From memory, online and offline transactions are usually split out by BIN number (first six digits)
The BIN will tell you which bank was the issuer and which class of card you have, like standard or premium, though most readers probably don't take that into account beyond the card scheme and card type associated with the range that the individual BIN is in. Many banks will have multiple BINs for the same card type if they are large.
Credit / online debit / offline debit usually get different ranges. The reader gets a list of the ranges when it updates and they don't change super often. Offline readers can be configured to reject cards with a number in an online only range.
It's usually based on the chip settings. Rules aren't as simple as "always online" or "never offline"; an issuer can e.g. convey that they'd prefer online transactions for certain types of payments, while offline is ok for others, via relatively complex configurations of the code of the chip application.
Before that, there was the service code on the magnetic stripe, which also can convey things like "online only" or "domestic use only".
The BIN is only involved in risk management on the terminal's side: Many of these in-flight terminal accept deferred online transactions, which means that, even though they're completely offline, they take the risk of accepting an online-only card. (For truly offline capable cards, the risk is often with the issuing bank.)
That type of risk management can benefit from knowing what type of card it is, and prepaid cards are often seen as riskier (because customers might intentionally drain them before a flight). Of course, debit and credit cards can also be empty/marked as stolen, but these are marginally harder to get and replace.
Yep you are completely correct; people don't realise how complex the chip is - it has what you'd legitimately recognise as an operating system! It can also be reprogrammed over the wire, if your chip and pin is taking a bit toooo long that might be what's happening.
Your correct on the risk spread. I wasn't confident last night (I'm not totally versed on the terminals) but looked it up. As I understand if you choose to accept offline only payments then you accept the risk of the transaction failing. If it's the issuers choice they own the risk.
My employer in the UK had a machine in around 2014, but it was only used for sales of their own products to employees.
It put all the transaction risk onto the employer, and had a high fee per-use, but since they only had these 'stock clearance' sales to employees once a year it was fine.
I used to have an online maestro card (was solo and now known as debit mastercard) and an offline card (was switch, now also known as debit mastercard) from a UK bank, due to having two current accounts there.
The offline card was from a current account with an overdraft and also worked as a cheque guarantee card, for cheques up to £250 under the (discontinued ~2011) cheque guarantee scheme[0] and had a special hologram on the back. The retailer would watch you sign the cheque and write details about you, the card and any CCTV etc. on the back of the cheque. I imagine the offline behavior of the card was similar, and was a carry over from that.
The online card was from a basic account with no overdraft facility and acted a bit like a prepaid debit card.
Often you will obtain a vulnerability in some software and then search for companies using it. You can often use Google or Shodan to do the searching, but perhaps ingested LLM data could also work.
In the simplest case if you get remote code execution in SuperServer9000 (made up product) and that has a banner on error / status pages that reads "Powered with pride by SuperServer9000 version 2.1", then you could just search for that string (or part of it) and use your remote code execution bug against any sites that come up.
It can get behavior based or more complicated than that though, or rely on information that an LLM has ingested about a company from public sources.
Then either grab data and sell it or sell your access to a broker or whatever else.
Would it even be possible to enumerate all edge cases and test all the permutations of them in non-trivial codebases or interconnected systems? How do you know when you have all of the edge cases?
With fuzzing you can randomly generate bad input that passes all of your test cases that were written using by whatever method you have already been using but still causes the application to crash or behave badly. This may mean that there are more tests that you could write that would catch the issue related to the fuzz case, or the fuzz case itself could be used as a test.
Using probability you can get to 90 or 99% or 99.999% or whatever confidence level you need that the software is unaffected by bugs based on the input size / number of fuzz test cases. In many non-critical situations the goal may not be 100% but 'statistically very unlikely with a known probability and error'
It is highly recommended to configure two or more DNS servers incase one is down.
I would count not configuring at least two as 'user error'. Many systems require you to enter a primary and alternate server in order to save a configuration.
The default setting on most computers seems to be: use the (wifi) router. I suppose telcos like that because it keeps the number of DNS requests down. So I wouldn't necessarily see it as user error.
The funny part with that is that sites like cloudflare say "Oh, yeah, just use 1.0.0.1 as your alternate", when, in reality, it should be an entirely different service.
> So if you want to use DNS over HTTPS on Android, it is not possible to provide a fallback.
Not true. If the (DoH) host has multiple A/AAAA records (multiple IPs), any decent DoH client would retry its requests over multiple or all of those IPs.
Does Cloudflare offer any hostname that also resolves to a different organization’s resolver (which must also have a TLS certificate for the Cloudflare hostname or DoH clients won’t be able to connect)?
DoH hosts can resolve to multiple IPs (and even different IPs for different clients)?
Also see TFA
It's worth noting that DoH (DNS-over-HTTPS) traffic remained relatively stable as most DoH users use the domain cloudflare-dns.com, configured manually or through their browser, to access the public DNS resolver, rather than by IP address. DoH remained available and traffic was mostly unaffected as cloudflare-dns.com uses a different set of IP addresses.
> A cross-organizational fallback is not possible with DoH in many clients, but it is with plain old DNS.
That's client implementation lacking, not some issue inherent to DoH?
The DoH client is configured with a URI Template, which describes how to construct the URL to use for resolution. Configuration, discovery, and updating of the URI Template is done out of band from this protocol.
Note that configuration might be manual (such as a user typing URI Templates in a user interface for "options") or automatic (such as URI Templates being supplied in responses from DHCP or similar protocols). DoH servers MAY support more than one URI Template. This allows the different endpoints to have different properties, such as different authentication requirements or service-level guarantees.
Yes, but this restriction of only a single DoH URL seems to be the norm for many popular implementations. The protocol theoretically allowing better behavior doesn't really help people using these.
Sometimes devs rely on Chrome specific quirks, or are shipping broken apps that Chrome manages to make the correct guesses for it to be functional.
Many see 'it works on Chrome and mobile Safari' as 'it works' and they can get project signoff / ship / get paid / whatever and don't care about other users
The company that has the application may not know until a few users complain (if they complain) and by that point it could be too late due to the contract, or they may not understand what a different browser is or care either.
The BIN will tell you which bank was the issuer and which class of card you have, like standard or premium, though most readers probably don't take that into account beyond the card scheme and card type associated with the range that the individual BIN is in. Many banks will have multiple BINs for the same card type if they are large.
Credit / online debit / offline debit usually get different ranges. The reader gets a list of the ranges when it updates and they don't change super often. Offline readers can be configured to reject cards with a number in an online only range.
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