use pbkdf2 to generate AES CTR Input

encryption.go

@@ -3,11 +3,24 @@ package bip39
 import (
 	"crypto/aes"
 	"crypto/cipher"
-	"crypto/sha256"
+	"crypto/sha512"
+	"golang.org/x/crypto/pbkdf2"
 )
 
+func EncryptMnemonic(mnemonic string, password string) (string, error) {
+	entropy, err := EntropyFromMnemonic(mnemonic)
+	if err != nil {
+		return "", err
+	}
+	encEntropy, err := EncryptEntropy(entropy, password)
+	if err != nil {
+		return "", err
+	}
+	return NewMnemonic(encEntropy)
+}
+
 func EncryptEntropy(entropy []byte, password string) ([]byte, error) {
-	pwHash := sha256.Sum256([]byte(password))
+	pwHash := pbkdf2.Key([]byte(password), []byte("mnemonic-encryption"), 2048, 32, sha512.New)
 
 	ci, err := aes.NewCipher(pwHash[:])
 	if err != nil {

encyrption_test.go

@@ -7,7 +7,17 @@ import (
 
 func TestEcryptMnemonic(t *testing.T) {
 	mnmonic := "all hour make first leader extend hole alien behind guard gospel lava path output census museum junior mass reopen famous sing advance salt reform"
-	expectedEncMnemonic := "artist depart host scheme update hen short doctor lemon coffee they walk drill welcome mimic expect renew purse wear slow punch need comic team"
+	expectedEncMnemonic := "father level place shallow review foil illegal elbow wine warm soft penalty token banner cage century someone warfare horn vote crumble now attack gorilla"
+	password := "securePassword"
+
+	encMnemonic, err := EncryptMnemonic(mnmonic, password)
+	assert.NoError(t, err)
+	assert.Equal(t, expectedEncMnemonic, encMnemonic)
+}
+
+func TestEcryptEntropy(t *testing.T) {
+	mnmonic := "all hour make first leader extend hole alien behind guard gospel lava path output census museum junior mass reopen famous sing advance salt reform"
+	expectedEncMnemonic := "father level place shallow review foil illegal elbow wine warm soft penalty token banner cage century someone warfare horn vote crumble now attack gorilla"
 	password := "securePassword"
 
 	entropy, err := EntropyFromMnemonic(mnmonic)