core/: Introduce rsa feature flag to avoid ring dependency (#2860)

- Introduce `rsa` feature flag to `libp2p-core`.
- Expose `rsa` feature in `libp2p`.
- Add `rsa` feature to `libp2p` `default`.

core/src/identity.rs

@@ -35,7 +35,7 @@
 #[cfg(feature = "ecdsa")]
 pub mod ecdsa;
 pub mod ed25519;
-#[cfg(not(target_arch = "wasm32"))]
+#[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
 pub mod rsa;
 #[cfg(feature = "secp256k1")]
 pub mod secp256k1;
@@ -68,8 +68,8 @@ use std::convert::{TryFrom, TryInto};
 pub enum Keypair {
     /// An Ed25519 keypair.
     Ed25519(ed25519::Keypair),
-    #[cfg(not(target_arch = "wasm32"))]
     /// An RSA keypair.
+    #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
     Rsa(rsa::Keypair),
     /// A Secp256k1 keypair.
     #[cfg(feature = "secp256k1")]
@@ -101,7 +101,7 @@ impl Keypair {
     /// format (i.e. unencrypted) as defined in [RFC5208].
     ///
     /// [RFC5208]: https://tools.ietf.org/html/rfc5208#section-5
-    #[cfg(not(target_arch = "wasm32"))]
+    #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
     pub fn rsa_from_pkcs8(pkcs8_der: &mut [u8]) -> Result<Keypair, DecodingError> {
         rsa::Keypair::from_pkcs8(pkcs8_der).map(Keypair::Rsa)
     }
@@ -122,7 +122,7 @@ impl Keypair {
         use Keypair::*;
         match self {
             Ed25519(ref pair) => Ok(pair.sign(msg)),
-            #[cfg(not(target_arch = "wasm32"))]
+            #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
             Rsa(ref pair) => pair.sign(msg),
             #[cfg(feature = "secp256k1")]
             Secp256k1(ref pair) => pair.secret().sign(msg),
@@ -136,7 +136,7 @@ impl Keypair {
         use Keypair::*;
         match self {
             Ed25519(pair) => PublicKey::Ed25519(pair.public()),
-            #[cfg(not(target_arch = "wasm32"))]
+            #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
             Rsa(pair) => PublicKey::Rsa(pair.public()),
             #[cfg(feature = "secp256k1")]
             Secp256k1(pair) => PublicKey::Secp256k1(pair.public().clone()),
@@ -154,7 +154,7 @@ impl Keypair {
                 r#type: keys_proto::KeyType::Ed25519.into(),
                 data: data.encode().into(),
             },
-            #[cfg(not(target_arch = "wasm32"))]
+            #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
             Self::Rsa(_) => {
                 return Err(DecodingError::new(
                     "Encoding RSA key into Protobuf is unsupported",
@@ -218,7 +218,7 @@ impl zeroize::Zeroize for keys_proto::PrivateKey {
 pub enum PublicKey {
     /// A public Ed25519 key.
     Ed25519(ed25519::PublicKey),
-    #[cfg(not(target_arch = "wasm32"))]
+    #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
     /// A public RSA key.
     Rsa(rsa::PublicKey),
     #[cfg(feature = "secp256k1")]
@@ -239,7 +239,7 @@ impl PublicKey {
         use PublicKey::*;
         match self {
             Ed25519(pk) => pk.verify(msg, sig),
-            #[cfg(not(target_arch = "wasm32"))]
+            #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
             Rsa(pk) => pk.verify(msg, sig),
             #[cfg(feature = "secp256k1")]
             Secp256k1(pk) => pk.verify(msg, sig),
@@ -286,7 +286,7 @@ impl From<&PublicKey> for keys_proto::PublicKey {
                 r#type: keys_proto::KeyType::Ed25519 as i32,
                 data: key.encode().to_vec(),
             },
-            #[cfg(not(target_arch = "wasm32"))]
+            #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
             PublicKey::Rsa(key) => keys_proto::PublicKey {
                 r#type: keys_proto::KeyType::Rsa as i32,
                 data: key.encode_x509(),
@@ -316,11 +316,11 @@ impl TryFrom<keys_proto::PublicKey> for PublicKey {
             keys_proto::KeyType::Ed25519 => {
                 ed25519::PublicKey::decode(&pubkey.data).map(PublicKey::Ed25519)
             }
-            #[cfg(not(target_arch = "wasm32"))]
+            #[cfg(all(feature = "rsa", not(target_arch = "wasm32")))]
             keys_proto::KeyType::Rsa => {
                 rsa::PublicKey::decode_x509(&pubkey.data).map(PublicKey::Rsa)
             }
-            #[cfg(target_arch = "wasm32")]
+            #[cfg(any(not(feature = "rsa"), target_arch = "wasm32"))]
             keys_proto::KeyType::Rsa => {
                 log::debug!("support for RSA was disabled at compile-time");
                 Err(DecodingError::new("Unsupported"))

core/src/identity/error.rs

@@ -67,6 +67,7 @@ pub struct SigningError {
 
 /// An error during encoding of key material.
 impl SigningError {
+    #[cfg(any(feature = "secp256k1", feature = "rsa"))]
     pub(crate) fn new<S: ToString>(msg: S) -> Self {
         Self {
             msg: msg.to_string(),
@@ -74,6 +75,7 @@ impl SigningError {
         }
     }
 
+    #[cfg(feature = "rsa")]
     pub(crate) fn source(self, source: impl Error + Send + Sync + 'static) -> Self {
         Self {
             source: Some(Box::new(source)),