nebula/cert/crypto.go

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package cert
import (
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"fmt"
"io"
"golang.org/x/crypto/argon2"
)
// KDF factors
type Argon2Parameters struct {
version rune
Memory uint32 // KiB
Parallelism uint8
Iterations uint32
salt []byte
}
// Returns a new Argon2Parameters object with current version set
func NewArgon2Parameters(memory uint32, parallelism uint8, iterations uint32) *Argon2Parameters {
return &Argon2Parameters{
version: argon2.Version,
Memory: memory, // KiB
Parallelism: parallelism,
Iterations: iterations,
}
}
// Encrypts data using AES-256-GCM and the Argon2id key derivation function
func aes256Encrypt(passphrase []byte, kdfParams *Argon2Parameters, data []byte) ([]byte, error) {
key, err := aes256DeriveKey(passphrase, kdfParams)
if err != nil {
return nil, err
}
// this should never happen, but since this dictates how our calls into the
// aes package behave and could be catastraphic, let's sanity check this
if len(key) != 32 {
return nil, fmt.Errorf("invalid AES-256 key length (%d) - cowardly refusing to encrypt", len(key))
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
gcm, err := cipher.NewGCM(block)
if err != nil {
return nil, err
}
nonce := make([]byte, gcm.NonceSize())
if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
return nil, err
}
ciphertext := gcm.Seal(nil, nonce, data, nil)
blob := joinNonceCiphertext(nonce, ciphertext)
return blob, nil
}
// Decrypts data using AES-256-GCM and the Argon2id key derivation function
// Expects the data to include an Argon2id parameter string before the encrypted data
func aes256Decrypt(passphrase []byte, kdfParams *Argon2Parameters, data []byte) ([]byte, error) {
key, err := aes256DeriveKey(passphrase, kdfParams)
if err != nil {
return nil, err
}
block, err := aes.NewCipher(key)
if err != nil {
return nil, err
}
gcm, err := cipher.NewGCM(block)
nonce, ciphertext, err := splitNonceCiphertext(data, gcm.NonceSize())
if err != nil {
return nil, err
}
plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
if err != nil {
return nil, fmt.Errorf("invalid passphrase or corrupt private key")
}
return plaintext, nil
}
func aes256DeriveKey(passphrase []byte, params *Argon2Parameters) ([]byte, error) {
if params.salt == nil {
params.salt = make([]byte, 32)
if _, err := rand.Read(params.salt); err != nil {
return nil, err
}
}
// keySize of 32 bytes will result in AES-256 encryption
key, err := deriveKey(passphrase, 32, params)
if err != nil {
return nil, err
}
return key, nil
}
// Derives a key from a passphrase using Argon2id
func deriveKey(passphrase []byte, keySize uint32, params *Argon2Parameters) ([]byte, error) {
if params.version != argon2.Version {
return nil, fmt.Errorf("incompatible Argon2 version: %d", params.version)
}
if params.salt == nil {
return nil, fmt.Errorf("salt must be set in argon2Parameters")
} else if len(params.salt) < 16 {
return nil, fmt.Errorf("salt must be at least 128 bits")
}
key := argon2.IDKey(passphrase, params.salt, params.Iterations, params.Memory, params.Parallelism, keySize)
return key, nil
}
// Prepends nonce to ciphertext
func joinNonceCiphertext(nonce []byte, ciphertext []byte) []byte {
return append(nonce, ciphertext...)
}
// Splits nonce from ciphertext
func splitNonceCiphertext(blob []byte, nonceSize int) ([]byte, []byte, error) {
if len(blob) <= nonceSize {
return nil, nil, fmt.Errorf("invalid ciphertext blob - blob shorter than nonce length")
}
return blob[:nonceSize], blob[nonceSize:], nil
}