.TH RSA 8
.SH NAME
rsagen, rsafill, asn12rsa, rsa2pub, rsa2ssh, rsa2x509 \- generate and format rsa keys
.SH SYNOPSIS
.PP
.B rsagen
[
.B -b
.I nbits
]
[
.B -t
.I tag
]
.PP
.B rsafill
[
.I file
]
.PP
.B asn12rsa
[
.B -t
.I tag
]
[
.I file
]
.PP
.B rsa2pub
[
.I file
]
.PP
.B rsa2ssh
[
.I file
]
.PP
.B rsa2x509
[
.B -e
.I expiretime
]
.I certinfo
[
.I file
]
.SH DESCRIPTION
Plan 9 represents an RSA key as an attribute-value pair list
prefixed with the string
.BR key ;
this is the generic key format used by
.IR factotum (4).
A full RSA private key has the following attributes:
.TP
.B proto
must be
.B rsa
.TP
.B size
the number of significant bits in
.B n
.TP
.B ek
the encryption exponent
.TP
.B n
the product of
.B !p
and
.B !q
.TP
.B !dk
the decryption exponent
.TP
.B !p
a large prime
.TP
.B !q
another large prime
.TP
.B "!kp\fR, \fL!kq\fR, \fL!c2
parameters derived from the other attributes, cached to speed decryption
.PD
.LP
All the numbers are in hexadecimal except
.I size ,
which is decimal.
An RSA public key omits the attributes beginning with
.L ! .
A key may have other attributes as well (for example, a
.B service
attribute identifying how this key is typically used),
but to these utilities such attributes are merely comments.
.PP
For example, a very small (and thus insecure) private key and corresponding
public key might be:
.IP
.EX
key proto=rsa size=8 ek=7 n=8F !dk=67 !p=B !q=D !kp=3 !kq=7 !c2=6
key proto=rsa size=8 ek=7 n=8F
.EE
.LP
Note that the order of the attributes does not matter.
.PP
.I Rsagen
prints a randomly generated RSA private key
whose
.B n
has exactly
.I nbits
(default 1024)
significant bits.
If
.I tag
is specified, it is printed between
.B key
and
.BR proto=rsa ;
typically,
.I tag
is a sequence of attribute-value comments describing the key.
.PP
.I Rsafill
reads a private key,
recomputes the
.BR !kp ,
.BR !kq ,
and
.BR !c2
attributes if they are missing,
and prints a full key.
.PP
.I Asn12rsa
reads an RSA private key stored as ASN.1
encoded in the binary Distinguished Encoding Rules (DER)
and prints a Plan 9 RSA key,
inserting
.I tag
exactly as
.I rsagen
does.
ASN.1/DER is a popular key format on Unix and Windows;
it is often encoded in text form using the Privacy Enhanced Mail (PEM) format
in a section labeled as an
.RB `` RSA
.B PRIVATE
.BR KEY .''
The command:
.IP
.EX
auth/pemdecode 'RSA PRIVATE KEY' | auth/asn12rsa
.EE
.LP
extracts the key section from a textual ASN.1/DER/PEM key
into binary ASN.1/DER format and then
converts it to a Plan 9 RSA key.
.PP
.I Rsa2pub
reads a Plan 9 RSA public or private key,
removes the private attributes, and prints the resulting public key.
Comment attributes are preserved.
.PP
.I Rsa2ssh
reads a Plan 9 RSA public or private key and prints the public portion 
in the format used by SSH: three space-separated decimal numbers
.BR size ,
.BR ek ,
and
.BR n .
For compatibility with external SSH implementations, the public keys in
.B /sys/lib/ssh/keyring
and
.B $home/lib/keyring
are stored in this format.
.PP
.I Rsa2x509
reads a Plan 9 RSA private key and writes a self-signed X.509 certificate
encoded in ASN.1/DER format to standard output.
(Note that ASN.1/DER X.509 certificates are different from ASN.1/DER private keys).
The certificate uses the current time as its start time and expires
.I expiretime
seconds
(default 3 years)
later.
It contains the public half of the key
and includes
.I certinfo
as the issuer/subject string (also known as a ``Distinguished Name'').
This info is typically in the form:
.IP
.EX
C=US ST=NJ L=07974 O=Lucent OU='Bell Labs' CN=G.R.Emlin
.EE
.LP
The X.509 ASN.1/DER format is often encoded in text using a PEM section
labeled as a
.RB `` CERTIFICATE .''
The command:
.IP
.EX
auth/rsa2x509 'C=US OU=''Bell Labs''' file |
auth/pemencode CERTIFICATE
.EE
.LP
generates such a textual certificate.
Applications that serve TLS-encrypted sessions (for example,
.IR httpd (8),
.IR pop3 (8),
and
.IR tlssrv (8))
expect certificates in ASN.1/DER/PEM format.
.SH EXAMPLES
Generate a fresh key and use it to start a TLS-enabled web server:
.IP
.EX
auth/rsagen -t 'service=tls owner=*' >key
auth/rsa2x509 'C=US CN=*.cs.bell-labs.com' key |
	auth/pemencode CERTIFICATE >cert
cat key >/mnt/factotum/ctl
ip/httpd/httpd -c cert
.EE
.PP
Generate a fresh key and configure a remote Unix system to
allow use of that key for logins:
.IP
.EX
auth/rsagen -t 'service=ssh' >key
auth/rsa2ssh key | ssh unix 'cat >>.ssh/authorized_keys'
cat key >/mnt/factotum/ctl
ssh unix
.EE
.SH SOURCE
.B /sys/src/cmd/auth
.SH "SEE ALSO
.IR factotum (4),
.IR pem (8),
.IR ssh (1)
.SH BUGS
There are too many key formats.