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9.1 Invoking gnutls-cli

Simple client program to set up a TLS connection to some other computer. It sets up a TLS connection and forwards data from the standard input to the secured socket and vice versa.

This section was generated by AutoGen, using the agtexi-cmd template and the option descriptions for the gnutls-cli program. This software is released under the GNU General Public License, version 3 or later.

gnutls-cli help/usage (--help)

This is the automatically generated usage text for gnutls-cli.

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 - GnuTLS client
Usage:  gnutls-cli [ -<flag> [<val>] | --<name>[{=| }<val>] ]... [hostname]

   -d, --debug=num            Enable debugging
                                - it must be in the range:
                                  0 to 9999
   -V, --verbose              More verbose output
                                - may appear multiple times
       --tofu                 Enable trust on first use authentication
                                - disabled as '--no-tofu'
       --strict-tofu          Fail to connect if a known certificate has changed
                                - disabled as '--no-strict-tofu'
       --dane                 Enable DANE certificate verification (DNSSEC)
                                - disabled as '--no-dane'
       --local-dns            Use the local DNS server for DNSSEC resolving
                                - disabled as '--no-local-dns'
       --ca-verification      Enable CA certificate verification
                                - disabled as '--no-ca-verification'
                                - enabled by default
       --ocsp                 Enable OCSP certificate verification
                                - disabled as '--no-ocsp'
   -r, --resume               Establish a session and resume
   -e, --rehandshake          Establish a session and rehandshake
       --sni-hostname=str     Server's hostname for server name indication extension
   -s, --starttls             Connect, establish a plain session and start TLS
       --app-proto=str        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)
                                - prohibits the option 'starttls'
   -u, --udp                  Use DTLS (datagram TLS) over UDP
       --mtu=num              Set MTU for datagram TLS
                                - it must be in the range:
                                  0 to 17000
       --crlf                 Send CR LF instead of LF
       --fastopen             Enable TCP Fast Open
       --x509fmtder           Use DER format for certificates to read from
   -f, --fingerprint          Send the openpgp fingerprint, instead of the key
       --print-cert           Print peer's certificate in PEM format
       --save-cert=str        Save the peer's certificate chain in the specified file in PEM format
       --save-ocsp=str        Save the peer's OCSP status response in the provided file
       --dh-bits=num          The minimum number of bits allowed for DH
       --priority=str         Priorities string
       --x509cafile=str       Certificate file or PKCS #11 URL to use
       --x509crlfile=file     CRL file to use
                                - file must pre-exist
       --pgpkeyfile=file      PGP Key file to use
                                - file must pre-exist
       --pgpkeyring=file      PGP Key ring file to use
                                - file must pre-exist
       --pgpcertfile=file     PGP Public Key (certificate) file to use
                                - requires the option 'pgpkeyfile'
                                - file must pre-exist
       --x509keyfile=str      X.509 key file or PKCS #11 URL to use
       --x509certfile=str     X.509 Certificate file or PKCS #11 URL to use
                                - requires the option 'x509keyfile'
       --pgpsubkey=str        PGP subkey to use (hex or auto)
       --srpusername=str      SRP username to use
       --srppasswd=str        SRP password to use
       --pskusername=str      PSK username to use
       --pskkey=str           PSK key (in hex) to use
   -p, --port=str             The port or service to connect to
       --insecure             Don't abort program if server certificate can't be validated
       --ranges               Use length-hiding padding to prevent traffic analysis
       --benchmark-ciphers    Benchmark individual ciphers
       --benchmark-tls-kx     Benchmark TLS key exchange methods
       --benchmark-tls-ciphers  Benchmark TLS ciphers
   -l, --list                 Print a list of the supported algorithms and modes
                                - prohibits the option 'port'
       --priority-list        Print a list of the supported priority strings
       --noticket             Don't allow session tickets
       --srtp-profiles=str    Offer SRTP profiles
       --alpn=str             Application layer protocol
                                - may appear multiple times
   -b, --heartbeat            Activate heartbeat support
       --recordsize=num       The maximum record size to advertize
                                - it must be in the range:
                                  0 to 4096
       --disable-sni          Do not send a Server Name Indication (SNI)
       --disable-extensions   Disable all the TLS extensions
       --inline-commands      Inline commands of the form ^<cmd>^
       --inline-commands-prefix=str Change the default delimiter for inline commands.
       --provider=file        Specify the PKCS #11 provider library
                                - file must pre-exist
       --fips140-mode         Reports the status of the FIPS140-2 mode in gnutls library
   -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.

Simple client program to set up a TLS connection to some other computer.  It
sets up a TLS connection and forwards data from the standard input to the
secured socket and vice versa.

debug option (-d)

This is the “enable debugging” option. This option takes a number argument. Specifies the debug level.

tofu option

This is the “enable trust on first use authentication” option.

This option has some usage constraints. It:

This option will, in addition to certificate authentication, perform authentication based on previously seen public keys, a model similar to SSH authentication. Note that when tofu is specified (PKI) and DANE authentication will become advisory to assist the public key acceptance process.

strict-tofu option

This is the “fail to connect if a known certificate has changed” option.

This option has some usage constraints. It:

This option will perform authentication as with option –tofu; however, while –tofu asks whether to trust a changed public key, this option will fail in case of public key changes.

dane option

This is the “enable dane certificate verification (dnssec)” option.

This option has some usage constraints. It:

This option will, in addition to certificate authentication using the trusted CAs, verify the server certificates using on the DANE information available via DNSSEC.

local-dns option

This is the “use the local dns server for dnssec resolving” option.

This option has some usage constraints. It:

This option will use the local DNS server for DNSSEC. This is disabled by default due to many servers not allowing DNSSEC.

ca-verification option

This is the “enable ca certificate verification” option.

This option has some usage constraints. It:

This option can be used to enable or disable CA certificate verification. It is to be used with the –dane or –tofu options.

ocsp option

This is the “enable ocsp certificate verification” option.

This option has some usage constraints. It:

This option will enable verification of the peer’s certificate using ocsp

resume option (-r)

This is the “establish a session and resume” option. Connect, establish a session, reconnect and resume.

rehandshake option (-e)

This is the “establish a session and rehandshake” option. Connect, establish a session and rehandshake immediately.

sni-hostname option

This is the “server’s hostname for server name indication extension” option. This option takes a string argument. Set explicitly the server name used in the TLS server name indication extension. That is useful when testing with servers setup on different DNS name than the intended. If not specified, the provided hostname is used.

starttls option (-s)

This is the “connect, establish a plain session and start tls” option. The TLS session will be initiated when EOF or a SIGALRM is received.

app-proto option

This is an alias for the starttls-proto option, see the starttls-proto option documentation.

starttls-proto option

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 string argument.

This option has some usage constraints. It:

Specify the application layer protocol for STARTTLS. If the protocol is supported, gnutls-cli will proceed to the TLS negotiation.

dh-bits option

This is the “the minimum number of bits allowed for dh” option. This option takes a number argument. This option sets the minimum number of bits allowed for a Diffie-Hellman key exchange. You may want to lower the default value if the peer sends a weak prime and you get an connection error with unacceptable prime.

priority option

This is the “priorities string” option. This option takes a string argument. TLS algorithms and protocols to enable. You can use predefined sets of ciphersuites such as PERFORMANCE, NORMAL, PFS, SECURE128, SECURE256. The default is NORMAL.

Check the GnuTLS manual on section “Priority strings” for more information on the allowed keywords

ranges option

This is the “use length-hiding padding to prevent traffic analysis” option. When possible (e.g., when using CBC ciphersuites), use length-hiding padding to prevent traffic analysis.

benchmark-ciphers option

This is the “benchmark individual ciphers” option. By default the benchmarked ciphers will utilize any capabilities of the local CPU to improve performance. To test against the raw software implementation set the environment variable GNUTLS_CPUID_OVERRIDE to 0x1.

benchmark-tls-ciphers option

This is the “benchmark tls ciphers” option. By default the benchmarked ciphers will utilize any capabilities of the local CPU to improve performance. To test against the raw software implementation set the environment variable GNUTLS_CPUID_OVERRIDE to 0x1.

list option (-l)

This is the “print a list of the supported algorithms and modes” option.

This option has some usage constraints. It:

Print a list of the supported algorithms and modes. If a priority string is given then only the enabled ciphersuites are shown.

priority-list option

This is the “print a list of the supported priority strings” option. Print a list of the supported priority strings. The ciphersuites corresponding to each priority string can be examined using -l -p.

alpn option

This is the “application layer protocol” option. This option takes a string argument.

This option has some usage constraints. It:

This option will set and enable the Application Layer Protocol Negotiation (ALPN) in the TLS protocol.

disable-extensions option

This is the “disable all the tls extensions” option. This option disables all TLS extensions. Deprecated option. Use the priority string.

inline-commands option

This is the “inline commands of the form ^<cmd>^” option. Enable inline commands of the form ^<cmd>^. The inline commands are expected to be in a line by themselves. The available commands are: resume and renegotiate.

inline-commands-prefix option

This is the “change the default delimiter for inline commands.” option. This option takes a string argument. Change the default delimiter (^) used for inline commands. The delimiter is expected to be a single US-ASCII character (octets 0 - 127). This option is only relevant if inline commands are enabled via the inline-commands option

provider option

This is the “specify the pkcs #11 provider library” option. This option takes a file argument. This will override the default options in /etc/gnutls/pkcs11.conf

gnutls-cli exit status

One of the following exit values will be returned:

0 (EXIT_SUCCESS)

Successful program execution.

1 (EXIT_FAILURE)

The operation failed or the command syntax was not valid.

gnutls-cli See Also

gnutls-cli-debug(1), gnutls-serv(1)

gnutls-cli Examples

Connecting using PSK authentication

To connect to a server using PSK authentication, you need to enable the choice of PSK by using a cipher priority parameter such as in the example below.

$ ./gnutls-cli -p 5556 localhost --pskusername psk_identity \
    --pskkey 88f3824b3e5659f52d00e959bacab954b6540344 \
    --priority NORMAL:-KX-ALL:+ECDHE-PSK:+DHE-PSK:+PSK
Resolving 'localhost'...
Connecting to '127.0.0.1:5556'...
- PSK authentication.
- Version: TLS1.1
- Key Exchange: PSK
- Cipher: AES-128-CBC
- MAC: SHA1
- Compression: NULL
- Handshake was completed
    
- Simple Client Mode:

By keeping the –pskusername parameter and removing the –pskkey parameter, it will query only for the password during the handshake.

Connecting to STARTTLS services

You could also use the client to connect to services with starttls capability.

$ gnutls-cli --starttls-proto smtp --port 25 localhost

Listing ciphersuites in a priority string

To list the ciphersuites in a priority string:

$ ./gnutls-cli --priority SECURE192 -l
Cipher suites for SECURE192
TLS_ECDHE_ECDSA_AES_256_CBC_SHA384         0xc0, 0x24	TLS1.2
TLS_ECDHE_ECDSA_AES_256_GCM_SHA384         0xc0, 0x2e	TLS1.2
TLS_ECDHE_RSA_AES_256_GCM_SHA384           0xc0, 0x30	TLS1.2
TLS_DHE_RSA_AES_256_CBC_SHA256             0x00, 0x6b	TLS1.2
TLS_DHE_DSS_AES_256_CBC_SHA256             0x00, 0x6a	TLS1.2
TLS_RSA_AES_256_CBC_SHA256                 0x00, 0x3d	TLS1.2

Certificate types: CTYPE-X.509
Protocols: VERS-TLS1.2, VERS-TLS1.1, VERS-TLS1.0, VERS-SSL3.0, VERS-DTLS1.0
Compression: COMP-NULL
Elliptic curves: CURVE-SECP384R1, CURVE-SECP521R1
PK-signatures: SIGN-RSA-SHA384, SIGN-ECDSA-SHA384, SIGN-RSA-SHA512, SIGN-ECDSA-SHA512

Connecting using a PKCS #11 token

To connect to a server using a certificate and a private key present in a PKCS #11 token you need to substitute the PKCS 11 URLs in the x509certfile and x509keyfile parameters.

Those can be found using "p11tool –list-tokens" and then listing all the objects in the needed token, and using the appropriate.

$ p11tool --list-tokens

Token 0:
URL: pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test
Label: Test
Manufacturer: EnterSafe
Model: PKCS15
Serial: 1234

$ p11tool --login --list-certs "pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test"

Object 0:
URL: pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test;object=client;type=cert
Type: X.509 Certificate
Label: client
ID: 2a:97:0d:58:d1:51:3c:23:07:ae:4e:0d:72:26:03:7d:99:06:02:6a

$ MYCERT="pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test;object=client;type=cert"
$ MYKEY="pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test;object=client;type=private"
$ export MYCERT MYKEY

$ gnutls-cli www.example.com --x509keyfile $MYKEY --x509certfile $MYCERT

Notice that the private key only differs from the certificate in the type.


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