I am on a website where I need to pay for something. This website has the following warning in the top left:
This site uses a weak security configuration (SHA-1 signatures) so your connection may not be private
Should I go ahead and enter my card details and pay for something on this site?
What are the security risks?
Extra Info:
I am using Google Chrome on a Windows 10 Machine.
In internet Explorer I get the following Message:
It's a bad sign, but it is still very unlikely that the connection is being eavesdropped on.
The website appears to have a valid certificate signed by a certificate authority, but it is signed with a weak and obsolete hash algorithm.
What does that mean?
It means the connection is encrypted and a passive eavesdropper can still not listen in. But a determined attacker with access to lots of processing power could generate a fake certificate for this website and use it to impersonate the website. So it is possible you aren't actually on the website you think you are but are instead on one controlled by a hacker. But such an attack would require quite a lot of resources and additionally require to be in control of a router between you and the website.
But even when we assume that no attack is taking place, we should keep in mind what impression this makes. SHA-1 is obsolete for quite a while now. When the admins of that site still do not bother to update, that's a quite bad sign for their general competence. It could mean that they are also quite lax regarding other aspects of security of their website. The final decision what information you provide them with is yours to make.
As others have said, technically the risk is small for a MiM attack. However this has a larger problem and implication.
Should I go ahead and enter my card details and pay for something on this site?
The SSL issue is, as stated by others, relatively minor, however, using a SHA-1 hash means two very important things.
Important notes:
Note when writing this answer and with comments, significant changes to the answer needed to be made. In short the use of SHA-1 hashes in a PCI compliant setting is very obscure, and relies on a mesh of different rules to allow it. While not currently out right forbidden in current PCI-DSS setups it soon will be. Currently it is allowed only though a combination of clauses meant to support odd/old client(browser) configurations. Most notably the "Older SSL" clauses that allow for insecure SSL setups with other means of security in order to support older (think IE6) browsers. This answer has changed a lot to reflect this. The notes below are from the original answer, but shows, IMO, an important process.
Note After some research this answer, based mostly on the fact that they didn't bother to do the PCI Audit at all, is largely wrong. They could have completed the PCI audit. That being said, the general idea is still true. If they "worked around" the SHA-1 issue instead of just updating to "something else" then my opinion stands. Keep in mind that allowing SHA-1 is supposed to be for "aging, old, and legacy" systems and not as an ongoing practice. You now (today) have to have a migration plan in place even to pass the audit.
More Notes I will have to address this and clean up this answer, but according to "the docs" there is some general rules. First older sites can still offer SHA1 as an encryption or signing option but only if other, stronger options are available too. New sites can not offer SHA-1 at all. Any sites using SHA-1 must have a migration plan. (AVS should auto fail, but you can get an exception). Lastly there is a clear cutoff date for SHA-1 (though it can be moved, yet again)
It means that the certificate used by the site is using an outdated signature algorithm to confirm the certificate identity. Google has been aggressively targeting SHA-1 signatures for site certificates for a couple of years, since there are some theoretical attacks which could result in a fraudulent certificate having a valid signature, although there has not been any evidence of this happening in the wild. Furthermore, the method of attack would require significant effort, and is unlikely to be profitable for anything other than really high value targets.
The main reason for the warnings is to encourage web site owners to update to more secure signing methods, which are usually available for free or low cost from their certificate providers, but offer longer term protection as computer technology improves - this process took 16 years in the case of MD5, the predecessor to SHA-1. The certificate itself is no weaker than any other - in fact, it is technically possible for a single certificate to be signed by both SHA-1 and SHA-256 methods. There may be other weaknesses in the certificate, but it's not possible to see from the screenshots provided.
Overall, it suggests a slightly shoddy approach to security of the site, but doesn't itself mean that your card details are likely to be stolen in transit. It may be worth contacting the company pointing out this error, and suggesting they update the certificate, especially if you need to make purchases from there regularly.
Also, see https://konklone.com/post/why-google-is-hurrying-the-web-to-kill-sha-1 for some more details on this.
Others have noted the problems getting the card info to the site, but you must also think about how they handle that information internally. I once worked at a dotcom that stored credit card info in our database in plain text. Anyone with access to client info could see them.
Lazy certification is only the tip of the iceberg, IMO.
Besides the normal Philip Dick kind of paranoia which tells you nothing is as it seems -- ever -- there is nothing that can be inferred from simply seeing that Chrome has alerted you to a site's using SHA-1 for their certificate's signature. Google said they were going to do this back in 2014. You could be on Amazon.com, using Chrome. The fact is, if Amazon hasn't started encrypting their certificates' signatures using SHA-2, Chrome will throw a warning.
