🚀 go-pugleaf

In article <1992Nov12.011804.12685@news.Hawaii.Edu> newsham@wiliki.eng.hawaii.edu (Timothy Newsham) writes:
>when few replies mentioned I should just use the CBC mode of DES
>it became apparent to myself that I hadn't stated my goals well
>enought either...

No, not CBC mode; CFB mode seems to do what you want.

>goal:  an encryption scheme that gives me the strength of DES
>along with the ability to send single characters one at a time.
>Also it would be nice if the scheme lended itself well to
>sending 7-bit characters in only 7 bits.

Cipher feedback mode allows you to send k bits (0 <= k <= blocksize)
at a time using a block cipher.  The gist is as follows:

The two ends agree on the session key and an initial-input vector
which they each feed through the block cipher.  The sender XORs the
high-order k bits of the output with the k bits of plaintext and
transmits the result to the receiver, who will do the same XOR to
recover the plaintext.  In addition, both ends take the ciphertext of
this iteration and append it to the end of the previous input vector
after first shifting the input vector k bits (and throwing away the
high-order k bits).  This modified input vector is re-encrypted with
the session key, setting up the output to be ready for the next
plaintext.

		--Ken Pizzini