tlswrapper(1)

NAME
tlswrapper - TLS encryption wrapper

SYNOPSIS
tlswrapper [ options ] prog

DESCRIPTION

The tlswrapper is a 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 proxy-protocol header from the upstream proxy and extracts client connection information. Supported versions: 1.

-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/tlswrapper/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. 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 as 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 assembles 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 its privileges. From here on both processes run jailed (see JAIL above). Note that PEM files are loaded under root privileges, but parsed in jailed unprivileged 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
TLS version (-m option -M option)
tls10 | TLS 1.0 | optional
tls11 | TLS 1.1 | optional
tls12 | TLS 1.2 | default
tls13 | TLS 1.3 | not supported
ciphers (-c option)
CHACHA20_POLY1305_SHA256 | ChaCha20+Poly1305 encryption (TLS 1.2+) | default
AES_256_GCM_SHA384 | AES-256/GCM encryption (TLS 1.2+) | default
AES_128_GCM_SHA256 | AES-128/GCM encryption (TLS 1.2+) | default
AES_256_CBC_SHA384 | AES-256/CBC + SHA-384 (TLS 1.2+) | optional
AES_128_CBC_SHA256 | AES-128/CBC + SHA-256 (TLS 1.2+) | optional
AES_256_CBC_SHA | AES-256/CBC + SHA-1 | optional
AES_128_CBC_SHA | AES-128/CBC + SHA-1 | optional
ephemeral (-e option)
x25519 | ECDHE using X25519 | default
secp256r1 | ECDHE using NIST P-256 | default
secp384r1 | ECDHE using NIST P-384 | optional
secp521r1 | ECDHE using NIST P-521 | optional

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)