include/openssl/hpke.h - boringssl - Git at Google

 /* Copyright (c) 2020, 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. */

 #ifndef OPENSSL_HEADER_CRYPTO_HPKE_INTERNAL_H
 #define OPENSSL_HEADER_CRYPTO_HPKE_INTERNAL_H

 #include <openssl/aead.h>
 #include <openssl/base.h>
 #include <openssl/curve25519.h>
 #include <openssl/digest.h>

 #if defined(__cplusplus)
 extern "C" {
 #endif


 // Hybrid Public Key Encryption.
 //
 // Hybrid Public Key Encryption (HPKE) enables a sender to encrypt messages to a
 // receiver with a public key.
 //
 // See https://tools.ietf.org/html/draft-irtf-cfrg-hpke-12.


 // Parameters.
 //
 // An HPKE context is parameterized by KEM, KDF, and AEAD algorithms,
 // represented by |EVP_HPKE_KEM|, |EVP_HPKE_KDF|, and |EVP_HPKE_AEAD| types,
 // respectively.

 // The following constants are KEM identifiers.
 #define EVP_HPKE_DHKEM_X25519_HKDF_SHA256 0x0020

 // The following functions are KEM algorithms which may be used with HPKE. Note
 // that, while some HPKE KEMs use KDFs internally, this is separate from the
 // |EVP_HPKE_KDF| selection.
 OPENSSL_EXPORT const EVP_HPKE_KEM *EVP_hpke_x25519_hkdf_sha256(void);

 // EVP_HPKE_KEM_id returns the HPKE KEM identifier for |kem|, which
 // will be one of the |EVP_HPKE_KEM_*| constants.
 OPENSSL_EXPORT uint16_t EVP_HPKE_KEM_id(const EVP_HPKE_KEM *kem);

 // The following constants are KDF identifiers.
 #define EVP_HPKE_HKDF_SHA256 0x0001

 // The following functions are KDF algorithms which may be used with HPKE.
 OPENSSL_EXPORT const EVP_HPKE_KDF *EVP_hpke_hkdf_sha256(void);

 // EVP_HPKE_KDF_id returns the HPKE KDF identifier for |kdf|.
 OPENSSL_EXPORT uint16_t EVP_HPKE_KDF_id(const EVP_HPKE_KDF *kdf);

 // The following constants are AEAD identifiers.
 #define EVP_HPKE_AES_128_GCM 0x0001
 #define EVP_HPKE_AES_256_GCM 0x0002
 #define EVP_HPKE_CHACHA20_POLY1305 0x0003

 // The following functions are AEAD algorithms which may be used with HPKE.
 OPENSSL_EXPORT const EVP_HPKE_AEAD *EVP_hpke_aes_128_gcm(void);
 OPENSSL_EXPORT const EVP_HPKE_AEAD *EVP_hpke_aes_256_gcm(void);
 OPENSSL_EXPORT const EVP_HPKE_AEAD *EVP_hpke_chacha20_poly1305(void);

 // EVP_HPKE_AEAD_id returns the HPKE AEAD identifier for |aead|.
 OPENSSL_EXPORT uint16_t EVP_HPKE_AEAD_id(const EVP_HPKE_AEAD *aead);

 // EVP_HPKE_AEAD_aead returns the |EVP_AEAD| corresponding to |aead|.
 OPENSSL_EXPORT const EVP_AEAD *EVP_HPKE_AEAD_aead(const EVP_HPKE_AEAD *aead);


 // Recipient keys.
 //
 // An HPKE recipient maintains a long-term KEM key. This library represents keys
 // with the |EVP_HPKE_KEY| type.

 // EVP_HPKE_KEY_zero sets an uninitialized |EVP_HPKE_KEY| to the zero state. The
 // caller should then use |EVP_HPKE_KEY_init|, |EVP_HPKE_KEY_copy|, or
 // |EVP_HPKE_KEY_generate| to finish initializing |key|.
 //
 // It is safe, but not necessary to call |EVP_HPKE_KEY_cleanup| in this state.
 // This may be used for more uniform cleanup of |EVP_HPKE_KEY|.
 OPENSSL_EXPORT void EVP_HPKE_KEY_zero(EVP_HPKE_KEY *key);

 // EVP_HPKE_KEY_cleanup releases memory referenced by |key|.
 OPENSSL_EXPORT void EVP_HPKE_KEY_cleanup(EVP_HPKE_KEY *key);

 // EVP_HPKE_KEY_new returns a newly-allocated |EVP_HPKE_KEY|, or NULL on error.
 // The caller must call |EVP_HPKE_KEY_free| on the result to release it.
 //
 // This is a convenience function for callers that need a heap-allocated
 // |EVP_HPKE_KEY|.
 OPENSSL_EXPORT EVP_HPKE_KEY *EVP_HPKE_KEY_new(void);

 // EVP_HPKE_KEY_free releases memory associated with |key|, which must have been
 // created with |EVP_HPKE_KEY_new|.
 OPENSSL_EXPORT void EVP_HPKE_KEY_free(EVP_HPKE_KEY *key);

 // EVP_HPKE_KEY_copy sets |dst| to a copy of |src|. It returns one on success
 // and zero on error. On success, the caller must call |EVP_HPKE_KEY_cleanup| to
 // release |dst|. On failure, calling |EVP_HPKE_KEY_cleanup| is safe, but not
 // necessary.
 OPENSSL_EXPORT int EVP_HPKE_KEY_copy(EVP_HPKE_KEY *dst,
                                      const EVP_HPKE_KEY *src);

 // EVP_HPKE_KEY_init decodes |priv_key| as a private key for |kem| and
 // initializes |key| with the result. It returns one on success and zero if
 // |priv_key| was invalid. On success, the caller must call
 // |EVP_HPKE_KEY_cleanup| to release the key. On failure, calling
 // |EVP_HPKE_KEY_cleanup| is safe, but not necessary.
 OPENSSL_EXPORT int EVP_HPKE_KEY_init(EVP_HPKE_KEY *key, const EVP_HPKE_KEM *kem,
                                      const uint8_t *priv_key,
                                      size_t priv_key_len);

 // EVP_HPKE_KEY_generate sets |key| to a newly-generated key using |kem|.
 OPENSSL_EXPORT int EVP_HPKE_KEY_generate(EVP_HPKE_KEY *key,
                                          const EVP_HPKE_KEM *kem);

 // EVP_HPKE_KEY_kem returns the HPKE KEM used by |key|.
 OPENSSL_EXPORT const EVP_HPKE_KEM *EVP_HPKE_KEY_kem(const EVP_HPKE_KEY *key);

 // EVP_HPKE_MAX_PUBLIC_KEY_LENGTH is the maximum length of a public key for all
 // KEMs supported by this library.
 #define EVP_HPKE_MAX_PUBLIC_KEY_LENGTH 32

 // EVP_HPKE_KEY_public_key writes |key|'s public key to |out| and sets
 // |*out_len| to the number of bytes written. On success, it returns one and
 // writes at most |max_out| bytes. If |max_out| is too small, it returns zero.
 // Setting |max_out| to |EVP_HPKE_MAX_PUBLIC_KEY_LENGTH| will ensure the public
 // key fits.
 OPENSSL_EXPORT int EVP_HPKE_KEY_public_key(const EVP_HPKE_KEY *key,
                                            uint8_t *out, size_t *out_len,
                                            size_t max_out);

 // EVP_HPKE_MAX_PRIVATE_KEY_LENGTH is the maximum length of a private key for
 // all KEMs supported by this library.
 #define EVP_HPKE_MAX_PRIVATE_KEY_LENGTH 32

 // EVP_HPKE_KEY_private_key writes |key|'s private key to |out| and sets
 // |*out_len| to the number of bytes written. On success, it returns one and
 // writes at most |max_out| bytes. If |max_out| is too small, it returns zero.
 // Setting |max_out| to |EVP_HPKE_MAX_PRIVATE_KEY_LENGTH| will ensure the
 // private key fits.
 OPENSSL_EXPORT int EVP_HPKE_KEY_private_key(const EVP_HPKE_KEY *key,
                                             uint8_t *out, size_t *out_len,
                                             size_t max_out);


 // Encryption contexts.
 //
 // An HPKE encryption context is represented by the |EVP_HPKE_CTX| type.

 // EVP_HPKE_CTX_zero sets an uninitialized |EVP_HPKE_CTX| to the zero state. The
 // caller should then use one of the |EVP_HPKE_CTX_setup_*| functions to finish
 // setting up |ctx|.
 //
 // It is safe, but not necessary to call |EVP_HPKE_CTX_cleanup| in this state.
 // This may be used for more uniform cleanup of |EVP_HPKE_CTX|.
 OPENSSL_EXPORT void EVP_HPKE_CTX_zero(EVP_HPKE_CTX *ctx);

 // EVP_HPKE_CTX_cleanup releases memory referenced by |ctx|. |ctx| must have
 // been initialized with |EVP_HPKE_CTX_zero| or one of the
 // |EVP_HPKE_CTX_setup_*| functions.
 OPENSSL_EXPORT void EVP_HPKE_CTX_cleanup(EVP_HPKE_CTX *ctx);

 // EVP_HPKE_CTX_new returns a newly-allocated |EVP_HPKE_CTX|, or NULL on error.
 // The caller must call |EVP_HPKE_CTX_free| on the result to release it.
 //
 // This is a convenience function for callers that need a heap-allocated
 // |EVP_HPKE_CTX|.
 OPENSSL_EXPORT EVP_HPKE_CTX *EVP_HPKE_CTX_new(void);

 // EVP_HPKE_CTX_free releases memory associated with |ctx|, which must have been
 // created with |EVP_HPKE_CTX_new|.
 OPENSSL_EXPORT void EVP_HPKE_CTX_free(EVP_HPKE_CTX *ctx);

 // EVP_HPKE_MAX_ENC_LENGTH is the maximum length of "enc", the encapsulated
 // shared secret, for all supported KEMs in this library.
 #define EVP_HPKE_MAX_ENC_LENGTH 32

 // EVP_HPKE_CTX_setup_sender implements the SetupBaseS HPKE operation. It
 // encapsulates a shared secret for |peer_public_key| and sets up |ctx| as a
 // sender context. It writes the encapsulated shared secret to |out_enc| and
 // sets |*out_enc_len| to the number of bytes written. It writes at most
 // |max_enc| bytes and fails if the buffer is too small. Setting |max_enc| to at
 // least |EVP_HPKE_MAX_ENC_LENGTH| will ensure the buffer is large enough.
 //
 // This function returns one on success and zero on error. Note that
 // |peer_public_key| may be invalid, in which case this function will return an
 // error.
 //
 // On success, callers may call |EVP_HPKE_CTX_seal| to encrypt messages for the
 // recipient. Callers must then call |EVP_HPKE_CTX_cleanup| when done. On
 // failure, calling |EVP_HPKE_CTX_cleanup| is safe, but not required.
 OPENSSL_EXPORT int EVP_HPKE_CTX_setup_sender(
     EVP_HPKE_CTX *ctx, uint8_t *out_enc, size_t *out_enc_len, size_t max_enc,
     const EVP_HPKE_KEM *kem, const EVP_HPKE_KDF *kdf, const EVP_HPKE_AEAD *aead,
     const uint8_t *peer_public_key, size_t peer_public_key_len,
     const uint8_t *info, size_t info_len);

 // EVP_HPKE_CTX_setup_sender_with_seed_for_testing behaves like
 // |EVP_HPKE_CTX_setup_sender|, but takes a seed to behave deterministically.
 // The seed's format depends on |kem|. For X25519, it is the sender's
 // ephemeral private key.
 OPENSSL_EXPORT int EVP_HPKE_CTX_setup_sender_with_seed_for_testing(
     EVP_HPKE_CTX *ctx, uint8_t *out_enc, size_t *out_enc_len, size_t max_enc,
     const EVP_HPKE_KEM *kem, const EVP_HPKE_KDF *kdf, const EVP_HPKE_AEAD *aead,
     const uint8_t *peer_public_key, size_t peer_public_key_len,
     const uint8_t *info, size_t info_len, const uint8_t *seed, size_t seed_len);

 // EVP_HPKE_CTX_setup_recipient implements the SetupBaseR HPKE operation. It
 // decapsulates the shared secret in |enc| with |key| and sets up |ctx| as a
 // recipient context. It returns one on success and zero on failure. Note that
 // |enc| may be invalid, in which case this function will return an error.
 //
 // On success, callers may call |EVP_HPKE_CTX_open| to decrypt messages from the
 // sender. Callers must then call |EVP_HPKE_CTX_cleanup| when done. On failure,
 // calling |EVP_HPKE_CTX_cleanup| is safe, but not required.
 OPENSSL_EXPORT int EVP_HPKE_CTX_setup_recipient(
     EVP_HPKE_CTX *ctx, const EVP_HPKE_KEY *key, const EVP_HPKE_KDF *kdf,
     const EVP_HPKE_AEAD *aead, const uint8_t *enc, size_t enc_len,
     const uint8_t *info, size_t info_len);


 // Using an HPKE context.
 //
 // Once set up, callers may encrypt or decrypt with an |EVP_HPKE_CTX| using the
 // following functions.

 // EVP_HPKE_CTX_open uses the HPKE context |ctx| to authenticate |in_len| bytes
 // from |in| and |ad_len| bytes from |ad| and to decrypt at most |in_len| bytes
 // into |out|. It returns one on success, and zero otherwise.
 //
 // This operation will fail if the |ctx| context is not set up as a receiver.
 //
 // Note that HPKE encryption is stateful and ordered. The sender's first call to
 // |EVP_HPKE_CTX_seal| must correspond to the recipient's first call to
 // |EVP_HPKE_CTX_open|, etc.
 //
 // At most |in_len| bytes are written to |out|. In order to ensure success,
 // |max_out_len| should be at least |in_len|. On successful return, |*out_len|
 // is set to the actual number of bytes written.
 OPENSSL_EXPORT int EVP_HPKE_CTX_open(EVP_HPKE_CTX *ctx, uint8_t *out,
                                      size_t *out_len, size_t max_out_len,
                                      const uint8_t *in, size_t in_len,
                                      const uint8_t *ad, size_t ad_len);

 // EVP_HPKE_CTX_seal uses the HPKE context |ctx| to encrypt and authenticate
 // |in_len| bytes of ciphertext |in| and authenticate |ad_len| bytes from |ad|,
 // writing the result to |out|. It returns one on success and zero otherwise.
 //
 // This operation will fail if the |ctx| context is not set up as a sender.
 //
 // Note that HPKE encryption is stateful and ordered. The sender's first call to
 // |EVP_HPKE_CTX_seal| must correspond to the recipient's first call to
 // |EVP_HPKE_CTX_open|, etc.
 //
 // At most, |max_out_len| encrypted bytes are written to |out|. On successful
 // return, |*out_len| is set to the actual number of bytes written.
 //
 // To ensure success, |max_out_len| should be |in_len| plus the result of
 // |EVP_HPKE_CTX_max_overhead| or |EVP_HPKE_MAX_OVERHEAD|.
 OPENSSL_EXPORT int EVP_HPKE_CTX_seal(EVP_HPKE_CTX *ctx, uint8_t *out,
                                      size_t *out_len, size_t max_out_len,
                                      const uint8_t *in, size_t in_len,
                                      const uint8_t *ad, size_t ad_len);

 // EVP_HPKE_CTX_export uses the HPKE context |ctx| to export a secret of
 // |secret_len| bytes into |out|. This function uses |context_len| bytes from
 // |context| as a context string for the secret. This is necessary to separate
 // different uses of exported secrets and bind relevant caller-specific context
 // into the output. It returns one on success and zero otherwise.
 OPENSSL_EXPORT int EVP_HPKE_CTX_export(const EVP_HPKE_CTX *ctx, uint8_t *out,
                                        size_t secret_len,
                                        const uint8_t *context,
                                        size_t context_len);

 // EVP_HPKE_MAX_OVERHEAD contains the largest value that
 // |EVP_HPKE_CTX_max_overhead| would ever return for any context.
 #define EVP_HPKE_MAX_OVERHEAD EVP_AEAD_MAX_OVERHEAD

 // EVP_HPKE_CTX_max_overhead returns the maximum number of additional bytes
 // added by sealing data with |EVP_HPKE_CTX_seal|. The |ctx| context must be set
 // up as a sender.
 OPENSSL_EXPORT size_t EVP_HPKE_CTX_max_overhead(const EVP_HPKE_CTX *ctx);

 // EVP_HPKE_CTX_aead returns |ctx|'s configured AEAD, or NULL if the context has
 // not been set up.
 OPENSSL_EXPORT const EVP_HPKE_AEAD *EVP_HPKE_CTX_aead(const EVP_HPKE_CTX *ctx);

 // EVP_HPKE_CTX_kdf returns |ctx|'s configured KDF, or NULL if the context has
 // not been set up.
 OPENSSL_EXPORT const EVP_HPKE_KDF *EVP_HPKE_CTX_kdf(const EVP_HPKE_CTX *ctx);


 // Private structures.
 //
 // The following structures are exported so their types are stack-allocatable,
 // but accessing or modifying their fields is forbidden.

 struct evp_hpke_ctx_st {
   const EVP_HPKE_AEAD *aead;
   const EVP_HPKE_KDF *kdf;
   EVP_AEAD_CTX aead_ctx;
   uint8_t base_nonce[EVP_AEAD_MAX_NONCE_LENGTH];
   uint8_t exporter_secret[EVP_MAX_MD_SIZE];
   uint64_t seq;
   int is_sender;
 };

 struct evp_hpke_key_st {
   const EVP_HPKE_KEM *kem;
   uint8_t private_key[X25519_PRIVATE_KEY_LEN];
   uint8_t public_key[X25519_PUBLIC_VALUE_LEN];
 };


 #if defined(__cplusplus)
 }  // extern C
 #endif

 #if !defined(BORINGSSL_NO_CXX)
 extern "C++" {

 BSSL_NAMESPACE_BEGIN

 using ScopedEVP_HPKE_CTX =
     internal::StackAllocated<EVP_HPKE_CTX, void, EVP_HPKE_CTX_zero,
                              EVP_HPKE_CTX_cleanup>;
 using ScopedEVP_HPKE_KEY =
     internal::StackAllocated<EVP_HPKE_KEY, void, EVP_HPKE_KEY_zero,
                              EVP_HPKE_KEY_cleanup>;

 BORINGSSL_MAKE_DELETER(EVP_HPKE_CTX, EVP_HPKE_CTX_free)
 BORINGSSL_MAKE_DELETER(EVP_HPKE_KEY, EVP_HPKE_KEY_free)

 BSSL_NAMESPACE_END

 }  // extern C++
 #endif

 #endif  // OPENSSL_HEADER_CRYPTO_HPKE_INTERNAL_H
	/* Copyright (c) 2020, 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. */

	#ifndef OPENSSL_HEADER_CRYPTO_HPKE_INTERNAL_H
	#define OPENSSL_HEADER_CRYPTO_HPKE_INTERNAL_H

	#include <openssl/aead.h>
	#include <openssl/base.h>
	#include <openssl/curve25519.h>
	#include <openssl/digest.h>

	#if defined(__cplusplus)
	extern "C" {
	#endif


	// Hybrid Public Key Encryption.
	//
	// Hybrid Public Key Encryption (HPKE) enables a sender to encrypt messages to a
	// receiver with a public key.
	//
	// See https://tools.ietf.org/html/draft-irtf-cfrg-hpke-12.


	// Parameters.
	//
	// An HPKE context is parameterized by KEM, KDF, and AEAD algorithms,
	// represented by \|EVP_HPKE_KEM\|, \|EVP_HPKE_KDF\|, and \|EVP_HPKE_AEAD\| types,
	// respectively.

	// The following constants are KEM identifiers.
	#define EVP_HPKE_DHKEM_X25519_HKDF_SHA256 0x0020

	// The following functions are KEM algorithms which may be used with HPKE. Note
	// that, while some HPKE KEMs use KDFs internally, this is separate from the
	// \|EVP_HPKE_KDF\| selection.
	OPENSSL_EXPORT const EVP_HPKE_KEM *EVP_hpke_x25519_hkdf_sha256(void);

	// EVP_HPKE_KEM_id returns the HPKE KEM identifier for \|kem\|, which
	// will be one of the \|EVP_HPKE_KEM_*\| constants.
	OPENSSL_EXPORT uint16_t EVP_HPKE_KEM_id(const EVP_HPKE_KEM *kem);

	// The following constants are KDF identifiers.
	#define EVP_HPKE_HKDF_SHA256 0x0001

	// The following functions are KDF algorithms which may be used with HPKE.
	OPENSSL_EXPORT const EVP_HPKE_KDF *EVP_hpke_hkdf_sha256(void);

	// EVP_HPKE_KDF_id returns the HPKE KDF identifier for \|kdf\|.
	OPENSSL_EXPORT uint16_t EVP_HPKE_KDF_id(const EVP_HPKE_KDF *kdf);

	// The following constants are AEAD identifiers.
	#define EVP_HPKE_AES_128_GCM 0x0001
	#define EVP_HPKE_AES_256_GCM 0x0002
	#define EVP_HPKE_CHACHA20_POLY1305 0x0003

	// The following functions are AEAD algorithms which may be used with HPKE.
	OPENSSL_EXPORT const EVP_HPKE_AEAD *EVP_hpke_aes_128_gcm(void);
	OPENSSL_EXPORT const EVP_HPKE_AEAD *EVP_hpke_aes_256_gcm(void);
	OPENSSL_EXPORT const EVP_HPKE_AEAD *EVP_hpke_chacha20_poly1305(void);

	// EVP_HPKE_AEAD_id returns the HPKE AEAD identifier for \|aead\|.
	OPENSSL_EXPORT uint16_t EVP_HPKE_AEAD_id(const EVP_HPKE_AEAD *aead);

	// EVP_HPKE_AEAD_aead returns the \|EVP_AEAD\| corresponding to \|aead\|.
	OPENSSL_EXPORT const EVP_AEAD EVP_HPKE_AEAD_aead(const EVP_HPKE_AEAD aead);


	// Recipient keys.
	//
	// An HPKE recipient maintains a long-term KEM key. This library represents keys
	// with the \|EVP_HPKE_KEY\| type.

	// EVP_HPKE_KEY_zero sets an uninitialized \|EVP_HPKE_KEY\| to the zero state. The
	// caller should then use \|EVP_HPKE_KEY_init\|, \|EVP_HPKE_KEY_copy\|, or
	// \|EVP_HPKE_KEY_generate\| to finish initializing \|key\|.
	//
	// It is safe, but not necessary to call \|EVP_HPKE_KEY_cleanup\| in this state.
	// This may be used for more uniform cleanup of \|EVP_HPKE_KEY\|.
	OPENSSL_EXPORT void EVP_HPKE_KEY_zero(EVP_HPKE_KEY *key);

	// EVP_HPKE_KEY_cleanup releases memory referenced by \|key\|.
	OPENSSL_EXPORT void EVP_HPKE_KEY_cleanup(EVP_HPKE_KEY *key);

	// EVP_HPKE_KEY_new returns a newly-allocated \|EVP_HPKE_KEY\|, or NULL on error.
	// The caller must call \|EVP_HPKE_KEY_free\| on the result to release it.
	//
	// This is a convenience function for callers that need a heap-allocated
	// \|EVP_HPKE_KEY\|.
	OPENSSL_EXPORT EVP_HPKE_KEY *EVP_HPKE_KEY_new(void);

	// EVP_HPKE_KEY_free releases memory associated with \|key\|, which must have been
	// created with \|EVP_HPKE_KEY_new\|.
	OPENSSL_EXPORT void EVP_HPKE_KEY_free(EVP_HPKE_KEY *key);

	// EVP_HPKE_KEY_copy sets \|dst\| to a copy of \|src\|. It returns one on success
	// and zero on error. On success, the caller must call \|EVP_HPKE_KEY_cleanup\| to
	// release \|dst\|. On failure, calling \|EVP_HPKE_KEY_cleanup\| is safe, but not
	// necessary.
	OPENSSL_EXPORT int EVP_HPKE_KEY_copy(EVP_HPKE_KEY *dst,
	const EVP_HPKE_KEY *src);

	// EVP_HPKE_KEY_init decodes \|priv_key\| as a private key for \|kem\| and
	// initializes \|key\| with the result. It returns one on success and zero if
	// \|priv_key\| was invalid. On success, the caller must call
	// \|EVP_HPKE_KEY_cleanup\| to release the key. On failure, calling
	// \|EVP_HPKE_KEY_cleanup\| is safe, but not necessary.
	OPENSSL_EXPORT int EVP_HPKE_KEY_init(EVP_HPKE_KEY key, const EVP_HPKE_KEM kem,
	const uint8_t *priv_key,
	size_t priv_key_len);

	// EVP_HPKE_KEY_generate sets \|key\| to a newly-generated key using \|kem\|.
	OPENSSL_EXPORT int EVP_HPKE_KEY_generate(EVP_HPKE_KEY *key,
	const EVP_HPKE_KEM *kem);

	// EVP_HPKE_KEY_kem returns the HPKE KEM used by \|key\|.
	OPENSSL_EXPORT const EVP_HPKE_KEM EVP_HPKE_KEY_kem(const EVP_HPKE_KEY key);

	// EVP_HPKE_MAX_PUBLIC_KEY_LENGTH is the maximum length of a public key for all
	// KEMs supported by this library.
	#define EVP_HPKE_MAX_PUBLIC_KEY_LENGTH 32

	// EVP_HPKE_KEY_public_key writes \|key\|'s public key to \|out\| and sets
	// \|*out_len\| to the number of bytes written. On success, it returns one and
	// writes at most \|max_out\| bytes. If \|max_out\| is too small, it returns zero.
	// Setting \|max_out\| to \|EVP_HPKE_MAX_PUBLIC_KEY_LENGTH\| will ensure the public
	// key fits.
	OPENSSL_EXPORT int EVP_HPKE_KEY_public_key(const EVP_HPKE_KEY *key,
	uint8_t out, size_t out_len,
	size_t max_out);

	// EVP_HPKE_MAX_PRIVATE_KEY_LENGTH is the maximum length of a private key for
	// all KEMs supported by this library.
	#define EVP_HPKE_MAX_PRIVATE_KEY_LENGTH 32

	// EVP_HPKE_KEY_private_key writes \|key\|'s private key to \|out\| and sets
	// \|*out_len\| to the number of bytes written. On success, it returns one and
	// writes at most \|max_out\| bytes. If \|max_out\| is too small, it returns zero.
	// Setting \|max_out\| to \|EVP_HPKE_MAX_PRIVATE_KEY_LENGTH\| will ensure the
	// private key fits.
	OPENSSL_EXPORT int EVP_HPKE_KEY_private_key(const EVP_HPKE_KEY *key,
	uint8_t out, size_t out_len,
	size_t max_out);


	// Encryption contexts.
	//
	// An HPKE encryption context is represented by the \|EVP_HPKE_CTX\| type.

	// EVP_HPKE_CTX_zero sets an uninitialized \|EVP_HPKE_CTX\| to the zero state. The
	// caller should then use one of the \|EVP_HPKE_CTX_setup_*\| functions to finish
	// setting up \|ctx\|.
	//
	// It is safe, but not necessary to call \|EVP_HPKE_CTX_cleanup\| in this state.
	// This may be used for more uniform cleanup of \|EVP_HPKE_CTX\|.
	OPENSSL_EXPORT void EVP_HPKE_CTX_zero(EVP_HPKE_CTX *ctx);

	// EVP_HPKE_CTX_cleanup releases memory referenced by \|ctx\|. \|ctx\| must have
	// been initialized with \|EVP_HPKE_CTX_zero\| or one of the
	// \|EVP_HPKE_CTX_setup_*\| functions.
	OPENSSL_EXPORT void EVP_HPKE_CTX_cleanup(EVP_HPKE_CTX *ctx);

	// EVP_HPKE_CTX_new returns a newly-allocated \|EVP_HPKE_CTX\|, or NULL on error.
	// The caller must call \|EVP_HPKE_CTX_free\| on the result to release it.
	//
	// This is a convenience function for callers that need a heap-allocated
	// \|EVP_HPKE_CTX\|.
	OPENSSL_EXPORT EVP_HPKE_CTX *EVP_HPKE_CTX_new(void);

	// EVP_HPKE_CTX_free releases memory associated with \|ctx\|, which must have been
	// created with \|EVP_HPKE_CTX_new\|.
	OPENSSL_EXPORT void EVP_HPKE_CTX_free(EVP_HPKE_CTX *ctx);

	// EVP_HPKE_MAX_ENC_LENGTH is the maximum length of "enc", the encapsulated
	// shared secret, for all supported KEMs in this library.
	#define EVP_HPKE_MAX_ENC_LENGTH 32

	// EVP_HPKE_CTX_setup_sender implements the SetupBaseS HPKE operation. It
	// encapsulates a shared secret for \|peer_public_key\| and sets up \|ctx\| as a
	// sender context. It writes the encapsulated shared secret to \|out_enc\| and
	// sets \|*out_enc_len\| to the number of bytes written. It writes at most
	// \|max_enc\| bytes and fails if the buffer is too small. Setting \|max_enc\| to at
	// least \|EVP_HPKE_MAX_ENC_LENGTH\| will ensure the buffer is large enough.
	//
	// This function returns one on success and zero on error. Note that
	// \|peer_public_key\| may be invalid, in which case this function will return an
	// error.
	//
	// On success, callers may call \|EVP_HPKE_CTX_seal\| to encrypt messages for the
	// recipient. Callers must then call \|EVP_HPKE_CTX_cleanup\| when done. On
	// failure, calling \|EVP_HPKE_CTX_cleanup\| is safe, but not required.
	OPENSSL_EXPORT int EVP_HPKE_CTX_setup_sender(
	EVP_HPKE_CTX ctx, uint8_t out_enc, size_t *out_enc_len, size_t max_enc,
	const EVP_HPKE_KEM kem, const EVP_HPKE_KDF kdf, const EVP_HPKE_AEAD *aead,
	const uint8_t *peer_public_key, size_t peer_public_key_len,
	const uint8_t *info, size_t info_len);

	// EVP_HPKE_CTX_setup_sender_with_seed_for_testing behaves like
	// \|EVP_HPKE_CTX_setup_sender\|, but takes a seed to behave deterministically.
	// The seed's format depends on \|kem\|. For X25519, it is the sender's
	// ephemeral private key.
	OPENSSL_EXPORT int EVP_HPKE_CTX_setup_sender_with_seed_for_testing(
	EVP_HPKE_CTX ctx, uint8_t out_enc, size_t *out_enc_len, size_t max_enc,
	const EVP_HPKE_KEM kem, const EVP_HPKE_KDF kdf, const EVP_HPKE_AEAD *aead,
	const uint8_t *peer_public_key, size_t peer_public_key_len,
	const uint8_t info, size_t info_len, const uint8_t seed, size_t seed_len);

	// EVP_HPKE_CTX_setup_recipient implements the SetupBaseR HPKE operation. It
	// decapsulates the shared secret in \|enc\| with \|key\| and sets up \|ctx\| as a
	// recipient context. It returns one on success and zero on failure. Note that
	// \|enc\| may be invalid, in which case this function will return an error.
	//
	// On success, callers may call \|EVP_HPKE_CTX_open\| to decrypt messages from the
	// sender. Callers must then call \|EVP_HPKE_CTX_cleanup\| when done. On failure,
	// calling \|EVP_HPKE_CTX_cleanup\| is safe, but not required.
	OPENSSL_EXPORT int EVP_HPKE_CTX_setup_recipient(
	EVP_HPKE_CTX ctx, const EVP_HPKE_KEY key, const EVP_HPKE_KDF *kdf,
	const EVP_HPKE_AEAD aead, const uint8_t enc, size_t enc_len,
	const uint8_t *info, size_t info_len);


	// Using an HPKE context.
	//
	// Once set up, callers may encrypt or decrypt with an \|EVP_HPKE_CTX\| using the
	// following functions.

	// EVP_HPKE_CTX_open uses the HPKE context \|ctx\| to authenticate \|in_len\| bytes
	// from \|in\| and \|ad_len\| bytes from \|ad\| and to decrypt at most \|in_len\| bytes
	// into \|out\|. It returns one on success, and zero otherwise.
	//
	// This operation will fail if the \|ctx\| context is not set up as a receiver.
	//
	// Note that HPKE encryption is stateful and ordered. The sender's first call to
	// \|EVP_HPKE_CTX_seal\| must correspond to the recipient's first call to
	// \|EVP_HPKE_CTX_open\|, etc.
	//
	// At most \|in_len\| bytes are written to \|out\|. In order to ensure success,
	// \|max_out_len\| should be at least \|in_len\|. On successful return, \|*out_len\|
	// is set to the actual number of bytes written.
	OPENSSL_EXPORT int EVP_HPKE_CTX_open(EVP_HPKE_CTX ctx, uint8_t out,
	size_t *out_len, size_t max_out_len,
	const uint8_t *in, size_t in_len,
	const uint8_t *ad, size_t ad_len);

	// EVP_HPKE_CTX_seal uses the HPKE context \|ctx\| to encrypt and authenticate
	// \|in_len\| bytes of ciphertext \|in\| and authenticate \|ad_len\| bytes from \|ad\|,
	// writing the result to \|out\|. It returns one on success and zero otherwise.
	//
	// This operation will fail if the \|ctx\| context is not set up as a sender.
	//
	// Note that HPKE encryption is stateful and ordered. The sender's first call to
	// \|EVP_HPKE_CTX_seal\| must correspond to the recipient's first call to
	// \|EVP_HPKE_CTX_open\|, etc.
	//
	// At most, \|max_out_len\| encrypted bytes are written to \|out\|. On successful
	// return, \|*out_len\| is set to the actual number of bytes written.
	//
	// To ensure success, \|max_out_len\| should be \|in_len\| plus the result of
	// \|EVP_HPKE_CTX_max_overhead\| or \|EVP_HPKE_MAX_OVERHEAD\|.
	OPENSSL_EXPORT int EVP_HPKE_CTX_seal(EVP_HPKE_CTX ctx, uint8_t out,
	size_t *out_len, size_t max_out_len,
	const uint8_t *in, size_t in_len,
	const uint8_t *ad, size_t ad_len);

	// EVP_HPKE_CTX_export uses the HPKE context \|ctx\| to export a secret of
	// \|secret_len\| bytes into \|out\|. This function uses \|context_len\| bytes from
	// \|context\| as a context string for the secret. This is necessary to separate
	// different uses of exported secrets and bind relevant caller-specific context
	// into the output. It returns one on success and zero otherwise.
	OPENSSL_EXPORT int EVP_HPKE_CTX_export(const EVP_HPKE_CTX ctx, uint8_t out,
	size_t secret_len,
	const uint8_t *context,
	size_t context_len);

	// EVP_HPKE_MAX_OVERHEAD contains the largest value that
	// \|EVP_HPKE_CTX_max_overhead\| would ever return for any context.
	#define EVP_HPKE_MAX_OVERHEAD EVP_AEAD_MAX_OVERHEAD

	// EVP_HPKE_CTX_max_overhead returns the maximum number of additional bytes
	// added by sealing data with \|EVP_HPKE_CTX_seal\|. The \|ctx\| context must be set
	// up as a sender.
	OPENSSL_EXPORT size_t EVP_HPKE_CTX_max_overhead(const EVP_HPKE_CTX *ctx);

	// EVP_HPKE_CTX_aead returns \|ctx\|'s configured AEAD, or NULL if the context has
	// not been set up.
	OPENSSL_EXPORT const EVP_HPKE_AEAD EVP_HPKE_CTX_aead(const EVP_HPKE_CTX ctx);

	// EVP_HPKE_CTX_kdf returns \|ctx\|'s configured KDF, or NULL if the context has
	// not been set up.
	OPENSSL_EXPORT const EVP_HPKE_KDF EVP_HPKE_CTX_kdf(const EVP_HPKE_CTX ctx);


	// Private structures.
	//
	// The following structures are exported so their types are stack-allocatable,
	// but accessing or modifying their fields is forbidden.

	struct evp_hpke_ctx_st {
	const EVP_HPKE_AEAD *aead;
	const EVP_HPKE_KDF *kdf;
	EVP_AEAD_CTX aead_ctx;
	uint8_t base_nonce[EVP_AEAD_MAX_NONCE_LENGTH];
	uint8_t exporter_secret[EVP_MAX_MD_SIZE];
	uint64_t seq;
	int is_sender;
	};

	struct evp_hpke_key_st {
	const EVP_HPKE_KEM *kem;
	uint8_t private_key[X25519_PRIVATE_KEY_LEN];
	uint8_t public_key[X25519_PUBLIC_VALUE_LEN];
	};


	#if defined(__cplusplus)
	} // extern C
	#endif

	#if !defined(BORINGSSL_NO_CXX)
	extern "C++" {

	BSSL_NAMESPACE_BEGIN

	using ScopedEVP_HPKE_CTX =
	internal::StackAllocated<EVP_HPKE_CTX, void, EVP_HPKE_CTX_zero,
	EVP_HPKE_CTX_cleanup>;
	using ScopedEVP_HPKE_KEY =
	internal::StackAllocated<EVP_HPKE_KEY, void, EVP_HPKE_KEY_zero,
	EVP_HPKE_KEY_cleanup>;

	BORINGSSL_MAKE_DELETER(EVP_HPKE_CTX, EVP_HPKE_CTX_free)
	BORINGSSL_MAKE_DELETER(EVP_HPKE_KEY, EVP_HPKE_KEY_free)

	BSSL_NAMESPACE_END

	} // extern C++
	#endif

	#endif // OPENSSL_HEADER_CRYPTO_HPKE_INTERNAL_H