feat: voice-service von lehrer nach core verschoben, Pipeline erweitert (voice, BQAS, embedding, night-scheduler)
This commit is contained in:
Benjamin Boenisch
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voice-service/services/encryption_service.py
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231
voice-service/services/encryption_service.py
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"""
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Encryption Service - Namespace Key Management
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Client-side encryption for DSGVO compliance
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The encryption key NEVER leaves the teacher's device.
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Server only sees:
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- Key hash (for verification)
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- Encrypted blobs
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- Namespace ID (pseudonym)
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"""
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import structlog
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import hashlib
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import base64
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import secrets
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from typing import Optional
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from cryptography.hazmat.primitives.ciphers.aead import AESGCM
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from cryptography.hazmat.primitives import hashes
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from cryptography.hazmat.primitives.kdf.pbkdf2 import PBKDF2HMAC
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from config import settings
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logger = structlog.get_logger(__name__)
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class EncryptionService:
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"""
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Handles namespace key verification and server-side encryption.
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Important: This service does NOT have access to the actual encryption key.
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The key is stored only on the teacher's device.
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This service only verifies key hashes and manages encrypted blobs.
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"""
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def __init__(self):
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self._key_hashes: dict[str, str] = {} # namespace_id -> key_hash
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self._server_key = secrets.token_bytes(32) # Server-side encryption for transit
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def verify_key_hash(self, key_hash: str) -> bool:
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"""
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Verify that a key hash is valid format.
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Does NOT verify the actual key - that's client-side only.
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Accepts "disabled" for development over HTTP (where crypto.subtle is unavailable).
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In production, always use HTTPS to enable proper encryption.
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"""
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if not key_hash:
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return False
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# Allow "disabled" for development (HTTP context where crypto.subtle is unavailable)
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if key_hash == "disabled":
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logger.warning(
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"Encryption disabled - client running in non-secure context (HTTP). "
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"Use HTTPS in production!"
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)
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return True
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# Expected format: "sha256:base64encodedHash"
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if not key_hash.startswith("sha256:"):
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return False
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try:
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hash_part = key_hash[7:] # Remove "sha256:" prefix
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decoded = base64.b64decode(hash_part)
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return len(decoded) == 32 # SHA-256 produces 32 bytes
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except Exception:
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return False
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def register_namespace_key(self, namespace_id: str, key_hash: str) -> bool:
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"""
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Register a namespace's key hash for future verification.
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"""
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if not self.verify_key_hash(key_hash):
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logger.warning("Invalid key hash format", namespace_id=namespace_id[:8])
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return False
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self._key_hashes[namespace_id] = key_hash
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if key_hash == "disabled":
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logger.info("Namespace registered (encryption disabled)", namespace_id=namespace_id[:8])
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else:
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logger.info("Namespace key registered", namespace_id=namespace_id[:8])
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return True
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def encrypt_content(self, plaintext: str, namespace_id: str) -> str:
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"""
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Encrypt content for server-side storage.
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Note: This is transit encryption only.
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The actual client-side encryption happens in the browser/app.
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This adds an additional layer for data at rest on the server.
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"""
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if not settings.encryption_enabled:
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return plaintext
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try:
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# Derive key from server key + namespace
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derived_key = self._derive_key(namespace_id)
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# Generate nonce
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nonce = secrets.token_bytes(12)
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# Encrypt
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aesgcm = AESGCM(derived_key)
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ciphertext = aesgcm.encrypt(nonce, plaintext.encode('utf-8'), None)
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# Combine nonce + ciphertext and encode
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encrypted = base64.b64encode(nonce + ciphertext).decode('utf-8')
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return f"encrypted:{encrypted}"
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except Exception as e:
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logger.error("Encryption failed", error=str(e))
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raise
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def decrypt_content(self, encrypted: str, namespace_id: str) -> str:
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"""
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Decrypt server-side encrypted content.
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"""
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if not settings.encryption_enabled:
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return encrypted
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if not encrypted.startswith("encrypted:"):
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return encrypted # Not encrypted
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try:
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# Decode
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encoded = encrypted[10:] # Remove "encrypted:" prefix
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data = base64.b64decode(encoded)
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# Split nonce and ciphertext
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nonce = data[:12]
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ciphertext = data[12:]
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# Derive key from server key + namespace
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derived_key = self._derive_key(namespace_id)
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# Decrypt
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aesgcm = AESGCM(derived_key)
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plaintext = aesgcm.decrypt(nonce, ciphertext, None)
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return plaintext.decode('utf-8')
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except Exception as e:
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logger.error("Decryption failed", error=str(e))
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raise
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def _derive_key(self, namespace_id: str) -> bytes:
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"""
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Derive a key from server key + namespace ID.
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This ensures each namespace has a unique encryption key.
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"""
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kdf = PBKDF2HMAC(
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algorithm=hashes.SHA256(),
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length=32,
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salt=namespace_id.encode('utf-8'),
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iterations=100000,
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)
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return kdf.derive(self._server_key)
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@staticmethod
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def generate_key_hash(key: bytes) -> str:
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"""
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Generate a key hash for client-side use.
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This is a utility method - actual implementation is in the client.
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"""
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hash_bytes = hashlib.sha256(key).digest()
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encoded = base64.b64encode(hash_bytes).decode('utf-8')
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return f"sha256:{encoded}"
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@staticmethod
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def generate_namespace_id() -> str:
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"""
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Generate a new namespace ID for a teacher.
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"""
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return f"ns-{secrets.token_hex(16)}"
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class ClientSideEncryption:
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"""
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Helper class documenting client-side encryption.
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This code runs in the browser/app, not on the server.
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Client-side encryption flow:
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1. Teacher generates a master key on first use
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2. Master key is stored in browser/app secure storage
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3. Key hash is sent to server for session verification
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4. All PII is encrypted with master key before sending to server
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5. Server only sees encrypted blobs
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JavaScript implementation:
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```javascript
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// Generate master key (one-time)
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const masterKey = await crypto.subtle.generateKey(
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{ name: "AES-GCM", length: 256 },
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true,
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["encrypt", "decrypt"]
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);
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// Store in IndexedDB (encrypted with device key)
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await storeSecurely("masterKey", masterKey);
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// Generate key hash for server
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const keyData = await crypto.subtle.exportKey("raw", masterKey);
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const hashBuffer = await crypto.subtle.digest("SHA-256", keyData);
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const keyHash = "sha256:" + btoa(String.fromCharCode(...new Uint8Array(hashBuffer)));
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// Encrypt content before sending
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async function encryptContent(content) {
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const iv = crypto.getRandomValues(new Uint8Array(12));
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const encoded = new TextEncoder().encode(content);
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const ciphertext = await crypto.subtle.encrypt(
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{ name: "AES-GCM", iv },
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masterKey,
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encoded
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);
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return btoa(String.fromCharCode(...iv, ...new Uint8Array(ciphertext)));
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}
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// Decrypt content after receiving
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async function decryptContent(encrypted) {
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const data = Uint8Array.from(atob(encrypted), c => c.charCodeAt(0));
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const iv = data.slice(0, 12);
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const ciphertext = data.slice(12);
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const decrypted = await crypto.subtle.decrypt(
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{ name: "AES-GCM", iv },
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masterKey,
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ciphertext
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);
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return new TextDecoder().decode(decrypted);
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}
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```
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"""
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pass
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