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TUM goscanner

goscanner is a tool for large-scale TLS, x509 Certificate, HTTP header, and SSH scans developed at the TUM Chair of Network Architectures and Services (see Authors).

2023-01-19 goscanner can now reconstruct the TLS configuration on a server with DissecTLS and collect JARM fingerprints
2022-05-24 goscanner is now able to actively fingerprint TLS servers


Steps for building goscanner:

  1. Set up your go environment
  2. Run make

Configuring Scans

goscanner supports multipe types of scans. Among them are [ tls, http, ssh, scvs, dissectls, jarm]. Some scans can be chained (e.g., tls and http to scan https). In these cases they will reuse the same TCP connection. See example.conf how to configure the default https scan.


goscanner needs a list of resolved IPv4 or Ipv6 address [:Port] [,domain name [,client hello]] tuples as input. The domain and client hello is optional. If a domain is present, it will be used as SNI. If present, the TLS scan will use the provided client hello for scanning.

Example input.csv:,,client_hello_1,,client_hello_2,,client_hello_2,

The IP, domain tuples can be generated, for example, with massdns

bin/massdns -r local_resolvers.txt input_domains.txt -q -o J \
| jq '[.name,.data.answers[-1].data]  | @csv' -r \
| csvtool col 1,2 - | awk -F, '$2!=""' > input.csv

goscanner provides a utility function to enhance the input with the client hellos (we recommend randomizing the input to reduce bursts on target servers). The new input files will contain the cross product between the set of client hellos and the original input set of targets. The names of the client hellos are the names of all json files in the --ch-dir (e.g., client_hello_1.json).

./goscanner create-ch-input --ch-dir ./client-hellos --input input.csv | shuf > input-chs.csv

For scanning, the client hellos can be loaded from a directory with the config option

client-hello-dir = ./client-hellos

Generating CHs

The Client Hellos (CHs) used for the TLS scan can be configured. They are loaded from .json files and several CHs are already built in the scanner (including CHs built after JARM). They can be generated with

./goscanner create-ch --out client-hellos -c custom
./goscanner create-ch --out client-hellos -c jarm

goscanner is also able to generate random CHs. However, there is no guarantee these are functional CHs. goscanner will download possible parameters for the CHs from IANA into the tmp directory.

./goscanner create-ch --out ./client-hellos -c random --num-random 1000 --tmp ./tmp

Active TLS Stack Fingerprinting

goscanner is able to fingerprint TLS servers as described by Additionally, this site provides optimized client hellos for fingerprinting. If you use the goscanner for fingerprinting, please cite our paper.

The goscanner is able to post-process a scan with multiple CHs per target to generate the fingerprints.

./goscanner generate-fingerprints --scanner-dir ./tls-scanner-output [-ch-dir ./client-hellos]


goscanner is able to reconstruct the TLS configuration from servers as described by If you use the DissecTLS functionality, please cite our paper. Information the goscanner can collect:

  • The supported TLS version (only 1.0, 1.1, 1.2, and 1.3)
  • The order of all supported ciphers, supported groups, and ALPNs
  • the ALPN, supported groups, supported groups with key share, and cipher preference: client or server
  • The order of the TLS extensions
  • Whether a server reacts to missing ciphers, supported group, and ALPNs with TLS Alerts, TCP Errors, or just ignores the values we send

Reading logs

To get better human-readable logs from the json output you can use

go get -u

Just pipe your logs to jl --format logfmt. e.g.

tail scanner.log | jl --format logfmt


goscanner is a tool for large-scale TLS and SSH scans







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