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TLS debug client. It sets up multiple TLS connections to a server and queries its capabilities. It was created to assist in debugging GnuTLS, but it might be useful to extract a TLS server’s capabilities. It connects to a TLS server, performs tests and print the server’s capabilities. If called with the ‘-V’ parameter more checks will be performed. Can be used to check for servers with special needs or bugs.
The text printed is the same whether selected with the help option
(--help) or the more-help option (--more-help). more-help will print
the usage text by passing it through a pager program.
more-help is disabled on platforms without a working
fork(2) function. The PAGER environment variable is
used to select the program, defaulting to more. Both will exit
with a status code of 0.
gnutls-cli-debug - GnuTLS debug client
Usage: gnutls-cli-debug [ -<flag> [<val>] | --<name>[{=| }<val>] ]... [hostname]
None:
-d, --debug=num Enable debugging
- it must be in the range:
0 to 9999
-V, --verbose More verbose output
-p, --port=num The port to connect to
- it must be in the range:
0 to 65536
--app-proto an alias for the 'starttls-proto' option
--starttls-proto=str The application protocol to be used to obtain the server's certificate (https, ftp, smtp, imap, ldap, xmpp, lmtp, pop3, nntp, sieve, postgres)
--attime=str Perform validation at the timestamp instead of the system time
Version, usage and configuration options:
-v, --version[=arg] output version information and exit
-h, --help display extended usage information and exit
-!, --more-help extended usage information passed thru pager
Options are specified by doubled hyphens and their name or by a single
hyphen and the flag character.
Operands and options may be intermixed. They will be reordered.
TLS debug client. It sets up multiple TLS connections to
a server and queries its capabilities. It was created to assist in debugging
GnuTLS, but it might be useful to extract a TLS server's capabilities.
It connects to a TLS server, performs tests and print the server's
capabilities. If called with the `-V' parameter more checks will be performed.
Can be used to check for servers with special needs or bugs.
Please send bug reports to: <bugs@gnutls.org>
This is the “enable debugging” option. This option takes a ArgumentType.NUMBER argument. Specifies the debug level.
This is an alias for the starttls-proto option,
see the starttls-proto option documentation.
This is the “the application protocol to be used to obtain the server’s certificate (https, ftp, smtp, imap, ldap, xmpp, lmtp, pop3, nntp, sieve, postgres)” option. This option takes a ArgumentType.STRING argument. Specify the application layer protocol for STARTTLS. If the protocol is supported, gnutls-cli will proceed to the TLS negotiation.
This is the “perform validation at the timestamp instead of the system time” option. This option takes a ArgumentType.STRING argument timestamp. timestamp is an instance in time encoded as Unix time or in a human readable timestring such as "29 Feb 2004", "2004-02-29". Full documentation available at <https://www.gnu.org/software/coreutils/manual/html_node/Date-input-formats.html> or locally via info ’(coreutils) date invocation’.
This is the “output version information and exit” option. This option takes a ArgumentType.KEYWORD argument. Output version of program and exit. The default mode is ‘v’, a simple version. The ‘c’ mode will print copyright information and ‘n’ will print the full copyright notice.
This is the “display extended usage information and exit” option. Display usage information and exit.
This is the “extended usage information passed thru pager” option. Pass the extended usage information through a pager.
One of the following exit values will be returned:
Successful program execution.
The operation failed or the command syntax was not valid.
gnutls-cli(1), gnutls-serv(1)
$ gnutls-cli-debug localhost
GnuTLS debug client 3.5.0
Checking localhost:443
for SSL 3.0 (RFC6101) support... yes
whether we need to disable TLS 1.2... no
whether we need to disable TLS 1.1... no
whether we need to disable TLS 1.0... no
whether %NO_EXTENSIONS is required... no
whether %COMPAT is required... no
for TLS 1.0 (RFC2246) support... yes
for TLS 1.1 (RFC4346) support... yes
for TLS 1.2 (RFC5246) support... yes
fallback from TLS 1.6 to... TLS1.2
for RFC7507 inappropriate fallback... yes
for HTTPS server name... Local
for certificate chain order... sorted
for safe renegotiation (RFC5746) support... yes
for Safe renegotiation support (SCSV)... no
for encrypt-then-MAC (RFC7366) support... no
for ext master secret (RFC7627) support... no
for heartbeat (RFC6520) support... no
for version rollback bug in RSA PMS... dunno
for version rollback bug in Client Hello... no
whether the server ignores the RSA PMS version... yes
whether small records (512 bytes) are tolerated on handshake... yes
whether cipher suites not in SSL 3.0 spec are accepted... yes
whether a bogus TLS record version in the client hello is accepted... yes
whether the server understands TLS closure alerts... partially
whether the server supports session resumption... yes
for anonymous authentication support... no
for ephemeral Diffie-Hellman support... no
for ephemeral EC Diffie-Hellman support... yes
ephemeral EC Diffie-Hellman group info... SECP256R1
for AES-128-GCM cipher (RFC5288) support... yes
for AES-128-CCM cipher (RFC6655) support... no
for AES-128-CCM-8 cipher (RFC6655) support... no
for AES-128-CBC cipher (RFC3268) support... yes
for CAMELLIA-128-GCM cipher (RFC6367) support... no
for CAMELLIA-128-CBC cipher (RFC5932) support... no
for 3DES-CBC cipher (RFC2246) support... yes
for ARCFOUR 128 cipher (RFC2246) support... yes
for MD5 MAC support... yes
for SHA1 MAC support... yes
for SHA256 MAC support... yes
for ZLIB compression support... no
for max record size (RFC6066) support... no
for OCSP status response (RFC6066) support... no
for OpenPGP authentication (RFC6091) support... no
You could also use the client to debug services with starttls capability.
$ gnutls-cli-debug --starttls-proto smtp --port 25 localhost
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