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(in-package :sasl)
(defclass digest-md5 (client)
((realm :initarg :realm
:accessor realm
:initform nil
:documentation "The realm to which the user's account belongs.
If it is not specified, the first realm that the server advertises will
be chosen. Many servers don't use realms.")
;; internal variables
(state :initform :start
:accessor state)
(nonce :accessor nonce)
(cnonce :accessor cnonce)
(digest-uri-value :accessor digest-uri-value)
(mechanism-name :initform "DIGEST-MD5"))
(:documentation "Client-side implementation of the SASL DIGEST-MD5 mechanism,
as specified in RFC 2831."))
(defmethod client-step ((c digest-md5) server-input)
(declare (type (or (vector (unsigned-byte 8))
(eql :success))
(ecase (state c)
;; The server goes first, so wait if no input yet
(if (zerop (length server-input))
(coerce #() '(vector (unsigned-byte 8)))
;; XXX: we assume that the challenge is pure ASCII. correct?
(let ((challenge (parse-challenge (map 'string #'code-char server-input))))
;; If we know what realm we want, make sure we get it:
(if (realm c)
(unless (find (cons "realm" (realm c))
challenge :test #'equal)
(error "Realm ~A not offered by server" (realm c)))
;; Else, just get the first one
(setf (realm c) (cdr (assoc "realm" challenge :test #'string=))))
(setf (nonce c) (cdr (assoc "nonce" challenge :test #'string=)))
;; This is recommended to contain at least 64 bits of entropy
(setf (cnonce c) (format nil "~A" (random #x10000000000000000)))
(setf (digest-uri-value c)
(apply #'concatenate 'string (service c) "/"
(host c)
(if (or (null (serv-name c))
(string= (host c) (serv-name c)))
(list "/" (serv-name c)))))
(setf (state c) :sent)
;; XXX: obey charset directive
(apply #'concatenate 'string
"username=\"" (authc-id c) "\","
"realm=\"" (realm c) "\","
"nonce=\"" (nonce c) "\","
"cnonce=\"" (cnonce c) "\","
"digest-uri=\"" (digest-uri-value c) "\","
"response=" (response-value c t)
(when (authz-id c)
(list ",authzid=\"" (authz-id c) "\"")))))))
;; XXX: we assume that the challenge is pure ASCII. correct?
(let ((challenge (parse-challenge (map 'string #'code-char server-input))))
(if (string= (cdr (assoc "rspauth" challenge :test #'string=))
(response-value c nil))
(setf (state c) :success)
(coerce #() '(vector (unsigned-byte 8))))
(if (eql server-input :success)
(defmethod response-value ((c digest-md5) request)
(response (authc-id c) (authz-id c) (realm c) (get-password (password c))
(digest-uri-value c) (nonce c) (cnonce c) "00000001" "auth" request))
(defun response (authc-id authz-id realm password digest-uri nonce cnonce nc qop request)
(labels ((c (&rest strings) (apply #'concatenate 'string strings))
(to-bytes (maybe-string)
(if (stringp maybe-string)
(string-to-latin1-or-utf8 maybe-string)
(c-b (&rest maybe-strings)
(apply #'concatenate
(unsigned-byte 8))
(map 'list #'to-bytes
(h (string) (ironclad:digest-sequence :md5 (to-bytes string)))
(kd (k s) (h (c k ":" s)))
(hex (hash) (ironclad:byte-array-to-hex-string hash)))
(let ((a1 (if authz-id
(c-b (h (c authc-id ":" realm ":" password))
":" nonce ":" cnonce ":" authz-id)
(c-b (h (c authc-id ":" realm ":" password))
":" nonce ":" cnonce)))
(a2 (let ((prefix (if request
(suffix (if (string= qop "auth")
(c prefix digest-uri suffix))))
(hex (kd (hex (h a1))
(c nonce ":" nc ":"
cnonce ":" qop ":" (hex (h a2))))))))
(defun parse-challenge (challenge &optional (start 0) accumulated)
"Parse CHALLENGE and return it as an alist.
Start at index START."
(declare (type string challenge))
(if (>= 0 (- (length challenge) start))
;; Directives are letters only - find the equal sign.
(let* ((equal-sign (position #\= challenge :start start))
(directive (string-trim
'(#\Space #\Tab #\Newline #\Linefeed)
(subseq challenge start equal-sign)))
comma-position value)
(unless equal-sign
(error "Couldn't parse challenge - missing equal sign"))
(if (not (eql (elt challenge (1+ equal-sign)) #\"))
;; token - just find the comma
(setf comma-position (position #\, challenge :start equal-sign))
(setf value
(string-trim '(#\Space #\Tab #\Newline #\Linefeed)
(subseq challenge (1+ equal-sign) comma-position))))
;; quoted value - watch for backslash escaping
(loop for index upfrom (+ 2 equal-sign)
until (eql (elt challenge index) #\")
(when (eql (elt challenge index) #\\)
(incf index))
(push (elt challenge index) value)
(setf value
(concatenate 'string (nreverse value)))
(setf comma-position (1+ index))))
(let ((new-entry (cons directive value)))
(if (null comma-position)
(cons new-entry accumulated)
(parse-challenge challenge (1+ comma-position) (cons new-entry accumulated)))))))
(defun string-to-latin1-or-utf8 (string)
"Convert STRING to ISO 8859-1 if possible, else to UTF-8.
Return a byte vector."
(if (every #'in-latin1-p string)
(map '(vector (unsigned-byte 8))
(string-to-utf8 string)))
;; arch-tag: bda651ac-39ec-11da-9ea5-000a95c2fcd0