puppeth: handle encrypted ssh keys (closes #15442) (#15443)

* cmd/puppeth: handle encrypted ssh keys

* cmd/puppeth: fix unconvert linter error

vendor/golang.org/x/crypto/curve25519/doc.go

@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // Package curve25519 provides an implementation of scalar multiplication on
-// the elliptic curve known as curve25519. See http://cr.yp.to/ecdh.html
+// the elliptic curve known as curve25519. See https://cr.yp.to/ecdh.html
 package curve25519 // import "golang.org/x/crypto/curve25519"
 
 // basePoint is the x coordinate of the generator of the curve.