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Add error logic to decoding methods.

This commit is contained in:
Sean Bowe 2017-07-17 09:06:03 -06:00
parent 7c35f2b8b0
commit 09531d0810
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GPG Key ID: 95684257D8F8B031
4 changed files with 155 additions and 68 deletions
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122
src/bls12_381/ec.rs
View File

@ -111,10 +111,6 @@ macro_rules! curve_impl {
self.infinity
}
fn is_valid(&self) -> bool {
self.is_on_curve() && self.is_in_correct_subgroup()
}
fn mul<S: Into<<Self::Scalar as PrimeField>::Repr>>(&self, by: S) -> $projective {
let mut res = $projective::zero();
@ -560,7 +556,7 @@ macro_rules! curve_impl {
pub mod g1 {
use rand::{Rand, Rng};
use super::super::{Fq, Fr, FrRepr, FqRepr};
use ::{CurveProjective, CurveAffine, PrimeField, SqrtField, PrimeFieldRepr, Field, BitIterator, EncodedPoint};
use ::{CurveProjective, CurveAffine, PrimeField, SqrtField, PrimeFieldRepr, Field, BitIterator, EncodedPoint, GroupDecodingError};
curve_impl!(G1, G1Affine, G1Prepared, Fq, Fr, G1Uncompressed, G1Compressed);
@ -583,7 +579,18 @@ pub mod g1 {
fn empty() -> Self { G1Uncompressed([0; 96]) }
fn size() -> usize { 96 }
fn into_affine_unchecked(&self) -> Result<G1Affine, ()> {
fn into_affine(&self) -> Result<G1Affine, GroupDecodingError> {
let affine = self.into_affine_unchecked()?;
if !affine.is_on_curve() {
Err(GroupDecodingError::NotOnCurve)
} else if !affine.is_in_correct_subgroup() {
Err(GroupDecodingError::NotInSubgroup)
} else {
Ok(affine)
}
}
fn into_affine_unchecked(&self) -> Result<G1Affine, GroupDecodingError> {
use byteorder::{ReadBytesExt, BigEndian};
// Create a copy of this representation.
@ -591,7 +598,7 @@ pub mod g1 {
if copy[0] & (1 << 7) != 0 {
// Distinguisher bit is set, but this should be uncompressed!
return Err(())
return Err(GroupDecodingError::UnexpectedCompressionMode)
}
if copy[0] & (1 << 6) != 0 {
@ -603,13 +610,13 @@ pub mod g1 {
if copy.iter().all(|b| *b == 0) {
Ok(G1Affine::zero())
} else {
Err(())
Err(GroupDecodingError::UnexpectedInformation)
}
} else {
if copy[0] & (1 << 5) != 0 {
// The bit indicating the y-coordinate should be lexicographically
// largest is set, but this is an uncompressed element.
return Err(())
return Err(GroupDecodingError::UnexpectedInformation)
}
// Unset the three most significant bits.
@ -631,8 +638,8 @@ pub mod g1 {
}
Ok(G1Affine {
x: Fq::from_repr(x)?,
y: Fq::from_repr(y)?,
x: Fq::from_repr(x).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate", e))?,
y: Fq::from_repr(y).map_err(|e| GroupDecodingError::CoordinateDecodingError("y coordinate", e))?,
infinity: false
})
}
@ -681,7 +688,18 @@ pub mod g1 {
fn empty() -> Self { G1Compressed([0; 48]) }
fn size() -> usize { 48 }
fn into_affine_unchecked(&self) -> Result<G1Affine, ()> {
fn into_affine(&self) -> Result<G1Affine, GroupDecodingError> {
let affine = self.into_affine_unchecked()?;
// NB: Decompression guarantees that it is on the curve already.
if !affine.is_in_correct_subgroup() {
Err(GroupDecodingError::NotInSubgroup)
} else {
Ok(affine)
}
}
fn into_affine_unchecked(&self) -> Result<G1Affine, GroupDecodingError> {
use byteorder::{ReadBytesExt, BigEndian};
// Create a copy of this representation.
@ -689,7 +707,7 @@ pub mod g1 {
if copy[0] & (1 << 7) == 0 {
// Distinguisher bit isn't set.
return Err(())
return Err(GroupDecodingError::UnexpectedCompressionMode)
}
if copy[0] & (1 << 6) != 0 {
@ -701,7 +719,7 @@ pub mod g1 {
if copy.iter().all(|b| *b == 0) {
Ok(G1Affine::zero())
} else {
Err(())
Err(GroupDecodingError::UnexpectedInformation)
}
} else {
// Determine if the intended y coordinate must be greater
@ -722,7 +740,7 @@ pub mod g1 {
}
// Interpret as Fq element.
let x = Fq::from_repr(x)?;
let x = Fq::from_repr(x).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate", e))?;
// Compute x^3 + b
let mut x3b = x;
@ -747,7 +765,7 @@ pub mod g1 {
},
None => {
// Point must not be on the curve.
Err(())
Err(GroupDecodingError::NotOnCurve)
}
}
}
@ -873,7 +891,7 @@ pub mod g1 {
infinity: false
};
assert!(!p.is_valid());
assert!(!p.is_in_correct_subgroup());
let mut g1 = G1::zero();
@ -895,7 +913,7 @@ pub mod g1 {
assert_eq!(i, 4);
let g1 = G1Affine::from(g1);
assert!(g1.is_valid());
assert!(g1.is_in_correct_subgroup());
assert_eq!(g1, G1Affine::one());
break;
@ -918,7 +936,6 @@ pub mod g1 {
};
assert!(!p.is_on_curve());
assert!(p.is_in_correct_subgroup());
assert!(!p.is_valid());
}
// Reject point on a twist (b = 3)
@ -930,7 +947,6 @@ pub mod g1 {
};
assert!(!p.is_on_curve());
assert!(!p.is_in_correct_subgroup());
assert!(!p.is_valid());
}
// Reject point in an invalid subgroup
@ -943,7 +959,6 @@ pub mod g1 {
};
assert!(p.is_on_curve());
assert!(!p.is_in_correct_subgroup());
assert!(!p.is_valid());
}
}
@ -1019,9 +1034,9 @@ pub mod g1 {
infinity: false
};
assert!(a.is_valid());
assert!(b.is_valid());
assert!(c.is_valid());
assert!(a.is_on_curve() && a.is_in_correct_subgroup());
assert!(b.is_on_curve() && b.is_in_correct_subgroup());
assert!(c.is_on_curve() && c.is_in_correct_subgroup());
let mut tmp1 = a.into_projective();
tmp1.add_assign(&b.into_projective());
@ -1097,7 +1112,7 @@ pub mod g1 {
pub mod g2 {
use rand::{Rand, Rng};
use super::super::{Fq2, Fr, Fq, FrRepr, FqRepr};
use ::{CurveProjective, CurveAffine, PrimeField, SqrtField, PrimeFieldRepr, Field, BitIterator, EncodedPoint};
use ::{CurveProjective, CurveAffine, PrimeField, SqrtField, PrimeFieldRepr, Field, BitIterator, EncodedPoint, GroupDecodingError};
curve_impl!(G2, G2Affine, G2Prepared, Fq2, Fr, G2Uncompressed, G2Compressed);
@ -1120,7 +1135,18 @@ pub mod g2 {
fn empty() -> Self { G2Uncompressed([0; 192]) }
fn size() -> usize { 192 }
fn into_affine_unchecked(&self) -> Result<G2Affine, ()> {
fn into_affine(&self) -> Result<G2Affine, GroupDecodingError> {
let affine = self.into_affine_unchecked()?;
if !affine.is_on_curve() {
Err(GroupDecodingError::NotOnCurve)
} else if !affine.is_in_correct_subgroup() {
Err(GroupDecodingError::NotInSubgroup)
} else {
Ok(affine)
}
}
fn into_affine_unchecked(&self) -> Result<G2Affine, GroupDecodingError> {
use byteorder::{ReadBytesExt, BigEndian};
// Create a copy of this representation.
@ -1128,7 +1154,7 @@ pub mod g2 {
if copy[0] & (1 << 7) != 0 {
// Distinguisher bit is set, but this should be uncompressed!
return Err(())
return Err(GroupDecodingError::UnexpectedCompressionMode)
}
if copy[0] & (1 << 6) != 0 {
@ -1140,13 +1166,13 @@ pub mod g2 {
if copy.iter().all(|b| *b == 0) {
Ok(G2Affine::zero())
} else {
Err(())
Err(GroupDecodingError::UnexpectedInformation)
}
} else {
if copy[0] & (1 << 5) != 0 {
// The bit indicating the y-coordinate should be lexicographically
// largest is set, but this is an uncompressed element.
return Err(())
return Err(GroupDecodingError::UnexpectedInformation)
}
// Unset the three most significant bits.
@ -1179,12 +1205,12 @@ pub mod g2 {
Ok(G2Affine {
x: Fq2 {
c0: Fq::from_repr(x_c0)?,
c1: Fq::from_repr(x_c1)?
c0: Fq::from_repr(x_c0).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate (c0)", e))?,
c1: Fq::from_repr(x_c1).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate (c1)", e))?,
},
y: Fq2 {
c0: Fq::from_repr(y_c0)?,
c1: Fq::from_repr(y_c1)?
c0: Fq::from_repr(y_c0).map_err(|e| GroupDecodingError::CoordinateDecodingError("y coordinate (c0)", e))?,
c1: Fq::from_repr(y_c1).map_err(|e| GroupDecodingError::CoordinateDecodingError("y coordinate (c1)", e))?,
},
infinity: false
})
@ -1242,7 +1268,18 @@ pub mod g2 {
fn empty() -> Self { G2Compressed([0; 96]) }
fn size() -> usize { 96 }
fn into_affine_unchecked(&self) -> Result<G2Affine, ()> {
fn into_affine(&self) -> Result<G2Affine, GroupDecodingError> {
let affine = self.into_affine_unchecked()?;
// NB: Decompression guarantees that it is on the curve already.
if !affine.is_in_correct_subgroup() {
Err(GroupDecodingError::NotInSubgroup)
} else {
Ok(affine)
}
}
fn into_affine_unchecked(&self) -> Result<G2Affine, GroupDecodingError> {
use byteorder::{ReadBytesExt, BigEndian};
// Create a copy of this representation.
@ -1250,7 +1287,7 @@ pub mod g2 {
if copy[0] & (1 << 7) == 0 {
// Distinguisher bit isn't set.
return Err(())
return Err(GroupDecodingError::UnexpectedCompressionMode)
}
if copy[0] & (1 << 6) != 0 {
@ -1262,7 +1299,7 @@ pub mod g2 {
if copy.iter().all(|b| *b == 0) {
Ok(G2Affine::zero())
} else {
Err(())
Err(GroupDecodingError::UnexpectedInformation)
}
} else {
// Determine if the intended y coordinate must be greater
@ -1289,8 +1326,8 @@ pub mod g2 {
// Interpret as Fq element.
let x = Fq2 {
c0: Fq::from_repr(x_c0)?,
c1: Fq::from_repr(x_c1)?
c0: Fq::from_repr(x_c0).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate (c0)", e))?,
c1: Fq::from_repr(x_c1).map_err(|e| GroupDecodingError::CoordinateDecodingError("x coordinate (c1)", e))?
};
// Compute x^3 + b
@ -1316,7 +1353,7 @@ pub mod g2 {
},
None => {
// Point must not be on the curve.
Err(())
Err(GroupDecodingError::NotOnCurve)
}
}
}
@ -1446,7 +1483,7 @@ pub mod g2 {
infinity: false
};
assert!(!p.is_valid());
assert!(!p.is_in_correct_subgroup());
let mut g2 = G2::zero();
@ -1468,7 +1505,7 @@ pub mod g2 {
assert_eq!(i, 2);
let g2 = G2Affine::from(g2);
assert!(g2.is_valid());
assert!(g2.is_in_correct_subgroup());
assert_eq!(g2, G2Affine::one());
break;
@ -1497,7 +1534,6 @@ pub mod g2 {
};
assert!(!p.is_on_curve());
assert!(p.is_in_correct_subgroup());
assert!(!p.is_valid());
}
// Reject point on a twist (b = 2 * (u + 1))
@ -1515,7 +1551,6 @@ pub mod g2 {
};
assert!(!p.is_on_curve());
assert!(!p.is_in_correct_subgroup());
assert!(!p.is_valid());
}
// Reject point in an invalid subgroup
@ -1534,7 +1569,6 @@ pub mod g2 {
};
assert!(p.is_on_curve());
assert!(!p.is_in_correct_subgroup());
assert!(!p.is_valid());
}
}

8
src/bls12_381/fq.rs
View File

@ -1,4 +1,4 @@
use ::{Field, PrimeField, SqrtField, PrimeFieldRepr};
use ::{Field, PrimeField, SqrtField, PrimeFieldRepr, PrimeFieldDecodingError};
use std::cmp::Ordering;
use super::fq2::Fq2;
@ -401,14 +401,14 @@ impl From<Fq> for FqRepr {
impl PrimeField for Fq {
type Repr = FqRepr;
fn from_repr(r: FqRepr) -> Result<Fq, ()> {
fn from_repr(r: FqRepr) -> Result<Fq, PrimeFieldDecodingError> {
let mut r = Fq(r);
if r.is_valid() {
r.mul_assign(&Fq(R2));
Ok(r)
} else {
Err(())
Err(PrimeFieldDecodingError::NotInField)
}
}
@ -1740,6 +1740,6 @@ fn test_fq_ordering() {
// FqRepr's ordering is well-tested, but we still need to make sure the Fq
// elements aren't being compared in Montgomery form.
for i in 0..100 {
assert!(Fq::from_repr(FqRepr::from(i+1)) > Fq::from_repr(FqRepr::from(i)));
assert!(Fq::from_repr(FqRepr::from(i+1)).unwrap() > Fq::from_repr(FqRepr::from(i)).unwrap());
}
}

6
src/bls12_381/fr.rs
View File

@ -1,4 +1,4 @@
use ::{Field, PrimeField, SqrtField, PrimeFieldRepr};
use ::{Field, PrimeField, SqrtField, PrimeFieldRepr, PrimeFieldDecodingError};
// r = 52435875175126190479447740508185965837690552500527637822603658699938581184513
const MODULUS: FrRepr = FrRepr([0xffffffff00000001, 0x53bda402fffe5bfe, 0x3339d80809a1d805, 0x73eda753299d7d48]);
@ -222,14 +222,14 @@ impl From<Fr> for FrRepr {
impl PrimeField for Fr {
type Repr = FrRepr;
fn from_repr(r: FrRepr) -> Result<Fr, ()> {
fn from_repr(r: FrRepr) -> Result<Fr, PrimeFieldDecodingError> {
let mut r = Fr(r);
if r.is_valid() {
r.mul_assign(&Fr(R2));
Ok(r)
} else {
Err(())
Err(PrimeFieldDecodingError::NotInField)
}
}

87
src/lib.rs
View File

@ -28,6 +28,7 @@ pub mod bls12_381;
pub mod wnaf;
use std::fmt;
use std::error::Error;
/// An "engine" is a collection of types (fields, elliptic curve groups, etc.)
/// with well-defined relationships. In particular, the G1/G2 curve groups are
@ -179,9 +180,6 @@ pub trait CurveAffine: Copy +
/// additive identity.
fn is_zero(&self) -> bool;
/// Determines if this point is on the curve and in the correct subgroup.
fn is_valid(&self) -> bool;
/// Negates this element.
fn negate(&mut self);
@ -224,21 +222,17 @@ pub trait EncodedPoint: Sized +
fn size() -> usize;
/// Converts an `EncodedPoint` into a `CurveAffine` element,
/// if the point is valid.
fn into_affine(&self) -> Result<Self::Affine, ()> {
let affine = self.into_affine_unchecked()?;
if affine.is_valid() {
Ok(affine)
} else {
Err(())
}
}
/// if the encoding represents a valid element.
fn into_affine(&self) -> Result<Self::Affine, GroupDecodingError>;
/// Converts an `EncodedPoint` into a `CurveAffine` element,
/// without checking if it's a valid point. Caller must be careful
/// when using this, as misuse can violate API invariants.
fn into_affine_unchecked(&self) -> Result<Self::Affine, ()>;
/// without guaranteeing that the encoding represents a valid
/// element. This is useful when the caller knows the encoding is
/// valid already.
///
/// If the encoding is invalid, this can break API invariants,
/// so caution is strongly encouraged.
fn into_affine_unchecked(&self) -> Result<Self::Affine, GroupDecodingError>;
/// Creates an `EncodedPoint` from an affine point, as long as the
/// point is not the point at infinity.
@ -368,6 +362,65 @@ pub trait PrimeFieldRepr: Sized +
fn mul2(&mut self);
}
#[derive(Debug)]
pub enum PrimeFieldDecodingError {
// The encoded value is not in the field
NotInField
}
impl Error for PrimeFieldDecodingError {
fn description(&self) -> &str {
match self {
&PrimeFieldDecodingError::NotInField => "not an element in the field"
}
}
}
impl fmt::Display for PrimeFieldDecodingError {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
write!(f, "{}", self.description())
}
}
#[derive(Debug)]
pub enum GroupDecodingError {
/// The coordinate(s) do not lie on the curve.
NotOnCurve,
/// The element is not part of the r-order subgroup.
NotInSubgroup,
/// One of the coordinates could not be decoded
CoordinateDecodingError(&'static str, PrimeFieldDecodingError),
/// The compression mode of the encoded elemnet was not as expected
UnexpectedCompressionMode,
/// The encoding contained bits that should not have been set
UnexpectedInformation
}
impl Error for GroupDecodingError {
fn description(&self) -> &str {
match self {
&GroupDecodingError::NotOnCurve => "coordinate(s) do not lie on the curve",
&GroupDecodingError::NotInSubgroup => "the element is not part of an r-order subgroup",
&GroupDecodingError::CoordinateDecodingError(..) => "coordinate(s) could not be decoded",
&GroupDecodingError::UnexpectedCompressionMode => "encoding has unexpected compression mode",
&GroupDecodingError::UnexpectedInformation => "encoding has unexpected information"
}
}
}
impl fmt::Display for GroupDecodingError {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match self {
&GroupDecodingError::CoordinateDecodingError(description, ref err) => {
write!(f, "{} decoding error: {}", description, err)
},
_ => {
write!(f, "{}", self.description())
}
}
}
}
/// This represents an element of a prime field.
pub trait PrimeField: Field
{
@ -376,7 +429,7 @@ pub trait PrimeField: Field
type Repr: PrimeFieldRepr + From<Self>;
/// Convert this prime field element into a biginteger representation.
fn from_repr(Self::Repr) -> Result<Self, ()>;
fn from_repr(Self::Repr) -> Result<Self, PrimeFieldDecodingError>;
/// Convert a biginteger reprensentation into a prime field element, if
/// the number is an element of the field.