# SimpleX Chat: private and secure messenger without any user IDs (not even random)
SimpleX Chat - a private and encrypted messenger without any user IDs (not even random ones)! Make a private connection via link / QR code to send messages and make calls.

# 重新定义隐私

## 首个
没有用户ID的即时通讯软件

其他应用——如Signal、Matrix、Session、Briar、Jami、Cwtch 等——都需要用户 ID。
而SimpleX 不需要用户ID，连随机生成的也不需要。
这从根本上改善了您的隐私。

为什么用户 ID 不利于隐私？

# 为什么用户 ID 不利于隐私？

当用户具有持久身份时，即使这只是一个随机数（如会话 ID），提供商或攻击者也有可能观察到用户如何连接以及他们发送了多少消息。

然后他们可以将这些信息与现有的公共社交网络相关联，并确定一些真实身份。

即使是使用 Tor v3 服务的最私密的应用程序，如果您通过同一个人资料与两个不同的联系人交谈，他们也可以证明他们与同一个人有联系。

为防止这些攻击，SimpleX 在其设计中不包含任何用户 ID 。 而且，如果您使用隐身模式，您将为每个联系人显示不同的名称，避免他们之间共享任何数据。

SimpleX 是如何工作的？

# SimpleX 是如何工作的？

许多用户问：如果 SimpleX 没有用户标识符，它怎么知道将消息传递到哪里？

SimpleX 使用消息队列的临时匿名成对标识符(而非其他网络使用的用户 ID)来传递消息，而每个连接的标识符均不尽相同 — 没有长期标识符这种东西。

您定义用于接收消息的服务器、您的联系人—— 您用来向他们发送消息的服务器。 每个会话都很可能会使用两个不同的服务器。

此设计可防止在应用程序级别泄漏任何用户元数据。 为了进一步改善隐私并保护您的 IP 地址，您可以通过 Tor 连接到消息服务器。

只有客户端设备存储用户配置文件、联系人和群组； 消息均使用两层端到端加密发送。

阅读 SimpleX 白皮书了解更多信息。

安全性评估

# 安全性评估

Trail of Bits 是一家领先的安全和技术咨询企业，其客户包括大型科技公司、政府机构和重要的区块链项目。

2022年11月份，Trail of Bits 审核了 SimpleX 平台的密码学和网络部件。更多内容见 该公告。

Trail of Bits 于 2024 年 7 月审核了 SimpleX 网络协议的加密设计。了解更多信息。

获取 SimpleX desktop app

## 建立私人连接

右侧的视频向您展示了如何通过一次性二维码、面对面交流或通过视频交换链接来连接到您的朋友。您同样可以通过共享邀请链接来进行连接。

为何选择 SimpleX 功能 SimpleX 的隐私性 SimpleX 网络

## 为什么隐私很重要

保护您的元数据的隐私— 您与谁交谈 — 保护您免受：

广告和价格歧视

隐私为您省钱

# 隐私为您省钱

许多大型公司会使用您的人际关系来估算您的收入，决定商品的价格，并向您兜售您并不真正需要的产品。

在线零售商知道收入较低的人更有可能在紧急情况下购买商品，因此他们可能会收取更高的价格或取消折扣。

一些金融和保险公司使用社交图谱来确定利率和保费。 它通常会让收入较低的人支付更多—它被称为“贫困溢价”。

SimpleX 网络比任何替代方案都能更好地保护您人际关系层面的隐私，防止您的社交图谱被任何公司或组织使用。 即使人们使用 SimpleX Chat 应用预配置的服务器，服务器运营方也不知道用户数量或他们的连接数。

对选举的操纵

隐私给您力量

# 隐私给您力量

不久前，我们观察到几次大选被一家知名咨询公司操纵，该公司使用我们的社交图谱扭曲我们对现实世界的看法并操纵我们的选票。

为了客观并做出独立的决定，您需要控制您的信息空间。 而这只有当您使用没有能力访问您的社交图谱的，注重隐私的通信网络时，这才有可能。

SimpleX 是第一个没有设计任何用户标识符的网络，这样能比任何已知的替代方案都更好地保护您的连接图谱。

因无辜结社而被起诉

隐私保您自由

# 隐私保您自由

每个人都应该关心他们通信的隐私和安全——无害的谈话会让您处于危险之中，即使您没有什么可隐瞒的。

最令人震惊的故事之一是 Mohamedou Ould Salahi 在他的回忆录中描述并在毛里塔尼亚电影中展示的经历。 他在未经审判的情况下被关进关塔那摩集中营，并在打电话给他在阿富汗的亲戚后在那里遭受了 15 年的折磨，他被怀疑参与了 9/11 袭击，尽管他在过去 10 年住在德国。

普通人会因为他们在网上分享的内容而被捕，即使是通过他们的“匿名”账户，即使是在民主国家。

使用端到端加密的即时通讯软件还不够，我们都应该使用保护我们个人网络隐私——即我们与谁有联系的即时通讯软件。

确保您的即时通讯软件无法访问您的数据！

## 为什么 SimpleX 是独特的

# #1

### 您有完整的隐私

SimpleX 保护您的个人资料、联系人和元数据的隐私，不让 SimpleX 网络服务器和任何观察者看到它们。

与任何其他现有的消息传递网络不同，SimpleX 没有分配给用户的标识符—— 甚至随机数也没有。

了解更多
更多信息
隐藏信息

# #2

### 您可以免受垃圾消息和平台滥用的侵害

因为您在 SimpleX 网络上没有标识符或固定地址，所以除非您以二维码或链接的形式分享一次性或临时用户地址，没有人可以联系您。

了解更多
更多信息
隐藏信息

# #3

### 您控制您的数据

SimpleX 以便携式加密数据库格式将所有用户数据存储在客户端设备上—— 它可以转移到另一个设备。

端到端加密的消息在被收到前会暂时保存在 SimpleX 中继服务器上，传送完成后它们会被永久删除。

了解更多
更多信息
隐藏信息

# #4

### 您拥有 SimpleX 网络

SimpleX 网络是完全去中心化的，并且独立于任何加密货币或除互联网以外的任何其他网络。

您可以搭配自己的服务器来使用 SimpleX 或使用我们提供的服务器 — 并仍然连接到任何用户。

了解更多
更多信息
隐藏信息

# 您的身份、个人资料、联系人和元数据的完整隐私

与其他消息网络不同，SimpleX 没有分配给用户的标识符。 它不依赖电话号码、基于域的地址（如电子邮件或 XMPP）、用户名、公钥甚至随机数来识别其用户—— SimpleX 服务器运营方不知道有多少人使用其服务器。

为了传递消息，SimpleX 使用单向消息队列的成对匿名地址，通常通过不同的服务器将接收和发送的消息分开。

这种设计保护了您正在与之通信的人的隐私，将其隐藏在 SimpleX 网络的服务器和任何观察者之外。 要对服务器隐藏您的 IP 地址，您可以通过 Tor 连接到 SimpleX 服务器。

# 防止垃圾消息和平台滥用的最佳保护

因为您在 SimpleX 网络上没有标识符，所以除非您以二维码或链接的形式分享一次性或临时用户地址，没有人可以联系您。

即使使用可选的用户地址，当它被用于发送垃圾邮件联系请求，您可以更改或完全删除它而不会丢失任何连接。

# 您数据的所有权、控制权和安全性

SimpleX Chat 使用便携式加密数据库格式仅将所有用户数据存储在客户端设备上，该格式可以导出并传输到任何支持的设备。

端到端加密的消息在被收到前会暂时保存在 SimpleX 中继服务器上，传送完成后它们会被永久删除。

与联合网络服务器（电子邮件、XMPP 或 Matrix）不同，SimpleX 服务器不存储用户帐户，它们仅中继消息，保护双方的隐私。

发送和接收的服务器流量之间没有共同的标识符或密文—— 如果有人在观察它，他们也无法轻易确定谁与谁通信，即使 TLS 受到威胁。

# 完全去中心化 —— 用户拥有 SimpleX 网络

您可以将 SimpleX 与您自己的服务器一起使用，并且仍然可以与使用应用中预配置服务器的人们进行通信。

SimpleX 网络使用开放协议并提供用于创建聊天机器人的 SDK， 允许用户实现通过 SimpleX Chat 应用程序与之交互的服务—我们真的很期待看到您会依托SimpleX构建哪些服务。

如果您正在考虑为在SimpleX 网络上开发，例如，为 SimpleX 应用程序用户开发聊天机器人，或将 SimpleX 聊天库集成到您的移动应用，请 联系我们获取建议和支持。

## 功能

端到端加密的文字消息，支持markdown和编辑

端到端加密的
图片、视频和文件

端到端加密的去中心化的秘密群组 —只有用户知道它们的存在

端到端加密的语音消息

支持消息自动销毁

端到端加密的音视频通话

便携的加密应用存储— 可将您的个人资料移至另一台设备

隐身模式 —
SimpleX Chat 独有

## 是什么让 SimpleX 能够保密

### 临时匿名成对标识符

SimpleX 为每个用户的联系人或群组成员均使用临时匿名成对地址和凭据。

它让在没有用户标识符的情况下传递消息成为可能，并提供比替代方案更好的元数据隐私。

点击关闭

### 带外密钥交换

许多通信平台容易受到服务器或网络提供商的中间人攻击。

为防止这种情况，当您将通讯地址作为链接或二维码共享时，SimpleX 应用程序会在带外传递一次性密钥。

点击关闭

### 双层端到端加密

双棘轮协议——具有完美前向保密和入侵恢复功能的 OTR(不留记录即时通讯) 消息传递。

每个队列中的网络与密码学库加密盒(NaCL cryptobox)可防止 TLS 受到威胁时消息队列之间的流量关联。

点击关闭

### 消息完整性验证

为了保证消息完整性，消息按顺序编号并会包含前一条消息的哈希值。

如果添加、删除或更改任何消息，收件人都会收到警告。

点击关闭

### 服务器提供的另一层加密

为来信附加服务器加密层，以防止在 TLS 受破坏时接收和发送的服务器流量之间发生关联。

点击关闭

### 通过消息混合减少相关性

SimpleX 服务器会充当低延迟混合节点，打乱传入和传出消息的顺序。

点击关闭

### 安全认证的TLS传输

客户端与服务器之间的连接只使用强加密的 TLS 1.2/1.3。

服务器指纹和通道绑定可防止中间人与重放攻击。

禁用连接恢复以防止会话攻击。

点击关闭

### 可选择通过 Tor 访问

为了保护您的 IP 地址，您可以通过 Tor 或其他传输覆盖网络访问服务器。

要通过 Tor 使用 SimpleX，请安装 Orbot 应用并启用 SOCKS5 代理（在 iOS上需要使用 VPN 模式）。

点击关闭

### 单向消息队列

每个消息队列都有不同的发送和接收地址，单向地传递消息。

与传统的消息代理相比，它减少了攻击媒介和可用的元数据。

点击关闭

### 多层级的内容填充

SimpleX 为每个加密层进行内容填充来对抗长度扩展攻击。

它使不同大小的消息在服务器和网络监视者看来是一样的。

点击关闭

## SimpleX 网络

SimpleX Chat 通过结合 P2P 和联邦网络的优势使其保密性无与伦比。

### 与 P2P 网络不同

所有消息都通过服务器发送，既能更好地保护元数据隐私和可靠地传递异步消息，同时也能避免许多 P2P网络存在的问题.

# 与 P2P 通讯协议的比较

P2P 消息传递协议和应用程序存在各种问题，使得它们不如 SimpleX 可靠，分析起来更复杂，并且 容易受到多种类型的攻击。

1. P2P 网络依赖于分布式散列表(DHT) 的某些变体来路由消息。 DHT 在设计上必须平衡可达性和延迟。 SimpleX 比 P2P 具有更好的可达性和更低的延迟，因为消息可以通过通讯双方选择的多个服务器并行地冗余传递。若是在 P2P 网络中，消息则需要使用算法选择，并依次通过 O(log N) 个节点。
2. 与大多数 P2P 网络不同，SimpleX 在设计上没有任何类型的全局用户标识符，甚至临时的也没有。SimpleX 仅使用临时的成对标识符，提供更好的匿名性和元数据保护。
3. P2P 并未解决中间人攻击(MITM Attack) 问题。大多数现有的 P2P 实现没有使用带外通讯来进行初始密钥的交换，而 SimpleX 使用带外通讯，或者在某些情况下，使用预先存在的安全和可信连接来进行初始密钥交换。
4. P2P 实现（如BitTorrent）可能会被某些互联网提供商阻止。 SimpleX 与传输协议无关 — 它可以在标准网络协议上工作，例如 WebSockets。
5. 所有已知的 P2P 网络都可能受到Sybil 攻击，因为每个节点都是可发现的，并且网络作为一个整体运行。 已知的缓解措施不是需要一个中心化的组件就是需要昂贵的工作量证明。而 SimpleX 网络没有服务器可发现性，它是碎片化的并且作为多个隔离的子网运行，这样全网络范围的攻击便无从实现。
6. P2P 网络可能受到 分布式反射拒绝服务攻击 。客户端有能力重新广播和放大流量，从而导致整个网络范围内的服务中断。 SimpleX 客户端仅中继来自已知连接的流量，因此不能被攻击者用来放大整个网络的流量。

### 不同于联邦网络

SimpleX 中继服务器不存储用户配置文件、联系人和传递的消息，不相互连接，并且没有服务器目录。

### SimpleX 网络

服务器提供单向队列来连接用户，但是他们看不到网络连接图图谱— 只有用户可以。

## SimpleX 简述

1. 用户会体验到什么
2. 背后的运作原理
3. 服务器能看到什么
1. 用户会体验到什么

您可以创建联系人和群组，并进行双向对话，就像是任何其他即时通讯软件一样。

它是如何利用单向消息队列并不利用用户识别符工作的？

2. 背后的运作原理

对于每个连接，您都会使用两个单独的消息队列，通过不同的服务器发送和接收消息。

服务器只单向传输消息，无法掌握用户的对话或连接的全貌。

3. 服务器能看到什么

服务器对每个队列都有单独的匿名凭证，并且不知道这些凭证属于哪些用户。

用户可以通过使用 Tor 访问服务器以进一步提高元数据隐私，防止通过 IP 地址关联实际身份。

## 与其他协议的比较

|  | Signal、其他大平台 | XMPP、Matrix | P2P协议
--- | --- | --- | --- | ---
需要全局身份 | 否 - 私密 | 是 1 | 是 2 | 是 3
中间人攻击的可能性 | 不可能 - 安全 4 | 是 5 | 是 | 是
对 DNS 的依赖 | 不依赖 - 有韧性 | 是 | 是 | 否
单一或中心化网络 | 不依赖 - 去中心化的 | 是 | 不依赖 - 联邦式网络 6 | 是 7
中央组件或其他全网攻击 | 不依赖 - 有韧性 | 是 | 是 2 | 是 8

1. 通常基于电话号码，在某些情况下基于用户名
2. 基于 DNS 的地址
3. 公钥或其他一些全球唯一的 ID
4. SimpleX 中继无法破坏 e2e 加密。 验证安全代码以减轻对带外通道的攻击
5. 如果运营商的服务器受到威胁。 验证 Signal 和其他一些应用程序中的安全代码以缓解该问题
6. 不保护用户的元数据隐私
7. P2P 是分布式的，但并非联邦式的 — 它们作为单个网络运行
8. P2P 网络要么拥有中央权威，要么整个网络可能被攻陷 - 参见此处

## 加入 SimpleX

我们邀请您加入对话

加入 REDDIT 社区 在 GitHub 上加入我们 在这里捐款来帮助我们

注册以接收我们的更新

获取 SimpleX desktop app

# Address portability

Similarly to phone number portability (the ability of the customer to transfer the service to another provider without changing the number), the address portability means the ability of a communication service customer to change the service provider without changing the service address. Many federated networks support SRV records to provide address portability, but allowing service users to set up their own domains for the addresses is not as commonly supported by the available server and client software as for email.

# Federated network

Federated network is provided by several entities that agree upon the standards and operate the network collectively. This allows the users to choose their provider, that will hold their account, their messaging history and contacts, and communicate with other providers' servers on behalf of the user. The examples are email, XMPP, Matrix and Mastodon.

The advantage of that design is that there is no single organization that all users depend on, and the standards are more difficult to change, unless it benefits all users. There are several disadvantages: 1) the innovation is slower, 2) each user account still depends on a single organization, and in most cases can't move to another provider without changing their network address – there is no address portability, 3) the security and privacy are inevitably worse than with the centralized networks.

Federation on Wikipedia

# Anonymous credentials

The credential that allows proving something, e.g. the right to access some resource, without identifying the user. This credential can either be generated by a trusted party or by the user themselves and provided together with the request to create the resource. The first approach creates some centralized dependency in most cases. The second approach does not require any trust - this is used in SimpleX network to authorize access to the messaging queues.

Digital credential on Wikipedia

# Blockchain

In a wide sense, blockchain means a sequence of blocks of data, where each block contains a cryptographic hash of the previous block, thus providing integrity to the whole chain. Blockchains are used in many communication and information storage systems to provide integrity and immutability of the data. For example, BluRay disks use blockchain. SimpleX messaging queues also use blockchain - each message includes the hash of the previous message, to ensure the integrity – if any message is modified it will be detected by the recipient when the next message is received. Blockchains are a subset of Merkle directed acyclic graphs.

In a more narrow sense, particularly in media, blockchain is used to refer specifically to distributed ledger, where each record also includes the hash of the previous record, but the blocks have to be agreed by the participating peers using some consensus protocol.

Wikipedia

# Merkle directed acyclic graph

Also known as Merkle DAG, a data structure based on a general graph structure where node contains the cryptographic hashes of the previous nodes that point to it. Merkle trees are a subset of Merkle DAGs - in this case each leaf contains a cryptographic hash of the parent.

This structure by design allows to verify the integrity of the whole structure by computing its hashes and comparing with the hashes included in the nodes, in the same way as with blockchain.

The motivation to use DAG in distributed environments instead of a simpler linear blockchain is to allow concurrent additions, when there is no requirement for a single order of added items. Merkle DAG is used, for example, in IPFS and will be used in decentralized SimpleX groups.

Wikipedia.

# Break-in recovery

The quality of the end-to-end encryption scheme allowing to recover security against a passive attacker who observes encrypted messages after compromising one (or both) of the parties. Also known as recovery from compromise or break-in recovery. Double-ratchet algorithm has this quality.

# Double ratchet algorithm

It is used by two parties to exchange end-to-end encrypted messages. The parties will use some key agreement protocol to agree on the initial shared secret key.

Double Ratchet algorithm provides perfect forward secrecy and post-compromise security. It is designed by Signal, and used in SimpleX Chat and many other secure messengers. Most experts consider it the state-of-the-art encryption protocol in message encryption.

# Centralized network

Centralized networks are provided or controlled by a single entity. The examples are Threema, Signal, WhatsApp and Telegram. The advantage of that design is that the provider can innovate faster, and has a centralized approach to security. But the disadvantage is that the provider can change or discontinue the service, and leak, sell or disclose in some other way all users' data, including who they are connected with.

# Content padding

Also known as content padding, it is the process of adding data to the beginning or the end of a message prior to encryption. Padding conceals the actual message size from any eavesdroppers. SimpleX has several encryption layers, and prior to each encryption the content is padded to a fixed size.

Wikipedia.

# Decentralized network

Decentralized network is often used to mean "the network based on decentralized blockchain". In its original meaning, decentralized network means that there is no central authority or any other point of centralization in the network, other than network protocols specification. The advantage of decentralized networks is that they are resilient to censorship and to the provider going out of business. The disadvantage is that they are often slower to innovate, and the security may be worse than with the centralized network.

The examples of decentralized networks are email, web, DNS, XMPP, Matrix, BitTorrent, etc. All these examples have a shared global application-level address space. Cryptocurrency blockchains not only have a shared address space, but also a shared state, so they are more centralized than email. Tor network also has a shared global address space, but also a central authority. SimpleX network does not have a shared application-level address space (it relies on the shared transport-level addresses - SMP relay hostnames or IP addresses), and it does not have any central authority or any shared state.

# Defense in depth

Originally, it is a military strategy that seeks to delay rather than prevent the advance of an attacker, buying time and causing additional casualties by yielding space.

In information security, defense in depth represents the use of multiple computer security techniques to help mitigate the risk of one component of the defense being compromised or circumvented. An example could be anti-virus software installed on individual workstations when there is already virus protection on the firewalls and servers within the same environment.

SimpleX network applies defense in depth approach to security by having multiple layers for the communication security and privacy:

- double ratchet algorithm for end-to-end encryption with perfect forward secrecy and post-compromise security,
- additional layer of end-to-end encryption for each messaging queue and another encryption layer of encryption from the server to the recipient inside TLS to prevent correlation by ciphertext,
- TLS with only strong ciphers allowed,
- mitigation of man-in-the-middle attack on client-server connection via server offline certificate verification,
- mitigation of replay attacks via signing over transport channel binding,
- multiple layers of message padding to reduce efficiency of traffic analysis,
- mitigation of man-in-the-middle attack on client-client out-of-band channel when sending the invitation,
- rotation of delivery queues to reduce efficiency of traffic analysis,
- etc.

Wikipedia

# End-to-end encryption

A communication system where only the communicating parties can read the messages. It is designed to protect message content from any potential eavesdroppers – telecom and Internet providers, malicious actors, and also the provider of the communication service.

End-to-end encryption requires agreeing cryptographic keys between the sender and the recipient in a way that no eavesdroppers can access the agreed keys. See key agreement protocol. This key exchange can be compromised via man-in-the-middle attack, particularly if key exchange happens via the same communication provider and no out-of-band channel is used to verify key exchange.

Wikipedia

# Forward secrecy

Also known as perfect forward secrecy, it is a feature of a key agreement protocol that ensures that session keys will not be compromised even if long-term secrets used in the session key exchange are compromised. Forward secrecy protects past sessions against future compromises of session or long-term keys.

Wikipedia

# Post-compromise security

The quality of the end-to-end encryption scheme allowing to recover security against a passive attacker who observes encrypted messages after compromising one (or both) of the parties. Also known as recovery from compromise or break-in recovery. Double-ratchet algorithm has this quality.

# Man-in-the-middle attack

The attack when the attacker secretly relays and possibly alters the communications between two parties who believe that they are directly communicating with each other.

This attack can be used to compromise end-to-end encryption by intercepting public keys during key exchange, substituting them with the attacker's keys, and then intercepting and re-encrypting all messages, without altering their content. With this attack, while the attacker does not change message content, but she can read the messages, while the communicating parties believe the messages are end-to-end encrypted.

Such attack is possible with any system that uses the same channel for key exchange as used to send messages - it includes almost all communication systems except SimpleX, where the initial public key is always passed out-of-band. Even with SimpleX, the attacker may intercept and substitute the key sent via another channel, gaining access to communication. This risk is substantially lower, as attacker does not know in advance which channel will be used to pass the key.

To mitigate such attack the communicating parties must verify the integrity of key exchange - SimpleX and many other messaging apps, e.g. Signal and WhatsApp, have the feature that allows it.

Wikipedia.

# Message padding

Also known as content padding, it is the process of adding data to the beginning or the end of a message prior to encryption. Padding conceals the actual message size from any eavesdroppers. SimpleX has several encryption layers, and prior to each encryption the content is padded to a fixed size.

Wikipedia.

# Key agreement protocol

Also known as key exchange, it is a process of agreeing cryptographic keys between the sender and the recipient(s) of the message. It is required for end-to-end encryption to work. Unless it is possible to secure the key exchange via some second factor, e.g. security code verification, it can be vulnerable to man-in-the-middle attack.

Wikipedia

# Key exchange

Also known as key exchange, it is a process of agreeing cryptographic keys between the sender and the recipient(s) of the message. It is required for end-to-end encryption to work. Unless it is possible to secure the key exchange via some second factor, e.g. security code verification, it can be vulnerable to man-in-the-middle attack.

Wikipedia

#### MITM attack

The attack when the attacker secretly relays and possibly alters the communications between two parties who believe that they are directly communicating with each other.

# MITM attack

The attack when the attacker secretly relays and possibly alters the communications between two parties who believe that they are directly communicating with each other.

This attack can be used to compromise end-to-end encryption by intercepting public keys during key exchange, substituting them with the attacker's keys, and then intercepting and re-encrypting all messages, without altering their content. With this attack, while the attacker does not change message content, but she can read the messages, while the communicating parties believe the messages are end-to-end encrypted.

Such attack is possible with any system that uses the same channel for key exchange as used to send messages - it includes almost all communication systems except SimpleX, where the initial public key is always passed out-of-band. Even with SimpleX, the attacker may intercept and substitute the key sent via another channel, gaining access to communication. This risk is substantially lower, as attacker does not know in advance which channel will be used to pass the key.

To mitigate such attack the communicating parties must verify the integrity of key exchange - SimpleX and many other messaging apps, e.g. Signal and WhatsApp, have the feature that allows it.

Wikipedia.

# Non-repudiation

Non-repudiation

# Onion routing

A technique for anonymous communication over a computer network that uses multiple layers of message encryption, analogous to the layers of an onion. The encrypted data is transmitted through a series of network nodes called "onion routers," each of which "peels" away a single layer, revealing the data's next destination. The sender remains anonymous because each intermediary knows only the location of the immediately preceding and following nodes.

The most widely used onion network is Tor.

Some elements of SimpleX network use similar ideas in their design - different addresses for the same resource used by different parties, and additional encryption layers. Currently though, SimpleX messaging protocol does not protect sender network address, as the relay server is chosen by the recipient. The delivery relays chosen by sender that are planned for the future would make SimpleX design closer to onion routing.

Wikipedia

# Overlay network

Nodes in the overlay network can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. Tor, for example, is an overlay network on top of IP network, which in its turn is also an overlay network over some underlying physical network.

SimpleX Clients also form a network using SMP relays and IP or some other overlay network (e.g., Tor), to communicate with each other. SMP relays, on another hand, do not form a network.

Wikipedia

# Non-repudiation

The property of the cryptographic or communication system that allows the recipient of the message to prove to any third party that the sender identified by some cryptographic key sent the message. It is the opposite to repudiation. While in some context non-repudiation may be desirable (e.g., for contractually binding messages), in the context of private communications it may be undesirable.

Wikipedia

# Repudiation

The property of the cryptographic or communication system that allows the sender of the message to plausibly deny having sent the message, because while the recipient can verify that the message was sent by the sender, they cannot prove it to any third party - the recipient has a technical ability to forge the same encrypted message. This is an important quality of private communications, as it allows to have the conversation that can later be denied, similarly to having a private face-to-face conversation.

See also non-repudiation.

# Pairwise pseudonymous identifier

Generalizing the definition from NIST Digital Identity Guidelines, it is an opaque unguessable identifier generated by a service used to access a resource by only one party.

In the context of SimpleX network, these are the identifiers generated by SMP relays to access anonymous messaging queues, with a separate identifier (and access credential) for each accessing party: recipient, sender and and optional notifications subscriber. The same approach is used by XFTP relays to access file chunks, with separate identifiers (and access credentials) for sender and each recipient.

# Peer-to-peer

Peer-to-peer (P2P) is the network architecture when participants have equal rights and communicate directly via a general purpose transport or overlay network. Unlike client-server architecture, all peers in a P2P network both provide and consume the resources. In the context of messaging, P2P architecture usually means that the messages are sent between peers, without user accounts or messages being stored on any servers. Examples are Tox, Briar, Cwtch and many others.

The advantage is that the participants do not depend on any servers. There are multiple downsides to that architecture, such as no asynchronous message delivery, the need for network-wide peer addresses, possibility of network-wide attacks, that are usually mitigated only by using a centralized authority. These disadvantages are avoided with proxied P2P architecture.

Wikipedia.

# Proxied peer-to-peer

Network topology of the communication system when peers communicate via proxies that do not form the network themselves. Such design is used in Pond, that has a fixed home server for each user, and in SimpleX, that uses multiple relays providing temporary connections.

# Perfect forward secrecy

Also known as perfect forward secrecy, it is a feature of a key agreement protocol that ensures that session keys will not be compromised even if long-term secrets used in the session key exchange are compromised. Forward secrecy protects past sessions against future compromises of session or long-term keys.

Wikipedia

# Post-quantum cryptography

Any of the proposed cryptographic systems or algorithms that are thought to be secure against an attack by a quantum computer. It appears that as of 2025 there is no system or algorithm that is proven to be secure against such attacks, or even to be secure against attacks by massively parallel conventional computers, so a general recommendation is to use post-quantum hybrid cryptography - combining post-quantum and traditional algorigthms.

Wikipedia

# Post-quantum hybrid crypto

Any of the proposed cryptographic systems or algorithms that are thought to be secure against an attack by a quantum computer. It appears that as of 2025 there is no system or algorithm that is proven to be secure against such attacks, or even to be secure against attacks by massively parallel conventional computers, so a general recommendation is to use post-quantum hybrid cryptography - combining post-quantum and traditional algorigthms.

Wikipedia

# Recovery from compromise

The quality of the end-to-end encryption scheme allowing to recover security against a passive attacker who observes encrypted messages after compromising one (or both) of the parties. Also known as recovery from compromise or break-in recovery. Double-ratchet algorithm has this quality.

# User identity

In a communication system it refers to anything that uniquely identifies the users to the network. Depending on the communication network, it can be a phone number, email address, username, public key or a random opaque identifier. Most messaging networks rely on some form of user identity. SimpleX appears to be the only messaging network that does not rely on any kind of user identity - see this comparison.