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Diffstat (limited to 'src/crypto/chacha_poly_aead.h')
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1 files changed, 0 insertions, 146 deletions
diff --git a/src/crypto/chacha_poly_aead.h b/src/crypto/chacha_poly_aead.h deleted file mode 100644 index 5d57b5a5e2..0000000000 --- a/src/crypto/chacha_poly_aead.h +++ /dev/null @@ -1,146 +0,0 @@ -// Copyright (c) 2019-2021 The Bitcoin Core developers -// Distributed under the MIT software license, see the accompanying -// file COPYING or http://www.opensource.org/licenses/mit-license.php. - -#ifndef BITCOIN_CRYPTO_CHACHA_POLY_AEAD_H -#define BITCOIN_CRYPTO_CHACHA_POLY_AEAD_H - -#include <crypto/chacha20.h> - -#include <cmath> - -static constexpr int CHACHA20_POLY1305_AEAD_KEY_LEN = 32; -static constexpr int CHACHA20_POLY1305_AEAD_AAD_LEN = 3; /* 3 bytes length */ -static constexpr int CHACHA20_ROUND_OUTPUT = 64; /* 64 bytes per round */ -static constexpr int AAD_PACKAGES_PER_ROUND = 21; /* 64 / 3 round down*/ - -/* A AEAD class for ChaCha20-Poly1305@bitcoin. - * - * ChaCha20 is a stream cipher designed by Daniel Bernstein and described in - * <ref>[https://cr.yp.to/chacha/chacha-20080128.pdf ChaCha20]</ref>. It operates - * by permuting 128 fixed bits, 128 or 256 bits of key, a 64 bit nonce and a 64 - * bit counter into 64 bytes of output. This output is used as a keystream, with - * any unused bytes simply discarded. - * - * Poly1305 <ref>[https://cr.yp.to/mac/poly1305-20050329.pdf Poly1305]</ref>, also - * by Daniel Bernstein, is a one-time Carter-Wegman MAC that computes a 128 bit - * integrity tag given a message and a single-use 256 bit secret key. - * - * The chacha20-poly1305@bitcoin combines these two primitives into an - * authenticated encryption mode. The construction used is based on that proposed - * for TLS by Adam Langley in - * <ref>[http://tools.ietf.org/html/draft-agl-tls-chacha20poly1305-03 "ChaCha20 - * and Poly1305 based Cipher Suites for TLS", Adam Langley]</ref>, but differs in - * the layout of data passed to the MAC and in the addition of encryption of the - * packet lengths. - * - * ==== Detailed Construction ==== - * - * The chacha20-poly1305@bitcoin cipher requires two 256 bits of key material as - * output from the key exchange. Each key (K_1 and K_2) are used by two separate - * instances of chacha20. - * - * The instance keyed by K_1 is a stream cipher that is used only to encrypt the 3 - * byte packet length field and has its own sequence number. The second instance, - * keyed by K_2, is used in conjunction with poly1305 to build an AEAD - * (Authenticated Encryption with Associated Data) that is used to encrypt and - * authenticate the entire packet. - * - * Two separate cipher instances are used here so as to keep the packet lengths - * confidential but not create an oracle for the packet payload cipher by - * decrypting and using the packet length prior to checking the MAC. By using an - * independently-keyed cipher instance to encrypt the length, an active attacker - * seeking to exploit the packet input handling as a decryption oracle can learn - * nothing about the payload contents or its MAC (assuming key derivation, - * ChaCha20 and Poly1305 are secure). - * - * The AEAD is constructed as follows: for each packet, generate a Poly1305 key by - * taking the first 256 bits of ChaCha20 stream output generated using K_2, an IV - * consisting of the packet sequence number encoded as an LE uint64 and a ChaCha20 - * block counter of zero. The K_2 ChaCha20 block counter is then set to the - * little-endian encoding of 1 (i.e. {1, 0, 0, 0, 0, 0, 0, 0}) and this instance - * is used for encryption of the packet payload. - * - * ==== Packet Handling ==== - * - * When receiving a packet, the length must be decrypted first. When 3 bytes of - * ciphertext length have been received, they may be decrypted. - * - * A ChaCha20 round always calculates 64bytes which is sufficient to crypt 21 - * times a 3 bytes length field (21*3 = 63). The length field sequence number can - * thus be used 21 times (keystream caching). - * - * The length field must be enc-/decrypted with the ChaCha20 keystream keyed with - * K_1 defined by block counter 0, the length field sequence number in little - * endian and a keystream position from 0 to 60. - * - * Once the entire packet has been received, the MAC MUST be checked before - * decryption. A per-packet Poly1305 key is generated as described above and the - * MAC tag calculated using Poly1305 with this key over the ciphertext of the - * packet length and the payload together. The calculated MAC is then compared in - * constant time with the one appended to the packet and the packet decrypted - * using ChaCha20 as described above (with K_2, the packet sequence number as - * nonce and a starting block counter of 1). - * - * Detection of an invalid MAC MUST lead to immediate connection termination. - * - * To send a packet, first encode the 3 byte length and encrypt it using K_1 as - * described above. Encrypt the packet payload (using K_2) and append it to the - * encrypted length. Finally, calculate a MAC tag and append it. - * - * The initiating peer MUST use <code>K_1_A, K_2_A</code> to encrypt messages on - * the send channel, <code>K_1_B, K_2_B</code> MUST be used to decrypt messages on - * the receive channel. - * - * The responding peer MUST use <code>K_1_A, K_2_A</code> to decrypt messages on - * the receive channel, <code>K_1_B, K_2_B</code> MUST be used to encrypt messages - * on the send channel. - * - * Optimized implementations of ChaCha20-Poly1305@bitcoin are relatively fast in - * general, therefore it is very likely that encrypted messages require not more - * CPU cycles per bytes then the current unencrypted p2p message format - * (ChaCha20/Poly1305 versus double SHA256). - * - * The initial packet sequence numbers are 0. - * - * K_2 ChaCha20 cipher instance (payload) must never reuse a {key, nonce} for - * encryption nor may it be used to encrypt more than 2^70 bytes under the same - * {key, nonce}. - * - * K_1 ChaCha20 cipher instance (length field/AAD) must never reuse a {key, nonce, - * position-in-keystream} for encryption nor may it be used to encrypt more than - * 2^70 bytes under the same {key, nonce}. - * - * We use message sequence numbers for both communication directions. - */ - -class ChaCha20Poly1305AEAD -{ -private: - ChaCha20 m_chacha_header; // AAD cipher instance (encrypted length) and poly1305 key-derivation cipher instance - ChaCha20 m_chacha_main; // payload - unsigned char m_aad_keystream_buffer[CHACHA20_ROUND_OUTPUT]; // aad keystream cache - uint64_t m_cached_aad_seqnr; // aad keystream cache hint - -public: - ChaCha20Poly1305AEAD(const unsigned char* K_1, size_t K_1_len, const unsigned char* K_2, size_t K_2_len); - - explicit ChaCha20Poly1305AEAD(const ChaCha20Poly1305AEAD&) = delete; - - /** Encrypts/decrypts a packet - seqnr_payload, the message sequence number - seqnr_aad, the messages AAD sequence number which allows reuse of the AAD keystream - aad_pos, position to use in the AAD keystream to encrypt the AAD - dest, output buffer, must be of a size equal or larger then CHACHA20_POLY1305_AEAD_AAD_LEN + payload (+ POLY1305_TAG_LEN in encryption) bytes - destlen, length of the destination buffer - src, the AAD+payload to encrypt or the AAD+payload+MAC to decrypt - src_len, the length of the source buffer - is_encrypt, set to true if we encrypt (creates and appends the MAC instead of verifying it) - */ - bool Crypt(uint64_t seqnr_payload, uint64_t seqnr_aad, int aad_pos, unsigned char* dest, size_t dest_len, const unsigned char* src, size_t src_len, bool is_encrypt); - - /** decrypts the 3 bytes AAD data and decodes it into a uint32_t field */ - bool GetLength(uint32_t* len24_out, uint64_t seqnr_aad, int aad_pos, const uint8_t* ciphertext); -}; - -#endif // BITCOIN_CRYPTO_CHACHA_POLY_AEAD_H |