DualQRCode.com offers a free online tool to create dual QR codes. These codes seamlessly embed a smaller QR code within a larger one, allowing for two distinct links to be accessed from a single image. The user provides two URLs, customizes the inner and outer QR code colors, and downloads the resulting combined code. This can be useful for scenarios like sharing a primary link with a secondary link for feedback, donations, or further information.
This post showcases a "lenticular" QR code that displays different content depending on the viewing angle. By precisely arranging two distinct QR code patterns within a single image, the creator effectively tricked standard QR code readers. When viewed head-on, the QR code directs users to the intended, legitimate destination. However, when viewed from a slightly different angle, the second, hidden QR code becomes readable, redirecting the user to an "adversarial" or unintended destination. This demonstrates a potential security vulnerability where malicious QR codes could mislead users into visiting harmful websites while appearing to link to safe ones.
Hacker News commenters discuss various aspects of the QR code attack described, focusing on its practicality and implications. Several highlight the difficulty of aligning a camera perfectly to trigger the attack, suggesting it's less a realistic threat and more a clever proof of concept. The potential for similar attacks using other mediums, such as NFC tags, is also explored. Some users debate the definition of "adversarial attack" in this context, arguing it doesn't fit the typical machine learning definition. Others delve into the feasibility of detection, proposing methods like analyzing slight color variations or inconsistencies in the printing to identify manipulated QR codes. Finally, there's a discussion about the trust implications and whether users should scan QR codes displayed on potentially compromised surfaces like public screens.
This post details the process of creating a QR Code by hand, using the example of encoding "Hello, world!". It breaks down the procedure into several key steps: data analysis (determining the appropriate encoding mode and error correction level), data encoding (converting the text into a bit stream), error correction coding (adding redundancy for robustness), module placement in the matrix (populating the QR code grid with black and white modules based on the encoded data and fixed patterns), data masking (applying a mask pattern for optimal readability), and format and version information encoding (adding metadata about the QR Code's configuration). The post thoroughly explains each step, including the relevant algorithms and calculations, ultimately demonstrating how the final QR Code image is generated from the initial text string.
HN users largely praised the article for its clarity and detailed breakdown of QR code generation. Several appreciated the focus on the underlying principles and math, rather than just abstracting it away. One commenter pointed out the significance of explaining Reed-Solomon error correction, highlighting its crucial role in QR code functionality. Another user found the interactive demo particularly helpful for visualizing the process. Some discussion arose around alternative encoding schemes and their potential benefits, along with mention of a similar article focusing on PDF417 barcodes. A few commenters shared personal experiences using the article's information for practical projects.
Summary of Comments ( 1 )
https://news.ycombinator.com/item?id=42824553
Hacker News users discussed the practicality and security implications of dual QR codes. Some questioned the real-world use cases, suggesting existing methods like shortened URLs or link-in-bio services are sufficient. Others raised security concerns, highlighting the potential for one QR code to be swapped with a malicious link while the other remains legitimate, thereby deceiving users. The technical implementation was also debated, with commenters discussing the potential for encoding information across both codes for redundancy or error correction, and the challenges of displaying two codes clearly on physical media. Several commenters suggested alternative approaches, such as using a single QR code that redirects to a page containing multiple links, or leveraging NFC technology. The overall sentiment leaned towards skepticism about the necessity and security of the dual QR code approach.
The Hacker News post for "Dual-Link QR Code Generator" (https://news.ycombinator.com/item?id=42824553) has several comments discussing the utility and security implications of the tool.
One commenter highlights the potential for abuse, suggesting that shortened URLs within the QR code could mask malicious links. They emphasize the importance of verifying the destination before clicking, mirroring the general caution surrounding shortened URLs. This concern is echoed by another commenter who points out that the dual QR code approach doesn't inherently address the underlying security issue of trusting shortened links. They argue that a single, verifiable QR code directly encoding the final destination is a more secure solution.
The practicality of the tool is questioned by a commenter who suggests it's simpler to just use a URL shortener and embed the shortened URL in a single QR code. This comment sparks a discussion about the specific use case presented by the tool's creator, which involves bypassing URL blocking in certain environments. The creator explains that the primary link is often blocked, necessitating a backup link accessible through a different domain. The dual QR code approach allows both links to be readily available.
This explanation leads to a discussion about alternative solutions to URL blocking, including using VPNs or different network configurations. One commenter suggests that if the primary link is frequently blocked, it might be a sign of a larger problem that requires a more robust solution than a dual QR code.
The technical implementation of decoding both URLs simultaneously is also discussed. A commenter inquires about how the decoder differentiates between the two QR codes and the creator explains that they are visually distinct, allowing a properly designed decoder to recognize and decode both.
Finally, there's a brief discussion about the visual design and whether the dual QR code is aesthetically pleasing. One commenter expresses a dislike for the design, while another suggests improvements to enhance its visual appeal.
Overall, the comments express a mixed reaction to the dual QR code generator. While some see a potential use case for bypassing URL blocks, others remain skeptical about its practicality and security benefits, suggesting alternative solutions might be more appropriate. The discussion also touches upon the technical implementation and visual design of the tool.