open_gather,
     NULL,  // get_iv
     NULL,  // tag_len
 };

 static const EVP_AEAD aead_xchacha20_poly1305 = {
     32,                // key len
     24,                // nonce len
     POLY1305_TAG_LEN,  // overhead
     POLY1305_TAG_LEN,  // max tag length
     1,                 // seal_scatter_supports_extra_in

     aead_chacha20_poly1305_init,
     NULL,  // init_with_direction
     aead_chacha20_poly1305_cleanup,
     NULL /* open */,
     aead_xchacha20_poly1305_seal_scatter,
     aead_xchacha20_poly1305_open_gather,
     NULL,  // get_iv
     NULL,  // tag_len
 };

 const EVP_AEAD *EVP_aead_chacha20_poly1305(void) {
   return &aead_chacha20_poly1305;
 }

 const EVP_AEAD *EVP_aead_xchacha20_poly1305(void) {
   return &aead_xchacha20_poly1305;
 }
	/* Copyright (c) 2014, Google Inc.
	*
	* Permission to use, copy, modify, and/or distribute this software for any
	* purpose with or without fee is hereby granted, provided that the above
	* copyright notice and this permission notice appear in all copies.
	*
	* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
	* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
	* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
	* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
	* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
	* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
	* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

	#include <openssl/aead.h>

	#include <assert.h>
	#include <string.h>

	#include <openssl/chacha.h>
	#include <openssl/cipher.h>
	#include <openssl/err.h>
	#include <openssl/mem.h>
	#include <openssl/poly1305.h>

	#include "internal.h"
	#include "../chacha/internal.h"
	#include "../fipsmodule/cipher/internal.h"
	#include "../internal.h"

	struct aead_chacha20_poly1305_ctx {
	uint8_t key[32];
	};

	static_assert(sizeof(((EVP_AEAD_CTX *)NULL)->state) >=
	sizeof(struct aead_chacha20_poly1305_ctx),
	"AEAD state is too small");
	static_assert(alignof(union evp_aead_ctx_st_state) >=
	alignof(struct aead_chacha20_poly1305_ctx),
	"AEAD state has insufficient alignment");

	static int aead_chacha20_poly1305_init(EVP_AEAD_CTX ctx, const uint8_t key,
	size_t key_len, size_t tag_len) {
	struct aead_chacha20_poly1305_ctx *c20_ctx =
	(struct aead_chacha20_poly1305_ctx *)&ctx->state;

	if (tag_len == 0) {
	tag_len = POLY1305_TAG_LEN;
	}

	if (tag_len > POLY1305_TAG_LEN) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
	return 0;
	}

	if (key_len != sizeof(c20_ctx->key)) {
	return 0; // internal error - EVP_AEAD_CTX_init should catch this.
	}

	OPENSSL_memcpy(c20_ctx->key, key, key_len);
	ctx->tag_len = tag_len;

	return 1;
	}

	static void aead_chacha20_poly1305_cleanup(EVP_AEAD_CTX *ctx) {}

	static void poly1305_update_length(poly1305_state *poly1305, size_t data_len) {
	uint8_t length_bytes[8];

	for (unsigned i = 0; i < sizeof(length_bytes); i++) {
	length_bytes[i] = data_len;
	data_len >>= 8;
	}

	CRYPTO_poly1305_update(poly1305, length_bytes, sizeof(length_bytes));
	}

	// calc_tag fills \|tag\| with the authentication tag for the given inputs.
	static void calc_tag(uint8_t tag[POLY1305_TAG_LEN], const uint8_t *key,
	const uint8_t nonce[12], const uint8_t *ad, size_t ad_len,
	const uint8_t *ciphertext, size_t ciphertext_len,
	const uint8_t *ciphertext_extra,
	size_t ciphertext_extra_len) {
	alignas(16) uint8_t poly1305_key[32];
	OPENSSL_memset(poly1305_key, 0, sizeof(poly1305_key));
	CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key), key, nonce,
	0);

	static const uint8_t padding[16] = { 0 }; // Padding is all zeros.
	poly1305_state ctx;
	CRYPTO_poly1305_init(&ctx, poly1305_key);
	CRYPTO_poly1305_update(&ctx, ad, ad_len);
	if (ad_len % 16 != 0) {
	CRYPTO_poly1305_update(&ctx, padding, sizeof(padding) - (ad_len % 16));
	}
	CRYPTO_poly1305_update(&ctx, ciphertext, ciphertext_len);
	CRYPTO_poly1305_update(&ctx, ciphertext_extra, ciphertext_extra_len);
	const size_t ciphertext_total = ciphertext_len + ciphertext_extra_len;
	if (ciphertext_total % 16 != 0) {
	CRYPTO_poly1305_update(&ctx, padding,
	sizeof(padding) - (ciphertext_total % 16));
	}
	poly1305_update_length(&ctx, ad_len);
	poly1305_update_length(&ctx, ciphertext_total);
	CRYPTO_poly1305_finish(&ctx, tag);
	}

	static int chacha20_poly1305_seal_scatter(
	const uint8_t key, uint8_t out, uint8_t *out_tag,
	size_t out_tag_len, size_t max_out_tag_len, const uint8_t nonce,
	size_t nonce_len, const uint8_t in, size_t in_len, const uint8_t extra_in,
	size_t extra_in_len, const uint8_t *ad, size_t ad_len, size_t tag_len) {
	if (extra_in_len + tag_len < tag_len) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
	return 0;
	}
	if (max_out_tag_len < tag_len + extra_in_len) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
	return 0;
	}
	if (nonce_len != 12) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
	return 0;
	}

	// \|CRYPTO_chacha_20\| uses a 32-bit block counter. Therefore we disallow
	// individual operations that work on more than 256GB at a time.
	// \|in_len_64\| is needed because, on 32-bit platforms, size_t is only
	// 32-bits and this produces a warning because it's always false.
	// Casting to uint64_t inside the conditional is not sufficient to stop
	// the warning.
	const uint64_t in_len_64 = in_len;
	if (in_len_64 >= (UINT64_C(1) << 32) * 64 - 64) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
	return 0;
	}

	if (max_out_tag_len < tag_len) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BUFFER_TOO_SMALL);
	return 0;
	}

	// The the extra input is given, it is expected to be very short and so is
	// encrypted byte-by-byte first.
	if (extra_in_len) {
	static const size_t kChaChaBlockSize = 64;
	uint32_t block_counter = 1 + (in_len / kChaChaBlockSize);
	size_t offset = in_len % kChaChaBlockSize;
	uint8_t block[64 /* kChaChaBlockSize */];

	for (size_t done = 0; done < extra_in_len; block_counter++) {
	memset(block, 0, sizeof(block));
	CRYPTO_chacha_20(block, block, sizeof(block), key, nonce,
	block_counter);
	for (size_t i = offset; i < sizeof(block) && done < extra_in_len;
	i++, done++) {
	out_tag[done] = extra_in[done] ^ block[i];
	}
	offset = 0;
	}
	}

	union chacha20_poly1305_seal_data data;
	if (chacha20_poly1305_asm_capable()) {
	OPENSSL_memcpy(data.in.key, key, 32);
	data.in.counter = 0;
	OPENSSL_memcpy(data.in.nonce, nonce, 12);
	data.in.extra_ciphertext = out_tag;
	data.in.extra_ciphertext_len = extra_in_len;
	chacha20_poly1305_seal(out, in, in_len, ad, ad_len, &data);
	} else {
	CRYPTO_chacha_20(out, in, in_len, key, nonce, 1);
	calc_tag(data.out.tag, key, nonce, ad, ad_len, out, in_len, out_tag,
	extra_in_len);
	}

	OPENSSL_memcpy(out_tag + extra_in_len, data.out.tag, tag_len);
	*out_tag_len = extra_in_len + tag_len;
	return 1;
	}

	static int aead_chacha20_poly1305_seal_scatter(
	const EVP_AEAD_CTX ctx, uint8_t out, uint8_t *out_tag,
	size_t out_tag_len, size_t max_out_tag_len, const uint8_t nonce,
	size_t nonce_len, const uint8_t in, size_t in_len, const uint8_t extra_in,
	size_t extra_in_len, const uint8_t *ad, size_t ad_len) {
	const struct aead_chacha20_poly1305_ctx *c20_ctx =
	(struct aead_chacha20_poly1305_ctx *)&ctx->state;

	return chacha20_poly1305_seal_scatter(
	c20_ctx->key, out, out_tag, out_tag_len, max_out_tag_len, nonce,
	nonce_len, in, in_len, extra_in, extra_in_len, ad, ad_len, ctx->tag_len);
	}

	static int aead_xchacha20_poly1305_seal_scatter(
	const EVP_AEAD_CTX ctx, uint8_t out, uint8_t *out_tag,
	size_t out_tag_len, size_t max_out_tag_len, const uint8_t nonce,
	size_t nonce_len, const uint8_t in, size_t in_len, const uint8_t extra_in,
	size_t extra_in_len, const uint8_t *ad, size_t ad_len) {
	const struct aead_chacha20_poly1305_ctx *c20_ctx =
	(struct aead_chacha20_poly1305_ctx *)&ctx->state;

	if (nonce_len != 24) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
	return 0;
	}

	alignas(4) uint8_t derived_key[32];
	alignas(4) uint8_t derived_nonce[12];
	CRYPTO_hchacha20(derived_key, c20_ctx->key, nonce);
	OPENSSL_memset(derived_nonce, 0, 4);
	OPENSSL_memcpy(&derived_nonce[4], &nonce[16], 8);

	return chacha20_poly1305_seal_scatter(
	derived_key, out, out_tag, out_tag_len, max_out_tag_len,
	derived_nonce, sizeof(derived_nonce), in, in_len, extra_in, extra_in_len,
	ad, ad_len, ctx->tag_len);
	}

	static int chacha20_poly1305_open_gather(
	const uint8_t key, uint8_t out, const uint8_t *nonce,
	size_t nonce_len, const uint8_t in, size_t in_len, const uint8_t in_tag,
	size_t in_tag_len, const uint8_t *ad, size_t ad_len, size_t tag_len) {
	if (nonce_len != 12) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
	return 0;
	}

	if (in_tag_len != tag_len) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
	return 0;
	}

	// \|CRYPTO_chacha_20\| uses a 32-bit block counter. Therefore we disallow
	// individual operations that work on more than 256GB at a time.
	// \|in_len_64\| is needed because, on 32-bit platforms, size_t is only
	// 32-bits and this produces a warning because it's always false.
	// Casting to uint64_t inside the conditional is not sufficient to stop
	// the warning.
	const uint64_t in_len_64 = in_len;
	if (in_len_64 >= (UINT64_C(1) << 32) * 64 - 64) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
	return 0;
	}

	union chacha20_poly1305_open_data data;
	if (chacha20_poly1305_asm_capable()) {
	OPENSSL_memcpy(data.in.key, key, 32);
	data.in.counter = 0;
	OPENSSL_memcpy(data.in.nonce, nonce, 12);
	chacha20_poly1305_open(out, in, in_len, ad, ad_len, &data);
	} else {
	calc_tag(data.out.tag, key, nonce, ad, ad_len, in, in_len, NULL, 0);
	CRYPTO_chacha_20(out, in, in_len, key, nonce, 1);
	}

	if (CRYPTO_memcmp(data.out.tag, in_tag, tag_len) != 0) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
	return 0;
	}

	return 1;
	}

	static int aead_chacha20_poly1305_open_gather(
	const EVP_AEAD_CTX ctx, uint8_t out, const uint8_t *nonce,
	size_t nonce_len, const uint8_t in, size_t in_len, const uint8_t in_tag,
	size_t in_tag_len, const uint8_t *ad, size_t ad_len) {
	const struct aead_chacha20_poly1305_ctx *c20_ctx =
	(struct aead_chacha20_poly1305_ctx *)&ctx->state;

	return chacha20_poly1305_open_gather(c20_ctx->key, out, nonce, nonce_len, in,
	in_len, in_tag, in_tag_len, ad, ad_len,
	ctx->tag_len);
	}

	static int aead_xchacha20_poly1305_open_gather(
	const EVP_AEAD_CTX ctx, uint8_t out, const uint8_t *nonce,
	size_t nonce_len, const uint8_t in, size_t in_len, const uint8_t in_tag,
	size_t in_tag_len, const uint8_t *ad, size_t ad_len) {
	const struct aead_chacha20_poly1305_ctx *c20_ctx =
	(struct aead_chacha20_poly1305_ctx *)&ctx->state;

	if (nonce_len != 24) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
	return 0;
	}

	alignas(4) uint8_t derived_key[32];
	alignas(4) uint8_t derived_nonce[12];
	CRYPTO_hchacha20(derived_key, c20_ctx->key, nonce);
	OPENSSL_memset(derived_nonce, 0, 4);
	OPENSSL_memcpy(&derived_nonce[4], &nonce[16], 8);

	return chacha20_poly1305_open_gather(
	derived_key, out, derived_nonce, sizeof(derived_nonce), in, in_len,
	in_tag, in_tag_len, ad, ad_len, ctx->tag_len);
	}

	static const EVP_AEAD aead_chacha20_poly1305 = {
	32, // key len
	12, // nonce len
	POLY1305_TAG_LEN, // overhead
	POLY1305_TAG_LEN, // max tag length
	1, // seal_scatter_supports_extra_in

	aead_chacha20_poly1305_init,
	NULL, // init_with_direction
	aead_chacha20_poly1305_cleanup,
	NULL /* open */,
	aead_chacha20_poly1305_seal_scatter,
	aead_chacha20_poly1305_open_gather,
	NULL, // get_iv
	NULL, // tag_len
	};

	static const EVP_AEAD aead_xchacha20_poly1305 = {
	32, // key len
	24, // nonce len
	POLY1305_TAG_LEN, // overhead
	POLY1305_TAG_LEN, // max tag length
	1, // seal_scatter_supports_extra_in

	aead_chacha20_poly1305_init,
	NULL, // init_with_direction
	aead_chacha20_poly1305_cleanup,
	NULL /* open */,
	aead_xchacha20_poly1305_seal_scatter,
	aead_xchacha20_poly1305_open_gather,
	NULL, // get_iv
	NULL, // tag_len
	};

	const EVP_AEAD *EVP_aead_chacha20_poly1305(void) {
	return &aead_chacha20_poly1305;
	}

	const EVP_AEAD *EVP_aead_xchacha20_poly1305(void) {
	return &aead_xchacha20_poly1305;
	}