Proposal to encrypt an mnemonic

encryption.go

@@ -0,0 +1,37 @@
+package bip39
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"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 := pbkdf2.Key([]byte(password), []byte("mnemonic-encryption"), 2048, 32, sha512.New)
+
+	ci, err := aes.NewCipher(pwHash[:])
+	if err != nil {
+		return nil, err
+	}
+
+	iv := make([]byte, 16)
+	enc := cipher.NewCTR(ci, iv)
+
+	out := make([]byte, len(entropy))
+	enc.XORKeyStream(out, entropy)
+
+	return out, nil
+}

encyrption_test.go

@@ -0,0 +1,48 @@
+package bip39
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+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 := "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)
+	assert.NoError(t, err)
+
+	mnemonicFromEntropy, err := NewMnemonic(entropy)
+	assert.NoError(t, err)
+	assert.Equal(t, mnemonicFromEntropy, mnmonic)
+
+	encEntropy, err := EncryptEntropy(entropy, password)
+	assert.NoError(t, err)
+	assert.Equal(t, len(encEntropy), len(entropy))
+
+	encMnemonic, err := NewMnemonic(encEntropy)
+	assert.NoError(t, err)
+
+	// Check the encMnemonic
+	assert.Equal(t, expectedEncMnemonic, encMnemonic)
+
+	// Get back to original mnemonic
+	encEntropyNew, err := EntropyFromMnemonic(encMnemonic)
+	assert.Equal(t, encEntropy, encEntropyNew)
+	assert.NoError(t, err)
+
+	// Decrypt the encrypted entropy
+	plainEntropy, err := EncryptEntropy(encEntropy, password)
+	assert.Equal(t, entropy, plainEntropy)
+}

go.mod

@@ -3,7 +3,7 @@ module github.com/tyler-smith/go-bip39
 go 1.11
 
 require (
+	github.com/stretchr/testify v1.7.0
 	github.com/tyler-smith/assert v1.0.1
 	golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9
-	golang.org/x/text v0.3.0
 )

go.sum

@@ -1,3 +1,10 @@
+github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/tyler-smith/assert v1.0.1 h1:AymyVNGyHOAVaDUEo0WouAMB/wwi5NdbJTDb7lsfFGk=
 github.com/tyler-smith/assert v1.0.1/go.mod h1:oPc3QyIN2k0t/9Xp0sNhi3suiWuGXzIcdf/dbKQ6QGk=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
@@ -6,5 +13,8 @@ golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=