Implement Lizard encoding/decoding (#826)

* Vendor lizard hash to curve from Signal

* Add invalid Lizard encoding test

* Added lizard details to readme and changelog

* Upgrade ristretto.sage to Python3

* Add lizard test vector generation to ristretto.sage

* Added map_to_curve and its inverse

* Use CtOption instead of bitmasks; other cleanup

* Add README to lizard folder

* Split map_to_curve into map_to_curve and map_to_curve_restricted; make its inverse return 16 elements

* Consolidate Ristretto Elligator functions into its own file

Author: rozbb

curve25519-dalek/ACKNOWLEDGEMENTS.md

@@ -0,0 +1,63 @@
+# Go ed25519
+
+Portions of curve25519-dalek were originally derived from Adam Langley's
+Go ed25519 implementation, found at <https://github.com/agl/ed25519/>,
+under the following licence:
+
+```
+Copyright (c) 2012 The Go Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+   * Neither the name of Google Inc. nor the names of its
+contributors may be used to endorse or promote products derived from
+this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
+OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+```
+
+# Lizard
+
+The `src/lizard` directory was copied from [Signal's curve25519-dalek repo]( https://github.com/signalapp/curve25519-dalek/tree/7c6d34756355a3566a704da84dce7b1c039a6572). Its license is copied below
+
+```
+MIT License
+
+Copyright (c) 2019 Bas Westerbaan
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+```

curve25519-dalek/CHANGELOG.md

@@ -5,6 +5,10 @@ major series.
 
 ## 5.x series
 
+## Unreleased
+
+* Add Lizard bytes-to-point injection for Ristretto. Gated under `lizard`.
+
 ## 5.0.0-pre.1
 
 * Rename `Scalar::batch_invert` -> `Scalar::invert_batch` for consistency. Also make it no-alloc.

curve25519-dalek/Cargo.toml

@@ -83,6 +83,7 @@ legacy_compatibility = []
 group = ["dep:group", "rand_core"]
 group-bits = ["group", "ff/bits"]
 digest = ["dep:digest"]
+lizard = ["digest"]
 
 [target.'cfg(all(not(curve25519_dalek_backend = "fiat"), not(curve25519_dalek_backend = "serial"), target_arch = "x86_64"))'.dependencies]
 curve25519-dalek-derive = "0.1"

curve25519-dalek/LICENSE

@@ -26,40 +26,4 @@ TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
-
-========================================================================
-
-Portions of curve25519-dalek were originally derived from Adam Langley's
-Go ed25519 implementation, found at <https://github.com/agl/ed25519/>,
-under the following licence:
-
-========================================================================
-
-Copyright (c) 2012 The Go Authors. All rights reserved.
-
-Redistribution and use in source and binary forms, with or without
-modification, are permitted provided that the following conditions are
-met:
-
-   * Redistributions of source code must retain the above copyright
-notice, this list of conditions and the following disclaimer.
-   * Redistributions in binary form must reproduce the above
-copyright notice, this list of conditions and the following disclaimer
-in the documentation and/or other materials provided with the
-distribution.
-   * Neither the name of Google Inc. nor the names of its
-contributors may be used to endorse or promote products derived from
-this software without specific prior written permission.
-
-THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
-IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
-TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
-PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
-OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
-EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
-PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
-PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
-LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
-NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

curve25519-dalek/README.md

@@ -57,6 +57,7 @@ curve25519-dalek = ">= 5.0, < 5.2"
 | `legacy_compatibility`|       | Enables `Scalar::from_bits`, which allows the user to build unreduced scalars whose arithmetic is broken. Do not use this unless you know what you're doing. |
 | `group`            |          | Enables external `group` and `ff` crate traits. |
 | `group-bits`       |          | Enables `group` and impls `ff::PrimeFieldBits` for `Scalar`.  |
+| `lizard`           |          | Enables the [Lizard](src/lizard/README.md) bytestring-to-point injection for `RistrettoPoint`. Specifically enables the methods `lizard_encode` and `lizard_decode`. |
 
 To disable the default features when using `curve25519-dalek` as a dependency,
 add `default-features = false` to the dependency in your `Cargo.toml`. To

curve25519-dalek/build.rs

@@ -17,7 +17,7 @@ impl std::fmt::Display for DalekBits {
             DalekBits::Dalek32 => "32",
             DalekBits::Dalek64 => "64",
         };
-        write!(f, "{}", w_bits)
+        write!(f, "{w_bits}")
     }
 }
 

curve25519-dalek/src/field.rs

@@ -98,6 +98,12 @@ impl ConstantTimeEq for FieldElement {
     }
 }
 
+impl Default for FieldElement {
+    fn default() -> Self {
+        FieldElement::ZERO
+    }
+}
+
 impl FieldElement {
     /// Load a `FieldElement` from 64 bytes, by reducing modulo q.
     #[cfg(feature = "digest")]

curve25519-dalek/src/lib.rs

@@ -90,6 +90,9 @@ pub(crate) mod backend;
 // Generic code for window lookups
 pub(crate) mod window;
 
+#[cfg(feature = "lizard")]
+pub mod lizard;
+
 pub use crate::{
     edwards::EdwardsPoint, montgomery::MontgomeryPoint, ristretto::RistrettoPoint, scalar::Scalar,
 };