feat: Add user scoped git ssh keys (#834)

coderd/gitsshkey/ed25519.go

@@ -0,0 +1,125 @@
+// This file contains an adapted version of the original implementation available
+// under the following URL: https://github.com/mikesmitty/edkey/blob/3356ea4e686a1d47ae5d2d4c3cbc1832ce2df626/edkey.go
+
+// The following changes have been made:
+// * Replaced usage of math/rand with crypto/rand
+
+// This should be removed soon as support for marshaling ED25519 private keys
+// is added to the Golang standard library.
+// See: https://github.com/golang/go/issues/37132
+
+// --- BEGIN ORIGINAL LICENSE ---
+// MIT License
+
+// Copyright (c) 2017 Michael Smith
+
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+// --- END ORIGINAL LICENSE ---
+
+package gitsshkey
+
+import (
+	"crypto/rand"
+	"encoding/binary"
+
+	"golang.org/x/crypto/ed25519"
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/xerrors"
+)
+
+func MarshalED25519PrivateKey(key ed25519.PrivateKey) ([]byte, error) {
+	// Add our key header (followed by a null byte)
+	magic := append([]byte("openssh-key-v1"), 0)
+
+	var msg struct {
+		CipherName   string
+		KdfName      string
+		KdfOpts      string
+		NumKeys      uint32
+		PubKey       []byte
+		PrivKeyBlock []byte
+	}
+
+	// Fill out the private key fields
+	pk1 := struct {
+		Check1  uint32
+		Check2  uint32
+		Keytype string
+		Pub     []byte
+		Priv    []byte
+		Comment string
+		Pad     []byte `ssh:"rest"`
+	}{}
+
+	// Random check bytes
+	var check uint32
+	if err := binary.Read(rand.Reader, binary.BigEndian, &check); err != nil {
+		return nil, xerrors.Errorf("generate random bytes: %w", err)
+	}
+
+	pk1.Check1 = check
+	pk1.Check2 = check
+
+	// Set our key type
+	pk1.Keytype = ssh.KeyAlgoED25519
+
+	// Add the pubkey to the optionally-encrypted block
+	pk, ok := key.Public().(ed25519.PublicKey)
+	if !ok {
+		return nil, xerrors.Errorf("ed25519.PublicKey type assertion failed on an ed25519 public key")
+	}
+	pubKey := []byte(pk)
+	pk1.Pub = pubKey
+
+	// Add our private key
+	pk1.Priv = []byte(key)
+
+	// Might be useful to put something in here at some point
+	pk1.Comment = ""
+
+	// Add some padding to match the encryption block size within PrivKeyBlock (without Pad field)
+	// 8 doesn't match the documentation, but that's what ssh-keygen uses for unencrypted keys. *shrug*
+	bs := 8
+	blockLen := len(ssh.Marshal(pk1))
+	padLen := (bs - (blockLen % bs)) % bs
+	pk1.Pad = make([]byte, padLen)
+
+	// Padding is a sequence of bytes like: 1, 2, 3...
+	for i := 0; i < padLen; i++ {
+		pk1.Pad[i] = byte(i + 1)
+	}
+
+	// Generate the pubkey prefix "\0\0\0\nssh-ed25519\0\0\0 "
+	prefix := []byte{0x0, 0x0, 0x0, 0x0b}
+	prefix = append(prefix, []byte(ssh.KeyAlgoED25519)...)
+	prefix = append(prefix, []byte{0x0, 0x0, 0x0, 0x20}...)
+	prefix = append(prefix, pubKey...)
+
+	// Only going to support unencrypted keys for now
+	msg.CipherName = "none"
+	msg.KdfName = "none"
+	msg.KdfOpts = ""
+	msg.NumKeys = 1
+	msg.PubKey = prefix
+	msg.PrivKeyBlock = ssh.Marshal(pk1)
+
+	magic = append(magic, ssh.Marshal(msg)...)
+
+	return magic, nil
+}