feat: encrypt private keys saved on disk and in database (#682)

Co-authored-by: Kyle Mendell <kmendell@ofkm.us>

backend/internal/utils/crypto/crypto.go

@@ -0,0 +1,69 @@
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// ErrDecrypt is returned by Decrypt when the operation failed for any reason
+var ErrDecrypt = errors.New("failed to decrypt data")
+
+// Encrypt a byte slice using AES-GCM and a random nonce
+// Important: do not encrypt more than ~4 billion messages with the same key!
+func Encrypt(key []byte, plaintext []byte, associatedData []byte) (ciphertext []byte, err error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create block cipher: %w", err)
+	}
+	aead, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create AEAD cipher: %w", err)
+	}
+
+	// Generate a random nonce
+	nonce := make([]byte, aead.NonceSize())
+	_, err = io.ReadFull(rand.Reader, nonce)
+	if err != nil {
+		return nil, fmt.Errorf("failed to generate random nonce: %w", err)
+	}
+
+	// Allocate the slice for the result, with additional space for the nonce and overhead
+	ciphertext = make([]byte, 0, len(plaintext)+aead.NonceSize()+aead.Overhead())
+	ciphertext = append(ciphertext, nonce...)
+
+	// Encrypt the plaintext
+	// Tag is automatically added at the end
+	ciphertext = aead.Seal(ciphertext, nonce, plaintext, associatedData)
+
+	return ciphertext, nil
+}
+
+// Decrypt a byte slice using AES-GCM
+func Decrypt(key []byte, ciphertext []byte, associatedData []byte) (plaintext []byte, err error) {
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create block cipher: %w", err)
+	}
+	aead, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create AEAD cipher: %w", err)
+	}
+
+	// Extract the nonce
+	if len(ciphertext) < (aead.NonceSize() + aead.Overhead()) {
+		return nil, ErrDecrypt
+	}
+
+	// Decrypt the data
+	plaintext, err = aead.Open(nil, ciphertext[:aead.NonceSize()], ciphertext[aead.NonceSize():], associatedData)
+	if err != nil {
+		// Note: we do not return the exact error here, to avoid disclosing information
+		return nil, ErrDecrypt
+	}
+
+	return plaintext, nil
+}

backend/internal/utils/crypto/crypto_test.go

@@ -0,0 +1,208 @@
+package crypto
+
+import (
+	"crypto/rand"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestEncryptDecrypt(t *testing.T) {
+	tests := []struct {
+		name           string
+		keySize        int
+		plaintext      string
+		associatedData []byte
+	}{
+		{
+			name:           "AES-128 with short plaintext",
+			keySize:        16,
+			plaintext:      "Hello, World!",
+			associatedData: []byte("test-aad"),
+		},
+		{
+			name:           "AES-192 with medium plaintext",
+			keySize:        24,
+			plaintext:      "This is a longer message to test encryption and decryption",
+			associatedData: []byte("associated-data-192"),
+		},
+		{
+			name:           "AES-256 with unicode",
+			keySize:        32,
+			plaintext:      "Hello 世界! 🌍 Testing unicode characters", //nolint:gosmopolitan
+			associatedData: []byte("unicode-test"),
+		},
+		{
+			name:           "No associated data",
+			keySize:        32,
+			plaintext:      "Testing without associated data",
+			associatedData: nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Generate random key
+			key := make([]byte, tt.keySize)
+			_, err := rand.Read(key)
+			require.NoError(t, err, "Failed to generate random key")
+
+			plaintext := []byte(tt.plaintext)
+
+			// Test encryption
+			ciphertext, err := Encrypt(key, plaintext, tt.associatedData)
+			require.NoError(t, err, "Encrypt should succeed")
+
+			// Verify ciphertext is different from plaintext (unless empty)
+			if len(plaintext) > 0 {
+				assert.NotEqual(t, plaintext, ciphertext)
+			}
+
+			// Test decryption
+			decrypted, err := Decrypt(key, ciphertext, tt.associatedData)
+			require.NoError(t, err, "Decrypt should succeed")
+
+			// Verify decrypted text matches original
+			assert.Equal(t, plaintext, decrypted, "Decrypted text should match original")
+		})
+	}
+}
+
+func TestEncryptWithInvalidKeySize(t *testing.T) {
+	invalidKeySizes := []int{8, 12, 33, 47, 55, 128}
+
+	for _, keySize := range invalidKeySizes {
+		t.Run(fmt.Sprintf("Key size %d", keySize), func(t *testing.T) {
+			key := make([]byte, keySize)
+			plaintext := []byte("test message")
+
+			_, err := Encrypt(key, plaintext, nil)
+			require.Error(t, err)
+			assert.ErrorContains(t, err, "invalid key size")
+		})
+	}
+}
+
+func TestDecryptWithInvalidKeySize(t *testing.T) {
+	invalidKeySizes := []int{8, 12, 33, 47, 55, 128}
+
+	for _, keySize := range invalidKeySizes {
+		t.Run(fmt.Sprintf("Key size %d", keySize), func(t *testing.T) {
+			key := make([]byte, keySize)
+			ciphertext := []byte("fake ciphertext")
+
+			_, err := Decrypt(key, ciphertext, nil)
+			require.Error(t, err)
+			assert.ErrorContains(t, err, "invalid key size")
+		})
+	}
+}
+
+func TestDecryptWithInvalidCiphertext(t *testing.T) {
+	key := make([]byte, 32)
+	_, err := rand.Read(key)
+	require.NoError(t, err, "Failed to generate random key")
+
+	tests := []struct {
+		name       string
+		ciphertext []byte
+	}{
+		{
+			name:       "empty ciphertext",
+			ciphertext: []byte{},
+		},
+		{
+			name:       "too short ciphertext",
+			ciphertext: []byte("short"),
+		},
+		{
+			name:       "random invalid data",
+			ciphertext: []byte("this is not valid encrypted data"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := Decrypt(key, tt.ciphertext, nil)
+			require.Error(t, err)
+			require.ErrorIs(t, err, ErrDecrypt)
+		})
+	}
+}
+
+func TestDecryptWithWrongKey(t *testing.T) {
+	// Generate two different keys
+	key1 := make([]byte, 32)
+	key2 := make([]byte, 32)
+	_, err := rand.Read(key1)
+	require.NoError(t, err)
+	_, err = rand.Read(key2)
+	require.NoError(t, err)
+
+	plaintext := []byte("secret message")
+
+	// Encrypt with key1
+	ciphertext, err := Encrypt(key1, plaintext, nil)
+	require.NoError(t, err)
+
+	// Try to decrypt with key2
+	_, err = Decrypt(key2, ciphertext, nil)
+	require.Error(t, err)
+	require.ErrorIs(t, err, ErrDecrypt)
+}
+
+func TestDecryptWithWrongAssociatedData(t *testing.T) {
+	key := make([]byte, 32)
+	_, err := rand.Read(key)
+	require.NoError(t, err, "Failed to generate random key")
+
+	plaintext := []byte("secret message")
+	correctAAD := []byte("correct-aad")
+	wrongAAD := []byte("wrong-aad")
+
+	// Encrypt with correct AAD
+	ciphertext, err := Encrypt(key, plaintext, correctAAD)
+	require.NoError(t, err)
+
+	// Try to decrypt with wrong AAD
+	_, err = Decrypt(key, ciphertext, wrongAAD)
+	require.Error(t, err)
+	require.ErrorIs(t, err, ErrDecrypt)
+
+	// Verify correct AAD works
+	decrypted, err := Decrypt(key, ciphertext, correctAAD)
+	require.NoError(t, err)
+	assert.Equal(t, plaintext, decrypted, "Decrypted text should match original when using correct AAD")
+}
+
+func TestEncryptDecryptConsistency(t *testing.T) {
+	key := make([]byte, 32)
+	_, err := rand.Read(key)
+	require.NoError(t, err)
+
+	plaintext := []byte("consistency test message")
+	associatedData := []byte("test-aad")
+
+	// Encrypt multiple times and verify we get different ciphertexts (due to random IV)
+	ciphertext1, err := Encrypt(key, plaintext, associatedData)
+	require.NoError(t, err)
+
+	ciphertext2, err := Encrypt(key, plaintext, associatedData)
+	require.NoError(t, err)
+
+	// Ciphertexts should be different (due to random IV)
+	assert.NotEqual(t, ciphertext1, ciphertext2, "Multiple encryptions of same plaintext should produce different ciphertexts")
+
+	// Both should decrypt to the same plaintext
+	decrypted1, err := Decrypt(key, ciphertext1, associatedData)
+	require.NoError(t, err)
+
+	decrypted2, err := Decrypt(key, ciphertext2, associatedData)
+	require.NoError(t, err)
+
+	assert.Equal(t, plaintext, decrypted1, "First decrypted text should match original")
+	assert.Equal(t, plaintext, decrypted2, "Second decrypted text should match original")
+	assert.Equal(t, decrypted1, decrypted2, "Both decrypted texts should be identical")
+}