/*
   SSHSecure - a program to harden OpenSSH from defaults
   Copyright (C) 2020  Brent Saner

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

package main

import (
	"crypto"
	"crypto/aes"
	"crypto/cipher"
	"crypto/ed25519"
	"encoding/hex"
	"fmt"

	"github.com/dchest/bcrypt_pbkdf"
)

// ssh-keygen -f /tmp/tmp2xzvpjhn -q -o -t ed25519 -N test -a 100
// private
/* on-disk format
-----BEGIN OPENSSH PRIVATE KEY-----
b3BlbnNzaC1rZXktdjEAAAAACmFlczI1Ni1jdHIAAAAGYmNyeXB0AAAAGAAAABAZQzNZ6B
eWtpsLgQvGbcuMAAAAZAAAAAEAAAAzAAAAC3NzaC1lZDI1NTE5AAAAIFjgZ791hHftK4GY
uhnIN/1JdZqA17hIlNdKr+ljJ9bfAAAAoN0XZgxeA2SLXGZXqZi9TqeQHU7PERiJA9F0+p
2NtNP4Y1Rey8C1EnF5mhzy8AZs6YJsE+xnQUSI/+Kbmi6MACQALaPO7CgtKwnfbFHuxzrD
1EG83K08w2NE2txlQPqflQcFoVBIzcXNVFv+3A5DM7BBz0jLFi5CCwl2PEhMhcpElvV+LW
PGXBV9IVdOeHm/hesRfuWTHcUalrqar1CmLWo=
-----END OPENSSH PRIVATE KEY-----
*/
/* actual bytes (hex repr)
00000000: 6f 70 65 6e 73 73 68 2d 6b 65 79 2d 76 31 00 00  openssh-key-v1..
00000010: 00 00 0a 61 65 73 32 35 36 2d 63 74 72 00 00 00  ...aes256-ctr...
00000020: 06 62 63 72 79 70 74 00 00 00 18 00 00 00 10 19  .bcrypt.........
00000030: 43 33 59 e8 17 96 b6 9b 0b 81 0b c6 6d cb 8c 00  C3Y.........m...
00000040: 00 00 64 00 00 00 01 00 00 00 33 00 00 00 0b 73  ..d.......3....s
00000050: 73 68 2d 65 64 32 35 35 31 39 00 00 00 20 58 e0  sh-ed25519... X.
00000060: 67 bf 75 84 77 ed 2b 81 98 ba 19 c8 37 fd 49 75  g.u.w.+.....7.Iu
00000070: 9a 80 d7 b8 48 94 d7 4a af e9 63 27 d6 df 00 00  ....H..J..c'....
00000080: 00 a0 dd 17 66 0c 5e 03 64 8b 5c 66 57 a9 98 bd  ....f.^.d.\fW...
00000090: 4e a7 90 1d 4e cf 11 18 89 03 d1 74 fa 9d 8d b4  N...N......t....
000000a0: d3 f8 63 54 5e cb c0 b5 12 71 79 9a 1c f2 f0 06  ..cT^....qy.....
000000b0: 6c e9 82 6c 13 ec 67 41 44 88 ff e2 9b 9a 2e 8c  l..l..gAD.......
000000c0: 00 24 00 2d a3 ce ec 28 2d 2b 09 df 6c 51 ee c7  .$.-...(-+..lQ..
000000d0: 3a c3 d4 41 bc dc ad 3c c3 63 44 da dc 65 40 fa  :..A...<.cD..e@.
000000e0: 9f 95 07 05 a1 50 48 cd c5 cd 54 5b fe dc 0e 43  .....PH...T[...C
000000f0: 33 b0 41 cf 48 cb 16 2e 42 0b 09 76 3c 48 4c 85  3.A.H...B..v<HL.
00000100: ca 44 96 f5 7e 2d 63 c6 5c 15 7d 21 57 4e 78 79  .D..~-c.\.}!WNxy
00000110: bf 85 eb 11 7e e5 93 1d c5 1a 96 ba 9a af 50 a6  ....~.........P.
00000120: 2d 6a                                            -j
//
6f70656e7373682d6b65792d763100  authmagic
0000000a  10
6165733235362d637472  "aes256-ctr"
00000006  6
626372797074  "bcrypt"
00000018  24
00000010  16
19433359e81796b69b0b810bc66dcb8c  salt
00000064  100
00000001  1
00000033  51
0000000b  11
7373682d65643235353139  "ssh-ed25519"
00000020  32
58e067bf758477ed2b8198ba19c837fd49759a80d7b84894d74aafe96327d6df  pubkey
000000a0  160  length of encrypted private info
dd17660c5e03648b5c6657a998bd4ea7  16*10 bytes (160 bytes)
901d4ecf11188903d174fa9d8db4d3f8
63545ecbc0b51271799a1cf2f0066ce9
826c13ec67414488ffe29b9a2e8c0024
002da3ceec282d2b09df6c51eec73ac3
d441bcdcad3cc36344dadc6540fa9f95
0705a15048cdc5cd545bfedc0e4333b0
41cf48cb162e420b09763c484c85ca44
96f57e2d63c65c157d21574e7879bf85
eb117ee5931dc51a96ba9aaf50a62d6a
*/
// public
/* on-disk format
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFjgZ791hHftK4GYuhnIN/1JdZqA17hIlNdKr+ljJ9bf bts@dawid.r00t.space
*/
/* actual bytes (hex repr)
00000000: 00 00 00 0b 73 73 68 2d 65 64 32 35 35 31 39 00  ....ssh-ed25519.
00000010: 00 00 20 58 e0 67 bf 75 84 77 ed 2b 81 98 ba 19  .. X.g.u.w.+....
00000020: c8 37 fd 49 75 9a 80 d7 b8 48 94 d7 4a af e9 63  .7.Iu....H..J..c
00000030: 27 d6 df                                         '..
//
0000000b  11
7373682d65643235353139  "ssh-ed25519"
00000020  32
58e067bf758477ed2b8198ba19c837fd49759a80d7b84894d74aafe96327d6df
*/

func main() {
	const (
		passphrase string = "test"
		rounds     int    = 100
		keySize    int    = 32
		lenPlain   int    = 160
	)
	var salt []byte
	var bcryptKey []byte
	var sk []byte
	var pk []byte
	var pubkey crypto.PublicKey
	var key ed25519.PrivateKey
	var decrypted []byte
	var aesCtx cipher.Block
	var encData []byte

	decrypted = make([]byte, lenPlain)
	encData = make([]byte, lenPlain)

	// Import salt
	if s, err := hex.DecodeString("19433359e81796b69b0b810bc66dcb8c"); err != nil {
		fmt.Println(err)
		return
	} else {
		salt = s
	}

	// Import encrypted data
	if b, err := hex.DecodeString("dd17660c5e03648b5c6657a998bd4ea7901d4ecf11188903d174fa9d8db4d3f863545ecbc0b51271799a1cf2f0066ce9826c13ec67414488ffe29b9a2e8c0024002da3ceec282d2b09df6c51eec73ac3d441bcdcad3cc36344dadc6540fa9f950705a15048cdc5cd545bfedc0e4333b041cf48cb162e420b09763c484c85ca4496f57e2d63c65c157d21574e7879bf85eb117ee5931dc51a96ba9aaf50a62d6a"); err != nil {
		fmt.Println(err)
		return
	} else {
		encData = b
	}

	// ED25519 keys
	// This is used to validate decrypted keys.
	if edk, err := hex.DecodeString("cceabbe370f139c3d3915018d8511e0663b62840d6b328426ac3df4e75ce6adf58e067bf758477ed2b8198ba19c837fd49759a80d7b84894d74aafe96327d6df"); err != nil {
		fmt.Println(err)
		return
	} else {
		key = edk
		// .Public() returns a crypto.PublicKey, which... is an interface that seemingly cannot be type asserted to anything.
		pubkey = key.Public()
	}
	sep := len(key) - ed25519.PublicKeySize
	pk = key[sep:]
	sk = key[0:sep]

	// Bcrypt_pbkdf2 derivation (used for deriving decryption key for AES encrypted private key)
	// if k, err := bcrypt_pbkdf.Key([]byte(passphrase), salt, rounds, keySize); err != nil {
	if k, err := bcrypt_pbkdf.Key([]byte(passphrase), salt, rounds, keySize+len(salt)); err != nil {
		fmt.Println(err)
		return
	} else {
		bcryptKey = k
	}
	realBcryptKey := bcryptKey[0:sep]
	realIV := bcryptKey[sep:]

	// Decrypter
	if a, err := aes.NewCipher(realBcryptKey); err != nil {
		fmt.Println(err)
		return
	} else {
		aesCtx = a
	}

	// Actual cipher setup. AES256-CBC
	// d := cipher.NewCBCDecrypter(aesCtx, realIV)
	// d.CryptBlocks(decrypted, encData)

	// Actual cipher setup. AES256-CTR
	d := cipher.NewCTR(aesCtx, realIV)
	d.XORKeyStream(decrypted, encData)

	/*
		if p, s, err := ed25519.GenerateKey(nil); err != nil {
			fmt.Println(err)
			return
		} else {
			pubkey = p
			key = s
			pk = key[(len(key) - ed25519.PublicKeySize):]
			sk = key[0:(len(key) - ed25519.PublicKeySize)]
		}
	*/

	fmt.Printf("ED25519 key: %v\n", hex.EncodeToString(key))
	fmt.Printf("Pubkey: %v\n", pubkey)
	fmt.Printf("SK: %v\n", hex.EncodeToString(sk))
	fmt.Printf("PK: %v\n", hex.EncodeToString(pk))
	fmt.Printf("Salt: %v\n", hex.EncodeToString(salt))
	fmt.Printf("Bcrypt Key: %v\n", hex.EncodeToString(bcryptKey))
	fmt.Printf("realBcryptKey: %v\n", hex.EncodeToString(realBcryptKey))
	fmt.Printf("realIV: %v\n", hex.EncodeToString(realIV))
	// fmt.Printf("Encrypted data: %v\n", hex.EncodeToString(encData))
	fmt.Printf("Decrypted data?: %v\n", hex.EncodeToString(decrypted))

	/* decrypted now correctly returns:
	54efc132  checksum
	54efc132  checksum matches!
	0000000b  11
	7373682d65643235353139  "ssh-ed25519"
	00000020  32
	58e067bf758477ed2b8198ba19c837fd49759a80d7b84894d74aafe96327d6df  pubkey
	00000040  64
	cceabbe370f139c3d3915018d8511e0663b62840d6b328426ac3df4e75ce6adf58e067bf758477ed2b8198ba19c837fd49759a80d7b84894d74aafe96327d6df  private key
	00000014  20
	6274734064617769642e723030742e7370616365  "bts@dawid.r00t.space"
	010203040506070809 (padding)
	*/
}