NAME¶

tlswrapper - TLS encryption wrapper

SYNOPSIS¶

tlswrapper [ options ] prog

DESCRIPTION¶

The tlswrapper is an TLS encryption wrapper between remote client and local program prog. Systemd.socket/inetd/tcpserver/... creates the server connection, tlswrapper encrypts/decrypts data stream and reads/writes data from/to the program prog as follows:

Internet <--> systemd.socket/inetd/tcpserver/... <--> tlswrapper <--> prog

OPTIONS¶

-q

Quiet mode. No error messages.

-Q

Normal mode (default). The tlswrapper prints only fatal messages, which means system errors (e.g. memory allocation problems), configuration errors (e.g. syntax errors) and problems with PEM certificates (missing files, etc... ). In this mode the tlswrapper doesn't print any information about TLS connections.

-v

Verbose mode. The tlswrapper prints also information/warnings/errors about TLS connection, but after TLS handshake is successfully done. In this mode TLS errors before the complete TLS handshake are suppressed.

-vv

Debug mode. The tlswrapper prints also debug information about TLS connection, including all TLS connection warnings/errors.

-vvv

Tracing mode. The tlswrapper prints also tracing messages, useful for bug hunting.

-f certfile

Add a file containing key+certificate(s) in PEM format.

-d certdir

Add a directory containing multiple key+certificate(s) files in PEM format. The file in the directory is selected by hostname extracted from SNI extension. Warning: For security reasons tlswrapper does not allow dots immediately after slashes in certdir name. It changes these dots to colons before attempting to open the PEM file.

-a anchorfile

Enable client certificate authentication. Use CA trust anchor anchorfile. Only one -a option supported.

-c cipher

Add symmetric encryption cipher. See ALGORITHMS. (default: -c CHACHA20_POLY1305_SHA256 -c AES_256_GCM_SHA384 -c AES_128_GCM_SHA256). The cipher preference depends on the -c option order.

-e ephemeral

Add ephemeral algorithm ephemeral. See ALGORITHMS. (default: -e x25519 -e secp256r1). The algorithm preference currently doesn't depend on the -e option order. Right now we use a fixed preference order x25519, secp256r1, secp384r1, secp521r1.

-m

The minimal TLS version. See ALGORITHMS. (default: tls12).

-M

The maximal TLS version. See ALGORITHMS. (default: tls12).

-t seconds

Set the network timeout to seconds seconds. (default 60).

-T seconds

Set the TLS handshake timeout to seconds seconds. (default 30).

-u user

Run program prog under a specified user's uid and gid

-U ASN.1 object

Extract the user from ASN.1 object from the client certificate and run program prog under user's uid and gid. Supported ASN.1 object objects are 'commonName' and 'emailAddress'.

-p version

Enable incoming proxy-protocol version version string. The tlswrapper receives the

-s

Enforce TLS server preferences. (default).

-S

Don't enforce TLS server preferences.

-J jaildir

Chroot network-process and key-process into a specified jaildir (default: /var/lib/tlswraper/empty).

-j jailuser

Run network-process and key-process under a specified jailuser's uid and gid. If unset run network-process and key-process under random uid and gid.

-n

Enable delayed encryption. It's experimental feature! This is useful for protocols which uses STARTTLS. tlswrapper creates to the child control pipe on filedescriptor 5 for writing. The child process starts communication in plaintext a encryption starts in the moment when child use the control pipe instead of startdard output, writes the initialization string (e.g. for SMTP protocol '220 ready to start TLS\r\n') and closes the control pipe. See e.g. tlswrapper-smtp(1).

-N

Disable delayed encryption (default).

prog

program

SECURITY¶

Separate process for every connection

The tlswrapper is executed from systemd.socket/inetd/tcpserver/... which runs separate instance of tlswrapper for each TLS connection. It ensures that a vulnerability in the code (e.g. bug in the TLS library) can't be used to compromise the memory of another connection.

Separate process for network connection and separate process for secret-key operation

To protect against secret-information leaks to the network connection (such Heartbleed) tlswrapper runs two independent processes for every TLS connection. One process holds secret-keys and runs secret-keys operations and second talks to the network. Processes communicate with each other through UNIX pipes.

JAIL - Privilege separation, filesystem isolation, limits

The tlswrapper processes run under dedicated non-zero uid to prohibit kill, ptrace, etc. Is chrooted into an empty, unwritable directory to prohibit filesystem access. Sets ulimits to prohibit new files, sockets, etc. Sets ulimits to prohibit forks.

PEM files

The tlswrapper uses for simplicity both secret-key and certificates in one PEM file. When the server starts, runs two independent UNIX processes, one for network communication, second for secret-key operations. The network-process is immediately jailed and starts TLS handshake. Secret-key-process starts under root privileges, waits when network-process receives SNI extension from client-hello packet. Then the network-process assemble the PEM filename and sends the name to the secret-key-process. Secret-key-process loads the PEM file and immediately is jailed and drops it's privileges. Since here both processes runs jailed (see JAIL above). Note that PEM files are loaded under root privileges, but parsed in jailed unpriviledged process. It ensures that a vulnerability in the parsing code can't be used to gain root privileges/information. Warning: For security reasons tlswrapper does not allow dots immediately after slashes in file names. It changes these dots to colons before attempting to open the PEM file.

TLS library

The tlswrapper uses BearSSL. BearSSL is an implementation of the SSL/TLS protocol (RFC 5246) written in C. It aims at offering the following features:
- Be correct and secure. In particular, insecure protocol versions and choices of algorithms are not supported, by design; cryptographic algorithm implementations are constant-time by default.
- Be small, both in RAM and code footprint. For instance, a minimal server implementation may fit in about 20 kilobytes of compiled code and 25 kilobytes of RAM.
- Be highly portable. BearSSL targets not only big operating systems like Linux and Windows, but also small embedded systems and even special contexts like bootstrap code.
- Be feature-rich and extensible. SSL/TLS has many defined cipher suites and extensions; BearSSL should implement most of them, and allow extra algorithm implementations to be added afterwards, possibly from third parties.

ALGORITHMS¶

EXAMPLES¶

Run tlswrapper using tcpserver/busybox/inetd on port 443.

tcpserver -HRDl0 0 443 tlswrapper [ options ] prog
busybox tcpsvd 0 443 tlswrapper [ options ] prog
inetd.conf line: https stream tcp nowait root /usr/bin/tlswrapper tlswrapper [ options ] prog

Simple usage, use one '/etc/.../rsa.pem' certificate:

 ... tlswrapper -f '/etc/.../rsa.pem' ...

Use '/etc/.../ecdsa.pem' certificate and fall-back to '/etc/.../rsa.pem' certificate, if the client doesn't support previous one.

 ... tlswrapper -f '/etc/.../ecdsa.pem' -f '/etc/.../rsa.pem' ...

Use certificate '/etc/.../rsa.d/{hostname}' where {hostname} is extracted from the SNI extension:

 ... tlswrapper -d '/etc/.../rsa.d/' ...

Use certificate '/etc/.../ecdsa.d/{hostname}' where {hostname} is extracted from the SNI extension, and fall-back to '/etc/.../rsa.d/{hostname}', if the client doesn't support previous one.

 ... tlswrapper -d '/etc/.../ecdsa.d/' -d '/etc/.../rsa.d/' ...

Use certificate '/etc/.../ecdsa.d/{hostname}' where {hostname} is extracted from the SNI extension, and fall-back to '/etc/.../rsa.pem', if the client doesn't support previous one.

 ... tlswrapper -d '/etc/.../ecdsa.d/' -f '/etc/.../rsa.pem' ...

Enable TLS 1.0 - TLS 1.2 and all supported algorithms:

 ... tlswrapper -m tls10 \


                -M tls12 \


                -c CHACHA20_POLY1305_SHA256 \


                -c AES_256_GCM_SHA384 \


                -c AES_128_GCM_SHA256 \


                -c AES_256_CBC_SHA384 \


                -c AES_128_CBC_SHA256 \


                -c AES_256_CBC_SHA \


                -c AES_128_CBC_SHA \


                -e x25519 \


                -e secp256r1 \


                -e secp384r1 \


                -e secp521r1 \


                ...

Enable TLS 1.0 - TLS 1.2 and all supported algorithms, but different order (prefer AES128):

 ... tlswrapper -m tls10 \


                -M tls12 \


                -c CHACHA20_POLY1305_SHA256 \


                -c AES_128_GCM_SHA256 \


                -c AES_128_CBC_SHA256 \


                -c AES_128_CBC_SHA \


                -c AES_256_GCM_SHA384 \


                -c AES_256_CBC_SHA384 \


                -c AES_256_CBC_SHA \


                -e x25519 \


                -e secp256r1 \


                -e secp384r1 \


                -e secp521r1 \


                ...

Enable only 256-bit symmetric ciphers:

 ... tlswrapper -c CHACHA20_POLY1305_SHA256 \


                -c AES_256_GCM_SHA384 \


                -c AES_256_CBC_SHA384 \


                -c AES_256_CBC_SHA \


                ...

Enable client certificate authentication:

 ... tlswrapper -a anchorCA.pem -f rsa.pem ...

Enable client certificate authentication, and run program under user extracted from client cert. from commonName:

 ... tlswrapper -a anchorCA.pem -U commonName -f rsa.pem ...

Enable client certificate authentication, and run program under user extracted from client cert. from emailAddress:

 ... tlswrapper -a anchorCA.pem -U emailAddress -f rsa.pem ...

SEE ALSO¶

tlswrapper-tcp(1), tlswrapper-smtp(1), systemd.socket(5), inetd(8), tcpserver(1)