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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,163 @@ | ||
| use crypto_bigint::{Encoding, Zero}; | ||
|
|
||
| use super::params::SchemeParams; | ||
| use crate::{ | ||
| curve::{Scalar, ORDER}, | ||
| paillier::PaillierParams, | ||
| tools::Secret, | ||
| uint::{PublicSigned, SecretSigned, SecretUnsigned}, | ||
| }; | ||
|
|
||
| fn uint_from_scalar<P: SchemeParams>(value: &Scalar) -> <P::Paillier as PaillierParams>::Uint { | ||
| let scalar_bytes = value.to_be_bytes(); | ||
| let mut repr = <P::Paillier as PaillierParams>::Uint::zero().to_be_bytes(); | ||
|
|
||
| let uint_len = repr.as_ref().len(); | ||
| let scalar_len = scalar_bytes.len(); | ||
|
|
||
| repr.as_mut() | ||
| .get_mut(uint_len - scalar_len..) | ||
| .expect("PaillierParams::Uint is expected to be bigger than a Scalar") | ||
| .copy_from_slice(&scalar_bytes); | ||
| <P::Paillier as PaillierParams>::Uint::from_be_bytes(repr) | ||
| } | ||
|
|
||
| /// Converts a [`Scalar`] to a [`PublicSigned`]. | ||
| /// | ||
| /// Assumes using a curve whose order is at most the width of `Uint` minus 1 bit. | ||
| pub(crate) fn public_signed_from_scalar<P: SchemeParams>( | ||
| value: &Scalar, | ||
| ) -> PublicSigned<<P::Paillier as PaillierParams>::Uint> { | ||
| PublicSigned::new_positive(uint_from_scalar::<P>(value), ORDER.bits_vartime() as u32).expect(concat![ | ||
| "a curve scalar value is smaller than the half of `PaillierParams::Uint` range, ", | ||
| "so it is still positive when treated as a 2-complement signed value" | ||
| ]) | ||
| } | ||
|
|
||
| /// Converts an integer to the associated curve scalar type. | ||
| pub(crate) fn scalar_from_uint<P: SchemeParams>(value: &<P::Paillier as PaillierParams>::Uint) -> Scalar { | ||
| let r = *value % P::CURVE_ORDER; | ||
|
|
||
| let repr = r.to_be_bytes(); | ||
| let uint_len = repr.as_ref().len(); | ||
| let scalar_len = Scalar::repr_len(); | ||
|
|
||
| // Can unwrap here since the value is within the Scalar range | ||
| Scalar::try_from_be_bytes( | ||
| repr.as_ref() | ||
| .get(uint_len - scalar_len..) | ||
| .expect("Uint is assumed to be bigger than Scalar"), | ||
| ) | ||
| .expect("the value was reduced modulo curve order, so it's a valid curve scalar") | ||
| } | ||
|
|
||
| /// Converts a `PublicSigned`-wrapped integer to the associated curve scalar type. | ||
| pub(crate) fn scalar_from_signed<P: SchemeParams>( | ||
| value: &PublicSigned<<P::Paillier as PaillierParams>::Uint>, | ||
| ) -> Scalar { | ||
| let abs_value = scalar_from_uint::<P>(&value.abs()); | ||
| if value.is_negative() { | ||
| -abs_value | ||
| } else { | ||
| abs_value | ||
| } | ||
| } | ||
|
|
||
| /// Converts a wide integer to the associated curve scalar type. | ||
| pub(crate) fn scalar_from_wide_uint<P: SchemeParams>(value: &<P::Paillier as PaillierParams>::WideUint) -> Scalar { | ||
| let r = *value % P::CURVE_ORDER_WIDE; | ||
|
|
||
| let repr = r.to_be_bytes(); | ||
| let uint_len = repr.as_ref().len(); | ||
| let scalar_len = Scalar::repr_len(); | ||
|
|
||
| // Can unwrap here since the value is within the Scalar range | ||
| Scalar::try_from_be_bytes( | ||
| repr.as_ref() | ||
| .get(uint_len - scalar_len..) | ||
| .expect("WideUint is assumed to be bigger than Scalar"), | ||
| ) | ||
| .expect("the value was reduced modulo curve order, so it's a valid curve scalar") | ||
| } | ||
|
|
||
| /// Converts a `PublicSigned`-wrapped wide integer to the associated curve scalar type. | ||
| pub(crate) fn scalar_from_wide_signed<P: SchemeParams>( | ||
| value: &PublicSigned<<P::Paillier as PaillierParams>::WideUint>, | ||
| ) -> Scalar { | ||
| let abs_value = scalar_from_wide_uint::<P>(&value.abs()); | ||
| if value.is_negative() { | ||
| -abs_value | ||
| } else { | ||
| abs_value | ||
| } | ||
| } | ||
|
|
||
| /// Converts a secret-wrapped uint to a secret-wrapped [`Scalar`], reducing the value modulo curve order. | ||
| pub(crate) fn secret_scalar_from_uint<P: SchemeParams>( | ||
| value: &Secret<<P::Paillier as PaillierParams>::Uint>, | ||
| ) -> Secret<Scalar> { | ||
| let r = value % &P::CURVE_ORDER; | ||
|
|
||
| let repr = Secret::init_with(|| r.expose_secret().to_be_bytes()); | ||
| let uint_len = repr.expose_secret().as_ref().len(); | ||
| let scalar_len = Scalar::repr_len(); | ||
|
|
||
| // Can unwrap here since the value is within the Scalar range | ||
| Secret::init_with(|| { | ||
| Scalar::try_from_be_bytes( | ||
| repr.expose_secret() | ||
| .as_ref() | ||
| .get(uint_len - scalar_len..) | ||
| .expect("Uint is assumed to be bigger than Scalar"), | ||
| ) | ||
| .expect("the value was reduced modulo `CURVE_ORDER`, so it's a valid curve scalar") | ||
| }) | ||
| } | ||
|
|
||
| fn secret_uint_from_scalar<P: SchemeParams>(value: &Secret<Scalar>) -> Secret<<P::Paillier as PaillierParams>::Uint> { | ||
| let scalar_bytes = Secret::init_with(|| value.expose_secret().to_be_bytes()); | ||
| let mut repr = Secret::init_with(|| <P::Paillier as PaillierParams>::Uint::zero().to_be_bytes()); | ||
|
|
||
| let uint_len = repr.expose_secret().as_ref().len(); | ||
| let scalar_len = scalar_bytes.expose_secret().len(); | ||
|
|
||
| debug_assert!(uint_len >= scalar_len); | ||
| repr.expose_secret_mut() | ||
| .as_mut() | ||
| .get_mut(uint_len - scalar_len..) | ||
| .expect("<P::Paillier as PaillierParams>::Uint is assumed to be configured to be bigger than Scalar") | ||
| .copy_from_slice(scalar_bytes.expose_secret()); | ||
| Secret::init_with(|| <P::Paillier as PaillierParams>::Uint::from_be_bytes(*repr.expose_secret())) | ||
| } | ||
|
|
||
| /// Converts a secret-wrapped [`Scalar`] to a [`SecretUnsigned`]. | ||
| /// | ||
| /// Assumes using a curve whose order fits in a [`PaillierParams::Uint`]. | ||
| pub(crate) fn secret_unsigned_from_scalar<P: SchemeParams>( | ||
| value: &Secret<Scalar>, | ||
| ) -> SecretUnsigned<<P::Paillier as PaillierParams>::Uint> { | ||
| SecretUnsigned::new(secret_uint_from_scalar::<P>(value), ORDER.bits_vartime() as u32).expect(concat![ | ||
| "a curve scalar value is smaller than the curve order, ", | ||
| "and the curve order fits in `PaillierParams::Uint`" | ||
| ]) | ||
| } | ||
|
|
||
| /// Converts a secret-wrapped [`Scalar`] to a [`SecretSigned`]. | ||
| /// | ||
| /// Assumes using a curve whose order is at most the width of `Uint` minus 1 bit. | ||
| pub(crate) fn secret_signed_from_scalar<P: SchemeParams>( | ||
| value: &Secret<Scalar>, | ||
| ) -> SecretSigned<<P::Paillier as PaillierParams>::Uint> { | ||
| SecretSigned::new_positive(secret_uint_from_scalar::<P>(value), ORDER.bits_vartime() as u32).expect(concat![ | ||
| "a curve scalar value is smaller than the curve order, ", | ||
| "and the curve order fits in `PaillierParams::Uint`" | ||
| ]) | ||
| } | ||
|
|
||
| /// Converts a [`SecretSigned`] to a secret-wrapped [`Scalar`]. | ||
| pub(crate) fn secret_scalar_from_signed<P: SchemeParams>( | ||
| value: &SecretSigned<<P::Paillier as PaillierParams>::Uint>, | ||
| ) -> Secret<Scalar> { | ||
| let abs_value = secret_scalar_from_uint::<P>(&value.abs_value()); | ||
| Secret::<Scalar>::conditional_select(&abs_value, &-&abs_value, value.is_negative()) | ||
| } |
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