pk-crypto: Use RFC6979 when signing with an ECC or DSA key.

* guix/pk-crypto.scm (bytevector->hash-data): Add #:key-type parameter.
  Use the 'pkcs1' flag when KEY-TYPE is 'rsa', and 'rfc6979' when
  KEY-TYPE is 'ecc' or 'dsa'.
  (key-type): New procedure.
* guix/scripts/authenticate.scm (read-hash-data): Add 'key-type'
  parameter.  Pass it to 'bytevector->hash-data'.  Adjust caller
  accordingly.
* tests/pk-crypto.scm (%ecc-key-pair): New variable.
  ("key-type"): New test.
  ("sign + verify"): Pass #:key-type to 'bytevector->hash-data'.
  ("sign + verify, Ed25519"): New test.

2 files changed, 27 insertions, 9 deletions

diff --git a/guix/pk-crypto.scm b/guix/pk-crypto.scm
index 50f709418c..b9ab02861c 100644
--- a/guix/pk-crypto.scm
+++ b/guix/pk-crypto.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2013 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2013, 2014 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -39,6 +39,7 @@
             canonical-sexp-list?
             bytevector->hash-data
             hash-data->bytevector
+            key-type
             sign
             verify
             generate-key
@@ -232,15 +233,31 @@ Return #f if that element does not exist, or if it's a list."
   "Return an s-expression representing NUMBER."
   (string->canonical-sexp (string-append "#" (number->string number 16) "#")))
 
-(define* (bytevector->hash-data bv #:optional (hash-algo "sha256"))
+(define* (bytevector->hash-data bv
+                                #:optional
+                                (hash-algo "sha256")
+                                #:key (key-type 'ecc))
   "Given BV, a bytevector containing a hash, return an s-expression suitable
-for use as the data for 'sign'."
+for use as the data for 'sign'.  KEY-TYPE must be a symbol: 'dsa, 'ecc, or
+'rsa."
   (string->canonical-sexp
-   (format #f "(data (flags pkcs1) (hash \"~a\" #~a#))"
+   (format #f "(data (flags ~a) (hash \"~a\" #~a#))"
+           (case key-type
+             ((ecc dsa) "rfc6979")
+             ((rsa)     "pkcs1")
+             (else (error "unknown key type" key-type)))
            hash-algo
            (bytevector->base16-string bv))))
 
-(define (hash-data->bytevector data)
+(define (key-type sexp)
+  "Return a symbol denoting the type of key representing by SEXP--e.g., 'rsa',
+'ecc'--or #f if SEXP does not denote a valid key."
+  (case (canonical-sexp-nth-data sexp 0)
+    ((public-key private-key)
+     (canonical-sexp-nth-data (canonical-sexp-nth sexp 1) 0))
+    (else #f)))
+
+(define* (hash-data->bytevector data)
   "Return two values: the hash value (a bytevector), and the hash algorithm (a
 string) extracted from DATA, an sexp as returned by 'bytevector->hash-data'.
 Return #f if DATA does not conform."
diff --git a/guix/scripts/authenticate.scm b/guix/scripts/authenticate.scm
index 27580dedff..927dbe8afc 100644
--- a/guix/scripts/authenticate.scm
+++ b/guix/scripts/authenticate.scm
@@ -39,11 +39,12 @@
   (call-with-input-file file
     (compose string->canonical-sexp get-string-all)))
 
-(define (read-hash-data file)
-  "Read sha256 hash data from FILE and return it as a gcrypt sexp."
+(define (read-hash-data file key-type)
+  "Read sha256 hash data from FILE and return it as a gcrypt sexp.  KEY-TYPE
+is a symbol representing the type of public key algo being used."
   (let* ((hex (call-with-input-file file get-string-all))
          (bv  (base16-string->bytevector (string-trim-both hex))))
-    (bytevector->hash-data bv)))
+    (bytevector->hash-data bv #:key-type key-type)))
 
 
 ;;;
@@ -64,7 +65,7 @@
                             (leave
                              (_ "cannot find public key for secret key '~a'~%")
                              key)))
-            (data       (read-hash-data hash-file))
+            (data       (read-hash-data hash-file (key-type public-key)))
             (signature  (signature-sexp data secret-key public-key)))
        (display (canonical-sexp->string signature))
        #t))