encryption - 与多个收件人的端到端加密

Question

WhatsApp 宣布支持普通对话和群聊的端到端加密。

假设没有共享私钥并且它是真正的端到端，那么当我向一个有 10 个 friend 的组发送 10MB 视频时，我必须将其加密 10 倍并发送 10 倍？否则它对我来说不是端到端的，因为服务器一定无法转发它。

那是对的吗？谢谢

Answer 1

Whatsapp 已实现 PKI(公钥基础设施)以加密消息。这意味着客户端使用 key 对自己进行身份验证，而服务器只存储公钥。

有关 whatsapp 安全性的更多信息，请查看他们发布的以下白皮书:

https://www.whatsapp.com/security/WhatsApp-Security-Whitepaper.pdf

答案

您的问题的答案在白皮书的第 7 页。

The first time a WhatsApp group member sends a message to a group:

1. The sender generates a random 32-byte Chain Key.
2. The sender generates a random Curve25519 Signature Key key pair.
3. The sender combines the 32-byte Chain Key and the public key from the Signature Key into a Sender Key message .
4. The sender individually encrypts the Sender Key to each member of the group, using the pairwise messaging protocol explained previously

For all subsequent messages to the group:

1. The sender derives a Message Key from the Chain Key, and updates the Chain Key.
2. The sender encrypts the message using AES256 in CBC mode
3. The sender signs the ciphertext using the Signature Key.
4. The sender transmits the single ciphertext message to the server, which does server-side fan-out to all group participants.