x/crypto/ssh: please provide unified parameter types for ed25519.PrivateKey

[dacapoday]

Hi,
When I want to use go to do some format cleaning for PEM file found that ssh.ParseRawPrivateKey and x509.MarshalPKCS8PrivateKey have different data type for ed25519.PrivateKey.
ssh.ParseRawPrivateKey actually output a Pointer, x509.MarshalPKCS8PrivateKey only receiver Value.
But other algorithms are both pointers. So I had to do type assertion for ed25519.PrivateKey.

example code:

package main

import (
	"crypto/ed25519"
	"crypto/x509"
	"encoding/base64"
	"encoding/pem"
	"fmt"

	"golang.org/x/crypto/ssh"
)

var pemfile []byte

func main() {
	prikey, err := ssh.ParseRawPrivateKey(pemfile)
	if err != nil {
		panic(err)
	}

	// workaround for golang.org/x/crypto/ssh/ed25519
	ed25519key, ok := prikey.(*ed25519.PrivateKey)
	if ok {
		prikey = *ed25519key
	}

	prikeycontent, err := x509.MarshalPKCS8PrivateKey(prikey)
	if err != nil {
		panic(err)
	}
	block := &pem.Block{
		Type:  "PRIVATE KEY",
		Bytes: prikeycontent,
	}
	prikeypem := pem.EncodeToMemory(block)
	fmt.Printf("prikey: \n%s\n", prikeypem)
}

func init() {
	var err error
	pemfile, err = base64.StdEncoding.DecodeString(samplePem)
	if err != nil {
		panic(err)
	}
}

var samplePem = `LS0tLS1CRUdJTiBPUEVOU1NIIFBSSVZBVEUgS0VZLS0tLS0KYjNCbGJuTnphQzFyWlhrdGRqRUFBQUFBQkc1dmJtVUFBQUFFYm05dVpRQUFBQUFBQUFBQkFBQUFNd0FBQUF0emMyZ3RaVwpReU5UVXhPUUFBQUNDc1pUcEpXZ0ljajFqcFR0OVJHQ2ovUktCTlJZSTFiWmZDZFJXNCtmNmJ2UUFBQUlqWExVaTYxeTFJCnVnQUFBQXR6YzJndFpXUXlOVFV4T1FBQUFDQ3NaVHBKV2dJY2oxanBUdDlSR0NqL1JLQk5SWUkxYlpmQ2RSVzQrZjZidlEKQUFBRUNPUm12SUdjaDVWMzRqSUpWSGFiU3FQbGl3RGJsL3diamNtNVpmeWZhRjdxeGxPa2xhQWh5UFdPbE8zMUVZS1A5RQpvRTFGZ2pWdGw4SjFGYmo1L3B1OUFBQUFBbmg0QVFJRAotLS0tLUVORCBPUEVOU1NIIFBSSVZBVEUgS0VZLS0tLS0K`

I think it's not necessary. Perhaps we can make x509.MarshalPKCS8PrivateKey receiver ed25519.PrivateKey Pointer and Value at same time or make ssh.ParseRawPrivateKey output Value because ed25519.PrivateKey underlying type is []byte.

[1999chato]

Chido

[1999chato]

Va

[seankhliao]

cc @golang/security

[FiloSottile]

It's even a little worse than this: ParseRawPrivateKey returns a value for PKCS8 encodings (because it calls x509.ParsePKCS8PrivateKey) and a pointer for the OpenSSH encoding.

The correct type is definitely the value type, which is what everything else expects, but it might be too late to change ParseRawPrivateKey, since most if not all Ed25519 keys are encoded in the OpenSSH encoding, so applications are probably expecting pointers there.

[FiloSottile]

It goes all the way back to 2016, so applications have surely come to rely on it: https://go-review.googlesource.com/22512

See also golang/crypto#119.

[gopherbot]

Change https://go.dev/cl/614278 mentions this issue: design/68723-crypto-ssh-v2.md: crypto.Signer returns ed25519 keys as value