From 0ed928c3e1ce027c160aef1c1296fd8f693d94a9 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Fri, 29 Mar 2019 12:19:19 -0700
Subject: [PATCH 1/4] Digestable signatures: signature::digest::Signature

Adds a marker trait for `Signature` types computable as `S(H(m))` where:

- `S`: signature algorithm
- `H`: hash (a.k.a. digest) function
- `m`: message

For signature types that implement this trait, a blanket impl of
`Signer` will be provided for all types that
`impl signature::digest::Signer`.
---
 signature-crate/src/digest/mod.rs       |  3 ++-
 signature-crate/src/digest/signature.rs | 13 +++++++++++++
 signature-crate/src/digest/signer.rs    | 12 +++++++++++-
 signature-crate/src/digest/verifier.rs  | 12 +++++++++++-
 4 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 signature-crate/src/digest/signature.rs

diff --git a/signature-crate/src/digest/mod.rs b/signature-crate/src/digest/mod.rs
index 406623be..ab0eb08e 100644
--- a/signature-crate/src/digest/mod.rs
+++ b/signature-crate/src/digest/mod.rs
@@ -1,6 +1,7 @@
 //! Support for using hash functions that impl the `Digest` trait in order
 //! to hash the input message in order to compute a signature.
 
+mod signature;
 mod signer;
 mod verifier;
 
@@ -8,4 +9,4 @@ mod verifier;
 /// trait this module depends on.
 pub use ::digest::Digest;
 
-pub use self::{signer::Signer, verifier::Verifier};
+pub use self::{signature::Signature, signer::Signer, verifier::Verifier};
diff --git a/signature-crate/src/digest/signature.rs b/signature-crate/src/digest/signature.rs
new file mode 100644
index 00000000..a54c7cc8
--- /dev/null
+++ b/signature-crate/src/digest/signature.rs
@@ -0,0 +1,13 @@
+use super::Digest;
+
+/// Marker trait for `Signature` types computable as `S(H(m))` where:
+///
+/// - `S`: signature algorithm
+/// - `H`: hash (a.k.a. digest) function
+/// - `m`: message
+///
+/// For signature types that implement this trait, a blanket impl of
+/// `Signer` will be provided for all types that `impl digest::Signer`.
+pub trait Signature: crate::signature::Signature {
+    type Digest: Digest;
+}
diff --git a/signature-crate/src/digest/signer.rs b/signature-crate/src/digest/signer.rs
index 008493f9..325c2887 100644
--- a/signature-crate/src/digest/signer.rs
+++ b/signature-crate/src/digest/signer.rs
@@ -13,5 +13,15 @@ where
     S: Signature,
 {
     /// Sign the given prehashed message `Digest`, returning a signature.
-    fn sign(&self, digest: D) -> Result<S, Error>;
+    fn sign_digest(&self, digest: D) -> Result<S, Error>;
+}
+
+impl<S, T> crate::Signer<S> for T
+where
+    S: crate::digest::Signature,
+    T: Signer<S::Digest, S>,
+{
+    fn sign(&self, msg: &[u8]) -> Result<S, Error> {
+        self.sign_digest(S::Digest::new().chain(msg))
+    }
 }
diff --git a/signature-crate/src/digest/verifier.rs b/signature-crate/src/digest/verifier.rs
index 865b422b..28dcca5f 100644
--- a/signature-crate/src/digest/verifier.rs
+++ b/signature-crate/src/digest/verifier.rs
@@ -14,5 +14,15 @@ where
     S: Signature,
 {
     /// Verify the signature against the given `Digest`
-    fn verify(&self, digest: D, signature: &S) -> Result<(), Error>;
+    fn verify_digest(&self, digest: D, signature: &S) -> Result<(), Error>;
+}
+
+impl<S, T> crate::Verifier<S> for T
+where
+    S: crate::digest::Signature,
+    T: Verifier<S::Digest, S>,
+{
+    fn verify(&self, msg: &[u8], signature: &S) -> Result<(), Error> {
+        self.verify_digest(S::Digest::new().chain(msg), signature)
+    }
 }

From 5082a5139fb286f2b7fe097d05ea285faa05ce51 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Fri, 29 Mar 2019 12:32:17 -0700
Subject: [PATCH 2/4] Rename digest::Signature to 'Digestable'

Re-exported as `signature::Digestable`, and acts as a marker trait for
cases where signatures can be computed using `Digest`.
---
 signature-crate/src/digest/{signature.rs => digestable.rs} | 5 +++--
 signature-crate/src/digest/mod.rs                          | 4 ++--
 signature-crate/src/digest/signer.rs                       | 7 ++++---
 signature-crate/src/digest/verifier.rs                     | 7 ++++---
 signature-crate/src/lib.rs                                 | 3 +++
 5 files changed, 16 insertions(+), 10 deletions(-)
 rename signature-crate/src/digest/{signature.rs => digestable.rs} (67%)

diff --git a/signature-crate/src/digest/signature.rs b/signature-crate/src/digest/digestable.rs
similarity index 67%
rename from signature-crate/src/digest/signature.rs
rename to signature-crate/src/digest/digestable.rs
index a54c7cc8..02f852fc 100644
--- a/signature-crate/src/digest/signature.rs
+++ b/signature-crate/src/digest/digestable.rs
@@ -1,4 +1,4 @@
-use super::Digest;
+use crate::{digest::Digest, signature::Signature};
 
 /// Marker trait for `Signature` types computable as `S(H(m))` where:
 ///
@@ -8,6 +8,7 @@ use super::Digest;
 ///
 /// For signature types that implement this trait, a blanket impl of
 /// `Signer` will be provided for all types that `impl digest::Signer`.
-pub trait Signature: crate::signature::Signature {
+pub trait Digestable: Signature {
+    /// Preferred `Digest` algorithm to use when computing this signature type.
     type Digest: Digest;
 }
diff --git a/signature-crate/src/digest/mod.rs b/signature-crate/src/digest/mod.rs
index ab0eb08e..3973d610 100644
--- a/signature-crate/src/digest/mod.rs
+++ b/signature-crate/src/digest/mod.rs
@@ -1,7 +1,7 @@
 //! Support for using hash functions that impl the `Digest` trait in order
 //! to hash the input message in order to compute a signature.
 
-mod signature;
+mod digestable;
 mod signer;
 mod verifier;
 
@@ -9,4 +9,4 @@ mod verifier;
 /// trait this module depends on.
 pub use ::digest::Digest;
 
-pub use self::{signature::Signature, signer::Signer, verifier::Verifier};
+pub use self::{digestable::Digestable, signer::Signer, verifier::Verifier};
diff --git a/signature-crate/src/digest/signer.rs b/signature-crate/src/digest/signer.rs
index 325c2887..d67e3763 100644
--- a/signature-crate/src/digest/signer.rs
+++ b/signature-crate/src/digest/signer.rs
@@ -4,7 +4,8 @@
 //! For use signature algorithms that support an Initialize-Update-Finalize
 //! (IUF) API, such as ECDSA or Ed25519ph.
 
-use crate::{digest::Digest, error::Error, Signature};
+use super::{Digest, Digestable};
+use crate::{error::Error, signature::Signature};
 
 /// Sign the given prehashed message `Digest` using `Self`.
 pub trait Signer<D, S>
@@ -16,9 +17,9 @@ where
     fn sign_digest(&self, digest: D) -> Result<S, Error>;
 }
 
-impl<S, T> crate::Signer<S> for T
+impl<S, T> crate::signer::Signer<S> for T
 where
-    S: crate::digest::Signature,
+    S: Digestable + Signature,
     T: Signer<S::Digest, S>,
 {
     fn sign(&self, msg: &[u8]) -> Result<S, Error> {
diff --git a/signature-crate/src/digest/verifier.rs b/signature-crate/src/digest/verifier.rs
index 28dcca5f..73804c9e 100644
--- a/signature-crate/src/digest/verifier.rs
+++ b/signature-crate/src/digest/verifier.rs
@@ -4,7 +4,8 @@
 //! For use signature algorithms that support an Initialize-Update-Finalize
 //! (IUF) API, such as ECDSA or Ed25519ph.
 
-use crate::{digest::Digest, error::Error, Signature};
+use super::{Digest, Digestable};
+use crate::{error::Error, signature::Signature};
 
 /// Verify the provided signature for the given prehashed message `Digest`
 /// is authentic.
@@ -17,9 +18,9 @@ where
     fn verify_digest(&self, digest: D, signature: &S) -> Result<(), Error>;
 }
 
-impl<S, T> crate::Verifier<S> for T
+impl<S, T> crate::verifier::Verifier<S> for T
 where
-    S: crate::digest::Signature,
+    S: Digestable + Signature,
     T: Verifier<S::Digest, S>,
 {
     fn verify(&self, msg: &[u8], signature: &S) -> Result<(), Error> {
diff --git a/signature-crate/src/lib.rs b/signature-crate/src/lib.rs
index 03c3e8e6..05f1802e 100644
--- a/signature-crate/src/lib.rs
+++ b/signature-crate/src/lib.rs
@@ -27,3 +27,6 @@ pub mod signer;
 pub mod verifier;
 
 pub use crate::{error::Error, signature::Signature, signer::Signer, verifier::Verifier};
+
+#[cfg(feature = "digest")]
+pub use crate::digest::Digestable;

From a1b59a16b42d9dad64ab87e6f081b9456ea7cd68 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Fri, 29 Mar 2019 12:44:44 -0700
Subject: [PATCH 3/4] Move blanket impls into 'digestable' module

The `Digestable` trait is used to constrain blanket impls of `Signer`
and `Verifier` for `digest::Signer` and `digest::Verifier` respectively.

Since that's what it's used for, it makes sense to put the blanket impls
in the same module.
---
 signature-crate/src/digest/digestable.rs | 28 +++++++++++++++++++++++-
 signature-crate/src/digest/signer.rs     | 12 +---------
 signature-crate/src/digest/verifier.rs   | 12 +---------
 3 files changed, 29 insertions(+), 23 deletions(-)

diff --git a/signature-crate/src/digest/digestable.rs b/signature-crate/src/digest/digestable.rs
index 02f852fc..2fbed70d 100644
--- a/signature-crate/src/digest/digestable.rs
+++ b/signature-crate/src/digest/digestable.rs
@@ -1,4 +1,10 @@
-use crate::{digest::Digest, signature::Signature};
+use crate::{
+    digest::{self, Digest},
+    error::Error,
+    signature::Signature,
+    signer::Signer,
+    verifier::Verifier,
+};
 
 /// Marker trait for `Signature` types computable as `S(H(m))` where:
 ///
@@ -12,3 +18,23 @@ pub trait Digestable: Signature {
     /// Preferred `Digest` algorithm to use when computing this signature type.
     type Digest: Digest;
 }
+
+impl<S, T> Signer<S> for T
+where
+    S: Digestable + Signature,
+    T: digest::Signer<S::Digest, S>,
+{
+    fn sign(&self, msg: &[u8]) -> Result<S, Error> {
+        self.sign_digest(S::Digest::new().chain(msg))
+    }
+}
+
+impl<S, T> Verifier<S> for T
+where
+    S: Digestable + Signature,
+    T: digest::Verifier<S::Digest, S>,
+{
+    fn verify(&self, msg: &[u8], signature: &S) -> Result<(), Error> {
+        self.verify_digest(S::Digest::new().chain(msg), signature)
+    }
+}
diff --git a/signature-crate/src/digest/signer.rs b/signature-crate/src/digest/signer.rs
index d67e3763..0f915b4f 100644
--- a/signature-crate/src/digest/signer.rs
+++ b/signature-crate/src/digest/signer.rs
@@ -4,7 +4,7 @@
 //! For use signature algorithms that support an Initialize-Update-Finalize
 //! (IUF) API, such as ECDSA or Ed25519ph.
 
-use super::{Digest, Digestable};
+use super::Digest;
 use crate::{error::Error, signature::Signature};
 
 /// Sign the given prehashed message `Digest` using `Self`.
@@ -16,13 +16,3 @@ where
     /// Sign the given prehashed message `Digest`, returning a signature.
     fn sign_digest(&self, digest: D) -> Result<S, Error>;
 }
-
-impl<S, T> crate::signer::Signer<S> for T
-where
-    S: Digestable + Signature,
-    T: Signer<S::Digest, S>,
-{
-    fn sign(&self, msg: &[u8]) -> Result<S, Error> {
-        self.sign_digest(S::Digest::new().chain(msg))
-    }
-}
diff --git a/signature-crate/src/digest/verifier.rs b/signature-crate/src/digest/verifier.rs
index 73804c9e..32c00118 100644
--- a/signature-crate/src/digest/verifier.rs
+++ b/signature-crate/src/digest/verifier.rs
@@ -4,7 +4,7 @@
 //! For use signature algorithms that support an Initialize-Update-Finalize
 //! (IUF) API, such as ECDSA or Ed25519ph.
 
-use super::{Digest, Digestable};
+use super::Digest;
 use crate::{error::Error, signature::Signature};
 
 /// Verify the provided signature for the given prehashed message `Digest`
@@ -17,13 +17,3 @@ where
     /// Verify the signature against the given `Digest`
     fn verify_digest(&self, digest: D, signature: &S) -> Result<(), Error>;
 }
-
-impl<S, T> crate::verifier::Verifier<S> for T
-where
-    S: Digestable + Signature,
-    T: Verifier<S::Digest, S>,
-{
-    fn verify(&self, msg: &[u8], signature: &S) -> Result<(), Error> {
-        self.verify_digest(S::Digest::new().chain(msg), signature)
-    }
-}

From 564a42c5a549b5557284f8a94e2dfa196fd14034 Mon Sep 17 00:00:00 2001
From: Tony Arcieri <bascule@gmail.com>
Date: Mon, 1 Apr 2019 07:01:34 -0700
Subject: [PATCH 4/4] Have digest Signer/Verifier take digest output as an
 argument

---
 signature-crate/src/digest/digestable.rs | 4 ++--
 signature-crate/src/digest/signer.rs     | 3 ++-
 signature-crate/src/digest/verifier.rs   | 7 ++++++-
 signature-crate/src/lib.rs               | 6 +++---
 4 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/signature-crate/src/digest/digestable.rs b/signature-crate/src/digest/digestable.rs
index 2fbed70d..0eff397e 100644
--- a/signature-crate/src/digest/digestable.rs
+++ b/signature-crate/src/digest/digestable.rs
@@ -25,7 +25,7 @@ where
     T: digest::Signer<S::Digest, S>,
 {
     fn sign(&self, msg: &[u8]) -> Result<S, Error> {
-        self.sign_digest(S::Digest::new().chain(msg))
+        self.sign_digest(S::Digest::digest(msg))
     }
 }
 
@@ -35,6 +35,6 @@ where
     T: digest::Verifier<S::Digest, S>,
 {
     fn verify(&self, msg: &[u8], signature: &S) -> Result<(), Error> {
-        self.verify_digest(S::Digest::new().chain(msg), signature)
+        self.verify_digest(S::Digest::digest(msg), signature)
     }
 }
diff --git a/signature-crate/src/digest/signer.rs b/signature-crate/src/digest/signer.rs
index 0f915b4f..65043b0a 100644
--- a/signature-crate/src/digest/signer.rs
+++ b/signature-crate/src/digest/signer.rs
@@ -6,6 +6,7 @@
 
 use super::Digest;
 use crate::{error::Error, signature::Signature};
+use digest::generic_array::GenericArray;
 
 /// Sign the given prehashed message `Digest` using `Self`.
 pub trait Signer<D, S>
@@ -14,5 +15,5 @@ where
     S: Signature,
 {
     /// Sign the given prehashed message `Digest`, returning a signature.
-    fn sign_digest(&self, digest: D) -> Result<S, Error>;
+    fn sign_digest(&self, digest: GenericArray<u8, D::OutputSize>) -> Result<S, Error>;
 }
diff --git a/signature-crate/src/digest/verifier.rs b/signature-crate/src/digest/verifier.rs
index 32c00118..72d5f017 100644
--- a/signature-crate/src/digest/verifier.rs
+++ b/signature-crate/src/digest/verifier.rs
@@ -6,6 +6,7 @@
 
 use super::Digest;
 use crate::{error::Error, signature::Signature};
+use digest::generic_array::GenericArray;
 
 /// Verify the provided signature for the given prehashed message `Digest`
 /// is authentic.
@@ -15,5 +16,9 @@ where
     S: Signature,
 {
     /// Verify the signature against the given `Digest`
-    fn verify_digest(&self, digest: D, signature: &S) -> Result<(), Error>;
+    fn verify_digest(
+        &self,
+        digest: GenericArray<u8, D::OutputSize>,
+        signature: &S,
+    ) -> Result<(), Error>;
 }
diff --git a/signature-crate/src/lib.rs b/signature-crate/src/lib.rs
index 05f1802e..688258fd 100644
--- a/signature-crate/src/lib.rs
+++ b/signature-crate/src/lib.rs
@@ -19,12 +19,12 @@
 extern crate std;
 
 #[cfg(feature = "digest")]
-mod digest;
+pub mod digest;
 mod error;
 mod prelude;
 mod signature;
-pub mod signer;
-pub mod verifier;
+mod signer;
+mod verifier;
 
 pub use crate::{error::Error, signature::Signature, signer::Signer, verifier::Verifier};