feat(identity): allow importing and exporting ECDSA keys

identity/Cargo.toml

@@ -19,7 +19,7 @@ libsecp256k1 = { version = "0.7.0", optional = true }
 log = "0.4"
 multiaddr = { version = "0.17.1", optional = true }
 multihash = { version = "0.17.0", default-features = false, features = ["std"], optional = true }
-p256 = { version = "0.12", default-features = false, features = ["ecdsa", "std"], optional = true }
+p256 = { version = "0.12", default-features = false, features = ["ecdsa", "std", "pem"], optional = true }
 quick-protobuf = { version = "0.8.1", optional = true }
 rand = { version = "0.8", optional = true }
 sec1 = { version = "0.3.0", features = ["std"], optional = true } # Activate `std` feature until https://github.com/RustCrypto/traits/pull/1131 is released.

identity/src/ecdsa.rs

@@ -24,6 +24,7 @@ use super::error::DecodingError;
 use core::cmp;
 use core::fmt;
 use core::hash;
+use p256::pkcs8::EncodePrivateKey;
 use p256::{
     ecdsa::{
         signature::{Signer, Verifier},
@@ -122,6 +123,23 @@ impl SecretKey {
             .map_err(|err| DecodingError::failed_to_parse("ecdsa p256 secret key", err))
             .map(SecretKey)
     }
+
+    /// Encode the secret key into DER-encoded PKCS#8 format.
+    pub fn encode_pkcs8_der(&self) -> Vec<u8> {
+        self.0
+            .to_pkcs8_der()
+            .expect("Encoding to pkcs#8 format to succeed")
+            .to_bytes()
+            .to_vec()
+    }
+
+    // Cannot implement this because error type does not implement `std::error::Error`
+    // pub fn try_decode_pkcs8_der(buf:&[u8])->Result<Self,DecodingError>{
+    //     match SigningKey::from_pkcs8_der(buf){
+    //         Ok(key) => Ok(SecretKey(key)),
+    //         Err(e) => Err(DecodingError::failed_to_parse("ECDSA", e)),
+    //     }
+    // }
 }
 
 impl fmt::Debug for SecretKey {