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(define-module (disfluid jwk)
#:use-module (disfluid i18n)
#:use-module (json)
#:use-module (gcrypt pk-crypto)
#:use-module (gcrypt base64)
#:use-module (gcrypt hash)
#:use-module (oop goops)
#:use-module (ice-9 optargs)
#:use-module (ice-9 exceptions)
#:use-module (ice-9 receive)
#:use-module (rnrs bytevectors)
#:declarative? #t
#:export (<jwk>
jwk->json
jwk-public->json
jkt
&invalid-key-parameters))
(define-exception-type
&invalid-key-parameters
&error
make-invalid-key-parameters
invalid-key-parameters?)
(define-class <jwk> ()
kid
key)
(define-method (initialize (key <jwk>) initargs)
(let-keywords
initargs #t
((n-size #f)
(e 0)
(canonical-sexp #f)
(kid #f))
(when (string? e)
(with-exception-handler
(lambda (exn)
(raise-exception
(make-exception
(make-invalid-key-parameters)
(make-exception-with-message
(format #f (G_ "the value of e could not be decoded from base64-url (~s)")
e))
exn)))
(lambda ()
(let ((as-data (base64-decode e base64url-alphabet)))
(set! e
(car (bytevector->uint-list
as-data
(endianness little)
(bytevector-length as-data))))))))
(cond
(canonical-sexp
(slot-set! key 'key canonical-sexp)
(unless kid
(set! kid (jkt key)))
(slot-set! key 'kid kid))
(n-size
(begin
(with-exception-handler
(lambda (exn)
(raise-exception
(make-exception
(make-invalid-key-parameters)
(make-exception-with-message
(format #f (G_ "a key with n-size=~s (e=~s) could not be built")
n-size e))
exn)))
(lambda ()
;; generate-key will abort complaining that n is less than
;; 16 for n up to 64 (!) To avoid much trouble and unsafe
;; keys, I’ll just require them to be at least 1024 bits
(unless (>= n-size 1024)
(raise-exception
(make-exception
(make-error)
(make-exception-with-message
(format #f (G_ "the key size is too small"))))))
(let ((parameters
(let ((n-size (number->string n-size))
(e (number->string e)))
(string->canonical-sexp
(format #f "(genkey (rsa (nbits ~a:~a) (rsa-use-e ~a:~a)))"
(string-length n-size) n-size
(string-length e) e)))))
(let ((key-pair (generate-key parameters)))
(slot-set! key 'key key-pair)))))
(slot-set! key 'kid (jkt key))))
(else
(raise-exception
(make-exception
(make-invalid-key-parameters)
(make-exception-with-message
(G_ "the key initialization requires at least #:n-size to generate it"))))))))
(define (encode bv)
(base64-encode bv 0 (bytevector-length bv) #f #t base64url-alphabet))
(define-method (jkt (key <jwk>))
(let* ((required-fields
(let* ((sexp (slot-ref key 'key))
(public-sexp (or (find-sexp-token sexp 'public-key)
(find-sexp-token sexp 'private-key))))
(let ((rsa (find-sexp-token public-sexp 'rsa)))
(cond
(rsa
(let ((e (cadr (canonical-sexp->sexp (find-sexp-token rsa 'e))))
(n (cadr (canonical-sexp->sexp (find-sexp-token rsa 'n)))))
`((kty . "rsa")
(e . ,(encode e))
(n . ,(encode n)))))
(else
(error "jkt: not implemented for this key type."))))))
(as-string (scm->json-string required-fields))
(as-data (string->utf8 as-string))
(hash (sha256 as-data))
(encoded (encode hash)))
encoded))
(define-method (kid (key <jwk>))
(slot-ref key 'kid))
(define-method (public-rsa-parameter (key <jwk>) name)
(let* ((sexp (slot-ref key 'key))
(public-sexp (or (find-sexp-token sexp 'public-key)
(find-sexp-token sexp 'private-key)))
(public-rsa (find-sexp-token sexp 'rsa)))
(and public-rsa
(let ((as-data (cadr (canonical-sexp->sexp (find-sexp-token public-rsa name)))))
(encode as-data)))))
(define-method (n (key <jwk>))
(public-rsa-parameter key 'n))
(define-method (e (key <jwk>))
(public-rsa-parameter key 'e))
(define-method (private-rsa-parameters (key <jwk>))
(let* ((sexp (slot-ref key 'key))
(private-sexp (find-sexp-token sexp 'private-key)))
(if private-sexp
(let ((rsa (find-sexp-token private-sexp 'rsa)))
(if rsa
(let ((d (canonical-sexp-nth-data (find-sexp-token rsa 'd) 1))
;; What libgcrypt calls p is in fact q and vice
;; versa
(p (canonical-sexp-nth-data (find-sexp-token rsa 'q) 1))
(q (canonical-sexp-nth-data (find-sexp-token rsa 'p) 1))
;; If this is the case, then u is what we want
;; as q^{-1} mod p
(qi (canonical-sexp-nth-data (find-sexp-token rsa 'u) 1)))
;; FIXME: gcrypt does not remember the dP and dQ
;; parameters.
(values (encode d) (encode p) (encode q) (encode qi)))
(values #f #f #f #f)))
(values #f #f #f #f))))
(define-method (jwk-public->json (key <jwk>))
(let ((kid (slot-ref key 'kid))
(n (n key))
(e (e key)))
(cond
((and n e)
`((kid . ,kid)
(kty . "RSA")
(n . ,n)
(e . ,e)))
(else
(error "unsupported conversion to json")))))
(define-method (jwk->json (key <jwk>))
;; Make sure to only call this function if it doesn’t have a private
;; key
(receive (d p q qi) (private-rsa-parameters key)
(cond
((and d p q qi)
`(,@(jwk-public->json key)
(d . ,d)
(p . ,p)
(q . ,q)
(qi . ,qi)))
(else
(error "unsupported conversion to json")))))
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