•秘钥生成算法HDhttps://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=15&ved=0ahUKEwj-hKjT8_3VAhUFqo8KHfBYDT0QFgiSATAO&url=https%3A%2F%2Fread01.com%2Fy2nAOd.html&usg=AFQjCNGk4pjRYbuo67m1sMyBtYP2VOLdkA
Identity Key Pair – A long-term Curve25519 key pair,
在应用安装的时候生成
• Signed Pre Key – A medium-term Curve25519 key pair,
在应用安装的时候生成，用IDK签名。generated at install time, signed by the Identity Key, and rotated
on a periodic timed basis.
• One-Time Pre Keys – A queue of Curve25519 key pairs
预先生成的只能使用一次的key。 WhatsAp是每次上传100个otpk到服务器。
session key types
ROOT KEY 根密钥
chain key 发送链密钥
message key
客户端注册: 上传IK, SPK,和一批otpk到服务器
session初始化:
1.sender 请求对方的IK, SPK,和一个otpk
2.服务器返回对应的key，由于otpk只能使用一次，所以当前使返回的otpk 会被删除
3.sender 保存从服务器拿到的key ，The initiator saves the recipient’s Identity Key as Irecipient, the
Signed Pre Key as Srecipient, and the One-Time Pre Key as Orecipient.
4.发起方生成一个ephemeral Curve25519 key pair, Einitiato
5.发起方 加载自己的IK 为Iinitiator
6.master_secret =
ECDH(Iinitiator, Srecipient) || ECDH(Einitiator, Irecipient) ||
ECDH(Einitiator, Srecipient) || ECDH(Einitiator, Orecipient).
The initiator uses HKDF to create a Root Key and Chain Keys
from the master_secret.
至此初始化方就可以直接发送消息到接收方
接收方的session创建