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9

TL;DR Anyone can send a message and say it is from Alice if it is not signed; there is no way for Alice to prove that she didn't send those unsigned messages. However, Alice can prove she sent a message by signing it with a private key. Similarly, anyone can say Bob read a message, and Bob can't prove he didn't. But Bob can prove he read a message by signing ...


8

In practice, unless Bob sends a signed receipt, you are out of luck. The underlying cryptographic problem is called fair exchange. If you consider a network protocol such that Alice and Bob want to send each other some data elements (e.g. in your case an email from Alice to Bob, and a receipt from Bob to Alice; but it also works as a model for payments), ...


6

You've evolved to mostly right, but to add several points and expand on @CoverosGene more than I felt comfortable doing in an edit: X.509 defines a certificate (and some other things not relevant here) in ASN.1, a (very!) general data structuring method which has several defined encodings, of which DER Distinguished Encoding Representation is quite common ...


4

You can have SSL/TLS without certificates. This is supported in the TLS standard: the "DH_anon" cipher suites involve no certificate whatsoever. But you have to remember that such an unauthenticated TLS is inherently weak against active attackers, since they cannot prevent client or server impersonation (or both at the same time, which is called a ...


4

SSL/TLS (the underlying protocol for HTTPS) provides two features: Encryption, so that nobody could passively listen to the data. Encryption is done using a key which is somehow shared between the peers. Identification, so that you can be sure who you are talking to. This is usually done with certificates. While you might have encryption without ...


4

Guess My educated guess from reading the spec: The browser will never see more than one server-certificate. Rather the cipher spec is negotiated in advance. And ONLY THEN does the server send the certificates. So if negotiation winds up with an an RSA-cert authenticated cipher suite, then the RSA cert chain will be sent. And if the negotiation winds up with ...


4

Fiddler captures HTTPS traffic by generating on-the-fly a fake certificate for the intended server, thereby running a complete Man-in-the-Middle attack. This requires that the client is configured to accept the Fiddler-controlled CA as a trusted CA, as described in the documentation. This kind of interception breaks client certificates. When there is a ...


3

Check if you're running Chrome 39, there are major changes to the way some certificates are treated - e.g. Chrome 39 starts to penalize sites with long-lived SHA1 certificates This release warns about SHA1 certificates that expire in 2017. Versions 40 and 41 will increase the scope of the warnings to include certificates that expire in 2016. More info can ...


3

If you want to require Bob to let Alice know whenever Bob has received a message, as far as I know there isn't any such system built into the most common cryptographic systems. You would need to go outside of cryptography for a bit and require a server which tracks every time a message is downloaded from it. For instance, Alice could send a secret URL to ...


2

If Charles proxy is able to intercept SSL/TLS traffic, then certificate validation has failed. This demonstrates that the mobile device is not properly verifying the server's certificate. In a mobile security assessment, certificate pinning can be disabled by hooking the platform's SSL/TLS implementation and changing how certificate validation works. An ...


2

Windows manages certificates and private keys separately. Each certificate may point to a private key; several certificates can point to the same key. Each such "pointer" is given as the name of the Cryptographic Service Provider (that morally contains the key), and the key name within that CSP. Windows does not keep track of how many certificates point to a ...


2

Any self-verification mechanism included in the executable file could be replaced or removed by the attacker who intercepts the file. Therefore, we must leave signature verification to a system external to the downloaded executable, for example, the operating system. There are three possible outcomes such a verification system can produce: The signature ...


2

Not only will they not issue new certificates for unvalidatable IPs, but also revoke them in 2016. https://www.digicert.com/internal-names.htm As from 1 October 2016, CAs shall revoke all unexpired Certificates. More info in Mozilla's Wiki: CA:Problematic_Practices#Certificates_referencing_hostnames_or_private_IP_addresses


2

For public IP it must be checked that the IP is actually owned by the one who requests the certificate. Issuing certificates for private (reserved) IP is deprecated because obviously the ownership cannot be checked. For more information see CA baseline requirements Sect 9.2.1.


2

I had a very similar problem with Postfix and Dovecot on Ubuntu. I had purchased the basic SSL certificate from Comodo and because I selected "other" as the server type I ended up with a zip file with four certificate files in it, as per the above posts. I wasn't getting security exceptions in the client. In my case I couldn't even get past the account ...


2

If you run the following command, you will see that when the person managing TLS for the server replaced the leaf certificate (the certificate for the server himself), he did not replace the chain (the certificates of the Certifying Authorities that build the chain of trust). echo |openssl s_client -connect www.prioenergie.de:443 -showcerts 2>&1 |grep ...


2

This is a purely technical error on the side of the website administrators. This is not a security issue. They simply exchanged the end entity certificate but forgot to exchange the chain. This makes it seem invalid to some browsers. It is required by the standards that the webserver must present this this chain. But this is a courtesy to the client and a ...


1

The certificate is not valid. By definition you cannot trust it. That's the whole point of having a certificate chain. In all evidence, it has simply been incorrectly configured; you can find the same problem - from the point of view of the webmaster - here. You might query Thawte... but I wouldn't hold my breath for an answer. They'll probably feel, quite ...


1

Can a page served by (1) call (2) by javascript ? Yes, using Cross-origin resource sharing (aka CORS). Access-Control-Allow-Origin: https://adomain.com Access-Control-Allow-Methods: GET, POST Can (1) and (2) "share" cookies ? Yes, you can share cookies setting them to domain = ".adomain.com".


1

Thanks to Milen I saw that I have had a version update of google chrome (from 38.0.2125.111 to 39.0.2171.71) just while downloading firefox. The Chrome's UI did the update without any notification, and this fooled me. Quite strange, from Google. I mean: would you like to know that an upgrade will change the security policy in the next execution of the ...


1

Verify that your Key is not protected by passphrase. Postfix does not supports passphrase protected Keys anyway you can remove the passphrase from the key using an openssl command openssl rsa -in passphrase.key -out nopassphrase.key is not necessary to include the Root CA if your CA Bundle does not include your CA Root you can append it: cat ...


1

(Edit 2014-11-25: Reworded flushed out to phased out.) Short answer: From what I can tell, they will be gracefully phased out, not flushed out. (At least by Microsoft.) The old SHA1 root certs will expire regularly and Microsoft will no longer accept NEW SHA1-roots starting 2016. The old ones will stay in I guess, since they were compliant to the guidelines ...


1

The whole goal of HTTPS is to prevent eavesdropping so that anyone monitoring your web traffic can't see what you're sending. As useful as it is, HTTPS presents a bit of a problem to antivirus software because when you visit sites over an encrypted connection, your antivirus software cannot see what sites you're visiting or what files you're downloading, at ...


1

While there doesn't appear to be any existing privacy-friendly CAs at this moment, all evidence suggests that the recently-announced Let's Encrypt CA (launching summer 2015) will not require users to provide personal information. This could change, but I doubt it will given EFF's involvement. If Let's Encrypt will not collect any personal information when ...


1

PKCS #7 can be thought of as a format that allows multiple certificates to be bundled together, either DER- or PEM- encoded, and may include certificates and certificate revocation lists (CRLs). Per RFC2315, PKCS#7 is a general syntax for data that may have cryptography applied to it, such as digital signatures and digital envelopes. The syntax admits ...


1

Because verification is up to clients. And some of these didn't do a good job. So to support these you had to fiddle with the certificates. MichaelHolm.Info: IP addresses in SubjectAltName in SSL website certificates #fail for some browsers


1

Why do CSR utilities give you the option to list an IP as an IP if this does not work? I don't know which CSR utilities you refer too, but some of them target people who know what they do. Certificates are not restricted to browsers and the rules how they get used differ in other contexts. Especially the often used openssl is a tool which is able to ...


1

In SSL/TLS, the server is supposed to send not only its certificate, but a complete chain that goes from the root to the server's certificate (the root itself may be omitted, but the intermediate CA should be sent). If the server does not send a complete chain, then it is up to the client to try to complete it, e.g. by downloading the missing certificate, ...


1

The question is, assuming you've decided which CA's (Certificate Authorities) to trust, how do you get their certs. If you trust "Starfield Services Root Certificate Authority - G2" and you want to know if you should trust the hypothetical ""Starfield Services Root Certificate Authority - G3" (for example), you do have to "get it from the horse's mouth" as ...


1

Sounds to me like you looking more at the integrity of the actual file or data. When it comes to checking to ensure it is not infested with a possible virus, that where your Antivirus comes into play, or a UTM on your Firewall. For instance; a Sonicwall Firewall appliance would be able to ensure the safety of that file. but the actual integrity of the file ...



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