Short of somehow convincing the victim to send you a copy of their message, you have no means of accessing your recently-leaked data.
Public-key signatures should always be considered public when anticipating attacks. Use HMACs if you want secret authentication.
That leaked data would be publicly available. Anyone with knowledge of your scheme would also be able to access that data. Any encryption would be worthless because the encryption would take place client-side and all credentials thus would be exposed to the public as well.
You explicitly mentioned Decoy in your article, and a similar method could be used to leak bits to an attacker with no one else being able to recover them. We’re discussing public key encryption in this article which means that completely public javascript can indeed securely encrypt data using a public key and only the owner of the corresponding private key can decrypt it.
Because the script runs client-side, it also makes it extremely easy for a potential victim to examine your code to determine if it’s malicious or not. And, even if they’re too lazy to do so...
Sure, the first five or ten times it’s served. And then one time the victim reloads the page, the compromised script runs, leaks as much or all of the private key as possible, and then never gets served again.
A private key is long. A PGP signature is short. So your victim’s compromised signature would be 10x longer than the length of a normal PGP signature.
An exported private key is long because it includes both factors, the private exponent, and the inverse of p mod q. In my other comment I was too lazy to decode the key and extract one of the RSA factors, but one factor will be ~50% of the size of the RSA signature and that’s all an attacker needs.
Well shit. This is the third time I’ve had to re type this post so forgive the brevity.
You are right but it makes the attack less effective, since it’s a phishing attack not a targeted one. I can’t think of an efficient way for an attacker to collect these compromised signatures without making it even more obvious to the victim.
This is correct, you could asymmetrically encrypt the data.
The intended use is for the user to download the script and run it locally. Seving a compromised copy 10% of the time would just lower the reach of the attack. Especially cause the visitor can still verify the source code, or verify the output of the signature.
Even if you cut the size of the private key in half, the signature would still be 5x longer than a standard PGP signature, and the fact that subpacket 20 has been padded with a large amount of data would be immediately visible to the victim upon verifying their own signature. (Note that I didn’t include a verification tool, so the visitor would have to do that on their own trusted software.)
Public-key signatures should always be considered public when anticipating attacks. Use HMACs if you want secret authentication.
You explicitly mentioned Decoy in your article, and a similar method could be used to leak bits to an attacker with no one else being able to recover them. We’re discussing public key encryption in this article which means that completely public javascript can indeed securely encrypt data using a public key and only the owner of the corresponding private key can decrypt it.
Sure, the first five or ten times it’s served. And then one time the victim reloads the page, the compromised script runs, leaks as much or all of the private key as possible, and then never gets served again.
An exported private key is long because it includes both factors, the private exponent, and the inverse of p mod q. In my other comment I was too lazy to decode the key and extract one of the RSA factors, but one factor will be ~50% of the size of the RSA signature and that’s all an attacker needs.
Well shit. This is the third time I’ve had to re type this post so forgive the brevity.
You are right but it makes the attack less effective, since it’s a phishing attack not a targeted one. I can’t think of an efficient way for an attacker to collect these compromised signatures without making it even more obvious to the victim.
This is correct, you could asymmetrically encrypt the data.
The intended use is for the user to download the script and run it locally. Seving a compromised copy 10% of the time would just lower the reach of the attack. Especially cause the visitor can still verify the source code, or verify the output of the signature.
Even if you cut the size of the private key in half, the signature would still be 5x longer than a standard PGP signature, and the fact that subpacket 20 has been padded with a large amount of data would be immediately visible to the victim upon verifying their own signature. (Note that I didn’t include a verification tool, so the visitor would have to do that on their own trusted software.)