transmission/libtransmission/peer-mse.h

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// This file Copyright © 2007-2023 Mnemosyne LLC.
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// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
// NB: crypto-test-ref.h needs this, so use it instead of #pragma once
#ifndef TR_ENCRYPTION_H
#define TR_ENCRYPTION_H
#ifndef __TRANSMISSION__
#error only libtransmission should #include this header.
#endif
#include <algorithm> // for std::copy_n()
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#include <array>
#include <cstddef> // size_t, std::byte
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#include <cstdint> // uint8_t
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#include "libtransmission/tr-macros.h" // tr_sha1_digest_t
#include "libtransmission/tr-arc4.h"
// Spec: https://wiki.vuze.com/w/Message_Stream_Encryption
namespace tr_message_stream_encryption
{
/**
* Holds state for the Diffie-Hellman key exchange that takes place
* during encrypted peer handshakes
*/
class DH
{
public:
// MSE spec: "Minimum length [for the private key] is 128 bit.
// Anything beyond 180 bit is not believed to add any further
// security and only increases the necessary calculation time.
// You should use a length of 160bits whenever possible[.]
static auto constexpr PrivateKeySize = size_t{ 20 };
// MSE spec: "P, S [the shared secret], Ya and Yb
// [the public keys] are 768bits long[.]"
static auto constexpr KeySize = size_t{ 96 };
// big-endian byte arrays holding the keys and shared secret.
// MSE spec: "The entire handshake is in big-endian."
using private_key_bigend_t = std::array<std::byte, PrivateKeySize>;
using key_bigend_t = std::array<std::byte, KeySize>;
// By default, a private key is randomly generated.
// Providing a predefined one is useful for reproducible unit tests.
constexpr DH(private_key_bigend_t const& private_key = randomPrivateKey()) noexcept
: private_key_{ private_key }
{
}
// Returns our own public key to be shared with a peer.
[[nodiscard]] key_bigend_t publicKey() noexcept;
// Compute the shared secret from our private key and the peer's public key.
void setPeerPublicKey(key_bigend_t const& peer_public_key);
// Returns the shared secret.
[[nodiscard]] constexpr auto const& secret() const noexcept
{
return secret_;
}
[[nodiscard]] static private_key_bigend_t randomPrivateKey() noexcept;
private:
private_key_bigend_t private_key_;
key_bigend_t public_key_ = {};
key_bigend_t secret_ = {};
};
// --- arc4 encryption for both incoming and outgoing stream
class Filter
{
public:
void decrypt_init(bool is_incoming, DH const&, tr_sha1_digest_t const& info_hash);
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template<typename T>
constexpr void decrypt(T const* buf_in, size_t buf_len, T* buf_out) noexcept
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{
process(buf_in, buf_len, buf_out, dec_active_, dec_key_);
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}
void encrypt_init(bool is_incoming, DH const&, tr_sha1_digest_t const& info_hash);
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template<typename T>
constexpr void encrypt(T const* buf_in, size_t buf_len, T* buf_out) noexcept
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{
process(buf_in, buf_len, buf_out, enc_active_, enc_key_);
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}
[[nodiscard]] constexpr auto is_active() const noexcept
{
return dec_active_ || enc_active_;
}
private:
template<typename T>
static constexpr void process(T const* buf_in, size_t buf_len, T* buf_out, bool active, tr_arc4& arc4) noexcept
{
if (active)
{
arc4.process(reinterpret_cast<uint8_t const*>(buf_in), buf_len, reinterpret_cast<uint8_t*>(buf_out));
}
else
{
std::copy_n(buf_in, buf_len, buf_out);
}
}
tr_arc4 dec_key_ = {};
tr_arc4 enc_key_ = {};
bool dec_active_ = false;
bool enc_active_ = false;
};
} // namespace tr_message_stream_encryption
#endif // TR_ENCRYPTION_H