Anonymizers: What do they do?

Anonymity tools allow users to build connections with websites, for instance for communications, or commercial purposes, without revealing the user’s identity. There may be numerous reasons for individuals to protect their identity, for instance, fear of persecution, exercising the right of free speech, or to minimize risk, avoid activity monitoring and prevent identity theft. Anonymity tools are used by a variety of individuals, from law enforcement officers, to human rights workers, journalists, citizens of repressive governments and regular internet browsers. Anonymity tools enable users to browse the internet without revealing personal information.

Even while visiting websites that do not require personal information, internet browsers reveal IP addresses by default. The use of anonymizing proxies allows users to browse without exchanging any personal information, as the proxy makes requests to the websites on the user’s behalf.

Models of Anonymizers

Mix networks are one type model of anonymizer. Mix networks are made up of routers which use layered encryption, buffering and message reordering to create a path for the data to follow through the network. The routers store and forward messages at random intervals and can ensure that each message sent in the network is exactly the same length. Even if there is no data ready to be sent, the router can randomly create and send a message. An example of a mix network anonymity tool is Onion Routing, which uses an “onion,” or layered data structure to transmit data to recipients.

Another model is known as the Crowd system. It was first developed by AT&T, based on a similar concept to the mix network. With the Crowd system, users are grouped with other users in a “crowd.” The crowd forwards requests to a random member, without revealing the origin of the request. Unlike mix networks, which send data on pre-configured paths, the Crowd system dynamically creates paths for each request. This makes the Crowd system more flexible to network changes.

Anonymizers & Risks

There are a number of risks involved with using anonymizers. For instance, users who access the anonymizing proxy are revealing their IP addresses to that proxy. Some anonymizers may record incoming and outgoing connections. Even if an anonymizer claims not to log user activity, this is often difficult to ascertain. Internet service providers have also been known to log their customers’ online activities. Certain malicious anonymizers have been known to perpetrate “man in the middle” attacks, in which the anonymizer modifies the content being transmitted or received.

In order to limit risks, certain users will encrypt any private information that is exchanged outside of the anonymizer, for instance usernames, passwords, credit card information and email addresses.

Tor Network

Another option for limiting risks is to use one anonymizer to connect to another, a technique known as daisy chaining. This allows the user to appear anonymous to the exposed anonymizing tool. A well-known application of daisy chained anonymizers is the Tor network.

The Tor network is based on an onion routing system and is a network of encrypted connections. It works to hide users’ identity and their online activities from monitoring and analysis efforts. Since each layer is encrypted, the Tor network ensures that there is anonymity between the routers. When data is sent on a Tor network, it takes a random, private pathway through different relays. Each relay is only aware of the relay that came before it and the relay that comes next. No single relay will ever know all the relays in the sequence. The user’s circuit is changed every ten minutes, to prevent monitoring.

Like any anonymity network, the Tor system does have its shortcomings. Tor is mainly designed to ensure the secure transport of data. However, data sent on the Tor network may be monitored by any party that has access to both origin and destination of a user’s connection. In the US, the federal government is entitled to monitor domestic internet activity, in accordance with the Communications Assistance for Law Enforcement Act (CALEA).

Encryption

Many users rely on encryption tools to protect sensitive information transmitted online. Numerous encryption tools have been developed to enable users to protect their information. Encryption algorithms render information unreadable to individuals unless they have the encryption key. The longer the encryption key, the more difficult it is for an attacker to decrypt the information. While previous encryption keys were only 56-bits, most privacy professionals will recommend 128-bit encryption keys.

File Encryption

There are different types of encryption for different purposes. File encryption ensures that sensitive data transmitted over the internet, or that information stored on a home system is secured.

One example of file encryption software is Pretty Good Privacy (PGP), developed by Philip Zimmerman in 1991. PGP applies a combination of data compression, symmetric-key cryptography, hashing and public-key cryptography. PGP uses a web of trust to ensure that the public key is distributed to and used by the correct person. This software provides relatively high security. In a number of different incidents, the FBI and other law enforcement agencies were unable to access files that had been encrypted with PGP.

GNU Privacy Guard (GnuPG) is another suite of cryptographic software, developed by Werner Koch in 1999. It was designed to operate together with PGP. GnuPG works by using asymmetric keypairs to encrypt messages. The public keys are then exchanged with the appropriate individuals, verifying the recipient. GnuPG relies on a number of different encryption algorithms, such as block ciphers, asymmetric-key ciphers, cryptographic hashes and digital signatures.

Email Encryption

Emails may be vulnerable to interception from the point it leaves the sender until it arrives at its recipient. For instance, companies have the authority to monitor their employees’ email messages. Email server administrators also have access to the email stored on their servers. There are a number of different email encryption programs, with various security capabilities.

A common way to ensure the security of email messages is to use digital signatures. Digital signatures apply public-key cryptography attached to the email message. Digital signatures identify the sender, ensure that the message has not been modified or tampered with and underscore the legal consequences of the message for the sender and recipient. Digital signatures are also relatively efficient and offer a relatively high level of assurance of the authenticity of the sender. Digital certificates work together with digital signatures to verify the identity of the public key holder.

Like any other security model, there are shortcomings of the digital key system. Private keys are still vulnerable to theft or copying. For instance, a third party may gain enough information to create a copy of a private key. Digital certificates could theoretically be forged or cracked, though according to researchers, this would be highly difficult to do.

Filters

Filters are a broad category of tools that can selectively control the online content that appears on the user’s system. For example, a filter may be designed to block emails, HTML cookies, websites, HTML headers or other unwanted content. Filters may be used by organizations to prevent access to certain online content, by individuals who do not want spam messages, or by parents to protect their children from inappropriate content.

A cookie cutter is a type of filtering program that blocks a system from exchanging cookies with another website. Cookie cutters may also prevent websites from displaying specific types of cookies, or stop the user’s browser from sending header information to the website. One example of such a program is Internet Junkbuster, which blocks the browser from loading banner ads and other cookies. It functions as a proxy between the browser and the internet and allows the user to configure which cookies or files to block or allow.

Summary

This article introduces the importance of protecting online privacy through three major categories of tools: anonymizers, encryption and filters. Anonymizers prevent the user’s identity from being revealed, while allowing the user to browse on the internet. Encryption tools ensure the secure transmission of data, for instance files or email. Filters block specific content from being loaded by internet browsers. The article explains the functions of each of the privacy tools and offers some examples of each tool.

CIPP/IT Preparation

In preparation for the Certified Information Privacy Professional/Information Technology exam, a privacy professional should be comfortable with topics related to this post, including:

• Privacy-enhancing technologies (III.B.c.)
• Anonymity tools (III.B.d.)
• Applications of anonymity tools (III.B.d.iii.)
• Tor Anonymity System (III.B.d.iii.5.)

Several years ago, using software engineering methods, University of California San Diego researchers demonstrated SSH is provably secure.  And SSH has shown itself to be nearly as good as claimed, posting only 31 bugs since 1998, most of which were minor.  Until now…  Three researchers from the Royal Holloway Information Security Group (ISG) at the University of London, Martin Albrecht, Kenny Paterson and Gaven Watson, found flaws in the proof.  They’ve shown that SSH is vulnerable to a “Man-in-the-middle” attack, where someone inserts themselves between a sender and receiver, grabs information, changes it and sends it along.

The Problem

There are actually three problems that account for the ISG discovered flaw:

1. The first lies in the manner the original security models used for the proof were constructed. The original proof pre-supposes garbled information may simply be reset as a failure and will not impact the security of the encryption used to protect the data.  The model never distinguished between the various kinds of failure, but the failure information turns out to be accessible to an adversary.  
2. The second is an implementation decision made by the original software developers for SSH.  The developers had two choices: send how big the transmitted information is (packet length field) unencrypted, which gives a small amount of information that tells an attacker how much data they had to crack, or encrypt hacker detectable information in the packet length field, possibly creating a “known plaintext” attack and thereby decreasing the keyspace.  SSH’s developers chose the unknown.  
3. The last problem has to deal with encryption modes and feedback loops.  In order to efficiently create and keep an encrypted tunnel between two computers hard to break, information from the current set of mathematical operations is used to incrementally change the next set, preventing various encryption attacks.  What data are taken from the current packet and fed into the next depend on the “cryptographic mode” chosen.  By default, SSH uses cipher-block chaining (CBC) mode instead of counter (CTR) mode.

Exploiting the ssh flaws

The ISG researchers took the error information reported that the proof never accounted for, and the design decision made by SSH developers, and began tinkering.  They eventually found a method of reducing the security in the default settings of SSH.  They reduced the overall security by creating a guessing game where an attacker has a one in 262,144 chance of success versus a brute force attempt at 1 in 4.2 billion  (2^18 vs 2^32).  You’ll only recover a very small amount of information using this method (14 or 32 bits), but it is enough to be useful.  The researchers’ vulnerability was first announced in November 2008, when the UK Centre for the Protection of National Infrastructure (CNPI) simply could not ignore the problem and, working with the ISG, issued a CPNI advisory.  Full details of the flaw were not announced until this month, when the researchers presented at an IEEE Symposium in California.

Vulnerability mitigation strategies

Even though the attack will work “with probability 1″ in some circumstances, it’s somewhat difficult to pull-off in general, and is about as stealthy as a freight train.  OpenSSH v 5.2 and above should not be susceptible to this particular exploit.  According to the CPNI advisory, the SSH flaw may be mitigated in current SSH versions by using CTR mode instead of the default CBC mode.  

Takeaway

This same technology reliance problem shows up repeatedly.  Use new equipment and products to increase efficiency, but do not over-rely on automation and technology.  Someone somewhere will notice of something unexpected, even with proven secure products.  Audit system results and write policies to take into account that the technology eventually will fail, not just from hackers or even questionable coding decisions – hurricanes, fires and employee clumsiness can all accomplish the same thing.  If your systems fail, any private information exposed will cost money – in breach notifications, time resetting the systems and general reputation.   The ISG researchers summed up the situation succintly in their paper: 

Unfortunately, it seems that real world cryptographic implementations are more complex than the current security models for SSH handle.

CIPP Candidate Preparation

In preparation for the Certified Information Privacy Professional exam, a privacy professional should be comfortable with topics related to this post including:

• Managing Risk and compliance (Foundations:I.G.b) including: Privacy Policy Development, Risk Management, Compliance
• Information Security (Foundations: II.C) including: Encryption (data-in-motion) and Threats & Vulnerabilities