TLS debugging is an awesome introduction of using Wireshark to debug TLS issues (The presentation material can be found here). I just summarise how to decrypt TLS flows here:
(1) Set the filter and capture only TLS flows:
(2) Open chromium and save session secrets in command line:
SSLKEYLOGFILE="$PWD/keys.txt" /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --user-data-dir=/tmp/cr
(3)After saving pcap file, Load key and decrypt TLS flows:
Sometimes, to simulate one corner case, i.e., the TCP layer splits one application record into multiple packets, I need to use libpcap to tweak pcap files. E.g., for following diagram:
I split frame 8 into 3 parts, one will be appended to frame 7, and the remaining 2 parts will be 2 separated packets.
Generally speaking, only length field in IP header and Sequence number field in TCP header need to be modified. The source code and pcap file can be referenced here.
I couldn’t find some off-the-shelf QUIC pcap files which conform to IETF draft versions, so I decided to create them myself. Take Client Initial packet in draft-29 as an example:
(1) Copy following raw packet info into payload.txt:
c5ff00001d088394c8f03e5157080000 449e4a95245bfb66bc5f93032b7ddd89
fe0ff15d9c4f7050fccdb71c1cd80512 d4431643a53aafa1b0b518b44968b18b
......
Use awk command to create string from payload.txt:
$ awk '{for (i = 1; i <= NF; i++) {printf("\"%s\"\n", $i)}}' payload.txt
"c5ff00001d088394c8f03e5157080000"
"449e4a95245bfb66bc5f93032b7ddd89"
"fe0ff15d9c4f7050fccdb71c1cd80512"
"d4431643a53aafa1b0b518b44968b18b"
......
(2) Use a C program to generate payload array:
#include <stdio.h>
char payload[] =
"c5ff00001d088394c8f03e5157080000"
"449e4a95245bfb66bc5f93032b7ddd89"
......
;
int main(void) {
size_t count = 0;
printf("const uint8_t payload[] = {\n");
for (size_t i = 0; i < strlen(payload); i += 2) {
printf("0x%c%c,", payload[i], payload[i + 1]);
if (++count == 8) {
count = 0;
printf("\n");
} else {
printf(" ");
}
}
printf("};");
return 0;
}
(3) Forge ethernet, IP and UDP headers and use libpcap APIs to generate pcap file. The code can be referred here.
Like my previous post, I used OpenSSL to simulate server initial of QUIC protocol, and the code can be downloaded here.
References:
stackoverflow;
EVP Authenticated Encryption and Decryption.
Many openssl APIs return const EVP_MD pointers (e.g., EVP_sha256), and sometimes you need to resolve following errors:
error: cast discards 'const' qualifier from pointer target type [-Werror=cast-qual]
You can either suppress the warning like this or duplicate EVP_MD:
EVP_MD *md = EVP_MD_meth_dup(EVP_sha256());
......
EVP_MD_meth_free(md);