如何在服务器端 Swift HTTPS 端点中验证 SNS 消息？

Question

Amazon 提供文档，用于验证路由到 HTTP/HTTPS 端点的 SNS 消息是否有效。在服务器上使用 Vapor 和 Swift，以及 swift-certificates 和 swift-crypto，我实现了验证逻辑：

func messageHasValidSignature<Message: VerifiableMessage>(_ message: Message) async throws -> Bool {
    guard let certificateBytes = try await client.get(.init(message.signingCertificateURL)).body else {
        logger.error("Failed to get signing certificate body")
        throw Abort(.badRequest)
    }

    let certificateString = String(buffer: certificateBytes)
    let certificate = try Certificate(pemEncoded: certificateString)
    let publicKey = try _RSA.Signing.PublicKey(derRepresentation: certificate.publicKey.subjectPublicKeyInfoBytes)
    guard let signatureData = Data(base64Encoded: message.signature) else {
        logger.error("Failed to decode signature")
        throw Abort(.badRequest)
    }

    let signature = _RSA.Signing.RSASignature(rawRepresentation: signatureData)

    guard let dataToSign = message.stringToSign.data(using: .utf8) else {
        logger.error("Failed to convert string to sign to data")
        throw Abort(.badRequest)
    }

    let digest: any Digest
    switch message.signatureVersion {
    case ._1:
        digest = Insecure.SHA1.hash(data: dataToSign)
    case ._2:
        digest = SHA256.hash(data: dataToSign)
    }

    return publicKey.isValidSignature(signature, for: digest)
}

我正在构建要签名的字符串，如下所示：

extension SubscriptionConfirmationMessage: VerifiableMessage {
    var stringToSign: String {
        """
        Message
        \(message)
        MessageId
        \(messageID)
        SubscribeURL
        \(subscribeURL)
        Timestamp
        \(timestamp)
        Token
        \(token)
        TopicArn
        \(topicARN)
        Type
        SubscriptionConfirmation

        """
    }
}

但是

isValidSignature

总是返回 false。如何正确验证消息？

Answer 1

问题在于传递给

isValidSignature

的填充。默认值为

PSS

（“使用 MGF1 的 PSS 填充”）。通过检查C#实现的来源，我发现它应该是

insecurePKCS1v1_5

（“PKCS#1 v1.5”）。

所以验证签名的正确方法是：

return publicKey.isValidSignature(signature, for: digest,  padding: .insecurePKCS1v1_5)