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
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
//! OpenPGP Header.
use {
Error,
Result,
BodyLength,
};
use packet::tag::Tag;
use packet::ctb::CTB;
/// An OpenPGP packet's header.
#[derive(Clone, Debug)]
pub struct Header {
/// The packet's CTB.
pub ctb: CTB,
/// The packet's length.
pub length: BodyLength,
}
impl Header {
/// Syntax checks the header.
///
/// A header is consider invalid if:
///
/// - The tag is Tag::Reserved.
/// - The tag is unknown (if future_compatible is false).
/// - The [length encoding] is invalid for the packet.
/// - The lengths are unreasonable for a packet (e.g., a
/// >10 kb large PKESK or SKESK).
///
/// [length encoding]: https://tools.ietf.org/html/rfc4880#section-4.2.2.4
///
/// This function does not check the packet's content. Use
/// `PacketParser::plausible` for that.
pub fn valid(&self, future_compatible: bool) -> Result<()> {
let tag = self.ctb.tag;
// Reserved packets are never valid.
if tag == Tag::Reserved {
return Err(Error::UnsupportedPacketType(tag).into());
}
// Unknown packets are not valid unless we want future
// compatibility.
if ! future_compatible
&& (destructures_to!(Tag::Unknown(_) = tag)
|| destructures_to!(Tag::Private(_) = tag))
{
return Err(Error::UnsupportedPacketType(tag).into());
}
// An implementation MAY use Partial Body Lengths for data
// packets, be they literal, compressed, or encrypted. The
// first partial length MUST be at least 512 octets long.
// Partial Body Lengths MUST NOT be used for any other packet
// types.
//
// https://tools.ietf.org/html/rfc4880#section-4.2.2.4
if tag == Tag::Literal || tag == Tag::CompressedData
|| tag == Tag::SED || tag == Tag::SEIP
|| tag == Tag::AED
{
// Data packet.
match self.length {
BodyLength::Indeterminate => (),
BodyLength::Partial(l) => {
if l < 512 {
return Err(Error::MalformedPacket(
format!("Partial body length must be \
at least 512 (got: {})",
l)).into());
}
}
BodyLength::Full(l) => {
// In the following block cipher length checks, we
// conservatively assume a block size of 8 bytes,
// because Twofish, TripleDES, IDEA, and CAST-5
// have a block size of 64 bits.
if tag == Tag::SED && (l < (8 // Random block.
+ 2 // Quickcheck bytes.
+ 6)) { // Smallest literal.
return Err(Error::MalformedPacket(
format!("{} packet's length must be \
at least 16 bytes in length (got: {})",
tag, l)).into());
} else if tag == Tag::SEIP
&& (l < (1 // Version.
+ 8 // Random block.
+ 2 // Quickcheck bytes.
+ 6 // Smallest literal.
+ 20)) // MDC packet.
{
return Err(Error::MalformedPacket(
format!("{} packet's length minus 1 must be \
at least 37 bytes in length (got: {})",
tag, l)).into());
} else if tag == Tag::CompressedData && l == 0 {
// One byte header.
return Err(Error::MalformedPacket(
format!("{} packet's length must be \
at least 1 byte (got ({})",
tag, l)).into());
} else if tag == Tag::Literal && l < 6 {
// Smallest literal packet consists of 6 octets.
return Err(Error::MalformedPacket(
format!("{} packet's length must be \
at least 6 bytes (got: ({})",
tag, l)).into());
}
}
}
} else {
// Non-data packet.
match self.length {
BodyLength::Indeterminate =>
return Err(Error::MalformedPacket(
format!("Indeterminite length encoding \
not allowed for {} packets",
tag)).into()),
BodyLength::Partial(_) =>
return Err(Error::MalformedPacket(
format!("Partial Body Chunking not allowed \
for {} packets",
tag)).into()),
BodyLength::Full(l) => {
let valid = match tag {
Tag::Signature =>
// A V3 signature is 19 bytes plus the
// MPIs. A V4 is 10 bytes plus the hash
// areas and the MPIs.
10 <= l
&& l < (10 // Header, fixed sized fields.
+ 2 * 64 * 1024 // Hashed & Unhashed areas.
+ 64 * 1024 // MPIs.
),
Tag::SKESK =>
// 2 bytes of fixed header. An s2k
// specification (at least 1 byte), an
// optional encryption session key.
3 <= l && l < 10 * 1024,
Tag::PKESK =>
// 10 bytes of fixed header, plus the
// encrypted session key.
10 < l && l < 10 * 1024,
Tag::OnePassSig if ! future_compatible => l == 13,
Tag::OnePassSig => l < 1024,
Tag::PublicKey | Tag::PublicSubkey
| Tag::SecretKey | Tag::SecretSubkey =>
// A V3 key is 8 bytes of fixed header
// plus MPIs. A V4 key is 6 bytes of
// fixed headers plus MPIs.
6 < l && l < 1024 * 1024,
Tag::Trust => true,
Tag::UserID =>
// Avoid insane user ids.
l < 32 * 1024,
Tag::UserAttribute =>
// The header is at least 2 bytes.
2 <= l,
Tag::MDC => l == 20,
Tag::Literal | Tag::CompressedData
| Tag::SED | Tag::SEIP | Tag::AED =>
unreachable!("handled in the data-packet branch"),
Tag::Unknown(_) | Tag::Private(_) => true,
Tag::Marker => l == 3,
Tag::Reserved => true,
};
if ! valid {
return Err(Error::MalformedPacket(
format!("Invalid size ({} bytes) for a {} packet",
l, tag)).into())
}
}
}
}
Ok(())
}
}