A blacklist is a list of one form of entity or another that the list’s curator has determined to be unwanted. The list is then used to actively restrict the listed entities in one form or another depending on the specific use case. Blacklists may be extremely specific against particular individuals, or software programs for example. Alternatively, they can also be quite general such as with a location-based blacklist. Lists can end up affecting innocent parties but there may or may not be an appeals process depending on the list and its curators.
Examples of general use
A classic class of a blacklist is a list of blocked URLs. There are plenty of potential reasons to block websites. Common classes of sites that get blocked include sites that serve malware. Phishing sites, gambling sites, adult content, and social media are all common targets of blacklists. These blacklists may be enabled by installing some management software, through settings on routers, via ISP settings, and may even be government-mandated.
Very closely related to URL blacklists are IP blacklists. These are more typically implemented on servers against malicious users. For example, a user running an online password brute force attack may generate enough failed login attempts that an automated system adds the attacker’s IP address to a blacklist. Depending on the implementation, this sort of blacklist may be temporary, expiring a set amount of time after the attack stops. It may, however, be a permanent block.
To prevent users from selecting known weak passwords, some organisations and sites implement a password blacklist. Technically, password complexity rules don’t qualify as a blacklist as they are more of a validation rule. Nevertheless, some sites check new passwords against lists of passwords that have previously been involved in data breaches. These passwords are significantly more likely to be attempted by a hacker in the future and so are considered extremely weak.
Some governments or organisations may implement regional blacklists. For example, blocking access to their services to users in an authoritarian country with a repressive regime. Conversely, authoritarian countries with repressive regimes may blacklist access to external content. This often targets external news sources, social media platforms, or the wider Internet in general.
Methods of bypassing blacklists
It may not be possible to bypass all blacklists. This is especially the case when dealing with systems primarily controlled by a third party. Additionally, bypassing, or even attempting to bypass a blacklist may be considered a criminal act, a fireable offence, or viewed negatively in some other way depending on the blacklist and who implemented it.
VPNs are a classic way of bypassing blacklists. They involve setting up an encrypted connection to a third party and then routing all traffic through there. From the perspective of a network monitor, all they see is encrypted traffic to the third party, not where that traffic goes after that. Some blacklists are implemented by using a custom DNS server. These are typically ineffective as they can be bypassed by manually switching DNS server to a public unfiltered one such as 8.8.8.8 run by Google or 1.1.1.1 run by Cloudflare.
IP blacklists can often be dodged by power cycling your router. This typically results in your ISP providing you with a new public IP address to use that is unblocked. This can negatively affect other innocent users if they later get assigned the blacklisted IP. This is why IP-based blacklisting is typically temporary.
Controversies
There is little difference between mandatory blacklist implementation and censorship, especially when enforced by a government. In some cases, affected parties may not generally object to the application, in other cases the filters may be regarded as oppressive. Attitudes on the subject tend to vary by culture and by the type of content blocked.
There is social tension over the use of the word “Blacklist”; specifically, the use of the word black. Parallels are drawn between racism and the fact that the polar opposite of a blacklist is referred to as a whitelist. Arguments typically state that the word black and its actively negative connotations contributes to or is at least an example of the use of racist language. There is considerable and often quite emotive discussion on the subject and even the validity of some of the arguments. A similar argument, however, is brought up regarding the use of the terms “master” and “slave” in computing. On that subject, there are still some willing to debate but it is generally much more of a clear-cut issue.
Suggested alternatives to the term blacklist include “deny-list” and “block-list”. Whitelist primarily sees the alternative term “allow-list”. Master and slave terminology is typically replaced with the terms “primary” and “secondary” respectively, though some other terms have been suggested or adopted. While some may not agree with the suggested reasoning for the change in terminology, there are benefits. Firstly, it does address any potential racial issues, increasing inclusivity. Additionally, it also makes the language clearer to understand. Most of the suggested alternative terms are instantly understandable to people for whom English is not their first language. Some of the older terms can require a deeper cultural understanding and context rather than simply knowing the language.
Conclusion
A blacklist is a list of some form of entities that is used to prevent access to, or potentially from, the listed entities. The curator of the list may or may not have some sort of appeals process. Blacklists are often used to deny access to content deemed objectionable. They may also be used to prevent access from senders deemed objectionable. Blacklists can be implemented at many levels, by many different curators, and are complementary. By design an entity on the blacklist is blocked, implying all other unspecified entities are allowed. The opposite is a whitelist. A whitelist is typically a list of exclusively allowed entities, but may not necessarily be exclusive, instead being a way to prevent an entity from being blacklisted. The term blacklist is challenged for its potentially racially insensitive connotations. The alternative terms “block-list” and “deny-list” are intended as objectionable drop-in replacement terms.
