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package pemutil
import (
"crypto"
"crypto/x509"
"encoding/json"
"github.com/pkg/errors"
"golang.org/x/crypto/nacl/secretbox"
"golang.org/x/crypto/scrypt"
)
type cosignEnvelope struct {
KDF cosignKDF `json:"kdf"`
Cipher cosignCipher `json:"cipher"`
Ciphertext []byte `json:"ciphertext"`
}
type cosignKDF struct {
Name string `json:"name"`
Params cosignScryptParams `json:"params"`
Salt []byte `json:"salt"`
}
type cosignScryptParams struct {
N int `json:"N"`
R int `json:"r"`
P int `json:"p"`
}
type cosignCipher struct {
Name string `json:"name"`
Nonce []byte `json:"nonce"`
}
// ParseCosignPrivateKey returns the private key encoded using cosign envelope.
// If an incorrect password is detected an x509.IncorrectPasswordError is
// returned.
//
// Cosign keys are encrypted under a password using scrypt as a KDF and
// nacl/secretbox for encryption.
func ParseCosignPrivateKey(data, password []byte) (crypto.PrivateKey, error) {
var env cosignEnvelope
if err := json.Unmarshal(data, &env); err != nil {
return nil, errors.Wrap(err, "error unmarshaling key")
}
if env.KDF.Name != "scrypt" {
return nil, errors.Errorf("error parsing key: unsupported kdf %s", env.KDF.Name)
}
if env.Cipher.Name != "nacl/secretbox" {
return nil, errors.Errorf("error parsing key: unsupported cipher %s", env.Cipher.Name)
}
if len(env.Cipher.Nonce) != 24 {
return nil, errors.New("error parsing key: nonce must be 24 bytes long")
}
params := env.KDF.Params
k, err := scrypt.Key(password, env.KDF.Salt, params.N, params.R, params.P, 32)
if err != nil {
return nil, errors.Wrap(err, "error generating key")
}
var nonce [24]byte
var key [32]byte
copy(nonce[:], env.Cipher.Nonce)
copy(key[:], k)
out, ok := secretbox.Open(nil, env.Ciphertext, &nonce, &key)
if !ok {
return nil, x509.IncorrectPasswordError
}
priv, err := x509.ParsePKCS8PrivateKey(out)
if err != nil {
return nil, errors.Wrap(err, "error parsing pkcs8 key")
}
return priv, nil
}
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