1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
|
// Copyright (c) 2019-2022 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#if defined(HAVE_CONFIG_H)
#include <config/bitcoin-config.h>
#endif
#include <crypto/chacha_poly_aead.h>
#include <crypto/poly1305.h>
#include <support/cleanse.h>
#include <assert.h>
#include <string.h>
#include <cstdio>
#include <limits>
#ifndef HAVE_TIMINGSAFE_BCMP
int timingsafe_bcmp(const unsigned char* b1, const unsigned char* b2, size_t n)
{
const unsigned char *p1 = b1, *p2 = b2;
int ret = 0;
for (; n > 0; n--)
ret |= *p1++ ^ *p2++;
return (ret != 0);
}
#endif // TIMINGSAFE_BCMP
ChaCha20Poly1305AEAD::ChaCha20Poly1305AEAD(const unsigned char* K_1, size_t K_1_len, const unsigned char* K_2, size_t K_2_len)
{
assert(K_1_len == CHACHA20_POLY1305_AEAD_KEY_LEN);
assert(K_2_len == CHACHA20_POLY1305_AEAD_KEY_LEN);
m_chacha_header.SetKey(K_1, CHACHA20_POLY1305_AEAD_KEY_LEN);
m_chacha_main.SetKey(K_2, CHACHA20_POLY1305_AEAD_KEY_LEN);
// set the cached sequence number to uint64 max which hints for an unset cache.
// we can't hit uint64 max since the rekey rule (which resets the sequence number) is 1GB
m_cached_aad_seqnr = std::numeric_limits<uint64_t>::max();
}
bool ChaCha20Poly1305AEAD::Crypt(uint64_t seqnr_payload, uint64_t seqnr_aad, int aad_pos, unsigned char* dest, size_t dest_len /* length of the output buffer for sanity checks */, const unsigned char* src, size_t src_len, bool is_encrypt)
{
// check buffer boundaries
if (
// if we encrypt, make sure the source contains at least the expected AAD and the destination has at least space for the source + MAC
(is_encrypt && (src_len < CHACHA20_POLY1305_AEAD_AAD_LEN || dest_len < src_len + POLY1305_TAGLEN)) ||
// if we decrypt, make sure the source contains at least the expected AAD+MAC and the destination has at least space for the source - MAC
(!is_encrypt && (src_len < CHACHA20_POLY1305_AEAD_AAD_LEN + POLY1305_TAGLEN || dest_len < src_len - POLY1305_TAGLEN))) {
return false;
}
unsigned char expected_tag[POLY1305_TAGLEN], poly_key[POLY1305_KEYLEN];
memset(poly_key, 0, sizeof(poly_key));
m_chacha_main.SetIV(seqnr_payload);
// block counter 0 for the poly1305 key
// use lower 32bytes for the poly1305 key
// (throws away 32 unused bytes (upper 32) from this ChaCha20 round)
m_chacha_main.Seek(0);
m_chacha_main.Crypt(poly_key, poly_key, sizeof(poly_key));
// if decrypting, verify the tag prior to decryption
if (!is_encrypt) {
const unsigned char* tag = src + src_len - POLY1305_TAGLEN;
poly1305_auth(expected_tag, src, src_len - POLY1305_TAGLEN, poly_key);
// constant time compare the calculated MAC with the provided MAC
if (timingsafe_bcmp(expected_tag, tag, POLY1305_TAGLEN) != 0) {
memory_cleanse(expected_tag, sizeof(expected_tag));
memory_cleanse(poly_key, sizeof(poly_key));
return false;
}
memory_cleanse(expected_tag, sizeof(expected_tag));
// MAC has been successfully verified, make sure we don't convert it in decryption
src_len -= POLY1305_TAGLEN;
}
// calculate and cache the next 64byte keystream block if requested sequence number is not yet the cache
if (m_cached_aad_seqnr != seqnr_aad) {
m_cached_aad_seqnr = seqnr_aad;
m_chacha_header.SetIV(seqnr_aad);
m_chacha_header.Seek(0);
m_chacha_header.Keystream(m_aad_keystream_buffer, CHACHA20_ROUND_OUTPUT);
}
// crypt the AAD (3 bytes message length) with given position in AAD cipher instance keystream
dest[0] = src[0] ^ m_aad_keystream_buffer[aad_pos];
dest[1] = src[1] ^ m_aad_keystream_buffer[aad_pos + 1];
dest[2] = src[2] ^ m_aad_keystream_buffer[aad_pos + 2];
// Set the playload ChaCha instance block counter to 1 and crypt the payload
m_chacha_main.Seek(1);
m_chacha_main.Crypt(src + CHACHA20_POLY1305_AEAD_AAD_LEN, dest + CHACHA20_POLY1305_AEAD_AAD_LEN, src_len - CHACHA20_POLY1305_AEAD_AAD_LEN);
// If encrypting, calculate and append tag
if (is_encrypt) {
// the poly1305 tag expands over the AAD (3 bytes length) & encrypted payload
poly1305_auth(dest + src_len, dest, src_len, poly_key);
}
// cleanse no longer required MAC and polykey
memory_cleanse(poly_key, sizeof(poly_key));
return true;
}
bool ChaCha20Poly1305AEAD::GetLength(uint32_t* len24_out, uint64_t seqnr_aad, int aad_pos, const uint8_t* ciphertext)
{
// enforce valid aad position to avoid accessing outside of the 64byte keystream cache
// (there is space for 21 times 3 bytes)
assert(aad_pos >= 0 && aad_pos < CHACHA20_ROUND_OUTPUT - CHACHA20_POLY1305_AEAD_AAD_LEN);
if (m_cached_aad_seqnr != seqnr_aad) {
// we need to calculate the 64 keystream bytes since we reached a new aad sequence number
m_cached_aad_seqnr = seqnr_aad;
m_chacha_header.SetIV(seqnr_aad); // use LE for the nonce
m_chacha_header.Seek(0); // block counter 0
m_chacha_header.Keystream(m_aad_keystream_buffer, CHACHA20_ROUND_OUTPUT); // write keystream to the cache
}
// decrypt the ciphertext length by XORing the right position of the 64byte keystream cache with the ciphertext
*len24_out = (ciphertext[0] ^ m_aad_keystream_buffer[aad_pos + 0]) |
(ciphertext[1] ^ m_aad_keystream_buffer[aad_pos + 1]) << 8 |
(ciphertext[2] ^ m_aad_keystream_buffer[aad_pos + 2]) << 16;
return true;
}
|
