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|
//! OpenPGP packet headers.
//!
//! An OpenPGP packet header contains packet meta-data. Specifically,
//! it includes the [packet's type] (its so-called *tag*), and the
//! [packet's length].
//!
//! Decades ago, when OpenPGP was conceived, saving even a few bits
//! was considered important. As such, OpenPGP uses very compact
//! encodings. The encoding schemes have evolved so that there are
//! now two families: the so-called old format, and new format
//! encodings.
//!
//! [packet's type]: https://tools.ietf.org/html/rfc4880#section-4.3
//! [packet's length]: https://tools.ietf.org/html/rfc4880#section-4.2.1
use crate::{
Error,
Result,
};
use crate::packet::tag::Tag;
mod ctb;
pub use self::ctb::{
CTB,
CTBOld,
CTBNew,
PacketLengthType,
};
/// A packet's header.
///
/// See [Section 4.2 of RFC 4880] for details.
///
/// [Section 4.2 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-4.2
#[derive(Clone, Debug)]
pub struct Header {
/// The packet's CTB.
ctb: CTB,
/// The packet's length.
length: BodyLength,
}
assert_send_and_sync!(Header);
impl Header {
/// Creates a new header.
pub fn new(ctb: CTB, length: BodyLength) -> Self {
Header { ctb, length }
}
/// Returns the header's CTB.
pub fn ctb(&self) -> &CTB {
&self.ctb
}
/// Returns the header's length.
pub fn length(&self) -> &BodyLength {
&self.length
}
/// Checks the header for validity.
///
/// A header is consider invalid if:
///
/// - The tag is [`Tag::Reserved`].
/// - The tag is [`Tag::Unknown`] or [`Tag::Private`] and
/// `future_compatible` is false.
/// - The [length encoding] is invalid for the packet (e.g.,
/// partial body encoding may not be used for [`PKESK`] packets)
/// - The lengths are unreasonable for a packet (e.g., a
/// `PKESK` or [`SKESK`] larger than 10 KB).
///
/// [`Tag::Reserved`]: super::Tag::Reserved
/// [`Tag::Unknown`]: super::Tag::Unknown
/// [`Tag::Private`]: super::Tag::Private
/// [length encoding]: https://tools.ietf.org/html/rfc4880#section-4.2.2.4
/// [`PKESK`]: super::PKESK
/// [`SKESK`]: super::SKESK
// Note: To check the packet's content, use
// `PacketParser::plausible`.
pub fn valid(&self, future_compatible: bool) -> Result<()> {
let tag = self.ctb.tag();
match tag {
// Reserved packets are never valid.
Tag::Reserved =>
return Err(Error::UnsupportedPacketType(tag).into()),
// Unknown packets are not valid unless we want future compatibility.
Tag::Unknown(_) | Tag::Private(_) if !future_compatible =>
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..(10 // Header, fixed sized fields.
+ 2 * 64 * 1024 // Hashed & Unhashed areas.
+ 64 * 1024 // MPIs.
)).contains(&l),
Tag::SKESK =>
// 2 bytes of fixed header. An s2k
// specification (at least 1 byte), an
// optional encryption session key.
(3..10 * 1024).contains(&l),
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,
Tag::Padding => true,
};
if ! valid {
return Err(Error::MalformedPacket(
format!("Invalid size ({} bytes) for a {} packet",
l, tag)).into())
}
}
}
}
Ok(())
}
}
/// A packet's size.
///
/// A packet's size can be expressed in three different ways. Either
/// the size of the packet is fully known (`Full`), the packet is
/// chunked using OpenPGP's partial body encoding (`Partial`), or the
/// packet extends to the end of the file (`Indeterminate`). See
/// [Section 4.2 of RFC 4880] for more details.
///
/// [Section 4.2 of RFC 4880]: https://tools.ietf.org/html/rfc4880#section-4.2
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