Export the HPKE implementation.
Bug: 410
Change-Id: I633eab7f2d148c9158a5bb29d73e07f1f18b7105
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/47331
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/hpke.h b/include/openssl/hpke.h
new file mode 100644
index 0000000..358ca23
--- /dev/null
+++ b/include/openssl/hpke.h
@@ -0,0 +1,294 @@
+/* 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-08.
+
+
+// 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);
+
+
+// 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| 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_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_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);
+
+
+// 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_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>;
+
+BSSL_NAMESPACE_END
+
+} // extern C++
+#endif
+
+#endif // OPENSSL_HEADER_CRYPTO_HPKE_INTERNAL_H
