开发笔记:Flutter上线项目实战——即时通讯端对端加密(E2E)

1.背景知识

• 数字签名算法EdDSA: ed25519
• 密钥交换算法ECDH: x25519
• 加密算法AES
• 参考阅读: http://www.freebuf.com/articles/database/113855.html

2.设计思路

>> image link

3.流程代码

1. 引入加解密库

cryptography: ^1.4.0


2. 主流程

static Future mainLogic() async {
// User A 生成密钥
var keyPairEd25519App1 &＃61; await ed25519.newKeyPair();
var keyPairX25519App1 &＃61; await x25519.newKeyPair();
// User B 生成密钥
var keyPairEd25519App2 &＃61; await ed25519.newKeyPair();
var keyPairX25519App2 &＃61; await x25519.newKeyPair();

// User A通过 ed25519 密钥对对 x25519 的公钥进行签名
var signature1 &＃61; await EncryptUtil.sign(keyPairX25519App1.publicKey.bytes, keyPairEd25519App1);
// User B通过 ed25519 密钥对对 x25519 的公钥进行签名
var signature2 &＃61; await EncryptUtil.sign(keyPairX25519App2.publicKey.bytes, keyPairEd25519App2);

// User A验证签名
var publicKeyEd25519App2 &＃61; base64.encode(keyPairEd25519App2.publicKey.bytes);
var publicKeyX25519App2 &＃61; base64.encode(keyPairX25519App2.publicKey.bytes);
var isMatch1 &＃61; await EncryptUtil.verify(publicKeyEd25519App2, publicKeyX25519App2, signature2);
assert(isMatch1);
// User B验证签名
var publicKeyEd25519App1 &＃61; base64.encode(keyPairEd25519App1.publicKey.bytes);
var publicKeyX25519App1 &＃61; base64.encode(keyPairX25519App1.publicKey.bytes);
var isMatch2 &＃61; await EncryptUtil.verify(publicKeyEd25519App1, publicKeyX25519App1, signature1);
assert(isMatch2);
// User A 生成共享密钥
var commomKey1 &＃61; await EncryptUtil.sharedSecret(keyPairX25519App1.privateKey, publicKeyX25519App2);
L.d(&＃39;app1 计算共享密钥: ${base64.encode(sc1)}&＃39;);
// User B 生成共享密钥
var commomKey2 &＃61; await EncryptUtil.sharedSecret(keyPairX25519App2.privateKey, publicKeyX25519App1);
L.d(&＃39;app2 计算共享密钥: ${base64.encode(sc2)}&＃39;);
assert(base64.encode(commomKey1) &＃61;&＃61; base64.encode(commomKey2));


// User A 加密消息
SecretKey secretKey &＃61; SecretKey(base64.decode(commonKey1));
Nonce nonce &＃61; Nonce.randomBytes(12);
List message &＃61; utf8.encode(&＃39;要加密的消息&＃39;);
Uint8List encrypted &＃61; await EncryptUtil.encrypt(message, secretKey, nonce);
// 发送加密消息
String nonceString &＃61; nonce.bytes.toString();
String body &＃61; base64Encode(encrypted);
sendMsg(body, nonceString);

// User B 解密
SecretKey secretKey &＃61; SecretKey(base64.decode(commonKey2));
Nonce nonce &＃61; await getNonceByString(nonceString);
Uint8List decrypted &＃61; await EncryptUtil.decrypt(base64Decode(body), secretKey, nonce);
// 打印明文
String result &＃61; utf8.decode(decrypted);
}


3. 元子操作

class EncryptUtil {
// 根据本地密钥和远程公钥&＃xff0c;计算出共享密钥
static Future> sharedSecret(PrivateKey localPrivateKey, String remotePublicKey) async {
PublicKey pk &＃61; PublicKey(base64.decode(remotePublicKey));
// We can now calculate a shared 256-bit secret
SecretKey sharedSecret &＃61; await x25519.sharedSecret(
localPrivateKey: localPrivateKey,
remotePublicKey: pk,
);
List secretBytes &＃61; await sharedSecret.extract();
return secretBytes;
}
/// 用 ED25519 key pair 对 X25519 publicKey 签名
static Future sign(List publicKeyX25519, KeyPair keyPairEd25519) async {
// Sign
Signature signature &＃61; await ed25519.sign(publicKeyX25519, keyPairEd25519);
return base64.encode(signature.bytes);
}
/// 验证公钥与签名是否匹配
static Future verify(publicKeyEd25519, publicKeyX25519, String signature) async {
PublicKey pk &＃61; PublicKey(base64.decode(publicKeyEd25519));
Signature s2 &＃61; Signature(base64.decode(signature), publicKey: pk);
bool isSignatureCorrect &＃61; await ed25519.verify(base64.decode(publicKeyX25519), s2);
return isSignatureCorrect;
}
/// AES-CTR加密消息&＃xff0c; 并附加Hmac签名
static Future encrypt(Uint8List byte, SecretKey secretKey, Nonce nonce) async {
CipherWithAppendedMac cipher &＃61; CipherWithAppendedMac(aesCtr, Hmac(sha512));
Uint8List encrypted &＃61; await cipher.encrypt(
byte,
secretKey: secretKey,
nonce: nonce,
);
return encrypted;
}
/// AES-CTR解密消息&＃xff0c; 并验证Hmac签名
static Future decrypt(Uint8List encrypted, SecretKey secretKey, Nonce nonce) async {
CipherWithAppendedMac cipher &＃61; CipherWithAppendedMac(aesCtr, Hmac(sha512));
Uint8List decrypted &＃61; await cipher.decrypt(
encrypted,
secretKey: secretKey,
nonce: nonce,
);
return decrypted;
}

static Future getNonceByString(String nonceStr) async {
String str &＃61; nonceStr.substring(1, nonceStr.length - 1);
List nonceList &＃61; str.split(&＃39;,&＃39;);
List nonceResult &＃61; [];
for (int i &＃61; 0; i nonceResult.add(int.parse(nonceList[i]));
}
Nonce nonce &＃61; Nonce(nonceResult);
return nonce;
}
}


完结&＃xff0c;撒花&＃x1f389;