Firebase服务器与设备间（含FCM）传输数据的加密情况及算法咨询

Great question—let’s break down the details clearly for you:

核心结论：FCM双向传输全程加密 #

First off, rest easy knowing all data passed between Firebase servers and Android devices via FCM is encrypted in transit. Google enforces this for both directions of communication, so neither server-to-device messages nor device-to-server messages are sent in plaintext.

1. 下行传输（Firebase服务器 → Android设备） #

When Firebase’s FCM server pushes messages to an Android device:

• The connection between the Android device and Google’s FCM connection servers uses TLS 1.2 or later (older, less secure protocols like TLS 1.0 are strictly blocked).
• The encryption suites used are modern, industry-standard options—examples include ECDHE-ECDSA-AES128-GCM-SHA256 and ECDHE-RSA-AES128-GCM-SHA256. These combine elliptic curve key exchange for forward secrecy, AES-GCM for authenticated encryption, and SHA-256 for hashing to ensure both confidentiality and integrity.
• If you’re sending messages from your own backend server to Firebase’s FCM server, that hop also uses HTTPS (TLS 1.2+) to encrypt data before it reaches Firebase.

2. 上行传输（Android设备 → Firebase服务器） #

When an Android device sends messages (like FCM upstream messages or data to Firebase services via FCM’s underlying transport):

• The same TLS 1.2+ encryption applies. The device establishes a secure HTTPS connection to Firebase’s servers, using the same strong encryption suites mentioned above.
• Before any data is sent, the device must authenticate with Firebase using a valid registration token, ensuring only authorized devices can initiate this encrypted communication.

额外安全细节 #

Beyond transit encryption, FCM adds extra safeguards:

• Message integrity: The encryption includes authentication checks, so you can trust messages haven’t been tampered with during transmission.
• Forward secrecy: The key exchange methods used mean even if a long-term key is compromised, past communications can’t be decrypted.

内容的提问来源于stack exchange，提问作者user3145102