crypto/cipher_extra/e_chacha20poly1305.c - third_party/boringssl/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 <string.h>

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

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


 #define POLY1305_TAG_LEN 16

 struct aead_chacha20_poly1305_ctx {
   unsigned char key[32];
 };

 #if defined(OPENSSL_X86_64) && !defined(OPENSSL_NO_ASM) && \
     !defined(OPENSSL_WINDOWS)
 static int asm_capable(void) {
   const int sse41_capable = (OPENSSL_ia32cap_P[1] & (1 << 19)) != 0;
   return sse41_capable;
 }

 // chacha20_poly1305_open is defined in chacha20_poly1305_x86_64.pl. It
 // decrypts |plaintext_len| bytes from |ciphertext| and writes them to
 // |out_plaintext|. On entry, |aead_data| must contain the final 48 bytes of
 // the initial ChaCha20 block, i.e. the key, followed by four zeros, followed
 // by the nonce. On exit, it will contain the calculated tag value, which the
 // caller must check.
 extern void chacha20_poly1305_open(uint8_t *out_plaintext,
                                    const uint8_t *ciphertext,
                                    size_t plaintext_len, const uint8_t *ad,
                                    size_t ad_len, uint8_t *aead_data);

 // chacha20_poly1305_open is defined in chacha20_poly1305_x86_64.pl. It
 // encrypts |plaintext_len| bytes from |plaintext| and writes them to
 // |out_ciphertext|. On entry, |aead_data| must contain the final 48 bytes of
 // the initial ChaCha20 block, i.e. the key, followed by four zeros, followed
 // by the nonce. On exit, it will contain the calculated tag value, which the
 // caller must append to the ciphertext.
 extern void chacha20_poly1305_seal(uint8_t *out_ciphertext,
                                    const uint8_t *plaintext,
                                    size_t plaintext_len, const uint8_t *ad,
                                    size_t ad_len, uint8_t *aead_data);
 #else
 static int asm_capable(void) {
   return 0;
 }


 static void chacha20_poly1305_open(uint8_t *out_plaintext,
                                    const uint8_t *ciphertext,
                                    size_t plaintext_len, const uint8_t *ad,
                                    size_t ad_len, uint8_t *aead_data) {}

 static void chacha20_poly1305_seal(uint8_t *out_ciphertext,
                                    const uint8_t *plaintext,
                                    size_t plaintext_len, const uint8_t *ad,
                                    size_t ad_len, uint8_t *aead_data) {}
 #endif

 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;

   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. */
   }

   c20_ctx = OPENSSL_malloc(sizeof(struct aead_chacha20_poly1305_ctx));
   if (c20_ctx == NULL) {
     return 0;
   }

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

   return 1;
 }

 static void aead_chacha20_poly1305_cleanup(EVP_AEAD_CTX *ctx) {
   struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
   OPENSSL_cleanse(c20_ctx->key, sizeof(c20_ctx->key));
   OPENSSL_free(c20_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 struct aead_chacha20_poly1305_ctx *c20_ctx,
                      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),
                    c20_ctx->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 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 = ctx->aead_state;

   if (extra_in_len + ctx->tag_len < ctx->tag_len) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
     return 0;
   }
   if (max_out_tag_len < ctx->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 < ctx->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), c20_ctx->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;
     }
   }

   alignas(16) uint8_t tag[48 + 8 + 8];

   if (asm_capable()) {
     OPENSSL_memcpy(tag, c20_ctx->key, 32);
     OPENSSL_memset(tag + 32, 0, 4);
     OPENSSL_memcpy(tag + 32 + 4, nonce, 12);
     OPENSSL_memcpy(tag + 48, &out_tag, sizeof(out_tag));
     OPENSSL_memcpy(tag + 56, &extra_in_len, sizeof(extra_in_len));
     chacha20_poly1305_seal(out, in, in_len, ad, ad_len, tag);
   } else {
     CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
     calc_tag(tag, c20_ctx, nonce, ad, ad_len, out, in_len,
              out_tag, extra_in_len);
   }

   OPENSSL_memcpy(out_tag + extra_in_len, tag, ctx->tag_len);
   *out_tag_len = extra_in_len + ctx->tag_len;
   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 = ctx->aead_state;

   if (nonce_len != 12) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
     return 0;
   }

   if (in_tag_len != ctx->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;
   }

   alignas(16) uint8_t tag[48];

   if (asm_capable()) {
     OPENSSL_memcpy(tag, c20_ctx->key, 32);
     OPENSSL_memset(tag + 32, 0, 4);
     OPENSSL_memcpy(tag + 32 + 4, nonce, 12);
     chacha20_poly1305_open(out, in, in_len, ad, ad_len, tag);
   } else {
     calc_tag(tag, c20_ctx, nonce, ad, ad_len, in, in_len, NULL, 0);
     CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
   }

   if (CRYPTO_memcmp(tag, in_tag, ctx->tag_len) != 0) {
     OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
     return 0;
   }

   return 1;
 }

 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 */
 };

 const EVP_AEAD *EVP_aead_chacha20_poly1305(void) {
   return &aead_chacha20_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 <string.h>

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

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


	#define POLY1305_TAG_LEN 16

	struct aead_chacha20_poly1305_ctx {
	unsigned char key[32];
	};

	#if defined(OPENSSL_X86_64) && !defined(OPENSSL_NO_ASM) && \
	!defined(OPENSSL_WINDOWS)
	static int asm_capable(void) {
	const int sse41_capable = (OPENSSL_ia32cap_P[1] & (1 << 19)) != 0;
	return sse41_capable;
	}

	// chacha20_poly1305_open is defined in chacha20_poly1305_x86_64.pl. It
	// decrypts \|plaintext_len\| bytes from \|ciphertext\| and writes them to
	// \|out_plaintext\|. On entry, \|aead_data\| must contain the final 48 bytes of
	// the initial ChaCha20 block, i.e. the key, followed by four zeros, followed
	// by the nonce. On exit, it will contain the calculated tag value, which the
	// caller must check.
	extern void chacha20_poly1305_open(uint8_t *out_plaintext,
	const uint8_t *ciphertext,
	size_t plaintext_len, const uint8_t *ad,
	size_t ad_len, uint8_t *aead_data);

	// chacha20_poly1305_open is defined in chacha20_poly1305_x86_64.pl. It
	// encrypts \|plaintext_len\| bytes from \|plaintext\| and writes them to
	// \|out_ciphertext\|. On entry, \|aead_data\| must contain the final 48 bytes of
	// the initial ChaCha20 block, i.e. the key, followed by four zeros, followed
	// by the nonce. On exit, it will contain the calculated tag value, which the
	// caller must append to the ciphertext.
	extern void chacha20_poly1305_seal(uint8_t *out_ciphertext,
	const uint8_t *plaintext,
	size_t plaintext_len, const uint8_t *ad,
	size_t ad_len, uint8_t *aead_data);
	#else
	static int asm_capable(void) {
	return 0;
	}


	static void chacha20_poly1305_open(uint8_t *out_plaintext,
	const uint8_t *ciphertext,
	size_t plaintext_len, const uint8_t *ad,
	size_t ad_len, uint8_t *aead_data) {}

	static void chacha20_poly1305_seal(uint8_t *out_ciphertext,
	const uint8_t *plaintext,
	size_t plaintext_len, const uint8_t *ad,
	size_t ad_len, uint8_t *aead_data) {}
	#endif

	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;

	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. */
	}

	c20_ctx = OPENSSL_malloc(sizeof(struct aead_chacha20_poly1305_ctx));
	if (c20_ctx == NULL) {
	return 0;
	}

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

	return 1;
	}

	static void aead_chacha20_poly1305_cleanup(EVP_AEAD_CTX *ctx) {
	struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
	OPENSSL_cleanse(c20_ctx->key, sizeof(c20_ctx->key));
	OPENSSL_free(c20_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 struct aead_chacha20_poly1305_ctx *c20_ctx,
	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),
	c20_ctx->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 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 = ctx->aead_state;

	if (extra_in_len + ctx->tag_len < ctx->tag_len) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_TOO_LARGE);
	return 0;
	}
	if (max_out_tag_len < ctx->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 < ctx->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), c20_ctx->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;
	}
	}

	alignas(16) uint8_t tag[48 + 8 + 8];

	if (asm_capable()) {
	OPENSSL_memcpy(tag, c20_ctx->key, 32);
	OPENSSL_memset(tag + 32, 0, 4);
	OPENSSL_memcpy(tag + 32 + 4, nonce, 12);
	OPENSSL_memcpy(tag + 48, &out_tag, sizeof(out_tag));
	OPENSSL_memcpy(tag + 56, &extra_in_len, sizeof(extra_in_len));
	chacha20_poly1305_seal(out, in, in_len, ad, ad_len, tag);
	} else {
	CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
	calc_tag(tag, c20_ctx, nonce, ad, ad_len, out, in_len,
	out_tag, extra_in_len);
	}

	OPENSSL_memcpy(out_tag + extra_in_len, tag, ctx->tag_len);
	*out_tag_len = extra_in_len + ctx->tag_len;
	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 = ctx->aead_state;

	if (nonce_len != 12) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_UNSUPPORTED_NONCE_SIZE);
	return 0;
	}

	if (in_tag_len != ctx->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;
	}

	alignas(16) uint8_t tag[48];

	if (asm_capable()) {
	OPENSSL_memcpy(tag, c20_ctx->key, 32);
	OPENSSL_memset(tag + 32, 0, 4);
	OPENSSL_memcpy(tag + 32 + 4, nonce, 12);
	chacha20_poly1305_open(out, in, in_len, ad, ad_len, tag);
	} else {
	calc_tag(tag, c20_ctx, nonce, ad, ad_len, in, in_len, NULL, 0);
	CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
	}

	if (CRYPTO_memcmp(tag, in_tag, ctx->tag_len) != 0) {
	OPENSSL_PUT_ERROR(CIPHER, CIPHER_R_BAD_DECRYPT);
	return 0;
	}

	return 1;
	}

	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 */
	};

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