/* Copyright (c) 2015, 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_CURVE25519_H
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#define OPENSSL_HEADER_CURVE25519_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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// Curve25519.
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//
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// Curve25519 is an elliptic curve. See https://tools.ietf.org/html/rfc7748.
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// X25519.
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//
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// X25519 is the Diffie-Hellman primitive built from curve25519. It is
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// sometimes referred to as “curve25519”, but “X25519” is a more precise name.
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// See http://cr.yp.to/ecdh.html and https://tools.ietf.org/html/rfc7748.
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#define X25519_PRIVATE_KEY_LEN 32
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#define X25519_PUBLIC_VALUE_LEN 32
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#define X25519_SHARED_KEY_LEN 32
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// X25519_keypair sets |out_public_value| and |out_private_key| to a freshly
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// generated, public–private key pair.
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OPENSSL_EXPORT void X25519_keypair(uint8_t out_public_value[32],
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uint8_t out_private_key[32]);
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// X25519 writes a shared key to |out_shared_key| that is calculated from the
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// given private key and the peer's public value. It returns one on success and
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// zero on error.
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//
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// Don't use the shared key directly, rather use a KDF and also include the two
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// public values as inputs.
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OPENSSL_EXPORT int X25519(uint8_t out_shared_key[32],
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const uint8_t private_key[32],
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const uint8_t peer_public_value[32]);
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// X25519_public_from_private calculates a Diffie-Hellman public value from the
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// given private key and writes it to |out_public_value|.
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OPENSSL_EXPORT void X25519_public_from_private(uint8_t out_public_value[32],
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const uint8_t private_key[32]);
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// Ed25519.
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//
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// Ed25519 is a signature scheme using a twisted-Edwards curve that is
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// birationally equivalent to curve25519.
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//
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// Note that, unlike RFC 8032's formulation, our private key representation
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// includes a public key suffix to make multiple key signing operations with the
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// same key more efficient. The RFC 8032 key private key is referred to in this
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// implementation as the "seed" and is the first 32 bytes of our private key.
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#define ED25519_PRIVATE_KEY_LEN 64
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#define ED25519_PUBLIC_KEY_LEN 32
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#define ED25519_SIGNATURE_LEN 64
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// ED25519_keypair sets |out_public_key| and |out_private_key| to a freshly
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// generated, public–private key pair.
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OPENSSL_EXPORT void ED25519_keypair(uint8_t out_public_key[32],
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uint8_t out_private_key[64]);
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// ED25519_sign sets |out_sig| to be a signature of |message_len| bytes from
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// |message| using |private_key|. It returns one on success or zero on
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// error.
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OPENSSL_EXPORT int ED25519_sign(uint8_t out_sig[64], const uint8_t *message,
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size_t message_len,
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const uint8_t private_key[64]);
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// ED25519_verify returns one iff |signature| is a valid signature, by
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// |public_key| of |message_len| bytes from |message|. It returns zero
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// otherwise.
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OPENSSL_EXPORT int ED25519_verify(const uint8_t *message, size_t message_len,
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const uint8_t signature[64],
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const uint8_t public_key[32]);
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// ED25519_keypair_from_seed calculates a public and private key from an
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// Ed25519 “seed”. Seed values are not exposed by this API (although they
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// happen to be the first 32 bytes of a private key) so this function is for
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// interoperating with systems that may store just a seed instead of a full
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// private key.
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OPENSSL_EXPORT void ED25519_keypair_from_seed(uint8_t out_public_key[32],
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uint8_t out_private_key[64],
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const uint8_t seed[32]);
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// SPAKE2.
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//
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// SPAKE2 is a password-authenticated key-exchange. It allows two parties,
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// who share a low-entropy secret (i.e. password), to agree on a shared key.
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// An attacker can only make one guess of the password per execution of the
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// protocol.
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//
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// See https://tools.ietf.org/html/draft-irtf-cfrg-spake2-02.
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// spake2_role_t enumerates the different “roles” in SPAKE2. The protocol
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// requires that the symmetry of the two parties be broken so one participant
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// must be “Alice” and the other be “Bob”.
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enum spake2_role_t {
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spake2_role_alice,
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spake2_role_bob,
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};
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// SPAKE2_CTX_new creates a new |SPAKE2_CTX| (which can only be used for a
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// single execution of the protocol). SPAKE2 requires the symmetry of the two
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// parties to be broken which is indicated via |my_role| – each party must pass
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// a different value for this argument.
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//
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// The |my_name| and |their_name| arguments allow optional, opaque names to be
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// bound into the protocol. For example MAC addresses, hostnames, usernames
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// etc. These values are not exposed and can avoid context-confusion attacks
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// when a password is shared between several devices.
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OPENSSL_EXPORT SPAKE2_CTX *SPAKE2_CTX_new(
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enum spake2_role_t my_role,
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const uint8_t *my_name, size_t my_name_len,
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const uint8_t *their_name, size_t their_name_len);
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// SPAKE2_CTX_free frees |ctx| and all the resources that it has allocated.
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OPENSSL_EXPORT void SPAKE2_CTX_free(SPAKE2_CTX *ctx);
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// SPAKE2_MAX_MSG_SIZE is the maximum size of a SPAKE2 message.
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#define SPAKE2_MAX_MSG_SIZE 32
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// SPAKE2_generate_msg generates a SPAKE2 message given |password|, writes
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// it to |out| and sets |*out_len| to the number of bytes written.
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//
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// At most |max_out_len| bytes are written to |out| and, in order to ensure
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// success, |max_out_len| should be at least |SPAKE2_MAX_MSG_SIZE| bytes.
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//
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// This function can only be called once for a given |SPAKE2_CTX|.
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//
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// It returns one on success and zero on error.
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OPENSSL_EXPORT int SPAKE2_generate_msg(SPAKE2_CTX *ctx, uint8_t *out,
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size_t *out_len, size_t max_out_len,
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const uint8_t *password,
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size_t password_len);
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// SPAKE2_MAX_KEY_SIZE is the maximum amount of key material that SPAKE2 will
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// produce.
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#define SPAKE2_MAX_KEY_SIZE 64
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// SPAKE2_process_msg completes the SPAKE2 exchange given the peer's message in
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// |their_msg|, writes at most |max_out_key_len| bytes to |out_key| and sets
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// |*out_key_len| to the number of bytes written.
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//
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// The resulting keying material is suitable for:
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// a) Using directly in a key-confirmation step: i.e. each side could
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// transmit a hash of their role, a channel-binding value and the key
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// material to prove to the other side that they know the shared key.
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// b) Using as input keying material to HKDF to generate a variety of subkeys
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// for encryption etc.
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//
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// If |max_out_key_key| is smaller than the amount of key material generated
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// then the key is silently truncated. If you want to ensure that no truncation
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// occurs then |max_out_key| should be at least |SPAKE2_MAX_KEY_SIZE|.
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//
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// You must call |SPAKE2_generate_msg| on a given |SPAKE2_CTX| before calling
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// this function. On successful return, |ctx| is complete and calling
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// |SPAKE2_CTX_free| is the only acceptable operation on it.
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//
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// Returns one on success or zero on error.
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OPENSSL_EXPORT int SPAKE2_process_msg(SPAKE2_CTX *ctx, uint8_t *out_key,
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size_t *out_key_len,
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size_t max_out_key_len,
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const uint8_t *their_msg,
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size_t their_msg_len);
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#if defined(__cplusplus)
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} // extern C
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extern "C++" {
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namespace bssl {
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BORINGSSL_MAKE_DELETER(SPAKE2_CTX, SPAKE2_CTX_free)
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} // namespace bssl
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} // extern C++
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#endif
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#endif // OPENSSL_HEADER_CURVE25519_H
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