Trim the leading zero from PuTTY ECDSA private keys (#1827)

Fixes #1825

Author: darinkes

src/Renci.SshNet/PrivateKeyFile.PuTTY.cs

@@ -175,7 +175,7 @@ public Key Parse()
                         var curve = publicKeyReader.ReadString(Encoding.ASCII);
                         var pub = publicKeyReader.ReadBinary();
                         var prv = privateKeyReader.ReadBinary();
-                        parsedKey = new EcdsaKey(curve, pub, prv);
+                        parsedKey = new EcdsaKey(curve, pub, prv.TrimLeadingZeros());
                         break;
                     case "ssh-rsa":
                         var exponent = publicKeyReader.ReadBigInt();

test/Data/Key.PuTTY3.ECDSA.LeadingZero.ppk

@@ -0,0 +1,10 @@
+PuTTY-User-Key-File-3: ecdsa-sha2-nistp256
+Encryption: none
+Comment: imported-openssh-key
+Public-Lines: 3
+AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBNhE4rS0CTev
+/VEC6BJ/142eE3dU88t1rpzrSJ3iEcyp+3itM0+182eXSswmunZo/TNyvFE1sXKK
+1x0COQJl6hU=
+Private-Lines: 1
+AAAAIQDTj7+GAKceovRR6/NV8TFi+Mc5cHl555sVVokgFkofYA==
+Private-MAC: 71bc2b8cbe9f209ff693afb9b217f060f5dc4d4ae73e136e28fa1034b0fdd982

test/Renci.SshNet.Tests/Classes/PrivateKeyFileTest.cs

@@ -346,6 +346,7 @@ public void ConstructorWithFileNameAndPassPhraseShouldBeAbleToReadFileThatIsShar
         [DataRow("Key.PuTTY2.RSA.Encrypted.12345.ppk", "12345", typeof(RsaKey))]
         [DataRow("Key.PuTTY2.RSA.ppk", null, typeof(RsaKey))]
         [DataRow("Key.PuTTY3.ECDSA.Encrypted.Argon2id.12345.ppk", "12345", typeof(EcdsaKey))]
+        [DataRow("Key.PuTTY3.ECDSA.LeadingZero.ppk", null, typeof(EcdsaKey))]
         [DataRow("Key.PuTTY3.ECDSA.ppk", null, typeof(EcdsaKey))]
         [DataRow("Key.PuTTY3.Ed25519.Encrypted.Argon2i.12345.ppk", "12345", typeof(ED25519Key))]
         [DataRow("Key.PuTTY3.Ed25519.Encrypted.Argon2d.12345.ppk", "12345", typeof(ED25519Key))]