Skip to content

ecdsa: rename asn1::Signature; impl signature trait #102

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
tarcieri merged 1 commit into from
Jul 23, 2020
Merged

ecdsa: rename asn1::Signature; impl signature trait #102

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
172 changes: 97 additions & 75 deletions ecdsa/src/asn1.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,8 @@ use crate::{
Error,
};
use core::{
convert::TryFrom,
convert::{TryFrom, TryInto},
fmt,
ops::{Add, Range},
};
use elliptic_curve::{consts::U9, ScalarBytes};
Expand All @@ -35,7 +36,7 @@ pub type MaxOverhead = U9;
/// Maximum size of an ASN.1 DER encoded signature for the given elliptic curve.
pub type MaxSize<ScalarSize> = <<ScalarSize as Add>::Output as Add<MaxOverhead>>::Output;

/// Byte array containing a serialized ASN.1 document
/// Byte array containing a serialized ASN.1 signature
type DocumentBytes<ScalarSize> = GenericArray<u8, MaxSize<ScalarSize>>;

/// ASN.1 `INTEGER` tag
Expand All @@ -44,10 +45,10 @@ const INTEGER_TAG: u8 = 0x02;
/// ASN.1 `SEQUENCE` tag
const SEQUENCE_TAG: u8 = 0x30;

/// Document containing an ASN.1 DER-encoded signature.
/// ASN.1 DER-encoded signature.
///
/// Generic over the scalar size of the elliptic curve.
pub struct Document<ScalarSize>
pub struct Signature<ScalarSize>
where
ScalarSize: Add + ArrayLength<u8>,
MaxSize<ScalarSize>: ArrayLength<u8>,
Expand All @@ -56,86 +57,33 @@ where
/// ASN.1 DER-encoded signature data
bytes: DocumentBytes<ScalarSize>,

/// Range of the `r` value within the document
/// Range of the `r` value within the signature
r_range: Range<usize>,

/// Range of the `s` value within the document
/// Range of the `s` value within the signature
s_range: Range<usize>,
}

#[allow(clippy::len_without_is_empty)]
impl<ScalarSize> Document<ScalarSize>
impl<ScalarSize> signature::Signature for Signature<ScalarSize>
where
ScalarSize: Add + ArrayLength<u8>,
MaxSize<ScalarSize>: ArrayLength<u8>,
<ScalarSize as Add>::Output: Add<MaxOverhead> + ArrayLength<u8>,
{
/// Parse an ASN.1 DER-encoded ECDSA signature from a byte slice
pub fn from_bytes(bytes: impl AsRef<[u8]>) -> Result<Self, Error> {
let input = bytes.as_ref();

// Signature format is a SEQUENCE of two INTEGER values. We
// support only integers of less than 127 bytes each (signed
// encoding) so the resulting raw signature will have length
// at most 254 bytes.
//
// First byte is SEQUENCE tag.
if input[0] != SEQUENCE_TAG as u8 {
return Err(Error::new());
}

// The SEQUENCE length will be encoded over one or two bytes. We
// limit the total SEQUENCE contents to 255 bytes, because it
// makes things simpler; this is enough for subgroup orders up
// to 999 bits.
let mut zlen = input[1] as usize;

let offset = if zlen > 0x80 {
if zlen != 0x81 {
return Err(Error::new());
}

zlen = input[2] as usize;
3
} else {
2
};

if zlen != input.len().checked_sub(offset).unwrap() {
return Err(Error::new());
}

// First INTEGER (r)
let r_range = parse_int(&input[offset..], ScalarSize::to_usize())?;
let r_start = offset.checked_add(r_range.start).unwrap();
let r_end = offset.checked_add(r_range.end).unwrap();

// Second INTEGER (s)
let s_range = parse_int(&input[r_end..], ScalarSize::to_usize())?;
let s_start = r_end.checked_add(s_range.start).unwrap();
let s_end = r_end.checked_add(s_range.end).unwrap();

if s_end != bytes.as_ref().len() {
return Err(Error::new());
}

let mut byte_arr = DocumentBytes::<ScalarSize>::default();
byte_arr[..s_end].copy_from_slice(bytes.as_ref());

Ok(Document {
bytes: byte_arr,
r_range: Range {
start: r_start,
end: r_end,
},
s_range: Range {
start: s_start,
end: s_end,
},
})
fn from_bytes(bytes: &[u8]) -> Result<Self, Error> {
bytes.try_into()
}
}

/// Get the length of the document
#[allow(clippy::len_without_is_empty)]
impl<ScalarSize> Signature<ScalarSize>
where
ScalarSize: Add + ArrayLength<u8>,
MaxSize<ScalarSize>: ArrayLength<u8>,
<ScalarSize as Add>::Output: Add<MaxOverhead> + ArrayLength<u8>,
{
/// Get the length of the signature in bytes
pub fn len(&self) -> usize {
self.s_range.end
}
Expand Down Expand Up @@ -168,7 +116,9 @@ where
serialize_int(s.as_slice(), &mut bytes[r_end..], s_len, scalar_size);
let s_end = r_end.checked_add(2).unwrap().checked_add(s_len).unwrap();

Self::from_bytes(&bytes[..s_end]).expect("generated invalid ASN.1 DER")
bytes[..s_end]
.try_into()
.expect("generated invalid ASN.1 DER")
}

/// Get the `r` component of the signature (leading zeros removed)
Expand All @@ -182,7 +132,7 @@ where
}
}

impl<ScalarSize> AsRef<[u8]> for Document<ScalarSize>
impl<ScalarSize> AsRef<[u8]> for Signature<ScalarSize>
where
ScalarSize: Add + ArrayLength<u8>,
MaxSize<ScalarSize>: ArrayLength<u8>,
Expand All @@ -193,7 +143,21 @@ where
}
}

impl<ScalarSize> TryFrom<&[u8]> for Document<ScalarSize>
impl<ScalarSize> fmt::Debug for Signature<ScalarSize>
where
ScalarSize: Add + ArrayLength<u8>,
MaxSize<ScalarSize>: ArrayLength<u8>,
<ScalarSize as Add>::Output: Add<MaxOverhead> + ArrayLength<u8>,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("asn1::Signature")
.field("r", &self.r())
.field("s", &self.s())
.finish()
}
}

impl<ScalarSize> TryFrom<&[u8]> for Signature<ScalarSize>
where
ScalarSize: Add + ArrayLength<u8>,
MaxSize<ScalarSize>: ArrayLength<u8>,
Expand All @@ -202,7 +166,65 @@ where
type Error = Error;

fn try_from(bytes: &[u8]) -> Result<Self, Error> {
Self::from_bytes(bytes)
// Signature format is a SEQUENCE of two INTEGER values. We
// support only integers of less than 127 bytes each (signed
// encoding) so the resulting raw signature will have length
// at most 254 bytes.
//
// First byte is SEQUENCE tag.
if bytes[0] != SEQUENCE_TAG as u8 {
return Err(Error::new());
}

// The SEQUENCE length will be encoded over one or two bytes. We
// limit the total SEQUENCE contents to 255 bytes, because it
// makes things simpler; this is enough for subgroup orders up
// to 999 bits.
let mut zlen = bytes[1] as usize;

let offset = if zlen > 0x80 {
if zlen != 0x81 {
return Err(Error::new());
}

zlen = bytes[2] as usize;
3
} else {
2
};

if zlen != bytes.len().checked_sub(offset).unwrap() {
return Err(Error::new());
}

// First INTEGER (r)
let r_range = parse_int(&bytes[offset..], ScalarSize::to_usize())?;
let r_start = offset.checked_add(r_range.start).unwrap();
let r_end = offset.checked_add(r_range.end).unwrap();

// Second INTEGER (s)
let s_range = parse_int(&bytes[r_end..], ScalarSize::to_usize())?;
let s_start = r_end.checked_add(s_range.start).unwrap();
let s_end = r_end.checked_add(s_range.end).unwrap();

if s_end != bytes.as_ref().len() {
return Err(Error::new());
}

let mut byte_arr = DocumentBytes::<ScalarSize>::default();
byte_arr[..s_end].copy_from_slice(bytes.as_ref());

Ok(Signature {
bytes: byte_arr,
r_range: Range {
start: r_start,
end: r_end,
},
s_range: Range {
start: s_start,
end: s_end,
},
})
}
}

Expand Down
10 changes: 5 additions & 5 deletions ecdsa/src/lib.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -97,17 +97,17 @@ where
asn1::MaxSize<C::ScalarSize>: ArrayLength<u8>,
<C::ScalarSize as Add>::Output: Add<asn1::MaxOverhead> + ArrayLength<u8>,
{
asn1::Document::<C::ScalarSize>::from_bytes(bytes).map(Into::into)
asn1::Signature::<C::ScalarSize>::try_from(bytes).map(Into::into)
}

/// Serialize this signature as ASN.1 DER
pub fn to_asn1(&self) -> asn1::Document<C::ScalarSize>
pub fn to_asn1(&self) -> asn1::Signature<C::ScalarSize>
where
C::ScalarSize: Add + ArrayLength<u8>,
asn1::MaxSize<C::ScalarSize>: ArrayLength<u8>,
<C::ScalarSize as Add>::Output: Add<asn1::MaxOverhead> + ArrayLength<u8>,
{
asn1::Document::from_scalars(self.r(), self.s())
asn1::Signature::from_scalars(self.r(), self.s())
}

/// Get the `r` component of this signature
Expand Down Expand Up @@ -170,14 +170,14 @@ where
}
}

impl<C> From<asn1::Document<C::ScalarSize>> for Signature<C>
impl<C> From<asn1::Signature<C::ScalarSize>> for Signature<C>
where
C: Curve,
C::ScalarSize: Add + ArrayLength<u8>,
asn1::MaxSize<C::ScalarSize>: ArrayLength<u8>,
<C::ScalarSize as Add>::Output: Add<asn1::MaxOverhead> + ArrayLength<u8>,
{
fn from(doc: asn1::Document<C::ScalarSize>) -> Signature<C> {
fn from(doc: asn1::Signature<C::ScalarSize>) -> Signature<C> {
let mut bytes = SignatureBytes::<C>::default();
let scalar_size = C::ScalarSize::to_usize();
let r_begin = scalar_size.checked_sub(doc.r().len()).unwrap();
Expand Down