feat: usos sign-in, private calendar feed and timetable archive

internal/seal/seal.go

@@ -0,0 +1,53 @@
+package seal
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+)
+
+const keySize = 32
+
+var ErrKey = errors.New("seal: key must be 32 random bytes in base64")
+
+type Box struct {
+	aead cipher.AEAD
+}
+
+func New(encodedKey string) (*Box, error) {
+	key, err := base64.StdEncoding.DecodeString(encodedKey)
+	if err != nil || len(key) != keySize {
+		return nil, ErrKey
+	}
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	aead, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+	return &Box{aead: aead}, nil
+}
+
+func (b *Box) Seal(plain, purpose string) []byte {
+	nonce := make([]byte, b.aead.NonceSize())
+	if _, err := rand.Read(nonce); err != nil {
+		panic(err)
+	}
+	return b.aead.Seal(nonce, nonce, []byte(plain), []byte(purpose))
+}
+
+func (b *Box) Open(sealed []byte, purpose string) (string, error) {
+	size := b.aead.NonceSize()
+	if len(sealed) < size {
+		return "", errors.New("seal: ciphertext too short")
+	}
+	plain, err := b.aead.Open(nil, sealed[:size], sealed[size:], []byte(purpose))
+	if err != nil {
+		return "", errors.New("seal: cannot decrypt")
+	}
+	return string(plain), nil
+}

internal/seal/seal_test.go

@@ -0,0 +1,36 @@
+package seal
+
+import (
+	"bytes"
+	"encoding/base64"
+	"testing"
+)
+
+func TestRoundTripAndBinding(t *testing.T) {
+	key := base64.StdEncoding.EncodeToString(bytes.Repeat([]byte{7}, keySize))
+	box, err := New(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	sealed := box.Seal("secret-value", "42/usos_token")
+	if bytes.Contains(sealed, []byte("secret-value")) {
+		t.Fatal("plaintext is visible in the sealed value")
+	}
+	if got, err := box.Open(sealed, "42/usos_token"); err != nil || got != "secret-value" {
+		t.Fatalf("Open = %q, %v", got, err)
+	}
+	if _, err := box.Open(sealed, "43/usos_token"); err == nil {
+		t.Fatal("a value sealed for one user opened for another")
+	}
+	if bytes.Equal(sealed, box.Seal("secret-value", "42/usos_token")) {
+		t.Fatal("sealing twice produced the same bytes")
+	}
+}
+
+func TestRejectsWeakKeys(t *testing.T) {
+	for _, key := range []string{"", "CHANGEME", base64.StdEncoding.EncodeToString([]byte("short"))} {
+		if _, err := New(key); err == nil {
+			t.Errorf("New(%q) accepted a bad key", key)
+		}
+	}
+}