/* Copyright (c) 2018, Google Inc.
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*
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* Permission to use, copy, modify, and/or distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
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* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
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* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
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* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
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#ifndef OPENSSL_HEADER_HRSS_H
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#define OPENSSL_HEADER_HRSS_H
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#include <openssl/base.h>
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#if defined(__cplusplus)
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extern "C" {
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#endif
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// HRSS
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//
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// HRSS is a structured-lattice-based post-quantum key encapsulation mechanism.
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// The best exposition is https://eprint.iacr.org/2017/667.pdf although this
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// implementation uses a different KEM construction based on
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// https://eprint.iacr.org/2017/1005.pdf.
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struct HRSS_private_key {
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uint8_t opaque[1808];
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};
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struct HRSS_public_key {
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uint8_t opaque[1424];
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};
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// HRSS_SAMPLE_BYTES is the number of bytes of entropy needed to generate a
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// short vector. There are 701 coefficients, but the final one is always set to
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// zero when sampling. Otherwise, we need one byte of input per coefficient.
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#define HRSS_SAMPLE_BYTES (701 - 1)
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// HRSS_GENERATE_KEY_BYTES is the number of bytes of entropy needed to generate
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// an HRSS key pair.
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#define HRSS_GENERATE_KEY_BYTES (HRSS_SAMPLE_BYTES + HRSS_SAMPLE_BYTES + 32)
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// HRSS_ENCAP_BYTES is the number of bytes of entropy needed to encapsulate a
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// session key.
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#define HRSS_ENCAP_BYTES (HRSS_SAMPLE_BYTES + HRSS_SAMPLE_BYTES)
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// HRSS_PUBLIC_KEY_BYTES is the number of bytes in a public key.
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#define HRSS_PUBLIC_KEY_BYTES 1138
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// HRSS_CIPHERTEXT_BYTES is the number of bytes in a ciphertext.
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#define HRSS_CIPHERTEXT_BYTES 1138
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// HRSS_KEY_BYTES is the number of bytes in a shared key.
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#define HRSS_KEY_BYTES 32
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// HRSS_POLY3_BYTES is the number of bytes needed to serialise a mod 3
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// polynomial.
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#define HRSS_POLY3_BYTES 140
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#define HRSS_PRIVATE_KEY_BYTES (HRSS_POLY3_BYTES * 2 + HRSS_PUBLIC_KEY_BYTES + 2 + 32)
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// HRSS_generate_key is a deterministic function that outputs a public and
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// private key based on the given entropy.
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OPENSSL_EXPORT void HRSS_generate_key(struct HRSS_public_key* out_pub, struct HRSS_private_key* out_priv,
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const uint8_t input[HRSS_GENERATE_KEY_BYTES]);
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// HRSS_encap is a deterministic function the generates and encrypts a random
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// session key from the given entropy, writing those values to |out_shared_key|
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// and |out_ciphertext|, respectively.
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OPENSSL_EXPORT void HRSS_encap(uint8_t out_ciphertext[HRSS_CIPHERTEXT_BYTES], uint8_t out_shared_key[HRSS_KEY_BYTES],
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const struct HRSS_public_key* in_pub, const uint8_t in[HRSS_ENCAP_BYTES]);
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// HRSS_decap decrypts a session key from |ciphertext_len| bytes of
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// |ciphertext|. If the ciphertext is valid, the decrypted key is written to
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// |out_shared_key|. Otherwise the HMAC of |ciphertext| under a secret key (kept
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// in |in_priv|) is written. If the ciphertext is the wrong length then it will
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// leak which was done via side-channels. Otherwise it should perform either
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// action in constant-time.
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OPENSSL_EXPORT void HRSS_decap(uint8_t out_shared_key[HRSS_KEY_BYTES], const struct HRSS_private_key* in_priv,
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const uint8_t* ciphertext, size_t ciphertext_len);
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// HRSS_marshal_public_key serialises |in_pub| to |out|.
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OPENSSL_EXPORT void HRSS_marshal_public_key(uint8_t out[HRSS_PUBLIC_KEY_BYTES], const struct HRSS_public_key* in_pub);
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// HRSS_parse_public_key sets |*out| to the public-key encoded in |in|. It
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// returns true on success and zero on error.
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OPENSSL_EXPORT int HRSS_parse_public_key(struct HRSS_public_key* out, const uint8_t in[HRSS_PUBLIC_KEY_BYTES]);
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#if defined(__cplusplus)
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} // extern C
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#endif
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#endif // OPENSSL_HEADER_HRSS_H
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