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shrub/pkg/arvo/lib/der.hoon
2020-12-02 01:00:09 -08:00

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/- asn1
:: |der: distinguished encoding rules for ASN.1
::
:: DER is a tag-length-value binary encoding for ASN.1, designed
:: so that there is only one (distinguished) valid encoding for an
:: instance of a type.
::
|%
:: +en:der: encode +spec:asn1 to +octs (kindof)
::
++ en
=< |= a=spec:asn1
^- [len=@ud dat=@ux]
=/ b ~(ren raw a)
[(lent b) (rep 3 b)]
|%
:: +raw:en:der: door for encoding +spec:asn1 to list of bytes
::
++ raw
|_ pec=spec:asn1
:: +ren:raw:en:der: render +spec:asn1 to tag-length-value bytes
::
++ ren
^- (list @D)
=/ a lem
[tag (weld (len a) a)]
:: +tag:raw:en:der: tag byte
::
++ tag
^- @D
?- pec
[%int *] 2
[%bit *] 3
[%oct *] 4
[%nul *] 5
[%obj *] 6
[%seq *] 48 :: constructed: (con 0x20 16)
[%set *] 49 :: constructed: (con 0x20 17)
[%con *] ;: con
0x80 :: context-specifc
?:(imp.bes.pec 0 0x20) :: implicit?
(dis 0x1f tag.bes.pec) :: 5 bits of custom tag
==
==
:: +lem:raw:en:der: element bytes
::
++ lem
^- (list @D)
?- pec
:: unsigned only, interpreted as positive-signed and
:: rendered in big-endian byte order. negative-signed would
:: be two's complement
::
[%int *] =/ a (flop (rip 3 int.pec))
?~ a [0 ~]
?:((lte i.a 127) a [0 a])
:: padded to byte-width, must be already byte-aligned
::
[%bit *] =/ a (rip 3 bit.pec)
=/ b ~| %der-invalid-bit
?. =(0 (mod len.pec 8))
~|(%der-invalid-bit-alignment !!)
(sub (div len.pec 8) (lent a))
[0 (weld a (reap b 0))]
:: padded to byte-width
::
[%oct *] =/ a (rip 3 oct.pec)
=/ b ~| %der-invalid-oct
(sub len.pec (lent a))
(weld a (reap b 0))
::
[%nul *] ~
[%obj *] (rip 3 obj.pec)
::
[%seq *] %- zing
|- ^- (list (list @))
?~ seq.pec ~
:- ren(pec i.seq.pec)
$(seq.pec t.seq.pec)
:: presumed to be already deduplicated and sorted
::
[%set *] %- zing
|- ^- (list (list @))
?~ set.pec ~
:- ren(pec i.set.pec)
$(set.pec t.set.pec)
:: already constructed
::
[%con *] con.pec
==
:: +len:raw:en:der: length bytes
::
++ len
|= a=(list @D)
^- (list @D)
=/ b (lent a)
?: (lte b 127)
[b ~] :: note: big-endian
[(con 0x80 (met 3 b)) (flop (rip 3 b))]
--
--
:: +de:der: decode atom to +spec:asn1
::
++ de
|= [len=@ud dat=@ux]
^- (unit spec:asn1)
:: XX refactor into +parse
=/ a (rip 3 dat)
=/ b ~| %der-invalid-len
(sub len (lent a))
(rust `(list @D)`(weld a (reap b 0)) parse)
:: +parse:der: DER parser combinator
::
++ parse
=< ^- $-(nail (like spec:asn1))
;~ pose
(stag %int (bass 256 (sear int ;~(pfix (tag 2) till))))
(stag %bit (sear bit (boss 256 ;~(pfix (tag 3) till))))
(stag %oct (boss 256 ;~(pfix (tag 4) till)))
(stag %nul (cold ~ ;~(plug (tag 5) (tag 0))))
(stag %obj (^boss 256 ;~(pfix (tag 6) till)))
(stag %seq (sear recur ;~(pfix (tag 48) till)))
(stag %set (sear recur ;~(pfix (tag 49) till)))
(stag %con ;~(plug (sear context next) till))
==
|%
:: +tag:parse:der: parse tag byte
::
++ tag
|=(a=@D (just a))
:: +int:parse:der: sear unsigned big-endian bytes
::
++ int
|= a=(list @D)
^- (unit (list @D))
?~ a ~
?: ?=([@ ~] a) `a
?. =(0 i.a) `a
?.((gth i.t.a 127) ~ `t.a)
:: +bit:parse:der: convert bytewidth to bitwidth
::
++ bit
|= [len=@ud dat=@ux]
^- (unit [len=@ud dat=@ux])
?. =(0 (end 3 dat)) ~
:+ ~
(mul 8 (dec len))
(rsh 3 dat)
:: +recur:parse:der: parse bytes for a list of +spec:asn1
::
++ recur
|=(a=(list @) (rust a (star parse)))
:: +context:parse:der: decode context-specific tag byte
::
++ context
|= a=@D
^- (unit bespoke:asn1)
?. =(1 (cut 0 [7 1] a)) ~
:+ ~
=(1 (cut 0 [5 1] a))
(dis 0x1f a)
:: +boss:parse:der: shadowed to count as well
::
:: Use for parsing +octs more broadly?
::
++ boss
|* [wuc=@ tyd=rule]
%+ cook
|= waq=(list @)
:- (lent waq)
(reel waq |=([p=@ q=@] (add p (mul wuc q))))
tyd
:: +till:parse:der: parser combinator for len-prefixed bytes
::
:: advance until
::
++ till
|= tub=nail
^- (like (list @D))
?~ q.tub
(fail tub)
:: fuz: first byte - length, or length of the length
::
=* fuz i.q.tub
:: nex: offset of value bytes from fuz
:: len: length of value bytes
::
=/ [nex=@ len=@]
:: faz: meaningful bits in fuz
::
=/ faz (end [0 7] fuz)
?: =(0 (cut 0 [7 1] fuz))
[0 faz]
[faz (rep 3 (flop (scag faz t.q.tub)))]
?: ?& !=(0 nex)
!=(nex (met 3 len))
==
(fail tub)
:: zuf: value bytes
::
=/ zuf (swag [nex len] t.q.tub)
?. =(len (lent zuf))
(fail tub)
:: zaf: product nail
::
=/ zaf [p.p.tub (add +(nex) q.p.tub)]
[zaf `[zuf zaf (slag (add nex len) t.q.tub)]]
--
--