To do this im going to use a tool I worked on about a year back called RsaCtfTool. A little bit suspicious don’t you think? The exponent doesn’t look to usual either but let’s focus on maybe trying to factor the modulus. There’s more information but the most interesting thing here is the modulus, it looks more like ASCII art than a proper modulus. Issuer: C=US, ST=New York, L=New York, O=E Corp, Before: Feb 1 00:39:00 2017 GMT Signature Algorithm: sha256WithRSAEncryption Let’s just get the human readable form of the openssl x509 -inform DER -in r -text We save the file as r and now we can examine it with the openssl command line tools.
If we expand the Secure Sockets Layer > TLSv1.2 Record Layer: Handshake Protocol: Certificate data, all the way until we isolate the actual certificate content, we can then right click the record and “ Export Packet Bytes…”: To do this we can use Wireshark to expert it as a DER format X509 certificate by drilling down in the “Server Hello” packet which is in frame 11 of this pcap. The verbage in the clue about “using TLS to protect the modulus fetch” though made me think of examining the certificate used in the TLS negotiation in some detail. If we examine the PCAP in wireshark to get a high level overview of the challenge here we see very little in the way of plaintext anything. Note: Flag does not follow the “Flag:” format but is recognizable Unfortunately I need someone who can do it in 60 seconds.
Now, I have been told that the best crackers in the world can do this in 60 minutes. Unfortunately it seems they’re using TLS to protect the modulus fetch. Our guy inside e-corp was able to get that packet capture of their backend PKI you asked for.
So hopefully a quick writeup! Here’s the clue:
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