1  // Copyright (c) 2023-present The Bitcoin Core developers
 2  // Distributed under the MIT software license, see the accompanying
 3  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 4  
 5  #ifndef BITCOIN_BIP324_H
 6  #define BITCOIN_BIP324_H
 7  
 8  #include <array>
 9  #include <cstddef>
10  #include <optional>
11  
12  #include <crypto/chacha20.h>
13  #include <crypto/chacha20poly1305.h>
14  #include <key.h>
15  #include <pubkey.h>
16  #include <span.h>
17  
18  /** The BIP324 packet cipher, encapsulating its key derivation, stream cipher, and AEAD. */
19  class BIP324Cipher
20  {
21  public:
22      static constexpr unsigned SESSION_ID_LEN{32};
23      static constexpr unsigned GARBAGE_TERMINATOR_LEN{16};
24      static constexpr unsigned REKEY_INTERVAL{224};
25      static constexpr unsigned LENGTH_LEN{3};
26      static constexpr unsigned HEADER_LEN{1};
27      static constexpr unsigned EXPANSION = LENGTH_LEN + HEADER_LEN + FSChaCha20Poly1305::EXPANSION;
28      static constexpr std::byte IGNORE_BIT{0x80};
29  
30  private:
31      std::optional<FSChaCha20> m_send_l_cipher;
32      std::optional<FSChaCha20> m_recv_l_cipher;
33      std::optional<FSChaCha20Poly1305> m_send_p_cipher;
34      std::optional<FSChaCha20Poly1305> m_recv_p_cipher;
35  
36      CKey m_key;
37      EllSwiftPubKey m_our_pubkey;
38  
39      std::array<std::byte, SESSION_ID_LEN> m_session_id;
40      std::array<std::byte, GARBAGE_TERMINATOR_LEN> m_send_garbage_terminator;
41      std::array<std::byte, GARBAGE_TERMINATOR_LEN> m_recv_garbage_terminator;
42  
43  public:
44      /** No default constructor; keys must be provided to create a BIP324Cipher. */
45      BIP324Cipher() = delete;
46  
47      /** Initialize a BIP324 cipher with specified key and encoding entropy (testing only). */
48      BIP324Cipher(const CKey& key, std::span<const std::byte> ent32) noexcept;
49  
50      /** Initialize a BIP324 cipher with specified key (testing only). */
51      BIP324Cipher(const CKey& key, const EllSwiftPubKey& pubkey) noexcept;
52  
53      /** Retrieve our public key. */
54      const EllSwiftPubKey& GetOurPubKey() const noexcept { return m_our_pubkey; }
55  
56      /** Initialize when the other side's public key is received. Can only be called once.
57       *
58       * initiator is set to true if we are the initiator establishing the v2 P2P connection.
59       * self_decrypt is only for testing, and swaps encryption/decryption keys, so that encryption
60       * and decryption can be tested without knowing the other side's private key.
61       */
62      void Initialize(const EllSwiftPubKey& their_pubkey, bool initiator, bool self_decrypt = false) noexcept;
63  
64      /** Determine whether this cipher is fully initialized. */
65      explicit operator bool() const noexcept { return m_send_l_cipher.has_value(); }
66  
67      /** Encrypt a packet. Only after Initialize().
68       *
69       * It must hold that output.size() == contents.size() + EXPANSION.
70       */
71      void Encrypt(std::span<const std::byte> contents, std::span<const std::byte> aad, bool ignore, std::span<std::byte> output) noexcept;
72  
73      /** Decrypt the length of a packet. Only after Initialize().
74       *
75       * It must hold that input.size() == LENGTH_LEN.
76       */
77      unsigned DecryptLength(std::span<const std::byte> input) noexcept;
78  
79      /** Decrypt a packet. Only after Initialize().
80       *
81       * It must hold that input.size() + LENGTH_LEN == contents.size() + EXPANSION.
82       * Contents.size() must equal the length returned by DecryptLength.
83       */
84      bool Decrypt(std::span<const std::byte> input, std::span<const std::byte> aad, bool& ignore, std::span<std::byte> contents) noexcept;
85  
86      /** Get the Session ID. Only after Initialize(). */
87      std::span<const std::byte> GetSessionID() const noexcept { return m_session_id; }
88  
89      /** Get the Garbage Terminator to send. Only after Initialize(). */
90      std::span<const std::byte> GetSendGarbageTerminator() const noexcept { return m_send_garbage_terminator; }
91  
92      /** Get the expected Garbage Terminator to receive. Only after Initialize(). */
93      std::span<const std::byte> GetReceiveGarbageTerminator() const noexcept { return m_recv_garbage_terminator; }
94  };
95  
96  #endif // BITCOIN_BIP324_H