You are provided with the abstract of a scientific paper and the abstracts of the papers it references. Your task is to write a Related Work section for the main paper. This section should concisely summarize and integrate the key points from the cited abstracts, reflecting how they relate to the main paper's contributions and context. In your summary, use numerical citation markers like [1], [2], etc., to refer to the corresponding papers.

Main Abstract:
Whistleblower laws protect individuals who inform the public or an authority about governmental or corporate misconduct. Despite these laws, whistleblowers frequently risk reprisals and sites such as WikiLeaks emerged to provide a level of anonymity to these individuals. However, as countries increase their level of network surveillance and Internet protocol data retention, the mere act of using anonymizing software such as Tor, or accessing a whistleblowing website through an SSL channel might be incriminating enough to lead to investigations and repercussions. As an alternative submission system we propose an online advertising network called AdLeaks. AdLeaks leverages the ubiquity of unsolicited online advertising to provide complete sender unobservability when submitting disclosures. AdLeaks ads compute a random function in a browser and submit the outcome to the AdLeaks infrastructure. Such a whistleblower's browser replaces the output with encrypted information so that the transmission is indistinguishable from that of a regular browser. Its back-end design assures that AdLeaks must process only a fraction of the resulting traffic in order to receive disclosures with high probability. We describe the design of AdLeaks and evaluate its performance through analysis and experimentation.

Cited Abstract(s):
[1]: 

[2]: Keeping confidential who sends which messages, in a world where any physical transmission can be traced to its origin, seems impossible. The solution presented here is unconditionally or cryptographically secure, depending on whether it is based on one-time-use keys or on public keys, respectively. It can be adapted to address efficiently a wide variety of practical considerations.

[3]: In Journal of Cryptology 1 1 (1988) 65–75, CHAUM describes a beautiful technique, the DC-net, which should allow participants to send and receive messages anonymously in an arbitrary network. The untraceability of the senders is proved to be unconditional, but that of the recipients implicitly assumes a reliable broadcast network. This assumption is unrealistic in some networks, but it can be removed completely by using the fail-stop key generation schemes by WAIDNER (these proceedings). In both cases, however, each participant can untraceably and permanently disrupt the entire DC-net.

[4]: Recent web-based applications offer users free service in exchange for access to personal communication, such as on-line email services and instant messaging. The inspection and retention of user communication is generally intended to enable targeted marketing. However, unless specifically stated otherwise by the collecting service's privacy policy, such records have an indefinite lifetime and may be later used or sold without restriction. In this paper, we show that it is possible to protect a user's privacy from these risks by exploiting mutually oblivious, competing communication channels. We create virtual channels over online services (e.g., Google's Gmail, Microsoft's Hotmail) through which messages and cryptographic keys are delivered. The message recipient uses a shared secret to identify the shares and ultimately recover the original plaintext. In so doing, we create a wired “spread-spectrum” mechanism for protecting the privacy of web-based communication. We discuss the design and implementation of our open-source Java applet, Aquinas, and consider ways that the myriad of communication channels present on the Internet can be exploited to preserve privacy.

[5]: Current Internet e-mail facilities are built onto the foundation of standard rules and protocols, which usually allow a considerable amount of ''freedom'' to their designers. Each of these standards has been defined based on a number of vendor specific implementations, in order to provide common inter-working procedures for cross-vendor communication. Thus, a lot of optional and redundant information is being exchanged during e-mail sessions, which is available to implement versatile covert channel mechanisms. This work exploits this possibility by presenting a simple but effective steganographic scheme that can be used to deploy robust secret communication through spam e-mails. This scheme can offer unidirectional asynchronous one-to-one or one-to-many covert channel facilities that are able to bypass the most sophisticated firewalls and traffic analyzers. Its implementation neither affects the involved transport protocols nor causes any perceivable performance degradation or data loss to the end-users. The proposed scheme allows one to manage possible filtering loss of the e-mails being the vehicle of the secret information. A novel retransmission method based on the Raptor codes has been adopted. The use of Raptor codes is key to correctly and efficiently manage the difficulty or impossibility to retransmit e-mails in the case of a unidirectional secret communication starting from one sender and directed to many recipients. In order to evaluate the performance characteristics of the proposed scheme, an empirical estimation of the covert channel bandwidth has been performed.

[6]:
Closely related to our work, there is early work on DC Nets [2] [3] which aims to provide a cryptographic means to hide who sends messages, the use of Raptor codes [5] to implement an asynchronous unidirectional one-to-one and one-to-many covert channel using spam messages, and anonymous data aggregation [6] for distributed sensing and diagnostics. In preserving the privacy of web-based email [4] one can take advantage of a spread-spectrum approach for hiding the existence of a message, but it is not secure against a global attacker. Membership-concealment [1] can also be used to hide the real-world identities of participants in an overlay network, but this doesn't suffice for AdLeaks.