package main

import (
	`bytes`
	`crypto/cipher`
	`fmt`
	`log`

	`github.com/dchest/bcrypt_pbkdf`
	`golang.org/x/crypto/chacha20poly1305`
)

var (
	EncryptedBlob []byte = []byte{
		0x21, 0xca, 0x93, 0x7d, 0x6b, 0x81, 0x5c, 0x67,
		0x66, 0xc3, 0xd6, 0xa, 0xcc, 0x3a, 0xc7, 0x2d,
		0x7f, 0xf7, 0xae, 0x6a, 0x41, 0x85, 0x18, 0xad,
		0x37, 0x65, 0xfa, 0x8e, 0xb, 0x3b, 0x61, 0x72,
		0x70, 0xaa, 0xc5, 0x0, 0xf4, 0x43, 0xb8, 0x21,
		0xe6, 0x14, 0xe5, 0x7e, 0x81, 0x1f, 0x81, 0xe9,
		0x66, 0xa1, 0xd0, 0x44, 0x72, 0xca, 0xaf, 0xe7,
		0xbf, 0x6e, 0x95, 0x6f, 0xb3, 0x28, 0x3f, 0x92,
		0x8f, 0xc, 0x61, 0xc9, 0x39, 0x69, 0x1, 0xd5,
		0xe1, 0x43, 0x9b, 0xfe, 0x37, 0x7b, 0x4f, 0x9d,
		0xe0, 0x73, 0x33, 0x5c, 0xc9, 0x24, 0x7, 0x9c,
		0x5a, 0x96, 0x72, 0xb0, 0xe7, 0x36, 0x98, 0xc6,
		0xa, 0x63, 0x9b, 0xda, 0xf0, 0x4f, 0xa, 0x74,
		0xda, 0x77, 0xec, 0x8f, 0xc7, 0xdc, 0xe8, 0xa2,
		0x62, 0x5c, 0x19, 0x6b, 0x83, 0x41, 0xa4, 0x71,
		0x9f, 0x46, 0x78, 0x92, 0x64, 0x14, 0xc6, 0x63,
		0x41, 0x91, 0x4c, 0xe9, 0xc0, 0x9f, 0x4d, 0x33,
		0xb, 0x63, 0x1d, 0x96, 0x52, 0xa4, 0x68, 0x4a,
		0x4e, 0x13, 0xbd, 0xff, 0x64, 0x8a, 0xa7, 0xb6,
	}
	UnknownData []byte = []byte{
		0x9a, 0xa8, 0xaa, 0xa3,
		0x73, 0x64, 0xb3, 0xaa,
		0x78, 0x25, 0x23, 0x48,
		0x7e, 0x79, 0x57, 0xab,
	}
	CombinedEncrypted = append(EncryptedBlob, UnknownData...)

	// PLAIN
	PrivKey []byte = []byte{
		0xb9, 0x9a, 0xf2, 0xcb, 0x1e, 0xb3, 0x8c, 0xff,
		0xdf, 0x76, 0x31, 0x22, 0x72, 0x56, 0xda, 0xf,
		0xe3, 0xd1, 0xdb, 0x5a, 0xff, 0xea, 0x2e, 0x44,
		0xc8, 0x5, 0x8d, 0xcc, 0xe0, 0x21, 0xae, 0x7e,
	}
	PubKey []byte = []byte{
		0x9c, 0xf1, 0x14, 0x2f, 0xbb, 0x71, 0xac, 0xeb,
		0xf3, 0xae, 0xa8, 0xd8, 0x9c, 0x51, 0x8c, 0x3,
		0xa6, 0xd3, 0x66, 0x59, 0x4c, 0xee, 0xc5, 0x77,
		0x4c, 0x4f, 0xf4, 0x7d, 0x57, 0xba, 0x26, 0x75,
	}
	EdKey []byte = append(PrivKey, PubKey...)
)

func main() {

	var err error
	var c cipher.AEAD
	var kdfSalt []byte = []byte{
		0xfa, 0x99, 0x09, 0xfd,
		0xa2, 0xf5, 0xad, 0x42,
		0xd2, 0x8e, 0x21, 0xe3,
		0xb1, 0xcc, 0x6c, 0x94,
	}
	// https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.chacha20poly1305
	// https://rus-cert.github.io/ssh-chacha20-poly1305-drafts/ssh-chacha20-poly1305@openssh.html
	// https://datatracker.ietf.org/doc/html/draft-josefsson-ssh-chacha20-poly1305-openssh-00
	// https://pkg.go.dev/golang.org/x/crypto/chacha20poly1305
	// var kdfKeyLen int = 512 / 8 // uses fixed 256 bits for chacha key, but it generates two keys...?
	// var kdfKeyLen int = 256 // uses fixed 256 bits for chacha key
	// var kdfKeyLen int = 32 // per golang pkg docs, 32 bytes (128 bits)...
	var kdfKeyLen int = 64 // but per OpenSSH, 64
	// var ivLen int = 0      // ??? per golang pkg docs, 12 bytes. per ssh package, though, 8(? or 0? seems to actually be 0). but needs 16 from...somewhere.
	var ivLen int = 16
	var kdfKey []byte
	var subkey1, subkey2 []byte
	var key []byte
	var iv []byte
	var nonce []byte
	var plain []byte

	if kdfKey, err = bcrypt_pbkdf.Key([]byte("testpassword"), kdfSalt, 16, kdfKeyLen+ivLen); err != nil {
		log.Panicln(err)
	}
	key = kdfKey[0:kdfKeyLen]
	iv = kdfKey[kdfKeyLen:(kdfKeyLen + ivLen)]
	subkey1 = kdfKey[0:32]
	subkey2 = kdfKey[32:]
	// iv = subkey2[0:12]
	nonce = []byte{
		0x0, 0x0, 0x0, 0x0,
		0x0, 0x0, 0x0, 0x0,
		0x0, 0x0, 0x0, 0x0,
		0x0, 0x0, 0x0, 0x0,
	}

	fmt.Printf("kdf key (%d bytes): %#v\n", len(key), key)
	fmt.Printf("kdf iv (%d bytes): %#v\n\n", len(iv), iv)

	// if c, err = chacha20poly1305.New(key); err != nil {
	if c, err = chacha20poly1305.New(subkey1); err != nil {
		// if c, err = chacha20poly1305.New(subkey2); err != nil {
		log.Panicln(err)
	}
	fmt.Printf("nonce size: %d\n", c.NonceSize())

	plain = make([]byte, len(EncryptedBlob))
	// if plain, err = c.Open(plain, iv, EncryptedBlob, UnknownData); err != nil {
	// if plain, err = c.Open(plain, iv, CombinedEncrypted, nil); err != nil {
	if plain, err = c.Open(plain, nonce, EncryptedBlob, nil); err != nil {
		log.Panicln(err)
	}

	// fmt.Printf("%#v\n", c)

	fmt.Printf("Decrypted:\n%#v\n", plain)
	if bytes.Compare(plain, EdKey) != 0 {
		fmt.Printf("\nOriginal:\n%#v\n", EdKey)
	}

	_ = subkey1
	_ = subkey2
}