NAME

rsa - toy RSA public-key cryptosystem

SYNOPSIS

rsa (-i | -e <correspondent> | -d)

DESCRIPTION

'Rsa' is a simplified implementation of an RSA (Rivest-Shamir-Adleman)
public-key cryptosystem.
While interesting as a novelty, it does not provide sufficient
security to resist an informed attack.

'Rsa' has three options.
The "-i" (initialize) option must be selected by a user before any
other users can send him encrypted information.
The "-e correspondent" (encipher) option is used to encrypt standard
input to standard output using the public key of the named user.
(In a practical system, only the named user would then be able
to decrypt the result, using his private key.)
The "-d" (decipher) option is used to decrypt standard input to
standard output using the private key of the current user.
Thus, if the current user has login name "BOZO", the network


rsa -e bozo | rsa -d


effects an identity transformation.

Further information on public-key cryptosystems in general and
the RSA algorithm in particular can be found in the following
references:


Hellman, Martin E.
"The Mathematics of Public-Key Cryptography,"
in

Scientific American,
Vol. 241, No. 2, pp. 146-157, August, 1979

Rivest, R. L., Adi Shamir, and Len Adleman

On Digital Signatures and Public-Key Cryptosystems,
Report MIT/LCS/Tm-82,
Laboratory for Computer Science,
Massachusetts Institute of Technology,
April, 1977

Rivest, R. L., A. Shamir, and A. Adleman
"A Method for Obtaining Digital Signatures and Public-Key
Cryptosystems,"
in

Communications of the ACM,
Vol. 21, No. 2, pages 120-126, February, 1978.


EXAMPLES


rsa -i   # initializes public and private key files
plaintext> rsa -e system >ciphertext
ciphertext> rsa -d >plaintext
rsa -e bozo >>=extra=/mail/bozo


FILES

"=varsdir=/.rsa_encipher" for public-key information;

"=varsdir=/.rsa_decipher" for private-key information.

MESSAGES

Various self-explanatory messages if key files are not present
or unreadable.

BUGS

32 bit arithmetic is insufficient to guarantee security.

Locally supported.

SEE ALSO

Subsystem Mathematical Function Library ('vswtml')