1 files changed, 131 insertions, 0 deletions
diff --git a/backend/internal/keys/gcp.go b/backend/internal/keys/gcp.go
new file mode 100644
index 0000000..9d10fc5
--- /dev/null
+++ b/backend/internal/keys/gcp.go
@@ -0,0 +1,131 @@
+package keys
+
+import (
+	"context"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"hash/crc32"
+	"sync"
+
+	kms "cloud.google.com/go/kms/apiv1"
+	"cloud.google.com/go/kms/apiv1/kmspb"
+	"google.golang.org/protobuf/types/known/wrapperspb"
+)
+
+type GoogleKMS struct {
+	client *kms.KeyManagementClient
+
+	mx       sync.RWMutex
+	keyCache map[string]*rsa.PublicKey
+}
+
+func NewGoogleKMS(ctx context.Context) (*GoogleKMS, error) {
+	client, err := kms.NewKeyManagementClient(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	return &GoogleKMS{
+		client:   client,
+		keyCache: make(map[string]*rsa.PublicKey),
+	}, nil
+}
+
+func (g *GoogleKMS) checkCache(keyName string) *rsa.PublicKey {
+	g.mx.RLock()
+	defer g.mx.RUnlock()
+
+	return g.keyCache[keyName]
+}
+
+func (g *GoogleKMS) getPublicKey(ctx context.Context, keyName string) (*rsa.PublicKey, error) {
+	if key := g.checkCache(keyName); key != nil {
+		return key, nil
+	}
+
+	response, err := g.client.GetPublicKey(ctx, &kmspb.GetPublicKeyRequest{Name: keyName})
+	if err != nil {
+		return nil, err
+	}
+
+	block, _ := pem.Decode([]byte(response.Pem))
+	if block == nil || block.Type != "PUBLIC KEY" {
+		return nil, errors.New("failed to decode PEM public key")
+	}
+	publicKey, err := x509.ParsePKIXPublicKey(block.Bytes)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse public key: %w", err)
+	}
+	rsaKey, ok := publicKey.(*rsa.PublicKey)
+	if !ok {
+		return nil, errors.New("public key is not an RSA key")
+	}
+
+	g.mx.Lock()
+	defer g.mx.Unlock()
+	g.keyCache[keyName] = rsaKey
+
+	return rsaKey, nil
+}
+
+func (g *GoogleKMS) Encrypt(ctx context.Context, keyName string, plaintext []byte) ([]byte, error) {
+	publicKey, err := g.getPublicKey(ctx, keyName)
+	if err != nil {
+		return nil, err
+	}
+
+	cipherText, err := rsa.EncryptOAEP(sha256.New(), rand.Reader, publicKey, plaintext, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to encrypt plaintext: %w", err)
+	}
+
+	return cipherText, nil
+}
+
+func (g *GoogleKMS) Decrypt(ctx context.Context, keyName string, ciphertext []byte) ([]byte, error) {
+	req := &kmspb.AsymmetricDecryptRequest{
+		Name:             keyName,
+		Ciphertext:       ciphertext,
+		CiphertextCrc32C: wrapperspb.Int64(int64(calcCRC32(ciphertext))),
+	}
+
+	result, err := g.client.AsymmetricDecrypt(ctx, req)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decrypt ciphertext: %w", err)
+	}
+
+	if !result.VerifiedCiphertextCrc32C {
+		return nil, errors.New("AsymmetricDecrypt: request corrupted in-transit")
+	}
+	if int64(calcCRC32(result.Plaintext)) != result.PlaintextCrc32C.Value {
+		return nil, fmt.Errorf("AsymmetricDecrypt: response corrupted in-transit")
+	}
+
+	return result.Plaintext, nil
+}
+
+func (g *GoogleKMS) Close() error {
+	return g.client.Close()
+}
+
+func calcCRC32(data []byte) uint32 {
+	t := crc32.MakeTable(crc32.Castagnoli)
+	return crc32.Checksum(data, t)
+}
+
+type GCPKeyName struct {
+	Project          string
+	Location         string
+	KeyRing          string
+	CryptoKey        string
+	CryptoKeyVersion string
+}
+
+func (k GCPKeyName) String() string {
+	return fmt.Sprintf("projects/%s/locations/%s/keyRings/%s/cryptoKeys/%s/cryptoKeyVersions/%s", k.Project, k.Location, k.KeyRing, k.CryptoKey, k.CryptoKeyVersion)
+}