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openpgp: Decode the issuer-fingerprint signature subpacket.

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* guix/openpgp.scm (SUBPACKET-ISSUER-FINGERPRINT): New variable.
(openpgp-signature-issuer-fingerprint): New procedure.
(key-id-matches-fingerprint?): New procedure.
(get-signature): Look for the 'issuer and 'issuer-fingerprint
subpackets.  Ensure the issuer key ID matches the fingerprint when both
are available.
(parse-subpackets): Handle SUBPACKET-ISSUER-FINGERPRINT.
* tests/openpgp.scm (%rsa-key-fingerprint)
(%dsa-key-fingerprint, %ed25519-key-fingerprint): New variables.
* tests/openpgp.scm ("get-openpgp-detached-signature/ascii"): Check the
result of 'openpgp-signature-issuer-fingerprint'.
This commit is contained in:
Ludovic Courtès 2020-04-25 23:23:51 +02:00
parent 43408e304f
commit 4459c7859c
No known key found for this signature in database
GPG key ID: 090B11993D9AEBB5
2 changed files with 56 additions and 10 deletions
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44
guix/openpgp.scm
View file

@ -33,6 +33,7 @@
openpgp-signature? openpgp-signature?
openpgp-signature-issuer openpgp-signature-issuer
openpgp-signature-issuer-fingerprint
openpgp-signature-public-key-algorithm openpgp-signature-public-key-algorithm
openpgp-signature-hash-algorithm openpgp-signature-hash-algorithm
openpgp-signature-creation-time openpgp-signature-creation-time
@ -345,7 +346,6 @@ hexadecimal format for fingerprints."
;; 12 = Revocation Key ;; 12 = Revocation Key
(define SUBPACKET-ISSUER 16) (define SUBPACKET-ISSUER 16)
;; TODO: hashed SUBPACKET-ISSUER-FINGERPRINT-V4
(define SUBPACKET-NOTATION-DATA 20) (define SUBPACKET-NOTATION-DATA 20)
(define SUBPACKET-PREFERRED-HASH-ALGORITHMS 21) (define SUBPACKET-PREFERRED-HASH-ALGORITHMS 21)
(define SUBPACKET-PREFERRED-COMPRESSION-ALGORITHMS 22) (define SUBPACKET-PREFERRED-COMPRESSION-ALGORITHMS 22)
@ -358,8 +358,8 @@ hexadecimal format for fingerprints."
(define SUBPACKET-REASON-FOR-REVOCATION 29) (define SUBPACKET-REASON-FOR-REVOCATION 29)
(define SUBPACKET-FEATURES 30) (define SUBPACKET-FEATURES 30)
;; 31 = Signature Target ;; 31 = Signature Target
(define SUBPACKET-EMBEDDED-SIGNATURE 32) (define SUBPACKET-EMBEDDED-SIGNATURE 32)
(define SUBPACKET-ISSUER-FINGERPRINT 33) ;defined in RFC4880bis
(define SIGNATURE-BINARY #x00) (define SIGNATURE-BINARY #x00)
(define SIGNATURE-TEXT #x01) (define SIGNATURE-TEXT #x01)
@ -486,6 +486,13 @@ hexadecimal format for fingerprints."
;; XXX: is the issuer always in the unhashed subpackets? ;; XXX: is the issuer always in the unhashed subpackets?
(else #f))) (else #f)))
(define (openpgp-signature-issuer-fingerprint sig)
"When it's available, return the fingerprint, a bytevector, or the issuer of
SIG. Otherwise, return #f."
(or (assoc-ref (openpgp-signature-hashed-subpackets sig) 'issuer-fingerprint)
(assoc-ref (openpgp-signature-unhashed-subpackets sig)
'issuer-fingerprint)))
(define (openpgp-signature-creation-time sig) (define (openpgp-signature-creation-time sig)
(cond ((assq 'signature-ctime (openpgp-signature-hashed-subpackets sig)) (cond ((assq 'signature-ctime (openpgp-signature-hashed-subpackets sig))
=> (lambda (x) (unixtime (cdr x)))) => (lambda (x) (unixtime (cdr x))))
@ -578,6 +585,14 @@ the issuer's OpenPGP public key extracted from KEYRING."
(values 'missing-key issuer)))) (values 'missing-key issuer))))
(values 'unsupported-signature sig))) (values 'unsupported-signature sig)))
(define (key-id-matches-fingerprint? key-id fingerprint)
"Return true if KEY-ID, a number, corresponds to the low 8 bytes of
FINGERPRINT, a bytevector."
(let* ((len (bytevector-length fingerprint))
(low (make-bytevector 8)))
(bytevector-copy! fingerprint (- len 8) low 0 8)
(= (bytevector->uint low) key-id)))
(define (get-signature p) (define (get-signature p)
(define (->hex n) (define (->hex n)
(string-hex-pad (number->string n 16))) (string-hex-pad (number->string n 16)))
@ -662,14 +677,26 @@ the issuer's OpenPGP public key extracted from KEYRING."
;; Errata ID: 2214. ;; Errata ID: 2214.
(integers->bytevector u8 #x04 (integers->bytevector u8 #x04
u8 #xff u8 #xff
u32 (+ 6 subpacket-len))))) u32 (+ 6 subpacket-len))))
(unhashed-subpackets
(parse-subpackets unhashed-subpackets))
(hashed-subpackets (parse-subpackets hashed-subpackets))
(subpackets (append hashed-subpackets
unhashed-subpackets))
(issuer-key-id (assoc-ref subpackets 'issuer))
(issuer (assoc-ref subpackets
'issuer-fingerprint)))
(unless (or (not issuer) (not issuer-key-id)
(key-id-matches-fingerprint? issuer-key-id issuer))
(error "issuer key id does not match fingerprint" issuer))
(make-openpgp-signature version type (make-openpgp-signature version type
(public-key-algorithm pkalg) (public-key-algorithm pkalg)
(openpgp-hash-algorithm halg) (openpgp-hash-algorithm halg)
hashl16 hashl16
append-data append-data
(parse-subpackets hashed-subpackets) hashed-subpackets
(parse-subpackets unhashed-subpackets) unhashed-subpackets
value))))) value)))))
(else (else
(print "Unsupported signature version: " version) (print "Unsupported signature version: " version)
@ -701,6 +728,13 @@ the issuer's OpenPGP public key extracted from KEYRING."
((= type SUBPACKET-ISSUER) ((= type SUBPACKET-ISSUER)
(cons 'issuer (cons 'issuer
(bytevector-u64-ref data 0 (endianness big)))) (bytevector-u64-ref data 0 (endianness big))))
((= type SUBPACKET-ISSUER-FINGERPRINT) ;v4+ only, RFC4880bis
(cons 'issuer-fingerprint
(let* ((version (bytevector-u8-ref data 0))
(len (match version (4 20) (5 32)) )
(fingerprint (make-bytevector len)))
(bytevector-copy! data 1 fingerprint 0 len)
fingerprint)))
((= type SUBPACKET-NOTATION-DATA) ((= type SUBPACKET-NOTATION-DATA)
(let ((p (open-bytevector-input-port data))) (let ((p (open-bytevector-input-port data)))
(let-values (((f1 nlen vlen) (let-values (((f1 nlen vlen)

22
tests/openpgp.scm
View file

@ -18,6 +18,7 @@
(define-module (tests-openpgp) (define-module (tests-openpgp)
#:use-module (guix openpgp) #:use-module (guix openpgp)
#:use-module (gcrypt base16)
#:use-module (gcrypt hash) #:use-module (gcrypt hash)
#:use-module (gcrypt pk-crypto) #:use-module (gcrypt pk-crypto)
#:use-module (ice-9 binary-ports) #:use-module (ice-9 binary-ports)
@ -65,6 +66,16 @@ vBSFjNSiVHsuAA==
(define %dsa-key-id #x587918047BE8BD2C) ;dsa.key (define %dsa-key-id #x587918047BE8BD2C) ;dsa.key
(define %ed25519-key-id #x771F49CBFAAE072D) ;ed25519.key (define %ed25519-key-id #x771F49CBFAAE072D) ;ed25519.key
(define %rsa-key-fingerprint
(base16-string->bytevector
(string-downcase "385F86CFC86B665A5C165E6BAE25DA2A70DEED59")))
(define %dsa-key-fingerprint
(base16-string->bytevector
(string-downcase "2884A980422330A4F33DD97F587918047BE8BD2C")))
(define %ed25519-key-fingerprint
(base16-string->bytevector
(string-downcase "44D31E21AF7138F9B632280A771F49CBFAAE072D")))
;;; The following are detached signatures created commands like: ;;; The following are detached signatures created commands like:
;;; echo 'Hello!' | gpg -sba --digest-algo sha512 ;;; echo 'Hello!' | gpg -sba --digest-algo sha512
@ -160,15 +171,16 @@ Pz7oopeN72xgggYUNT37ezqN3MeCqw0=
"Ludovic Courtès <ludo@gnu.org>")))))) "Ludovic Courtès <ludo@gnu.org>"))))))
(test-equal "get-openpgp-detached-signature/ascii" (test-equal "get-openpgp-detached-signature/ascii"
(list `(,%dsa-key-id dsa sha256) (list `(,%dsa-key-id ,%dsa-key-fingerprint dsa sha256)
`(,%rsa-key-id rsa sha256) `(,%rsa-key-id ,%rsa-key-fingerprint rsa sha256)
`(,%ed25519-key-id eddsa sha256) `(,%ed25519-key-id ,%ed25519-key-fingerprint eddsa sha256)
`(,%ed25519-key-id eddsa sha512) `(,%ed25519-key-id ,%ed25519-key-fingerprint eddsa sha512)
`(,%ed25519-key-id eddsa sha1)) `(,%ed25519-key-id ,%ed25519-key-fingerprint eddsa sha1))
(map (lambda (str) (map (lambda (str)
(let ((signature (get-openpgp-detached-signature/ascii (let ((signature (get-openpgp-detached-signature/ascii
(open-input-string str)))) (open-input-string str))))
(list (openpgp-signature-issuer signature) (list (openpgp-signature-issuer signature)
(openpgp-signature-issuer-fingerprint signature)
(openpgp-signature-public-key-algorithm signature) (openpgp-signature-public-key-algorithm signature)
(openpgp-signature-hash-algorithm signature)))) (openpgp-signature-hash-algorithm signature))))
(list %hello-signature/dsa (list %hello-signature/dsa