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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)
}
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