Re: Let us see how to encrypt with Emacs?

[Jean Louis <bugs@gnu.support>]

* Eli Zaretskii <eliz@gnu.org> [2021-07-09 13:40]:
> > (setq encrypted (gnutls-symmetric-encrypt "CHACHA20-64" (string-pad "MyPassword987" 32) (make-string 16 (random 100)) (string-pad "Text to encrypt" 64)))
> > 
> > And I can decrypt it:
> > 
> > (car (gnutls-symmetric-decrypt "CHACHA20-64" (string-pad "MyPassword987" 32) (cadr encrypted) (car encrypted))) ⇒ "Text to encrypt                                                 "
> > 
> > but that is not well integrated for practical encryption as I
> > have to employ padding even for string to be encrypted, and
> > chunking of string to 64 bytes.
> 
> No, you don't need to chunk, you just need to pad to a multiple of 64
> bytes.

I guess something like this unless I am making an error:

(defun pad-to-multiple-bytes (string max)
  "Return string padded to multiple of MAX bytes."
  (let* ((bytes (string-bytes string))
	 (multiple (truncate (/ bytes max)))
	 (multiple (if (zerop multiple) max (* (1+ multiple) max))))
    (string-pad string multiple)))

> What kind of help?  To use these functions, you need to learn about
> the various ciphers and what they require.  This is something the
> Emacs Lisp reference manual cannot teach you.
> 
> > ‘STRING’
> >      A string as input will be used directly.  It may be modified by the
> >      function (unlike most other Emacs Lisp functions) to reduce the
> > chance of exposing sensitive data after the function does its work.
> > 
> > I am trying to use list with STRING as following and that does not work:
> > 
> > (gnutls-symmetric-encrypt "CHACHA20-64" (string-pad "MyPassword987" 32) (make-string 16 (random 100)) '(STRING "Text to encrypt"))
> 
> What do you mean by "does not work"?

I get invalid object argument: STRING so I do not understand how to use STRING there.


Jean

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