From 64a438189e9ffb2aacf080af34efb51f5d4064d6 Mon Sep 17 00:00:00 2001 From: Dmitri Bogomolov <4glitch@gmail.com> Date: Sun, 31 Jan 2021 20:42:35 +0200 Subject: [PATCH] encrypted_payload.rst and encryption.rst docs, crossreferences --- docs/encrypted_payload.rst | 19 +++ docs/encryption.rst | 232 +++++++++++++++++++++++++++++++++++++ docs/protocol.rst | 22 +--- 3 files changed, 253 insertions(+), 20 deletions(-) create mode 100644 docs/encrypted_payload.rst create mode 100644 docs/encryption.rst diff --git a/docs/encrypted_payload.rst b/docs/encrypted_payload.rst new file mode 100644 index 00000000..346d370d --- /dev/null +++ b/docs/encrypted_payload.rst @@ -0,0 +1,19 @@ ++------------+-------------+-----------+--------------------------------------------+ +| Field Size | Description | Data type | Comments | ++============+=============+===========+============================================+ +| 16 | IV | uchar[] | Initialization Vector used for AES-256-CBC | ++------------+-------------+-----------+--------------------------------------------+ +| 2 | Curve type | uint16_t | Elliptic Curve type 0x02CA (714) | ++------------+-------------+-----------+--------------------------------------------+ +| 2 | X length | uint16_t | Length of X component of public key R | ++------------+-------------+-----------+--------------------------------------------+ +| X length | X | uchar[] | X component of public key R | ++------------+-------------+-----------+--------------------------------------------+ +| 2 | Y length | uint16_t | Length of Y component of public key R | ++------------+-------------+-----------+--------------------------------------------+ +| Y length | Y | uchar[] | Y component of public key R | ++------------+-------------+-----------+--------------------------------------------+ +| ? | encrypted | uchar[] | Cipher text | ++------------+-------------+-----------+--------------------------------------------+ +| 32 | MAC | uchar[] | HMACSHA256 Message Authentication Code | ++------------+-------------+-----------+--------------------------------------------+ diff --git a/docs/encryption.rst b/docs/encryption.rst new file mode 100644 index 00000000..925dd001 --- /dev/null +++ b/docs/encryption.rst @@ -0,0 +1,232 @@ +Encryption +========== + +Bitmessage uses the Elliptic Curve Integrated Encryption Scheme +`(ECIES) `_ +to encrypt the payload of the Message and Broadcast objects. + +The scheme uses Elliptic Curve Diffie-Hellman +`(ECDH) `_ to generate a shared secret used +to generate the encryption parameters for Advanced Encryption Standard with +256bit key and Cipher-Block Chaining +`(AES-256-CBC) `_. +The encrypted data will be padded to a 16 byte boundary in accordance to +`PKCS7 `_. This +means that the data is padded with N bytes of value N. + +The Key Derivation Function +`(KDF) `_ used to +generate the key material for AES is +`SHA512 `_. The Message Authentication +Code (MAC) scheme used is `HMACSHA256 `_. + +Format +------ + +(See also: :doc:`protocol`) + +.. include:: encrypted_payload.rst + +In order to reconstitute a usable (65 byte) public key (starting with 0x04), +the X and Y components need to be expanded by prepending them with 0x00 bytes +until the individual component lengths are 32 bytes. + +Encryption +---------- + + 1. The destination public key is called K. + 2. Generate 16 random bytes using a secure random number generator. + Call them IV. + 3. Generate a new random EC key pair with private key called r and public key + called R. + 4. Do an EC point multiply with public key K and private key r. This gives you + public key P. + 5. Use the X component of public key P and calculate the SHA512 hash H. + 6. The first 32 bytes of H are called key_e and the last 32 bytes are called + key_m. + 7. Pad the input text to a multiple of 16 bytes, in accordance to PKCS7. + 8. Encrypt the data with AES-256-CBC, using IV as initialization vector, + key_e as encryption key and the padded input text as payload. Call the + output cipher text. + 9. Calculate a 32 byte MAC with HMACSHA256, using key_m as salt and + IV + R + cipher text as data. Call the output MAC. + +The resulting data is: IV + R + cipher text + MAC + +Decryption +---------- + + 1. The private key used to decrypt is called k. + 2. Do an EC point multiply with private key k and public key R. This gives you + public key P. + 3. Use the X component of public key P and calculate the SHA512 hash H. + 4. The first 32 bytes of H are called key_e and the last 32 bytes are called + key_m. + 5. Calculate MAC' with HMACSHA256, using key_m as salt and + IV + R + cipher text as data. + 6. Compare MAC with MAC'. If not equal, decryption will fail. + 7. Decrypt the cipher text with AES-256-CBC, using IV as initialization + vector, key_e as decryption key and the cipher text as payload. The output + is the padded input text. + +.. highlight:: nasm + +Partial Example +--------------- + +.. list-table:: Public key K: + :header-rows: 1 + :widths: auto + + * - Data + - Comments + * - + + :: + + 04 09 d4 e5 c0 ab 3d 25 + fe 04 8c 64 c9 da 1a 24 + 2c 7f 19 41 7e 95 17 cd + 26 69 50 d7 2c 75 57 13 + 58 5c 61 78 e9 7f e0 92 + fc 89 7c 9a 1f 17 20 d5 + 77 0a e8 ea ad 2f a8 fc + bd 08 e9 32 4a 5d de 18 + 57 + - Public key, 0x04 prefix, then 32 bytes X and 32 bytes Y. + + +.. list-table:: Initialization Vector IV: + :header-rows: 1 + :widths: auto + + * - Data + - Comments + * - + + :: + + bd db 7c 28 29 b0 80 38 + 75 30 84 a2 f3 99 16 81 + - 16 bytes generated with a secure random number generator. + +.. list-table:: Randomly generated key pair with private key r and public key R: + :header-rows: 1 + :widths: auto + + * - Data + - Comments + * - + + :: + + 5b e6 fa cd 94 1b 76 e9 + d3 ea d0 30 29 fb db 6b + 6e 08 09 29 3f 7f b1 97 + d0 c5 1f 84 e9 6b 8b a4 + - Private key r + * - + + :: + + 04 02 93 21 3d cf 13 88 + b6 1c 2a e5 cf 80 fe e6 + ff ff c0 49 a2 f9 fe 73 + 65 fe 38 67 81 3c a8 12 + 92 df 94 68 6c 6a fb 56 + 5a c6 14 9b 15 3d 61 b3 + b2 87 ee 2c 7f 99 7c 14 + 23 87 96 c1 2b 43 a3 86 + 5a + - Public key R + +.. list-table:: Derived public key P (point multiply r with K): + :header-rows: 1 + :widths: auto + + * - Data + - Comments + * - + + :: + + 04 0d b8 e3 ad 8c 0c d7 + 3f a2 b3 46 71 b7 b2 47 + 72 9b 10 11 41 57 9d 19 + 9e 0d c0 bd 02 4e ae fd + 89 ca c8 f5 28 dc 90 b6 + 68 11 ab ac 51 7d 74 97 + be 52 92 93 12 29 be 0b + 74 3e 05 03 f4 43 c3 d2 + 96 + - Public key P + * - + + :: + + 0d b8 e3 ad 8c 0c d7 3f + a2 b3 46 71 b7 b2 47 72 + 9b 10 11 41 57 9d 19 9e + 0d c0 bd 02 4e ae fd 89 + - X component of public key P + +.. list-table:: SHA512 of public key P X component (H): + :header-rows: 1 + :widths: auto + + * - Data + - Comments + * - + + :: + + 17 05 43 82 82 67 86 71 + 05 26 3d 48 28 ef ff 82 + d9 d5 9c bf 08 74 3b 69 + 6b cc 5d 69 fa 18 97 b4 + - First 32 bytes of H called key_e + * - + + :: + + f8 3f 1e 9c c5 d6 b8 44 + 8d 39 dc 6a 9d 5f 5b 7f + 46 0e 4a 78 e9 28 6e e8 + d9 1c e1 66 0a 53 ea cd + - Last 32 bytes of H called key_m + +.. list-table:: Padded input: + :header-rows: 1 + :widths: auto + + * - Data + - Comments + * - + + :: + + 54 68 65 20 71 75 69 63 + 6b 20 62 72 6f 77 6e 20 + 66 6f 78 20 6a 75 6d 70 + 73 20 6f 76 65 72 20 74 + 68 65 20 6c 61 7a 79 20 + 64 6f 67 2e 04 04 04 04 + - The quick brown fox jumps over the lazy dog.0x04,0x04,0x04,0x04 + +.. list-table:: Cipher text: + :header-rows: 1 + :widths: auto + + * - Data + - Comments + * - + + :: + + 64 20 3d 5b 24 68 8e 25 + 47 bb a3 45 fa 13 9a 5a + 1d 96 22 20 d4 d4 8a 0c + f3 b1 57 2c 0d 95 b6 16 + 43 a6 f9 a0 d7 5a f7 ea + cc 1b d9 57 14 7b f7 23 + - 3 blocks of 16 bytes of encrypted data. diff --git a/docs/protocol.rst b/docs/protocol.rst index c814ecaf..2dc4c1bc 100644 --- a/docs/protocol.rst +++ b/docs/protocol.rst @@ -199,27 +199,9 @@ Inventory vectors consist of the following data format: Encrypted payload ^^^^^^^^^^^^^^^^^ -Bitmessage uses `ECIES `_ to encrypt its messages. For more information see Encryption +Bitmessage uses `ECIES `_ to encrypt its messages. For more information see :doc:`encryption` -+------------+-------------+-----------+--------------------------------------------+ -| Field Size | Description | Data type | Comments | -+============+=============+===========+============================================+ -| 16 | IV | uchar[] | Initialization Vector used for AES-256-CBC | -+------------+-------------+-----------+--------------------------------------------+ -| 2 | Curve type | uint16_t | Elliptic Curve type 0x02CA (714) | -+------------+-------------+-----------+--------------------------------------------+ -| 2 | X length | uint16_t | Length of X component of public key R | -+------------+-------------+-----------+--------------------------------------------+ -| X length | X | uchar[] | X component of public key R | -+------------+-------------+-----------+--------------------------------------------+ -| 2 | Y length | uint16_t | Length of Y component of public key R | -+------------+-------------+-----------+--------------------------------------------+ -| Y length | Y | uchar[] | Y component of public key R | -+------------+-------------+-----------+--------------------------------------------+ -| ? | encrypted | uchar[] | Cipher text | -+------------+-------------+-----------+--------------------------------------------+ -| 32 | MAC | uchar[] | HMACSHA256 Message Authentication Code | -+------------+-------------+-----------+--------------------------------------------+ +.. include:: encrypted_payload.rst Unencrypted Message Data ^^^^^^^^^^^^^^^^^^^^^^^^