kes: add support for encrypted private keys (#14650)

This commit adds support for encrypted KES
client private keys.

Now, it is possible to encrypt the KES client
private key (`MINIO_KMS_KES_KEY_FILE`) with
a password.

For example, KES CLI already supports the
creation of encrypted private keys:
```
kes identity new --encrypt --key client.key --cert client.crt MinIO
```

To decrypt an encrypted private key, the password
needs to be provided:
```
MINIO_KMS_KES_KEY_PASSWORD=<password>
```

Signed-off-by: Andreas Auernhammer <hi@aead.dev>

cmd/common-main.go

@@ -24,6 +24,7 @@ import (
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/gob"
+	"encoding/pem"
 	"errors"
 	"fmt"
 	"io/ioutil"
@@ -798,7 +799,29 @@ func handleCommonEnvVars() {
 				endpoints = append(endpoints, strings.Join(lbls, ""))
 			}
 		}
-		certificate, err := tls.LoadX509KeyPair(env.Get(config.EnvKESClientCert, ""), env.Get(config.EnvKESClientKey, ""))
+		// Manually load the certificate and private key into memory.
+		// We need to check whether the private key is encrypted, and
+		// if so, decrypt it using the user-provided password.
+		certBytes, err := os.ReadFile(env.Get(config.EnvKESClientCert, ""))
+		if err != nil {
+			logger.Fatal(err, "Unable to load KES client certificate as specified by the shell environment")
+		}
+		keyBytes, err := os.ReadFile(env.Get(config.EnvKESClientKey, ""))
+		if err != nil {
+			logger.Fatal(err, "Unable to load KES client private key as specified by the shell environment")
+		}
+		privateKeyPEM, rest := pem.Decode(bytes.TrimSpace(keyBytes))
+		if len(rest) != 0 {
+			logger.Fatal(errors.New("private key contains additional data"), "Unable to load KES client private key as specified by the shell environment")
+		}
+		if x509.IsEncryptedPEMBlock(privateKeyPEM) {
+			keyBytes, err = x509.DecryptPEMBlock(privateKeyPEM, []byte(env.Get(config.EnvKESClientPassword, "")))
+			if err != nil {
+				logger.Fatal(err, "Unable to decrypt KES client private key as specified by the shell environment")
+			}
+			keyBytes = pem.EncodeToMemory(&pem.Block{Type: privateKeyPEM.Type, Bytes: keyBytes})
+		}
+		certificate, err := tls.X509KeyPair(certBytes, keyBytes)
 		if err != nil {
 			logger.Fatal(err, "Unable to load KES client certificate as specified by the shell environment")
 		}

docs/kms/README.md

@@ -120,6 +120,20 @@ Encrypted :
   X-Amz-Server-Side-Encryption: AES256
 ```
 
+## Encrypted Private Key
+
+MinIO supports encrypted KES client private keys. Therefore, you can use
+an password-protected private keys for `MINIO_KMS_KES_KEY_FILE`. 
+
+When using password-protected private keys for accessing KES you need to
+provide the password via:
+```
+export MINIO_KMS_KES_KEY_PASSWORD=<your-password>
+``` 
+
+Note that MinIO only supports encrypted private keys - not encrypted certificates.
+Certificates are no secrets and sent in plaintext as part of the TLS handshake.
+
 ## Explore Further
 
 - [Use `mc` with MinIO Server](https://docs.min.io/docs/minio-client-quickstart-guide)

internal/config/constants.go

@@ -67,6 +67,7 @@ const (
 	EnvKESEndpoint       = "MINIO_KMS_KES_ENDPOINT"
 	EnvKESKeyName        = "MINIO_KMS_KES_KEY_NAME"
 	EnvKESClientKey      = "MINIO_KMS_KES_KEY_FILE"
+	EnvKESClientPassword = "MINIO_KMS_KES_KEY_PASSWORD"
 	EnvKESClientCert     = "MINIO_KMS_KES_CERT_FILE"
 	EnvKESServerCA       = "MINIO_KMS_KES_CAPATH"