initial commit

internal/secretbox/secretbox.go

@@ -0,0 +1,51 @@
+package secretbox
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"errors"
+	"fmt"
+)
+
+func Encrypt(master, plaintext string) ([]byte, error) {
+	block, err := aes.NewCipher(deriveKey(master))
+	if err != nil {
+		return nil, fmt.Errorf("create secret cipher: %w", err)
+	}
+	aead, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, fmt.Errorf("create secret AEAD: %w", err)
+	}
+	nonce := make([]byte, aead.NonceSize())
+	if _, err := rand.Read(nonce); err != nil {
+		return nil, fmt.Errorf("generate secret nonce: %w", err)
+	}
+	return aead.Seal(nonce, nonce, []byte(plaintext), []byte("go-loose-oidc-v1")), nil
+}
+
+func Decrypt(master string, ciphertext []byte) (string, error) {
+	block, err := aes.NewCipher(deriveKey(master))
+	if err != nil {
+		return "", fmt.Errorf("create secret cipher: %w", err)
+	}
+	aead, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", fmt.Errorf("create secret AEAD: %w", err)
+	}
+	if len(ciphertext) < aead.NonceSize() {
+		return "", errors.New("encrypted secret is truncated")
+	}
+	nonce, sealed := ciphertext[:aead.NonceSize()], ciphertext[aead.NonceSize():]
+	plaintext, err := aead.Open(nil, nonce, sealed, []byte("go-loose-oidc-v1"))
+	if err != nil {
+		return "", errors.New("encrypted secret cannot be opened")
+	}
+	return string(plaintext), nil
+}
+
+func deriveKey(master string) []byte {
+	sum := sha256.Sum256([]byte("go-loose/oidc/" + master))
+	return sum[:]
+}

internal/secretbox/secretbox_test.go

@@ -0,0 +1,20 @@
+package secretbox
+
+import "testing"
+
+func TestRoundTrip(t *testing.T) {
+	ciphertext, err := Encrypt("01234567890123456789012345678901", "client-secret")
+	if err != nil {
+		t.Fatalf("Encrypt() error = %v", err)
+	}
+	plaintext, err := Decrypt("01234567890123456789012345678901", ciphertext)
+	if err != nil {
+		t.Fatalf("Decrypt() error = %v", err)
+	}
+	if plaintext != "client-secret" {
+		t.Fatalf("plaintext = %q", plaintext)
+	}
+	if _, err := Decrypt("different-master-secret-value-0000", ciphertext); err == nil {
+		t.Fatal("expected wrong key to fail")
+	}
+}