The
ssl
device provides access to a Secure Socket Layer that implements the record layer protocol
of SSLv2
(but not its handshaking).
The device provides encrypting and digesting for many independent connections.
Once associated with a network connection, the
ssl
device can be thought of as a filter for the connection.
Ssl
can send data in the clear, digested or encrypted. In all cases, if
ssl
is associated with both ends of a connection, all messages are delimited.
As long as reads always specify buffers that are of equal or greater lengths than the writes at the other end of the connection, one write will correspond to one read.
The device is unusual because it is not bound into the name space but named directly by its local name,
#D.
That is because the interface described below requires writing a local file descriptor number to a file,
which will not work remotely.
The top-level directory contains a
clone
file and numbered directories, each representing a connection.
Opening the
clone
file reserves a connection; the file descriptor resulting from the
%sys-open(2)
will be open on the control file,
ctl,
in the directory that represents the new connection.
Reading the control file will return a text string giving the connection number
n,
and thus the directory name.
Writing to
ctl
controls the corresponding connection.
The following control messages are possible:
- fd m
- Associate the network connection on existing file descriptor
m
with the
ssl
device.
- alg clear
- Allow data to pass in the clear with only message delimiters added. The device starts in this mode.
- alg sha
- Append a SHA digest to each buffer written to
data.
The digest covers the outgoing secret (written to
secretout),
the message, and a message number which starts at 0 and increments by one for each message.
Messages read have their appended digests compared to a digest computed using the incoming secret (written to
secretin).
If the comparison fails, so will the read.
- alg md4
- Like
sha
but using the MD4 message digest algorithm.
- alg md5
- Like
sha
but using the MD5 message digest algorithm.
- alg rc4
- alg rc4_40
- alg rc4_128
- alg rc4_256
- RC4 encrypt each message written to
data
with the key written to
secretout,
using the key length as indicated (40-bit keys by default).
- alg des_56_cbc
- Encrypt the stream using DES and Cipher Block Chaining (CBC)
- alg des_56_ecb
- Encrypt the stream using DES and Electronic Code Book (ECB)
- alg ideacbc
- Encrypt the stream using IDEA and CBC
- alg ideaecb
- Encrypt the stream using IDEA and ECB
- alg digest/crypt
- Combine the use of the given
digest
algorithm and the stream encryption algorithm
crypt
Files
secretin
and
secretout
must be written before digesting or encryption is turned on. If only one is written, they are both assumed to be the same.
The mode may be changed at any time during a connection.
The list of algorithms supported by a given implementation of
ssl
may be read from the read-only text files
encalgs
(encryption algorithms)
and
hashalgs
(hashing algorithms for digests).
Each contains a space-separated list of algorithm names.