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
|
// OpenVPN -- An application to securely tunnel IP networks
// over a single port, with support for SSL/TLS-based
// session authentication and key exchange,
// packet encryption, packet authentication, and
// packet compression.
//
// Copyright (C) 2012- OpenVPN Inc.
//
// SPDX-License-Identifier: MPL-2.0 OR AGPL-3.0-only WITH openvpn3-openssl-exception
//
#ifndef OPENVPN_CRYPTO_CRYPTO_AEAD_USAGE_LIMIT_H
#define OPENVPN_CRYPTO_CRYPTO_AEAD_USAGE_LIMIT_H
#include <cstdint>
#include "openvpn/crypto/cryptoalgs.hpp"
namespace openvpn::Crypto {
/** Counts the number of plaintext blocks and cipher invocations to determine the limit for an AEAD cipher like GCM
* For more details see the OpenVPN RFC and the related documents */
class AEADUsageLimit
{
uint64_t invocations = 0;
uint64_t plaintext_blocks = 0;
/** Usage limit of plaintext_block + invocations, initialise with AES-GCM limit to be on safe side */
uint64_t limit = openvpn::CryptoAlgs::gcm_limit;
public:
AEADUsageLimit() = default;
AEADUsageLimit(openvpn::CryptoAlgs::Type type)
: limit(openvpn::CryptoAlgs::aead_usage_limit(type))
{
}
/* Since cipher_ctx_block_size() of OpenSSL is not reliable and will return 1 in many
* cases use a hardcoded blocksize instead. This is technically false for Chacha20-Poly1305 but
* Chacha20-Poly1305 also does not need the limit currently*/
static constexpr size_t aead_blocksize = 16;
/** Update the limit calculation with the amount of data encrypted */
void update(const std::size_t outlen)
{
/* update number of plaintext blocks encrypted. Use the x + (n-1)/n trick
* to round up the result to the number of blocked used */
plaintext_blocks += (outlen + (aead_blocksize - 1)) / aead_blocksize;
invocations++;
}
/** Returns true if the limit that is considered for the usage of the AEAD ciphers has been reached */
[[nodiscard]] bool usage_limit_reached() const
{
if (limit == 0)
return false;
return plaintext_blocks + invocations > limit;
}
/** Returns true if we are 7/8 of the usage limit. We use this limit to trigger a renegotiation */
[[nodiscard]] bool usage_limit_warn() const
{
if (limit == 0)
return false;
return plaintext_blocks + invocations > limit / 8 * 7;
}
};
} // namespace openvpn::Crypto
#endif
|
